What a wild weekend that was. Overall I am pleased with my result though I know I could have done better. While my memory is fresh a recap is in order. There are lessons to be learned. Not only for me, but for others as well, even those with better or worse stations.
I will not dwell on my score or my competitive placement. You can visit 3830 to find that. Keep in mind that any comparison must take into account location, category and the difficulty comparing US and Canada scores due to the CQ WW rules. I find it more useful to compare multipliers -- zones and countries -- with those in comparable locations.
Station recap
My new contest station is incomplete, and the gaps showed in how I did. If you ever wondered by 3 db makes a difference, well yes it does. Even 1 db can put several multipliers in your contest log. In several case I am down more than 3 db than where I plan to be, and in comparison to the best single op stations.
160: T-top vertical with 8 x 30 meter radials, suspended by catenary from 40 meters height.
80: Low inverted vee at 19 meters and 3-element vertical yagi fixed northeast. When complete the yagi array will be switchable in 4 directions and omni-directional.
40: Low inverted vee (fan combination with 80 meters) and XM240 up 46 meters.
20/15/10: TH7 at 21 meters, TH6 at 43 meters and Explorer 14 at 32 meters fixed to Europe. I used tri-banders for expediency (already in my stock).
160 meters
I struggled on top band more than I expected, especially since conditions were good and a large amount of DX was heard. Despite being able to hear them my 100 watts wasn't good enough. I had more luck the second night when signals were slightly stronger and I recovered some ground. For general DXing my antenna works very well and I can often win in pile up over those with more power and less antenna. This weekend it simply didn't make the grade.
After importing my contest log into my general logging software I was pleased to discover I had at passed 100 countries on 160 meters. It took almost exactly 12 months, dating from when I put up the 160 meter antenna, the first full size antenna I've ever had for top band.
80 meters
Similar to 160 my first night on 80 meters was dreadful. The band was filled with DX but few could copy me. Again, the second night was far better when I had no trouble running to Europe both before and after their sunrise. Even so my multiplier count is poor. Lots of what should be easy shots were heard, but they did not hear me.
Much of the trouble will go away once the 80 meter array switching system is built since the inverted vee did not do well, yet it was all I had for directions other than northeast.
40 meters
This is one of the two money bands (the other is 20) when the sunspots don't come out to play. Doing well on 40 meters is critical to a competitive score. But the competition and QRM are fierce. You need a signal that will not only stand out above others but also allow you to successfully run. I am not truly there yet but I am certainly getting closer.
The first night was difficult. Running was near impossible, especially considering that the European path is already diminishing when the contest starts at 00Z. It was discouraging. The sunrise opening produced fewer multipliers than I hoped for. The next night was significantly better, though running was not as productive as hoped. That all changed with sunrise when several double multipliers (zone and country) came with an over-the-pole opening with good signals. But not all fell to my low power signal. A small 2-element yagi can only do so much even when it is up so high.
My best result was Sunday afternoon. After picking off stations on the high bands I was able to fully move onto 40 meters at 3 PM (2000Z). For the next 90 minutes I had a great run, almost all Europe. Many needed countries, and even zones, came calling.
20 meters
You must do well on 20 to produce a good score. My result was good though not great with respect to DX QSO and multiplier totals. As usual it was the early morning path to Europe that produced the most productive runs. I moved there as soon as the possibilities on the low bands faded after sunrise. With my current antennas I really want to turn the prop pitch rotator to bring the high TH6 to bear on Europe, and that also moves my 40 meter yagi away from multiplier hunting to the north and west. That's a problem that will be solved next year.
I only used the slightly lower Explorer 14 when I needed the TH6 elsewhere since, although good, it does not deliver the same result. Since 15 meters is open to Europe at the same time and the higher antenna is far superior there is no question that 40 meters must be sacrificed. Later in the day I used the lower TH7 for shorter paths, leaving the TH6 to pick off distant multipliers in South America, the Pacific and Asia, and the Explorer 14 to catch any Europeans in the anomalous afternoon opening (late evening in Europe).
15 meters
Only brief runs to Europe were possible since 15 meters was marginal. Mostly I spent my time multiplier hunting, or working US stations when little else was workable. Normally strong signals from South America were not. Some easy multipliers in the Caribbean were missed due to the brief midday window for this fairly short path.
10 meters
This one's easy. I worked nothing. Despite regular checking and some CQing when the band was most likely to open no signals were heard. It appears others in this northerly region had similar luck. I did not ask any locals to move for me. That would be an easy two multipliers: zone 4 and VE.
Problems encountered
The weekend was largely free of equipment problems. The major difficulty was the direction indicators for both rotators: T2X on the 20 meter tower and prop pitch on the 43 meter tower. In part this appears to have been due to moisture getting into the prop pitch pot and into the T2X control cable. The latter has several splices. The prop pitch direction indicator resumed working once the rain stopped and it had a chance to dry.
Better weatherproofing for the prop pitch pot is called for, though not this season. The T2X cable is already slated for replacement, and I may get it done this winter.
There is some RFI with the computer display when using the TH7 and 80 meter inverted vee on the short tower. They are close to the house. Occasional weak RFI was present when yagis on the big tower were turned west, which is towards the house. This is tolerable now but will be a serious problem when I get an amplifier. I'll have to deal with it sooner rather than later.
Aside from a few software glitches that was it for technical problems. On the personal side I suffered no ill effects from operating over 40 hours (out of 48 possible). I do notice that when I get really tired I have more typos when running. Most were corrected while the keyer was playing provided I typed faster than the other's call sign was being sent. That's a challenge at 32 or 34 wpm!
Strategic options
My strategy was strongly constrained by my power level and antenna capabilities. It was often better to hunt for multipliers on less productive bands than run where I ought to be but could not do well. Sometimes the situation was reversed, when it was better to run, if only to the US, than hunt for multipliers that were not very workable.
Everybody's situation is different, so there is no need to go into particulars beyond the broader strategic choices implied. I will just say that running, when possible, is almost always the best choice. Most contest logging software will calculate and display the number of QSOs that are needed to equal one multiplier. If the number is 5 and you have a good run rate it is usually safe to continue.
But if there's a short opening expected to several needed multipliers it may be better to move and try that for a few minutes. It might be your only chance to work them. Of course if you are SO2R or multi-op you can do both! Indeed for most of us in non-rare areas that is the primary motivation to do SO2R. Secondary objectives are to work stations in general on another band or, for the mutants among us with super-stations, try 2BSIQ (two bands synchronous interleaved QSOs) to concurrently run on two bands.
Regrettably (or not) I am not a mutant and although my station is getting nice and big it will never be a super-station. I am content to aim for run of the mill big gun status and do SO2R. My station is very close to being SO2R compatible, low power CW only for now. I will finish the build mid-winter and then practice. In next year's CQ WW contest I should be able to improve my multiplier count.
Running
Do you truly want to easily and quickly improve your contest scores? You must run, even if you prefer not to do so. Most of the little gun contesters of my acquaintance won't do it. Either they find the prospect intimidating or simply assume that it not possible for a small station. This is never true. A big factor in my two world #1 QRP plaques in CQ WW SSB (and a #2 on CW) were only possible by running. Although that was when we had sunspots and there were excellent opening on 10 and 15 meters where 5 watts can be very effective. If a QRPer can do it so can anyone.
Unless I'm specifically looking for certain multipliers I will try to run. I resort to S & P only when that isn't possible, or late in the contest when I must find those big guns who seem to run all the time leaving no other way to work them. While scouring the bands for stations to work I find a clear frequency I will frequently try a bit of CQing. If nothing happens in a minute or two, or it does but after several minutes the rate is poor I'll resume S & P. Eventually it'll stick, whether due to a change in propagation or my chosen frequency is nice and clear over in the target continent.
Big guns run the majority of the time. You might think multipliers might be missed by doing this, but that would be wrong. Try running you will be surprised by who calls you! Soon you'll understand the value of running even if you're a little gun. To do it well you want to be quick, both in speed and procedure, so that callers you don't answer immediately will stick around rather than fret over time wasted and QSY.
As an example, consider my woes on 160 meters. After having no luck calling numerous DX stations for multipliers I parked low in the band and started CQing, hoping to work a few US stations. Within a few minutes I had several Europeans logged! It just goes to show that many stations who can hear you are S & P, and if you run you can work them.
On CW many callers will not be zero beat and for crowded band conditions where you must use a narrow filter you will have to become good at quickly adjusting the RIT. Logging software such as N1MM Logger that I use have convenient keyboard shortcuts to control RIT. I then clear the RIT using a macro key after the QSO. It is better that multiple callers not zero beat since it can be near impossible to pick out one call sign. As I said, be quick, so don't shy away from CW speeds over 30 wpm even when you run QRP.
Once you find a good run frequency don't be surprised that you may lose it. Another station in the skip zone might not hear you and will start running on what appears to be a clear frequency if you experience a lull in callers. Unfortunately some big guns are less than ethical in their operating and will deliberately steal your frequency, relying on their superior signal to drown yours. If you're a big gun yourself you'll have to make a judgment call whether to stay and fight or QSY.
Whatever you choose don't become angry and act on emotion rather your rate. I can be better to move. When I operated CQ WW SSB at VE3JM a month ago, where clear frequencies are rare, many times others tried to move in really close and run. They nearly always failed. That's one advantage of running a kilowatt and stacked yagis: you tend to win, and do it by simply continuing to do what you're doing.
The mighty decibel
There an old joke among contesters: would you risk your marriage for 1 db? How about 3 db? Contesters' spouses are not always fans of big towers and antennas. What is it worth to you? Should you take plunge will your score noticably improve when you go from a 4-element to a 5-element yagi, or stack two of them (or three)?
For general operating, perhaps not so much. Contesting is different. As an example, my small tri-bander fixed on Europe up 32 meters shows little difference on the S-meter compared with the larger tri-bander up 43 meters. Yet the higher one consistently delivers more callers when I run. The difference is certainly less than 3 db.
What more often makes the difference is not what you hear but what others hear. In a band crowded with loud, closely-packed signals a few decibels will make your signal stand out above the bedlam. Of course if everyone does this there is no advantage, but not everyone does and so it works. A small absolute increase in received signal strength is not the issue; S9 and S9+2 are both solidly Q5. Consider the mix of all signals being received and the threshold effect of one signal rising up has an outsize improvement on readability.
It's the same if your signal is close to the noise level, especially on 80 and 160. That readability entices callers. That's why a few decibels can greatly improve run rates. The same is true of QRO, but almost all big guns use QRO so antenna gain is where the focus needs to be.
On 40 meters I can get 2 to 3 db with a full size 3-element yagi. That is still in my plans, though perhaps not in 2019. It is slated for the top of my current tall tower at a height of 43 meters (where the TH6 currently resides). But I would like something powerful for the European path. I am eyeing a multi-element wire yagi fixed on Europe that could net me 2 db more than the planned full size yagi. That will be possible once the new tower is up. First I will have to address potential interactions with yagis on the two towers since this one will in between and in line towards the northeast.
I estimate that the mono-band yagis I am planning for 15 and 20 meters will be 2 and 3 db better, respectively, than the TH6. Add another 3 db (approximately) for stacking two of them. That's a huge difference that is well worth the time and expense for those with a passion for contests. I hope to be in that position this time next year.
Completion of the 80 meter vertical yagi is coming along, and that is as far as I'll go through at least 2019. Getting more decibels on 80 will be difficult. I can perhaps gain 1 db by doubling the radials. On 160 I have the possibility of using my big towers as yagi parasitic elements to get some badly needed gain. Again, probably not until after 2019. I am deferring 10 meters two years until we get a few more sunspots.
Operating improvements
I plan to start doing SO2R early in the new year. It will take time become effective. To begin it will be with CW, low power and the second radio for S & P only. By late 2019 I expect to be ready to try QRO on at least the run radio and SSB as well. Thus I will initially focus on boosting my multiplier count rather than total QSOs. The latter will come later once I become proficient.
Antenna, filter and switching automation is in the pipeline. The intent is to facilitate fast band changes to catch those multipliers. I expect to develop my own software and control hardware to suit the unique objectives I have for my station. Commercial solutions are very expensive and from perusing what's available none of it does quite what I want. The potential for experimentation by going my own way is another motivation.
There are features in N1MM Logger and other software that I do not use despite the potential value. Although I like to keep it simple that is not really consistent with improving my effectiveness as an operator of a big gun station. I'll have to push myself to do more. In the same vein I need to script my contests to remind myself where I need to be to run or catch those elusive multipliers. At present I tend to improvise depending on how I feel at the time.
The point of this long dissertation is to show just how much more I can do to improve my result in CQ WW, even though my category placing now is excellent. If done right it will be fun rather than a chore.
Thursday, November 29, 2018
Thursday, November 22, 2018
Early Winter Interlude
This year has not been as productive as originally planned. I could have done more during the warmer months, but life is more than amateur radio. Now that contest and DX season is in full swing on the HF bands and my energy to progress various projects is high we get this:
So far we've gotten ~30 cm of snow and temperatures that keep it on the ground. In the photo you see my new tower project abandoned in the hay field amidst 60 kph wind, blowing snow and -10° C temperature. It's only up 40', so there's till 100' to go. Overnight the temperature dipped even lower, to -20° C, which is in record low territory for November.
Ordinarily this time of year is perfect for raising towers, with cool temperatures and no hay or bugs to worry about. I have in the past raised towers in winter and I would happily do so again. It is not so easy with a tower this size since I use a vehicle for lifting muscle, and the only vehicle that can deal with snow pack is a tractor, which I don't have. Although a winch will work I only have a manual unit and that takes a lot of work to lift 130 lb tower sections up high. I am also reluctant to ask friends to work in these conditions.
While I wait for a thaw that may not come my thoughts turn elsewhere. In particular, preparation for the CQ WW CW contest this weekend. One good thing about the deep snow is that it is far easier to navigate the bush to maintain the long northeast Beverage receiving antenna. I've been waiting to do that since it has been not been performing at its best recently. On reaching the termination I saw that the ground rod clamp was loose. Tramping out for needed material and back in again I made the repair and tested it last night. It's much better now. Later I'll buy a suitable clamp and make the repair permanent.
For the contest the 3-element vertical yagi has been fixed towards Europe. Although I now have all the parts I need to finish the switching system and critical components have been prepared -- switching matrix and identical coils -- it has been delayed to focus on the tower project while the weather cooperated. The switching system can be worked on in winter conditions. Setting priorities this way has the unfortunate outcome that the yagi switching system is not ready for CQ WW.
There are other maintenance projects to be done when the frigid weather relents, even if just a little. These include cable organization, SO2R control lines, rig-controlled switching among many others. For the present it's all on hold. Despite all these issues I am pretty well set up for the contest. My preparation for the next contest will be better.
I think it's time for another cup of coffee. For the Americans out there, have a Happy Thanksgiving. I hope to work all of you in the contest. The warm shack is very inviting right now and there are lots of VE3s and others scattered across the Caribbean to be worked as they, and I, warm up for the contest.
So far we've gotten ~30 cm of snow and temperatures that keep it on the ground. In the photo you see my new tower project abandoned in the hay field amidst 60 kph wind, blowing snow and -10° C temperature. It's only up 40', so there's till 100' to go. Overnight the temperature dipped even lower, to -20° C, which is in record low territory for November.
Ordinarily this time of year is perfect for raising towers, with cool temperatures and no hay or bugs to worry about. I have in the past raised towers in winter and I would happily do so again. It is not so easy with a tower this size since I use a vehicle for lifting muscle, and the only vehicle that can deal with snow pack is a tractor, which I don't have. Although a winch will work I only have a manual unit and that takes a lot of work to lift 130 lb tower sections up high. I am also reluctant to ask friends to work in these conditions.
While I wait for a thaw that may not come my thoughts turn elsewhere. In particular, preparation for the CQ WW CW contest this weekend. One good thing about the deep snow is that it is far easier to navigate the bush to maintain the long northeast Beverage receiving antenna. I've been waiting to do that since it has been not been performing at its best recently. On reaching the termination I saw that the ground rod clamp was loose. Tramping out for needed material and back in again I made the repair and tested it last night. It's much better now. Later I'll buy a suitable clamp and make the repair permanent.
For the contest the 3-element vertical yagi has been fixed towards Europe. Although I now have all the parts I need to finish the switching system and critical components have been prepared -- switching matrix and identical coils -- it has been delayed to focus on the tower project while the weather cooperated. The switching system can be worked on in winter conditions. Setting priorities this way has the unfortunate outcome that the yagi switching system is not ready for CQ WW.
There are other maintenance projects to be done when the frigid weather relents, even if just a little. These include cable organization, SO2R control lines, rig-controlled switching among many others. For the present it's all on hold. Despite all these issues I am pretty well set up for the contest. My preparation for the next contest will be better.
I think it's time for another cup of coffee. For the Americans out there, have a Happy Thanksgiving. I hope to work all of you in the contest. The warm shack is very inviting right now and there are lots of VE3s and others scattered across the Caribbean to be worked as they, and I, warm up for the contest.
Monday, November 19, 2018
XM240 and 17 Meters
The station I have built, and continue to build, is primarily focussed on HF contesting with a secondary focus (though a very close second) on HF and 6 meter DXing. Due to time, budget and other practical considerations the so-called WARC bands -- 30, 17 and 12 meters -- have gotten limited attention. While my attention is indeed elsewhere these bands are not forgotten.
I have been happy to use my 80 meter antennas on 30 meters with the help of a tuner to bridge the small disparity between 10.1 MHz and the actual third harmonic. Having a choice between a horizontal and vertical antenna is beneficial. Building a gain antenna, one with two or more elements, is not at all in my plans and may never be due to the size, cost and effort involved.
The minimum of a solar cycle does not turn 12 meters into a hotbed of activity though there are sparks of interest, such as when I worked VP6D on both CW and SSB a few weeks ago. On 12 meters I use a tuner on one of my high yagis and hope for the best. This is usually good enough because extreme height makes up for many flaws.
Which brings us to 17 meters. This band remains very useful for DXing even during a solar minimum. Yet all I have for this band is my XM240, which performs similar to a dipole at 18.1 MHz and is resonant not far above the band. The moderately high SWR is managable with a tuner. Again, height is my friend.
Of these three bands it is 17 meters that is best positioned into inducing me to consider a better antenna. It is not urgent. What it does is make me conduct a few thought experiments on how I can achieve improved performance at little cost and effort. One of these thoughts was to turn the XM240 into a 2-element 17 meter yagi. The concept of adding a 17 meter reflector to the antenna is theoretically sound so I built a computer model to see what could be done.
Before we proceed I will be very explicit regarding the limits of this exercise. I have not built this antenna and I may never do so. I don't know how well it would really work. The greatest danger is that the XM240 cannot be properly modelled by the NEC2 engine; only NEC4 is up to the task and I don't have it. My EZNEC model of the XM240 is at best a proxy of the real antenna that allows me to explore its behaviour, but not to accurately derive physical dimensions. I'll have more to say about this later.
Model
When I purchased the XM240 it was placed in storage until it could be raised at my new QTH. At that time I developed a "naive" EZNEC model of the antenna using straight tube elements along with coils and capacity hats with the same values as the actual antenna. Because NEC2 cannot accurately model elements with loads (EZNEC 6 can with its NEC2 enhancements, but only somewhat) the element lengths are not correct. The model nevertheless permitted me to explore the antenna's behaviour.
My current exploration of 17 meters uses that same model. I added a reflector element, tuning its reactance and spacing to the driven element to optimize performance at 18.1 MHz. As with the rest of the model I used straight tubing rather than a taper schedule. That can be added later should I decide to build it. The model's value is not affected by this doing this, it's just that the element length will be different with tapered tubes.
Notice that the XM240 40 meter reflector has almost zero current flowing on it. This is one key to understanding why a 17 meter reflector can be added to the antenna so simply. Indeed it the same reason why a yagi can be correctly tuned close to the ground by pointing it upward. When the 17 meter reflector is correctly tuned there is effective cancellation of the fields from it and the driven element towards the rear. The 40 meter reflector is spaced far enough that it has low mutual impedance with the other elements at 18 MHz, and therefore has negligible effect on the 17 meter reflector and driven element.
The other key to understanding the design is that the tuning of the driven element has essentially zero effect on yagi performance, that is, gain and F/B. Whatever phase shift mistuning introduces does not affect the phase relationship to the reflector. It is only a concern for matching. However this can only be relied upon if the length of the driven element is not too short or long, which would affect the mutual impedance with the reflector. You can see above that current on the driven element is low beyond the 40 meter loading elements, which keeps its electrical length on 17 meters close to that of the reflector.
Some improvement in 17 meter performance could be gleaned by reducting element spacing. I decided against that in favour of placing the reflector close to the boom centre to minimize torque imbalance. The 3 meter spacing is 0.18λ at 18.1 MHz.
Performance
The width of the 17 meter band is only 0.5%. It is therefore good enough to tune the antenna for the centre of the band and have close to optimum performance across the full 100 kHz, despite the narrow gain and F/B bandwidth typical of 2-element yagis. I used 18.1 MHz to keep to round numbers, and because I favour CW.
It is possible to raise the gain a little higher than 6.2 dbi by narrowing the element spacing and centering the frequency of maximum gain within the band. This would come at the expense of poorer F/B, and matching challenge due to the drop of radiation resistance at peak gain. I chose not to do so in this design due to the aforementioned torque imbalance and because the F/B is already quite poor, though as expected for the parameters of this 2-element yagi design. For me these are reasons enough to sacrifice 0.4 db of additional gain.
When fed without the reflector the pattern of the XM240 on 17 meters is similar to that of a dipole, with a bidirectional gain of ~2.4 dbi. On the air I do not notice any F/B so the model may be reliable in this respect.
The question to ask is whether 4 db of gain and modest F/B is worth the trouble. It can be easily argued that a separate and better performing 17 meter mono-band yagi is preferable. In my situation a separate yagi would not be placed as high as where the XM240 is currently located: 46 meters up. I am undecided. It's food for thought until the time comes that I decide to do more on 17 meters.
I have not reported on the SWR or feed point impedance because the straight tubes model of the antenna is unreliable on 17 meters. The best I can predict, based on exploring the model, is that the R component of the impedance is in the region of 25 Ω. I will not predict the reactance other than to note that it should be comfortably low.
A switchable matching unit, such as an L-network can be employed for 17 meters if an SWR of 2 or 2.5 is problematic. The network can be mounted at the mast to avoid adding weight at the end of the boom, and the network designed to match the impedance measured at that point.
Of some concern is that the Cushcraft 1:1 common mode choke operating at 18 MHz, a kilowatt and a mismatch at the feed point. A better balun is advisable or the network and switch should be located at the driven element and the balun switched out of circuit when operating 17 meters. But this is all a lot of bother for a modest improvement of 17 meter performance.
Conclusion
As said, this is purely a thought experiment to consider my future alternatives for improved 17 meter performance. I don't know if anyone else has tried to do this with an XM240 and I didn't research the question.
Computer modelling makes these types of analyses easy to do in the comfort of our shacks. It's a lot easier than modifying the antenna, especially an antenna of this size, and measuring the results. The analysis will now be shelved. Time will tell whether I return to it in the next couple of years.
I have been happy to use my 80 meter antennas on 30 meters with the help of a tuner to bridge the small disparity between 10.1 MHz and the actual third harmonic. Having a choice between a horizontal and vertical antenna is beneficial. Building a gain antenna, one with two or more elements, is not at all in my plans and may never be due to the size, cost and effort involved.
The minimum of a solar cycle does not turn 12 meters into a hotbed of activity though there are sparks of interest, such as when I worked VP6D on both CW and SSB a few weeks ago. On 12 meters I use a tuner on one of my high yagis and hope for the best. This is usually good enough because extreme height makes up for many flaws.
Which brings us to 17 meters. This band remains very useful for DXing even during a solar minimum. Yet all I have for this band is my XM240, which performs similar to a dipole at 18.1 MHz and is resonant not far above the band. The moderately high SWR is managable with a tuner. Again, height is my friend.
Of these three bands it is 17 meters that is best positioned into inducing me to consider a better antenna. It is not urgent. What it does is make me conduct a few thought experiments on how I can achieve improved performance at little cost and effort. One of these thoughts was to turn the XM240 into a 2-element 17 meter yagi. The concept of adding a 17 meter reflector to the antenna is theoretically sound so I built a computer model to see what could be done.
Before we proceed I will be very explicit regarding the limits of this exercise. I have not built this antenna and I may never do so. I don't know how well it would really work. The greatest danger is that the XM240 cannot be properly modelled by the NEC2 engine; only NEC4 is up to the task and I don't have it. My EZNEC model of the XM240 is at best a proxy of the real antenna that allows me to explore its behaviour, but not to accurately derive physical dimensions. I'll have more to say about this later.
Model
When I purchased the XM240 it was placed in storage until it could be raised at my new QTH. At that time I developed a "naive" EZNEC model of the antenna using straight tube elements along with coils and capacity hats with the same values as the actual antenna. Because NEC2 cannot accurately model elements with loads (EZNEC 6 can with its NEC2 enhancements, but only somewhat) the element lengths are not correct. The model nevertheless permitted me to explore the antenna's behaviour.
My current exploration of 17 meters uses that same model. I added a reflector element, tuning its reactance and spacing to the driven element to optimize performance at 18.1 MHz. As with the rest of the model I used straight tubing rather than a taper schedule. That can be added later should I decide to build it. The model's value is not affected by this doing this, it's just that the element length will be different with tapered tubes.
Notice that the XM240 40 meter reflector has almost zero current flowing on it. This is one key to understanding why a 17 meter reflector can be added to the antenna so simply. Indeed it the same reason why a yagi can be correctly tuned close to the ground by pointing it upward. When the 17 meter reflector is correctly tuned there is effective cancellation of the fields from it and the driven element towards the rear. The 40 meter reflector is spaced far enough that it has low mutual impedance with the other elements at 18 MHz, and therefore has negligible effect on the 17 meter reflector and driven element.
The other key to understanding the design is that the tuning of the driven element has essentially zero effect on yagi performance, that is, gain and F/B. Whatever phase shift mistuning introduces does not affect the phase relationship to the reflector. It is only a concern for matching. However this can only be relied upon if the length of the driven element is not too short or long, which would affect the mutual impedance with the reflector. You can see above that current on the driven element is low beyond the 40 meter loading elements, which keeps its electrical length on 17 meters close to that of the reflector.
Some improvement in 17 meter performance could be gleaned by reducting element spacing. I decided against that in favour of placing the reflector close to the boom centre to minimize torque imbalance. The 3 meter spacing is 0.18λ at 18.1 MHz.
Performance
The width of the 17 meter band is only 0.5%. It is therefore good enough to tune the antenna for the centre of the band and have close to optimum performance across the full 100 kHz, despite the narrow gain and F/B bandwidth typical of 2-element yagis. I used 18.1 MHz to keep to round numbers, and because I favour CW.
It is possible to raise the gain a little higher than 6.2 dbi by narrowing the element spacing and centering the frequency of maximum gain within the band. This would come at the expense of poorer F/B, and matching challenge due to the drop of radiation resistance at peak gain. I chose not to do so in this design due to the aforementioned torque imbalance and because the F/B is already quite poor, though as expected for the parameters of this 2-element yagi design. For me these are reasons enough to sacrifice 0.4 db of additional gain.
When fed without the reflector the pattern of the XM240 on 17 meters is similar to that of a dipole, with a bidirectional gain of ~2.4 dbi. On the air I do not notice any F/B so the model may be reliable in this respect.
The question to ask is whether 4 db of gain and modest F/B is worth the trouble. It can be easily argued that a separate and better performing 17 meter mono-band yagi is preferable. In my situation a separate yagi would not be placed as high as where the XM240 is currently located: 46 meters up. I am undecided. It's food for thought until the time comes that I decide to do more on 17 meters.
I have not reported on the SWR or feed point impedance because the straight tubes model of the antenna is unreliable on 17 meters. The best I can predict, based on exploring the model, is that the R component of the impedance is in the region of 25 Ω. I will not predict the reactance other than to note that it should be comfortably low.
A switchable matching unit, such as an L-network can be employed for 17 meters if an SWR of 2 or 2.5 is problematic. The network can be mounted at the mast to avoid adding weight at the end of the boom, and the network designed to match the impedance measured at that point.
Of some concern is that the Cushcraft 1:1 common mode choke operating at 18 MHz, a kilowatt and a mismatch at the feed point. A better balun is advisable or the network and switch should be located at the driven element and the balun switched out of circuit when operating 17 meters. But this is all a lot of bother for a modest improvement of 17 meter performance.
Conclusion
As said, this is purely a thought experiment to consider my future alternatives for improved 17 meter performance. I don't know if anyone else has tried to do this with an XM240 and I didn't research the question.
Computer modelling makes these types of analyses easy to do in the comfort of our shacks. It's a lot easier than modifying the antenna, especially an antenna of this size, and measuring the results. The analysis will now be shelved. Time will tell whether I return to it in the next couple of years.
Tuesday, November 13, 2018
Ode to the Nyloc
The TH6 on top of the 150' tower had become increasingly intermittent over several months. At first I suspected a bad port on my antenna switch. With the switch repaired the problem continued. The next time I climbed the tower I noticed that the rotation loop connector to the LDF5 Heliax main run was slightly loose.
I didn't repair it just then since I didn't have the tools and weatherproofing material to open and close the connection. I tied it off more securely to the tower because I saw that the coax was just stiff enough to transfer a small torque to the connection when the antenna turned, which was likely responsible for the loosening.
That seemed to help. Then I became busy and my next climb was far in the future. Again I let it be. As you might guess the problem worsened to the point that the antenna could not be used at all. Of course by then the weather turned unseasonably cold, windy and wet, making a climb that high difficult and unwelcome.
A one day break in the weather combined with a dire forecast forced my hand. I packed all the material I would need and climbed the tower in cool, partly sunny weather with a stiff breeze that was thankfully at my back (as on many commercial towers it has only one climbing face). I terminated the bottom end of the coax with a small 50 Ω load and brought the antenna analyzer up the tower. This arrangement allowed me to test the antenna side and the transmission line so that I wouldn't be left guessing if my prognosis proved to be wrong.
After cutting through the layers of sealing tape and unscrewing the rotation loop I tightened the loose N-to-UHF adapter and attached the analyzer. Luckily the transmission line tested good. Going the other way so did the antenna side. All done? Not so fast.
Just to be sure all was well I ran the analyzer in continuous mode and wiggled the rotation loop. The analyzer jumped around like crazy. Reaching up and around blindly with one hand so that I keep my eyes on the analyzer I wiggled the all along the coax and then the balun connector. It got worse. When my fingers moved to the other side of the balun one of the wires was found to be loose.
Craning my head around I saw that a retaining nut and lock washer on the antenna side of the balun were missing. I my mind I thought: oh no, not again! At least this time I had found the root cause, and there was an easy fix.
Yagis vibrate in the breeze, and there's a lot of breeze that high up. Elements on Hy-Gain yagis are particularly prone to singing even when roped per the manufacturer's instructions. Eventually element tips fatigue and break. I wasn't too worried about breakage since the antenna is very old and temporary. Well, maybe not so temporary since my plan to replace it this year has been delayed.
Vibration also loosens fasteners. Lock washers are not as reliable as one might think, especially not on round aluminum tubes. I know professionals who avoid them in favour of flat washers and jam nuts or double nuts. The referenced experience (link) with the TH7 was not the first time and the current problem is not the second time. It happens too often. In the interests of minimizing maintenance at a station with multiple towers and antennas it helps to spend a few extra pennies on better fasteners.
This is a job for a Nyloc nut. I have lots of the right size ever since I stocked up on them to fix loose bolts on my three Hy-Gain tri-band yagis and other devices. But I didn't bring one up the tower with me. As a temporary fix I looked around and noticed that the studs on the Balun Designs balun are the same size as the bolts on all the Hy-Gain clamps: ¼" NC stainless.
I liberated a stainless nut and lock washer from the refurbished TH6 boom-to-mast clamp and fixed the balun connection. The analyzer gave a thumbs up sign as I wiggled everything in sight. I redid the weatherproofing and called it a day. It was cold up there! Weather for the next week looks horrendous and I can only hope it gets better after that. When it does I will be replacing the nuts with Nyloc nuts.
As I slowly build my next set of yagis (for use next year, not this year, unfortunately) I am making liberal use of Nyloc nuts. On long boom yagis this is especially important since, unlike a "small" TH6, the feed point is not accessible. When a nut falls off a balun far out on the boom there may be option other than taking the antenna down for repair. That's a lot of work! Better to spend a little extra on better fasteners.
This is my ode to the Nyloc. I've become a believer. So should you. While building my station I've learned about other specialty fasteners that will likely make appearances in future articles.
I didn't repair it just then since I didn't have the tools and weatherproofing material to open and close the connection. I tied it off more securely to the tower because I saw that the coax was just stiff enough to transfer a small torque to the connection when the antenna turned, which was likely responsible for the loosening.
That seemed to help. Then I became busy and my next climb was far in the future. Again I let it be. As you might guess the problem worsened to the point that the antenna could not be used at all. Of course by then the weather turned unseasonably cold, windy and wet, making a climb that high difficult and unwelcome.
A one day break in the weather combined with a dire forecast forced my hand. I packed all the material I would need and climbed the tower in cool, partly sunny weather with a stiff breeze that was thankfully at my back (as on many commercial towers it has only one climbing face). I terminated the bottom end of the coax with a small 50 Ω load and brought the antenna analyzer up the tower. This arrangement allowed me to test the antenna side and the transmission line so that I wouldn't be left guessing if my prognosis proved to be wrong.
After cutting through the layers of sealing tape and unscrewing the rotation loop I tightened the loose N-to-UHF adapter and attached the analyzer. Luckily the transmission line tested good. Going the other way so did the antenna side. All done? Not so fast.
Just to be sure all was well I ran the analyzer in continuous mode and wiggled the rotation loop. The analyzer jumped around like crazy. Reaching up and around blindly with one hand so that I keep my eyes on the analyzer I wiggled the all along the coax and then the balun connector. It got worse. When my fingers moved to the other side of the balun one of the wires was found to be loose.
Craning my head around I saw that a retaining nut and lock washer on the antenna side of the balun were missing. I my mind I thought: oh no, not again! At least this time I had found the root cause, and there was an easy fix.
Yagis vibrate in the breeze, and there's a lot of breeze that high up. Elements on Hy-Gain yagis are particularly prone to singing even when roped per the manufacturer's instructions. Eventually element tips fatigue and break. I wasn't too worried about breakage since the antenna is very old and temporary. Well, maybe not so temporary since my plan to replace it this year has been delayed.
Vibration also loosens fasteners. Lock washers are not as reliable as one might think, especially not on round aluminum tubes. I know professionals who avoid them in favour of flat washers and jam nuts or double nuts. The referenced experience (link) with the TH7 was not the first time and the current problem is not the second time. It happens too often. In the interests of minimizing maintenance at a station with multiple towers and antennas it helps to spend a few extra pennies on better fasteners.
This is a job for a Nyloc nut. I have lots of the right size ever since I stocked up on them to fix loose bolts on my three Hy-Gain tri-band yagis and other devices. But I didn't bring one up the tower with me. As a temporary fix I looked around and noticed that the studs on the Balun Designs balun are the same size as the bolts on all the Hy-Gain clamps: ¼" NC stainless.
I liberated a stainless nut and lock washer from the refurbished TH6 boom-to-mast clamp and fixed the balun connection. The analyzer gave a thumbs up sign as I wiggled everything in sight. I redid the weatherproofing and called it a day. It was cold up there! Weather for the next week looks horrendous and I can only hope it gets better after that. When it does I will be replacing the nuts with Nyloc nuts.
As I slowly build my next set of yagis (for use next year, not this year, unfortunately) I am making liberal use of Nyloc nuts. On long boom yagis this is especially important since, unlike a "small" TH6, the feed point is not accessible. When a nut falls off a balun far out on the boom there may be option other than taking the antenna down for repair. That's a lot of work! Better to spend a little extra on better fasteners.
This is my ode to the Nyloc. I've become a believer. So should you. While building my station I've learned about other specialty fasteners that will likely make appearances in future articles.
Friday, November 9, 2018
Contesting Big and Small
Unlike some contesters of my acquaintance I am happy to contest in most any category. Most often the categories are relevant to power -- QRP, 100 watts and maximum legal limit -- but there are also categories for numbers of operators and simultaneous transmitters, wire antennas or reliance on skimmers and spotting networks. For CQ WW SSB my category was high power multi-two (HP M2). Then QRP (SO QRP) a week later for CW Sweepstakes. It's quite the contrast!
Soon after I got into contesting and DX as a teenager I was all for more and more power. As with fast cars, power was more than I could afford and there could be undesirable consequences. An example of the latter was irate neighbours during contest weekends. Even 100 watts caused problems with televisions, telephones and stereos in the 1970s. In response to a firm suggestion from my parents I stopped inviting over friends to multi-op with their amplifiers.
When I got a real job and saved up for a house up went the tower and antennas, and a Collins 30S-1 entered my ham life. That was a big beast with a 4CX1500B (replacing the original 4CX1000A) and Peter Dahl plate transformer. It was capable of putting out a lot of power.
This was the late 1980s and all the above problems with power returned. Some of the neighbourhood problems could be fixed with a few toroids, but not all, and I never broached the idea of opening up anyone's appliances to insert RF bypass components. So the contests I entered from my home station were in the 100 watts category. I wasn't happy about it. The amplifier only saw action when DXing or on the low bands where there were few RFI difficulties.
Older and more mature when I returned to the hobby in 2013 I decided to start small, with QRP, and see where that led. DXing and contesting with 5 watts were a lot more fun than I expected. When I bought a 100 watt rig two years later I continued to enter many contests in the QRP category. Part of it was worry about keeping the peace with the neighbours (who were mostly the same ones that experienced the woes of living next to a kilowatt 20 years earlier), and also because I was more competitive in the QRP category with my modest antennas.
CQ WW SSB
Which brings us to the last full weekend in October and the biggest international contest on the calendar: CQ Worldwide SSB. Over a chat about towers early this fall Vlad VE3JM invited me to operate from his contest station an hour's drive east of Ottawa. If you contest his big signal should be familiar. Vlad has several towers with stacked yagis on the high bands and gain antennas on the low bands.
This would be my first foray into high power for many years. I had some trepidation about whether I'd remember all the tricks of QRO contesting, which is very different from low power and QRP. You might think it gets easier. It doesn't. In fact it's far more intense and competitive, and in many respects more challenging. There are no excuses in QRO: you are competing against the best contesters and the best equipped stations around the world.
Team: I have to say this was perhaps the most laid back and easygoing multi-op team I've ever been part of. We followed no schedule and no grand strategy. Operating as Multi Two we kept both stations going the full 48 hours, except for a few hours the second night when there was just one operator. In addition to myself there was Chris VE3FU/VO2AC, Rich VE3KI and, of course, Vlad VE3JM, all of whom are experienced contesters.
We were so polite that on wandering into the shack one of the operators would inevitably lift his headset and ask if you wanted to operate, even when they were in the middle of a big run. Someone always seemed to be cooking or heating up food, or cleaning the accumulated dirty dishes. When you wanted to sleep or take a short break there was rarely a problem recruiting a relief operator.
Strategy: The strategy we followed was simple: run, run, run, but keep an eye out for multipliers. When you have a dominating signal running is really the best way to score high, including multipliers. Where we perhaps fell short was on multipliers since without one operator scouring the bands many can be missed because on SSB there is no skimmer, only human spots. But to do this properly we'd need a third station for listening and another operator.
It wasn't always possible to run. Even though we can work Americans for points there were long periods overnight when we had to S & P for DX and, where possible, multipliers. This is entirely due to being at the bottom of the solar cycle. For example, with the high bands closing early the QRM on 40 meters is intense and even a big signal like ours is difficult to hear in Europe. Then 40 fades on the productive European path and everyone migrates to 80 and, if they can, 160. SSB is a big challenge on the low bands due to the intense QRM and higher noise level.
Learning curve: I was the only member of the team that hadn't operated at the station so my learning curve was the steepest. Although I've been to Vlad's station before that is very different from sitting down and operating. For one, the logging software was new to me. Before the contest I downloaded a trial version and familiarized myself with it as much as possible. It was important to focus on a small set of critical features that would be regularly used. A list of common commands was taped to the computer display.
Antennas and antenna sharing/switching are unique to every station. We went through it all on Friday afternoon and practiced. Tri-banders were shared, with their own custom switching software between stations. Rotators controlled yagis for multiple bands so you need to be aware of what the other operator was doing even when they weren't using the tower when you wanted to turn your antenna. Communication among operators was key to making this work. There were gain antennas on all bands, 160 through 10 meters. Directional receive antennas are shared by both operators.
For the most part we successfully navigated the software and hardware controls, though mistakes were occasionally made. It was necessary to learn the stacked yagi configuration that worked best on every path. Some of this was complicated by precipitation static (snow!) that affects the top antennas the most. On the low bands you have to flip through the directions quite a lot to cover the compass or to better copy weak callers.
Weak signals: Perhaps the most challenging aspect of operating a station with a big signal is that you are regularly called by much weaker signals. Many callers, and most on the low bands, are difficult to copy. It's a struggle, and one I had to relearn after being out of the kilowatt game for so many years. They hear you easily but you must play with antennas and filters and ask for repeats and fills to put them into the log. It can be mentally fatiguing but necessary to scoring well. All callers are appreciated despite how much work it can entail. At times I had to encourage callers to keep trying.
On the other hand, no matter how weak the DX station you find when doing S & P you can call them and expect to work them. That aspect of weak signal copying can be a real joy. All those years of "the one that got away" are forgotten. You hear them, you call them and they're in the log. Pile ups on the rare ones are quickly dealt with. You work them and move on to the next.
Problems: It is a rare contest where everything goes right. Our weekend included noise of unknown origin, loose rotator clamp, receive antennas among other problems. Certainly our score was impacted though not greatly. We were able to find workarounds for most by being smarter about using what we had and avoiding, if only temporarily, certain bands or antennas. That is perhaps one measure of a good team: that we found ways to do well despite the problems.
Not the biggest signal: Several times during the contest I was complimented on the dominance of our signal on the bands. We did indeed have a great station and it showed in our score. Yet it was not the best. As with anything, it seems no matter how much you've done there's always someone, or many someones, whose stations are bigger.
Many times we were beat in the multiplier pile ups by well known call signs of super-stations and had to wait our turn. On paths and bands with marginal conditions we missed out on multipliers that would have given our score a big boost. No matter how big your station there will be the ones that get away.
Despite everything we had fun and made a competitive score. The weekend was a success.
CW Sweepstakes
Operating QRP in Sweepstakes was quite different. My trusty (and much neglected these days) KX3 was dusted off and patched into the computer, antennas and other accessories. This is my only good option for QRP because my main rig, the FTdx5000, has a minimum power output of 10 watts and I don't have a 3 db outboard attenuator.
QRP gave me a relaxed way to enjoy the contest. QSO rates would be modest and stretched out over more hours. With higher power Sunday can be a real drag once all the most active hundreds of stations have been worked. Recall that in this contest you work each station just once, regardless of band.
Being in the eastern region of the continent in a solar minimum I knew that the low bands would deliver most of the contacts, and that is just how it happened. Despite running 5 watts my most productive band was 80 meters. I had no trouble running on Saturday evening. The 3-element vertical yagi fixed to the southwest delivered many west coast QSOs, some of whom answered my CQ. That was fun.
I sometimes joke with friends that the less power you run the bigger your antennas need to be, and that's why I am putting up big towers and antennas. There is indeed some truth to the antennas compensating for low power, though not as much as might be thought. It takes a lot of antenna to bridge the 23 db gulf between 5 watts and 1,000 watts!
Not only could I run it was also possible to crack a few pile ups on multipliers and the fresh meat (participants who only show up briefly late in the contest) on Sunday. A few stations seemed to doubt that my class was really 'Q' since my signal was S9+. That, too, was fun.
Overall this was a low intensity operation. I relaxed, ran when I wanted and hunted when I wanted, and I kept to regular mealtimes. Despite operating 3 and a half hours shy of the full 24 hours allowed I placed well in my category, at least with regard to self reported scores on 3830 and in advance of log checking. I know of a couple of QRP entrants with high scores that are not reported on 3830.
How I'll ultimately place I don't know or care. It is entirely possible I would have won had I stuck it out for the full 24 hours. I achieved my objective of having fun and seeing what QRP would do with my current crop of antenna. This is a very different sort of fun compared to CQ WW SSB a week earlier.
I know contesters who always operate QRO or QRP, and who are always serious or casual. For me any approach to contesting can be fun. In the future I will continue to mix it up from contest to contest. That's what works for me.
Soon after I got into contesting and DX as a teenager I was all for more and more power. As with fast cars, power was more than I could afford and there could be undesirable consequences. An example of the latter was irate neighbours during contest weekends. Even 100 watts caused problems with televisions, telephones and stereos in the 1970s. In response to a firm suggestion from my parents I stopped inviting over friends to multi-op with their amplifiers.
When I got a real job and saved up for a house up went the tower and antennas, and a Collins 30S-1 entered my ham life. That was a big beast with a 4CX1500B (replacing the original 4CX1000A) and Peter Dahl plate transformer. It was capable of putting out a lot of power.
This was the late 1980s and all the above problems with power returned. Some of the neighbourhood problems could be fixed with a few toroids, but not all, and I never broached the idea of opening up anyone's appliances to insert RF bypass components. So the contests I entered from my home station were in the 100 watts category. I wasn't happy about it. The amplifier only saw action when DXing or on the low bands where there were few RFI difficulties.
Older and more mature when I returned to the hobby in 2013 I decided to start small, with QRP, and see where that led. DXing and contesting with 5 watts were a lot more fun than I expected. When I bought a 100 watt rig two years later I continued to enter many contests in the QRP category. Part of it was worry about keeping the peace with the neighbours (who were mostly the same ones that experienced the woes of living next to a kilowatt 20 years earlier), and also because I was more competitive in the QRP category with my modest antennas.
CQ WW SSB
Which brings us to the last full weekend in October and the biggest international contest on the calendar: CQ Worldwide SSB. Over a chat about towers early this fall Vlad VE3JM invited me to operate from his contest station an hour's drive east of Ottawa. If you contest his big signal should be familiar. Vlad has several towers with stacked yagis on the high bands and gain antennas on the low bands.
This would be my first foray into high power for many years. I had some trepidation about whether I'd remember all the tricks of QRO contesting, which is very different from low power and QRP. You might think it gets easier. It doesn't. In fact it's far more intense and competitive, and in many respects more challenging. There are no excuses in QRO: you are competing against the best contesters and the best equipped stations around the world.
Team: I have to say this was perhaps the most laid back and easygoing multi-op team I've ever been part of. We followed no schedule and no grand strategy. Operating as Multi Two we kept both stations going the full 48 hours, except for a few hours the second night when there was just one operator. In addition to myself there was Chris VE3FU/VO2AC, Rich VE3KI and, of course, Vlad VE3JM, all of whom are experienced contesters.
We were so polite that on wandering into the shack one of the operators would inevitably lift his headset and ask if you wanted to operate, even when they were in the middle of a big run. Someone always seemed to be cooking or heating up food, or cleaning the accumulated dirty dishes. When you wanted to sleep or take a short break there was rarely a problem recruiting a relief operator.
Strategy: The strategy we followed was simple: run, run, run, but keep an eye out for multipliers. When you have a dominating signal running is really the best way to score high, including multipliers. Where we perhaps fell short was on multipliers since without one operator scouring the bands many can be missed because on SSB there is no skimmer, only human spots. But to do this properly we'd need a third station for listening and another operator.
It wasn't always possible to run. Even though we can work Americans for points there were long periods overnight when we had to S & P for DX and, where possible, multipliers. This is entirely due to being at the bottom of the solar cycle. For example, with the high bands closing early the QRM on 40 meters is intense and even a big signal like ours is difficult to hear in Europe. Then 40 fades on the productive European path and everyone migrates to 80 and, if they can, 160. SSB is a big challenge on the low bands due to the intense QRM and higher noise level.
Learning curve: I was the only member of the team that hadn't operated at the station so my learning curve was the steepest. Although I've been to Vlad's station before that is very different from sitting down and operating. For one, the logging software was new to me. Before the contest I downloaded a trial version and familiarized myself with it as much as possible. It was important to focus on a small set of critical features that would be regularly used. A list of common commands was taped to the computer display.
Antennas and antenna sharing/switching are unique to every station. We went through it all on Friday afternoon and practiced. Tri-banders were shared, with their own custom switching software between stations. Rotators controlled yagis for multiple bands so you need to be aware of what the other operator was doing even when they weren't using the tower when you wanted to turn your antenna. Communication among operators was key to making this work. There were gain antennas on all bands, 160 through 10 meters. Directional receive antennas are shared by both operators.
For the most part we successfully navigated the software and hardware controls, though mistakes were occasionally made. It was necessary to learn the stacked yagi configuration that worked best on every path. Some of this was complicated by precipitation static (snow!) that affects the top antennas the most. On the low bands you have to flip through the directions quite a lot to cover the compass or to better copy weak callers.
Weak signals: Perhaps the most challenging aspect of operating a station with a big signal is that you are regularly called by much weaker signals. Many callers, and most on the low bands, are difficult to copy. It's a struggle, and one I had to relearn after being out of the kilowatt game for so many years. They hear you easily but you must play with antennas and filters and ask for repeats and fills to put them into the log. It can be mentally fatiguing but necessary to scoring well. All callers are appreciated despite how much work it can entail. At times I had to encourage callers to keep trying.
On the other hand, no matter how weak the DX station you find when doing S & P you can call them and expect to work them. That aspect of weak signal copying can be a real joy. All those years of "the one that got away" are forgotten. You hear them, you call them and they're in the log. Pile ups on the rare ones are quickly dealt with. You work them and move on to the next.
Problems: It is a rare contest where everything goes right. Our weekend included noise of unknown origin, loose rotator clamp, receive antennas among other problems. Certainly our score was impacted though not greatly. We were able to find workarounds for most by being smarter about using what we had and avoiding, if only temporarily, certain bands or antennas. That is perhaps one measure of a good team: that we found ways to do well despite the problems.
Not the biggest signal: Several times during the contest I was complimented on the dominance of our signal on the bands. We did indeed have a great station and it showed in our score. Yet it was not the best. As with anything, it seems no matter how much you've done there's always someone, or many someones, whose stations are bigger.
Many times we were beat in the multiplier pile ups by well known call signs of super-stations and had to wait our turn. On paths and bands with marginal conditions we missed out on multipliers that would have given our score a big boost. No matter how big your station there will be the ones that get away.
Despite everything we had fun and made a competitive score. The weekend was a success.
CW Sweepstakes
Operating QRP in Sweepstakes was quite different. My trusty (and much neglected these days) KX3 was dusted off and patched into the computer, antennas and other accessories. This is my only good option for QRP because my main rig, the FTdx5000, has a minimum power output of 10 watts and I don't have a 3 db outboard attenuator.
QRP gave me a relaxed way to enjoy the contest. QSO rates would be modest and stretched out over more hours. With higher power Sunday can be a real drag once all the most active hundreds of stations have been worked. Recall that in this contest you work each station just once, regardless of band.
Being in the eastern region of the continent in a solar minimum I knew that the low bands would deliver most of the contacts, and that is just how it happened. Despite running 5 watts my most productive band was 80 meters. I had no trouble running on Saturday evening. The 3-element vertical yagi fixed to the southwest delivered many west coast QSOs, some of whom answered my CQ. That was fun.
I sometimes joke with friends that the less power you run the bigger your antennas need to be, and that's why I am putting up big towers and antennas. There is indeed some truth to the antennas compensating for low power, though not as much as might be thought. It takes a lot of antenna to bridge the 23 db gulf between 5 watts and 1,000 watts!
Not only could I run it was also possible to crack a few pile ups on multipliers and the fresh meat (participants who only show up briefly late in the contest) on Sunday. A few stations seemed to doubt that my class was really 'Q' since my signal was S9+. That, too, was fun.
Overall this was a low intensity operation. I relaxed, ran when I wanted and hunted when I wanted, and I kept to regular mealtimes. Despite operating 3 and a half hours shy of the full 24 hours allowed I placed well in my category, at least with regard to self reported scores on 3830 and in advance of log checking. I know of a couple of QRP entrants with high scores that are not reported on 3830.
How I'll ultimately place I don't know or care. It is entirely possible I would have won had I stuck it out for the full 24 hours. I achieved my objective of having fun and seeing what QRP would do with my current crop of antenna. This is a very different sort of fun compared to CQ WW SSB a week earlier.
I know contesters who always operate QRO or QRP, and who are always serious or casual. For me any approach to contesting can be fun. In the future I will continue to mix it up from contest to contest. That's what works for me.
Wednesday, October 31, 2018
Lurking, Waiting and Scheduling: Circumventing the Pile Up
Now that the Ducie island VP6D DXpedition is wrapping up I thought it worthwhile to review a few of the less competitive techniques for working the rare ones. I used all of them for at least one band slot to work VP6D. I call them "non-competitive" since none involves pile up busting skills, antennas, power or propagation prognostications.
These are complementary to those competitive skills, many of which I've discussed numerous times on this blog, though admittedly not for a while, and mostly in the context of QRP and modest antennas. Just do a search to find those articles. I prefer competitive skills since they are a path to improving my operating and contesting, and it's lots of fun to mix it up in the pile ups with the world's best stations and operators.
Lurking
My timing and luck were not with on 40 meters CW in the early days of the DXpedition. They got on 40 meters close to their sunset, which is prime evening operating time in eastern North America. The pile ups were fierce. Despite having a 2-element yagi up 46 meters my 200 watts could not compete with the mass of kilowatt signals.
According to their band plan they transmit on 7.010 MHz and listen up. One evening I set the receiver on this frequency and programmed a transmit split of 1.02 kHz. I then unplugged the headphones and reduced the volume on the speakers low enough that the noise wouldn't be objectionable. With that playing in the background I concentrated on non-ham tasks that I could do in the shack; my shack and home office share a converted bedroom.
Some time later I distinctly heard a high speed "VP6D up" emanating from the speakers. By the time I stood up and took the two steps to the desk with the rig the message repeated. I punched the memory button to send my call, waited a second and punched it again. My eagerness caused me to double with him. I waited and a second later I heard "VE3VN 599". With a "599 TU" I had them logged on 40 meters CW.
There were a couple of other lurkers but I got through first. To be courteous I waited a few seconds for one more lurker to work VP6D before spotting them. Within a minute the pile up was roaring.
Lurking is boring but it can work to circumvent the pile up. Unless you have a excess amount of time on your hands I suggest you do as I did by scheduling some useful tasks you can do in the shack while you wait. Many times the DX does not show up and you'll be disappointed.
Waiting
If the DXpedition is long enough and you are very patient most pile ups can be entirely avoided by waiting. Eventually all pile ups thin or disappear as most everyone has worked the DX on a particular band and mode.
This is how I worked VP6D on 30 meters. I had tried a few times to break through the pile up early in DXpedition but for some reason I had no success on this band. Waiting was not entirely voluntary because for numerous reasons I often could not get on the air when conditions were favourable. Other times they were not active on 30 meters or were on FT8 rather than CW.
The day after I got home after operating CQ WW SSB from another stration I worked them first call when heard on 30 meters CW. They were calling CQ with few takers. Waiting can work.
The danger with waiting is that DXpeditions can be wrapped up earlier than planned due to weather and other logistical problems. If you wait you lose. Consider the recent TT8KO DXpedition that lasted one day before the authorities shut it down. Wait if you must but don't be surprised when you miss the rare one because you waited.
Scheduling
I was only able to reinstall my 160 meter antenna the day before CQ WW SSB. Since the DXpedition was slated to end a few days after the contest and I would be unavailable during the contest I chose to schedule time to find and work them on 160 meters. It is typical that DXpeditions start dismantling antennas a couple of days in advance of the DXpedition's end and they usually start with the low bands. Waiting to work them on 160 meters after the contest would be risky.
Lurking on 160 meters isn't quite as reliable as on 40 meters since the noise is high and I don't yet have a low noise receiving antenna to the southwest, towards VP6. Instead I lurked at one remove by monitoring their DXA page on the shack computer. I would glance over from time to time to see if the 160 meter activity button was lit. Since I did not have have on 30 meters either I was watching for that one as well.
When it was midnight I became impatient. I needed to rest up before the big contest. So I tuned to their frequency and connected to the spotting network. Lo! There they were. DXA was not updating properly and I missed their first appearance on the band. By this time they were slowing working Europeans, which is a very difficult path. After listening for a few minutes I could see this would continue for some time. I reluctantly shut down and went to bed. However I had not given up.
I decided to risk contest fatigue by getting up 15 minutes before sunrise. Their fantastically strong signal was peaking towards S9 as the sun crept up to the horizon. At 5 minutes before sunrise they were in the log despite a good sized pile up. Perhaps I had the advantage due to a sunrise enhancement, or perhaps I was a little bit lucky. I didn't stick around to monitor their signal strength as daylight flooded through the windows.
Scheduling can feel like work rather than a hobby. But if you want to bag the DX it is something you will need to do occasionally even if you have a big signal. Knowing the schedule of rare DX and planning your schedule on the air to match has a long tradition. In the decades before DXpeditioning was common and spotting networks were non-existent this was a tried and true technique for the serious DXers. If you'd like to read more about it I recommend W9KNI's venerable book The Complete DX'er.
These are complementary to those competitive skills, many of which I've discussed numerous times on this blog, though admittedly not for a while, and mostly in the context of QRP and modest antennas. Just do a search to find those articles. I prefer competitive skills since they are a path to improving my operating and contesting, and it's lots of fun to mix it up in the pile ups with the world's best stations and operators.
Lurking
My timing and luck were not with on 40 meters CW in the early days of the DXpedition. They got on 40 meters close to their sunset, which is prime evening operating time in eastern North America. The pile ups were fierce. Despite having a 2-element yagi up 46 meters my 200 watts could not compete with the mass of kilowatt signals.
According to their band plan they transmit on 7.010 MHz and listen up. One evening I set the receiver on this frequency and programmed a transmit split of 1.02 kHz. I then unplugged the headphones and reduced the volume on the speakers low enough that the noise wouldn't be objectionable. With that playing in the background I concentrated on non-ham tasks that I could do in the shack; my shack and home office share a converted bedroom.
Some time later I distinctly heard a high speed "VP6D up" emanating from the speakers. By the time I stood up and took the two steps to the desk with the rig the message repeated. I punched the memory button to send my call, waited a second and punched it again. My eagerness caused me to double with him. I waited and a second later I heard "VE3VN 599". With a "599 TU" I had them logged on 40 meters CW.
There were a couple of other lurkers but I got through first. To be courteous I waited a few seconds for one more lurker to work VP6D before spotting them. Within a minute the pile up was roaring.
Lurking is boring but it can work to circumvent the pile up. Unless you have a excess amount of time on your hands I suggest you do as I did by scheduling some useful tasks you can do in the shack while you wait. Many times the DX does not show up and you'll be disappointed.
Waiting
If the DXpedition is long enough and you are very patient most pile ups can be entirely avoided by waiting. Eventually all pile ups thin or disappear as most everyone has worked the DX on a particular band and mode.
This is how I worked VP6D on 30 meters. I had tried a few times to break through the pile up early in DXpedition but for some reason I had no success on this band. Waiting was not entirely voluntary because for numerous reasons I often could not get on the air when conditions were favourable. Other times they were not active on 30 meters or were on FT8 rather than CW.
The day after I got home after operating CQ WW SSB from another stration I worked them first call when heard on 30 meters CW. They were calling CQ with few takers. Waiting can work.
The danger with waiting is that DXpeditions can be wrapped up earlier than planned due to weather and other logistical problems. If you wait you lose. Consider the recent TT8KO DXpedition that lasted one day before the authorities shut it down. Wait if you must but don't be surprised when you miss the rare one because you waited.
Scheduling
I was only able to reinstall my 160 meter antenna the day before CQ WW SSB. Since the DXpedition was slated to end a few days after the contest and I would be unavailable during the contest I chose to schedule time to find and work them on 160 meters. It is typical that DXpeditions start dismantling antennas a couple of days in advance of the DXpedition's end and they usually start with the low bands. Waiting to work them on 160 meters after the contest would be risky.Lurking on 160 meters isn't quite as reliable as on 40 meters since the noise is high and I don't yet have a low noise receiving antenna to the southwest, towards VP6. Instead I lurked at one remove by monitoring their DXA page on the shack computer. I would glance over from time to time to see if the 160 meter activity button was lit. Since I did not have have on 30 meters either I was watching for that one as well.
When it was midnight I became impatient. I needed to rest up before the big contest. So I tuned to their frequency and connected to the spotting network. Lo! There they were. DXA was not updating properly and I missed their first appearance on the band. By this time they were slowing working Europeans, which is a very difficult path. After listening for a few minutes I could see this would continue for some time. I reluctantly shut down and went to bed. However I had not given up.
I decided to risk contest fatigue by getting up 15 minutes before sunrise. Their fantastically strong signal was peaking towards S9 as the sun crept up to the horizon. At 5 minutes before sunrise they were in the log despite a good sized pile up. Perhaps I had the advantage due to a sunrise enhancement, or perhaps I was a little bit lucky. I didn't stick around to monitor their signal strength as daylight flooded through the windows.
Scheduling can feel like work rather than a hobby. But if you want to bag the DX it is something you will need to do occasionally even if you have a big signal. Knowing the schedule of rare DX and planning your schedule on the air to match has a long tradition. In the decades before DXpeditioning was common and spotting networks were non-existent this was a tried and true technique for the serious DXers. If you'd like to read more about it I recommend W9KNI's venerable book The Complete DX'er.
Thursday, October 25, 2018
DXCC: The Remaining 40
When I worked the KH1 DXpedition on several bands earlier this year I briefly celebrated. According to my records it was DXCC country #300 worked since I returned to the air in 2013. As it turned out my records contained a few errors. Baker Island was #299. Eventually #300 came along with Ducie Island VP6D, a DXpedition that is ongoing as I write this. Of these 280 are confirmed via LoTW, which is the only way I QSL nowadays.
It is a milestone that was achieved more slowly than I expected. Consider that I reached 225 countries in two years using a maximum of 10 watts and modest antennas. Spotting networks and information dissemination about activity in rare locales makes running up the country count easier than ever.
Amusingly, the first 100 countries were easy enough despite running QRP and recruiting the aluminum eaves of my house in Ottawa as a random wire antenna. That was great fun. Doing it that way -- with a tiny station and low expectations -- played an important role in rekindling my passion for the hobby.
With DXCC the law of diminishing returns applies: as the country count increases each incremental country requires more work than the last. By the time 300 countries are reached the required effort is quite high and the progress slow.
My lifetime total is perhaps 315 or 320, reduced by deleted countries during the years I was inactive. But that number doesn't interest me. I wanted a fresh start after a 20 year hiatus from the hobby as a way to measure my progress. DXCC doesn't mean much to me and I have never applied for the award. I likely never will. It is the activity of DXing that I find appealing.
Maybe it's the excitement, maybe it's the competition and maybe it's the simply the magic of radio. Perhaps it's explained by catching the DXing bug when I was young, decades ago, when global communication was a rarity, except for those who got into ham radio. Youthful passions tend to linger.
Rather than dwell on the 300 country milestone what I'd like to do in this article is discuss the ones I have yet to work. With 340 countries on the current DXCC list that there are 40 countries left. By the end of this article it should be evident why working them all, or achieving the lesser but still heady level of DXCC Honour Roll, is so incredibly difficult. Most DXers who have done it have taken a lifetime to get there.
I'll group countries together where it makes sense to do so to keep this article from becoming repetitive and too long. Apart from the grouping, countries will be ordered by prefix.
3D2C Conway: I vaguely recall some DXpedition activity but have yet to work this one. Perhaps all this one will take is paying more attention. It shouldn't be difficult to work.
3Y Bouvet and 3Y Peter I: These Antarctic islands are remote and battered by severe sea and weather conditions. There was one recent DXpedition attempt to Bouvet island that failed to land due to the weather. I have both countries confirmed back in the 1980s. All one can do is wait for intrepid and well-financed DXpeditioners to make the attempt.
4U1UN United Nations: Only this summer has the station been rebuilt in compliance with the severe security regulations at the UN complex in New York. I have heard them weakly on 20 meters but not workable. New York is too close for reliable communication on the higher HF bands except by scatter and high power. I would be surprised if I don't have this one in the log by 2019.
7O Yemen, YK Syria: One word says it all -- war. Very sad and tragic, and these won't be resolved soon. Going back a few decades I have lots of cards from 7O and a few from YK. But for now they are not workable.
BS7H Scarborough Reef: For one elderly ham who lives nearby this is the only country he needs to have them all. Another longtime DXer of my acquaintance doesn't believe it'll ever be active again. I have no opinion. Even if it were active it would be very difficult to work during a solar minimum from this part of the world.
BV9P Pratas: Like Scarborough Reef I know little about this one. Both have flown under my radar since they appear to have become entities during my 20 years away from the hobby.
CE0X San Felix: I've worked CE0Y and CE0Z, yet failed to work this one. If there's been recent activity I've missed it since I keep confusing these Chilean islands, forgetting which is the one I haven't worked. Like many other entities I worked this one decades ago. I'll just have to pay closer attention to catch the next visitor to San Felix island.
EZ Turkmenistan: This former Soviet republic was uncommon but not rare back in the days of the USSR. Since then Turkmenistan has been jinxed with totalitarian rule. Although that is not necessarily incompatible with amateur radio, it is not the case here. There have been signs that the political situation may be improving. We can only wait.
FR/g Glorioso: Another rare island waiting for a group to launch a DXpedition. Again, all I can do is wait.
FR/t Tromelin: There was an excellent DXpedition a few years ago, one which I completely failed to work. It happens. At the time my antenna and power situation made it difficult. I will just have to wait for the next DXpedition, and that may be years away.
FT5W Crozet and FT5X Kerguelen: Like the US, France has become fiercely protective of the environment on isolated islands with unique flora and fauna. French hams have been trying and failing to gain permission to land on these islands. There is (was?) a ham on Crozet Island although I am only aware that he has worked /MM when asea, and I did work him there. But that doesn't count for DXCC.
HK0M Malpelo: No recent DXpeditions. As with some other environmentally sensitive islands permission to land and operate is not routine. I am unfamiliar with how restrictive Colombia is with respect to Malpelo island.
JD1 Minami Torashima: As with a number of entities on this list, there is occasional activity from this one. Unfortunately the path is not the easiest during a solar minimum and I have yet to catch up with them. I need propagation and activity to coincide, and to pay enough attention to notice when it does occur.
JX Jan Mayen: This one ought to be easy and there has been some activity. Maybe I just need to pay attention and try harder.
KH3 Johnston, KH4 Midway, KH7K Kure, KP5 Desecheo: Permission for Kure island was recently denied (again) and the others are similarly difficult. When DXpeditions are permitted I expect these to be relatively easy to work. Back in the 1970s and 1980s I worked Johnston and Midway islands many times, and Kure island at least once. I have never worked Desecheo island.
KH8 Swains: The propagation path is fairly easy, so all I need right now is a DXpedition. I can't recall whether there has been any recent activity from this Pacific island.
KH9 Wake: The K9W DXpedition was a good one for working what has become quite a rare DXCC entity. At the time I was running QRP and little antennas. The best I did was "VE3?" on 17 meters CW. Although there is a ham on Wake Island his activity level hasn't made it easy. In fact I've never heard him. It's likely I'll have to wait a number of years until another DXpedition is permitted.
P2 Papua New Guinea, XU Cambodia, XZ Myanmar VR2 Hong Kong: Southeast Asia is a difficult path from this part of the world. During the most recent solar cycle peak my station was tiny. Now that I have bigger antennas suitable conditions are elusive. I have heard activity from all of these countries, including a few big DXpeditions, but have not succeeded in getting through. They'll come to me eventually if I pay attention and make the effort.
P5 North Korea: The short bursts of activity that pop up at rare intervals have satisfied few DXers. Some have been doggedly persistent while most that have worked North Korea have simply been lucky. A difficult propagation path and little activity makes this a tough one for many, including me.
PY0S St. Peter & St. Paul Rocks: Another one waiting for a DXpedition. I don't recall there being one over the past 5 years.
ST Sudan: For a brief period after independence Z8 South Sudan was not difficult to work. However Sudan itself has been and continues to be hostile to amateur radio. This one will likely require a change in the political winds. Years ago I worked Sudan a few times.
SV/a: Mount Athos: I've heard more pirates than legitimate activity from Mount Athos. At the moment I am unaware of any activity at all. The one resident monk with a license is inactive and visiting hams have not been welcome.
T31 Central Kiribati: This one takes an DXpedition, but otherwise should not be difficult. Patience is a virtue.
VK0/m: Macquarie: No DXpeditions in the past few years and little ham activity from the occasional Australian stationed on the island. Despite the great distance this area of the world is not overly challenging to reach, even during a solar cycle minimum.
VP8/o: South Orkney:You would think that since I've worked the other and far more rare VP8 Antarctic islands such as South Sandwich and South Georgia this one would be easy. Sadly, no. To be honest I haven't paid much attention to which island is which and so I've missed a few opportunities.
VU4 Andaman & Nicobar: There have several DXpeditions to this entity. Although I've worked its neighbour VU7 numerous times, and once with QRP, this one has eluded me. I have tried though perhaps not as much as I ought to since I keep thinking there will be a next time. The path over the pole will be a difficult one for the next two years.
YI Iraq: Although there are hams currently active it has proved elusive. From what I can tell their stations are modest and difficult to work from here. A couple that have been heard were very weak and working Europeans.
YV0 Aves: There have been no DXpeditions recently, and this one is notable in that it requires cooperation of the Venezuelan navy. The most recent attempt was ultimately cancelled due to...reasons.
ZL8 Kermadec, ZL9 New Zealand Subantarctic islands: These entities see occasional activity but have not grabbed my attention sufficiently to make the effort to chase them.
ZS8 Prince Edward & Marion: These days about the only activity on this protected island group is when a ham is stationed on the island. Unfortunately activity over the past 5 years has been fleeting and I haven't made a great effort to track them down.
If you took the time to read this far it should be evident that I am not at all fanatical about DXing. I love it, yes, though not nearly to the degree of many others. Notice that for more than a few of the countries I've yet to work I cannot recall whether there has been any activity since 2013 when I returned to the hobby and chose to reset my DXCC count to zero.
Yet there are indeed quite a few of these DXCC entities that have been either completely or almost completely absent from the airwaves since 2013 and therefore impossible to work. For these it will take patience for the political situation to change, permission from the relevant government authorities or money and persistence to mount DXpeditions. I am in no great rush so I can wait.
For me chasing DX is a fun challenge though not an obsessive compulsion. With a little more dedication and persistence I can do better at working the less active and more distant entities that are in fact active from time to time. Whether I'll ever do so I just don't know. Towers and antennas, and of course contests, are more interesting to me.
Amateur radio is a big hobby with diverse activities to meet many tastes. DXing and the DXCC pursuit can be a small or large focus for each of us, and our interests change with the years. There are hams who will only turn on the rig when one of the few remaining entities they have yet to work comes on the air. That's an attitude I'll never understand. I just don't see the point.
It is a milestone that was achieved more slowly than I expected. Consider that I reached 225 countries in two years using a maximum of 10 watts and modest antennas. Spotting networks and information dissemination about activity in rare locales makes running up the country count easier than ever.
Amusingly, the first 100 countries were easy enough despite running QRP and recruiting the aluminum eaves of my house in Ottawa as a random wire antenna. That was great fun. Doing it that way -- with a tiny station and low expectations -- played an important role in rekindling my passion for the hobby.
With DXCC the law of diminishing returns applies: as the country count increases each incremental country requires more work than the last. By the time 300 countries are reached the required effort is quite high and the progress slow.
My lifetime total is perhaps 315 or 320, reduced by deleted countries during the years I was inactive. But that number doesn't interest me. I wanted a fresh start after a 20 year hiatus from the hobby as a way to measure my progress. DXCC doesn't mean much to me and I have never applied for the award. I likely never will. It is the activity of DXing that I find appealing.
Maybe it's the excitement, maybe it's the competition and maybe it's the simply the magic of radio. Perhaps it's explained by catching the DXing bug when I was young, decades ago, when global communication was a rarity, except for those who got into ham radio. Youthful passions tend to linger.
Rather than dwell on the 300 country milestone what I'd like to do in this article is discuss the ones I have yet to work. With 340 countries on the current DXCC list that there are 40 countries left. By the end of this article it should be evident why working them all, or achieving the lesser but still heady level of DXCC Honour Roll, is so incredibly difficult. Most DXers who have done it have taken a lifetime to get there.
I'll group countries together where it makes sense to do so to keep this article from becoming repetitive and too long. Apart from the grouping, countries will be ordered by prefix.
3D2C Conway: I vaguely recall some DXpedition activity but have yet to work this one. Perhaps all this one will take is paying more attention. It shouldn't be difficult to work.
3Y Bouvet and 3Y Peter I: These Antarctic islands are remote and battered by severe sea and weather conditions. There was one recent DXpedition attempt to Bouvet island that failed to land due to the weather. I have both countries confirmed back in the 1980s. All one can do is wait for intrepid and well-financed DXpeditioners to make the attempt.
4U1UN United Nations: Only this summer has the station been rebuilt in compliance with the severe security regulations at the UN complex in New York. I have heard them weakly on 20 meters but not workable. New York is too close for reliable communication on the higher HF bands except by scatter and high power. I would be surprised if I don't have this one in the log by 2019.
7O Yemen, YK Syria: One word says it all -- war. Very sad and tragic, and these won't be resolved soon. Going back a few decades I have lots of cards from 7O and a few from YK. But for now they are not workable.
BS7H Scarborough Reef: For one elderly ham who lives nearby this is the only country he needs to have them all. Another longtime DXer of my acquaintance doesn't believe it'll ever be active again. I have no opinion. Even if it were active it would be very difficult to work during a solar minimum from this part of the world.
BV9P Pratas: Like Scarborough Reef I know little about this one. Both have flown under my radar since they appear to have become entities during my 20 years away from the hobby.
CE0X San Felix: I've worked CE0Y and CE0Z, yet failed to work this one. If there's been recent activity I've missed it since I keep confusing these Chilean islands, forgetting which is the one I haven't worked. Like many other entities I worked this one decades ago. I'll just have to pay closer attention to catch the next visitor to San Felix island.
EZ Turkmenistan: This former Soviet republic was uncommon but not rare back in the days of the USSR. Since then Turkmenistan has been jinxed with totalitarian rule. Although that is not necessarily incompatible with amateur radio, it is not the case here. There have been signs that the political situation may be improving. We can only wait.
FR/g Glorioso: Another rare island waiting for a group to launch a DXpedition. Again, all I can do is wait.
FR/t Tromelin: There was an excellent DXpedition a few years ago, one which I completely failed to work. It happens. At the time my antenna and power situation made it difficult. I will just have to wait for the next DXpedition, and that may be years away.
FT5W Crozet and FT5X Kerguelen: Like the US, France has become fiercely protective of the environment on isolated islands with unique flora and fauna. French hams have been trying and failing to gain permission to land on these islands. There is (was?) a ham on Crozet Island although I am only aware that he has worked /MM when asea, and I did work him there. But that doesn't count for DXCC.
HK0M Malpelo: No recent DXpeditions. As with some other environmentally sensitive islands permission to land and operate is not routine. I am unfamiliar with how restrictive Colombia is with respect to Malpelo island.
JD1 Minami Torashima: As with a number of entities on this list, there is occasional activity from this one. Unfortunately the path is not the easiest during a solar minimum and I have yet to catch up with them. I need propagation and activity to coincide, and to pay enough attention to notice when it does occur.
JX Jan Mayen: This one ought to be easy and there has been some activity. Maybe I just need to pay attention and try harder.
KH3 Johnston, KH4 Midway, KH7K Kure, KP5 Desecheo: Permission for Kure island was recently denied (again) and the others are similarly difficult. When DXpeditions are permitted I expect these to be relatively easy to work. Back in the 1970s and 1980s I worked Johnston and Midway islands many times, and Kure island at least once. I have never worked Desecheo island.
KH8 Swains: The propagation path is fairly easy, so all I need right now is a DXpedition. I can't recall whether there has been any recent activity from this Pacific island.
KH9 Wake: The K9W DXpedition was a good one for working what has become quite a rare DXCC entity. At the time I was running QRP and little antennas. The best I did was "VE3?" on 17 meters CW. Although there is a ham on Wake Island his activity level hasn't made it easy. In fact I've never heard him. It's likely I'll have to wait a number of years until another DXpedition is permitted.
P2 Papua New Guinea, XU Cambodia, XZ Myanmar VR2 Hong Kong: Southeast Asia is a difficult path from this part of the world. During the most recent solar cycle peak my station was tiny. Now that I have bigger antennas suitable conditions are elusive. I have heard activity from all of these countries, including a few big DXpeditions, but have not succeeded in getting through. They'll come to me eventually if I pay attention and make the effort.
P5 North Korea: The short bursts of activity that pop up at rare intervals have satisfied few DXers. Some have been doggedly persistent while most that have worked North Korea have simply been lucky. A difficult propagation path and little activity makes this a tough one for many, including me.
PY0S St. Peter & St. Paul Rocks: Another one waiting for a DXpedition. I don't recall there being one over the past 5 years.
ST Sudan: For a brief period after independence Z8 South Sudan was not difficult to work. However Sudan itself has been and continues to be hostile to amateur radio. This one will likely require a change in the political winds. Years ago I worked Sudan a few times.
SV/a: Mount Athos: I've heard more pirates than legitimate activity from Mount Athos. At the moment I am unaware of any activity at all. The one resident monk with a license is inactive and visiting hams have not been welcome.
T31 Central Kiribati: This one takes an DXpedition, but otherwise should not be difficult. Patience is a virtue.
VK0/m: Macquarie: No DXpeditions in the past few years and little ham activity from the occasional Australian stationed on the island. Despite the great distance this area of the world is not overly challenging to reach, even during a solar cycle minimum.
VP8/o: South Orkney:You would think that since I've worked the other and far more rare VP8 Antarctic islands such as South Sandwich and South Georgia this one would be easy. Sadly, no. To be honest I haven't paid much attention to which island is which and so I've missed a few opportunities.
VU4 Andaman & Nicobar: There have several DXpeditions to this entity. Although I've worked its neighbour VU7 numerous times, and once with QRP, this one has eluded me. I have tried though perhaps not as much as I ought to since I keep thinking there will be a next time. The path over the pole will be a difficult one for the next two years.
YI Iraq: Although there are hams currently active it has proved elusive. From what I can tell their stations are modest and difficult to work from here. A couple that have been heard were very weak and working Europeans.
YV0 Aves: There have been no DXpeditions recently, and this one is notable in that it requires cooperation of the Venezuelan navy. The most recent attempt was ultimately cancelled due to...reasons.
ZL8 Kermadec, ZL9 New Zealand Subantarctic islands: These entities see occasional activity but have not grabbed my attention sufficiently to make the effort to chase them.
ZS8 Prince Edward & Marion: These days about the only activity on this protected island group is when a ham is stationed on the island. Unfortunately activity over the past 5 years has been fleeting and I haven't made a great effort to track them down.
If you took the time to read this far it should be evident that I am not at all fanatical about DXing. I love it, yes, though not nearly to the degree of many others. Notice that for more than a few of the countries I've yet to work I cannot recall whether there has been any activity since 2013 when I returned to the hobby and chose to reset my DXCC count to zero.
Yet there are indeed quite a few of these DXCC entities that have been either completely or almost completely absent from the airwaves since 2013 and therefore impossible to work. For these it will take patience for the political situation to change, permission from the relevant government authorities or money and persistence to mount DXpeditions. I am in no great rush so I can wait.
For me chasing DX is a fun challenge though not an obsessive compulsion. With a little more dedication and persistence I can do better at working the less active and more distant entities that are in fact active from time to time. Whether I'll ever do so I just don't know. Towers and antennas, and of course contests, are more interesting to me.
Amateur radio is a big hobby with diverse activities to meet many tastes. DXing and the DXCC pursuit can be a small or large focus for each of us, and our interests change with the years. There are hams who will only turn on the rig when one of the few remaining entities they have yet to work comes on the air. That's an attitude I'll never understand. I just don't see the point.
Sunday, October 21, 2018
Deja Vu: Planting Another Big Tower
I've been busy getting ready for the planting of my second big LR20 tower, among other urgent tasks to be complete this fall. The blog has not gotten my full attention so the pace of articles has slowed. This will continue for a while.
Earlier this week the tower was planted. Now I am waiting on the concrete to cure and the machine shop to fabricate a few needed items. Then I can proceed. With luck the tower will be up this fall. Luck includes good weather, friends to come out to help and no serious mishaps. It's doable.
This is my last big tower -- two is enough for me to do what I want without incurring excessive maintenance during my golden years. For those who have been following along, this tower was in my original site plan for this QTH, and is located within meters of that plan. The tower will be a nominal 140', and actually ~133', or 40 to 41 meters, taking into account section overlap for splicing and base pillar height. This is an excellent height for DX work since it is 1λ on 40 meters and 2λ on 20 meters, and not quite 3λ at the top of the mast for 15 meters.
Unlike the disaster that was the planting of the first LR20 tower this one took only 7 hours. That's remarkable. It is thanks to the presence of an old hand leading his large crew of four, lots of planning and preparation beforehand and a large measure of good luck.
While it might not seem necessary with this crowd in attendance I was very busy on site working and supervising work. I got a good deal on the crew since for most of them it was their first time planting a guyed tower and my tower was a training exercise. Everyone wins. But the inevitable mistakes had to be noticed and pointed out, then corrected. Fortunately I have lots of management experience.
In this article I'll mainly focus on why the work went so well in comparison to the first big tower, which was a months long expensive headache. This should be more interesting to read about than simple repetition. There are relatively few pictures because I was less motivated to take them. The young guys on the crew took many more to, I suppose, remember what was for them a novel event.
First, the updated site plan. The changes are the approximate final positions of the new tower and the 80 meter array in the north field. Placing the new tower to meet my many requirements was difficult. The major impediment was avoiding the trees and rock wall surrounding the yard while achieving an ideal orientation of one tower face aligned with Europe for side mount yagis. A similar orientation on a line through the original big tower allows experimentation with wire antennas for the low bands.
I got pretty close to my objectives. A lesser objective was to minimize the transmission line run from the tower to the Trylon tower within the yard (yellow ellipse), which is the location of the antenna switch. The distance is similar to that for the other big tower, depending on how I ultimately choose to route the cables, both underground and above ground. There are several approaches to do this while avoiding tree roots and other obstacles. I have until next year to decide.
Surveying was similar to what I did for the first guyed tower. I'll refer you to that article rather than repeat myself.
Pretzel machine
Once again I opted to do my own rebar cages for the anchor and base. This time I had no outside help at all. I recruited material on hand to make the bending jigs and did a few tests to ensure each bend was exactly where I wanted them. I'm getting much better at this compared to the first time.
I again used an LR20 tower section and side mount bracket to build the jig for bending the rebar ties. I call it my pretzel machine. The design is an improvement over what I used before. It worked very well. The main challenge was determining how far the rebar would advance to the left as the hickey was rotated counter-clockwise on the leftmost stud. With that known it was easy to achieve consistent and accurate bends.
The circular stirrups were more of a challenge. The trick was to exploit the natural bend radius the jib imparted and repeatedly advance the rebar when the correct arc for a 12" circle was achieved. A circular template was used to check progress and to correct errors. The resulting stirrups aren't pretty but they're perfectly good.
When all was done I had 12 square pretzels, 18" on a side, and 5 circular pretzels of 12" diameter. Straight lengths of 20M rebar were cut and then combined with the ties and stirrups to form the 3 anchor cages and base pillar cage. The base platform grid is comprised of straight lengths of 20M rebar.
To bend the 20M bars for the base pillar (equivalent to US #6 bars) I needed a heftier jig. As in the past I recruited a suitable tree and steel pipes. After looking at several dozen trees (I have thousands on my property) I found a birch that was perfect. With this jig the 8 bars for the pillar were given a 90° hook on the end for joining to the base platform grid.
Notice the construction of the completed anchor cage. There are extra bars on the top and front that assist with distributing the tension of 4 guys across the load bearing faces of the anchor. Without them there is a risk that the concrete could split in the middle under severe wind load.
The cage is 18" × 18" × 90". This leaves a minimum 3" of concrete on all sides for the 2' × 2' × 8' reinforced concrete anchors. This is standard procedure to ensure long term corrosion protection of the rebar.
Excavation
I had a chance to chat with the backhoe operator before the tower crew arrived. He looked and sounded familiar. I soon realized that he was the plumber who came to my rescue when the house pressure system failed soon after I moved in. Turns out he had been laid off and returned to his earlier job as a backhoe operator.
While this is an interesting story what was more important is that I admired the skill and meticulousness he demonstrated on the plumbing job. He brought the same attributes to this job. There are ways to use a backhoe that can greatly improve the excavations, if the operator cares enough and has the requisite skill. This was my lucky day.
Knowing that the anchor holes were to be 2' × 2' × 8' he brought a 2' bucket on the front. He was able to made these 3 excavations between 24" and 27" wide. That's excellent. This was so accurate that I had to get the crew to use their shovel to clear 3" around all sides of the rebar cages, including squaring the bottom corners. There was little margin for error with this quality of backhoe work.
The advantage is that the quantity of concrete was kept to a minimum, which saved me a few hundred dollars. While it is possible to build casings for the anchors it is more costly in labour and materials, and if the casing is to be removed it is necessary to bring back the backhoe a day or two later to backfill the holes. Using what they call "mud holes" is faster and cheaper. But to do it you need the right soil and soil conditions and a good backhoe operator. On this day everything went right. Casing was only used for the base.
Concrete
Readers may remember the fiasco with concrete delivery for the first big tower. The truck got stuck in the boggy November hay field. It and the concrete had to be rescued by backhoe. I had no intention of letting that happen again.
When the driver arrived we did a walkabout to decide what to do. The backhoe has a big bucket (front end loader) for concrete delivery, if necessary.
The driver declared the ground just fine and drove onto the hay field. His judgment was good. Despite the 5 m³ of concrete onboard there were only light indentations left in the field.
Delivering the concrete direct to the excavation by chute is by far the superior method of delivery. It avoiding shifting of the steel when dropping concrete from the bucket and leaving time to push concrete into all the nooks and crannies to minimize air pockets. It is also much faster.
A handheld electric concrete vibrator made it easy to encourage the concrete to flow into all those spaces and level the surface. There is also less risk of shifting the rebar when shovels are used to pump the concrete.
Alignment
The crew did not spend time checking my surveying. There was no need. The crew leader aligned the anchor rods the old school way, with a string. In his experience it's the fastest and most reliable way of doing it. Too often he's found that transits are out of calibration or improperly used, but a string never lies.
When I did my surveying I measured the levelness of the ground. In one case I adjusted the distance to the anchor to account for the 18" drop in that direction. This ensures that the angle of all guys of each set come down from the tower at the same angle. My low tech method was to use a long level on a platform at the future position of the base pillar. Point it to a marked stake at the anchor site, ensure the level is level, then sight along it to measure the elevation difference.
More modern tools were used to set the 38° angle of the anchor rods. Every member of the crew would pull out their smart phones, lay them on rods and use inclinometer apps to adjust the angle. The angle was checked during and after the concrete pour.
The rule of thumb I was taught was that there are 30 minutes after the concrete is poured to move and align the anchor rods. Allow 2 hours before back filling over the exposed concrete, which allows it to firm up.
Back fill
When all but the back filling was complete the crew left, leaving me and the backhoe operator. While we waited for the concrete to firm up I had him move dirt around. This was the excess soil and subsoil from the excavations displaced by the concrete.
Some was left in small piles at the four excavations. I will use those to level the surface once the soil settles. That will take until spring. Since I forgot to leave extra soil at the excavations for the first big tower I also had him leave some at those four locations. I had done some wheelbarrow work in the spring but gave that up since it was tedious manual labour.
As the clock advanced we proceeded to back fill the three anchors. These were done in the same order they were filled with concrete and first poked to check firmness. He started slow with granular soil until the concrete was covered to 1' depth and the space under the anchor rods was filled. For the latter I used a shovel. This helped to prevent the weight of the back fill from pushing the rods downward to a lower than intended angle.
Over the next two days I spent a few hours raking and shovelling the extra soil. Large stones were removed by wheelbarrow. Last year I chose a spot within the bush to place the displaced soil and stones from the excavations.
Pier pin
The pier pin for the base section was embedded at the centre of the pillar soon after the concrete was poured. The pin in this case is a standard pipe with an OD ~1.3". The opening on the base section is 1.625". I may add a shim to fill the gap, however that is not really necessary.
One day later I filled the pipe with no-shrink grout and cleaned the pipe of stray grout and rust. It will be painted before the load bearing plate is slipped over the pin and grouted.
As you can see the 10' ground rod is already in. It was placed at a corner of the excavation then hammered down into the undisturbed soil. They crew would normally drive it below ground level and fill around it with gravel for future access. I prefer the ground rod to poke up a few inches. The difference in lightning protection is not large. I can drive it down later should I change my mind.
With that we're done! All that's left is final preparation of the tower sections and building upward. That stage of construction is scheduled after the CQ WW SSB contest. It should go faster than the first tower since the rigging can be reused and the lifting process has become routine. Hopefully I can get the same hams out to serve as ground crew. It's a race against winter.
Earlier this week the tower was planted. Now I am waiting on the concrete to cure and the machine shop to fabricate a few needed items. Then I can proceed. With luck the tower will be up this fall. Luck includes good weather, friends to come out to help and no serious mishaps. It's doable.
This is my last big tower -- two is enough for me to do what I want without incurring excessive maintenance during my golden years. For those who have been following along, this tower was in my original site plan for this QTH, and is located within meters of that plan. The tower will be a nominal 140', and actually ~133', or 40 to 41 meters, taking into account section overlap for splicing and base pillar height. This is an excellent height for DX work since it is 1λ on 40 meters and 2λ on 20 meters, and not quite 3λ at the top of the mast for 15 meters.
Unlike the disaster that was the planting of the first LR20 tower this one took only 7 hours. That's remarkable. It is thanks to the presence of an old hand leading his large crew of four, lots of planning and preparation beforehand and a large measure of good luck.
While it might not seem necessary with this crowd in attendance I was very busy on site working and supervising work. I got a good deal on the crew since for most of them it was their first time planting a guyed tower and my tower was a training exercise. Everyone wins. But the inevitable mistakes had to be noticed and pointed out, then corrected. Fortunately I have lots of management experience.
In this article I'll mainly focus on why the work went so well in comparison to the first big tower, which was a months long expensive headache. This should be more interesting to read about than simple repetition. There are relatively few pictures because I was less motivated to take them. The young guys on the crew took many more to, I suppose, remember what was for them a novel event.
First, the updated site plan. The changes are the approximate final positions of the new tower and the 80 meter array in the north field. Placing the new tower to meet my many requirements was difficult. The major impediment was avoiding the trees and rock wall surrounding the yard while achieving an ideal orientation of one tower face aligned with Europe for side mount yagis. A similar orientation on a line through the original big tower allows experimentation with wire antennas for the low bands.
I got pretty close to my objectives. A lesser objective was to minimize the transmission line run from the tower to the Trylon tower within the yard (yellow ellipse), which is the location of the antenna switch. The distance is similar to that for the other big tower, depending on how I ultimately choose to route the cables, both underground and above ground. There are several approaches to do this while avoiding tree roots and other obstacles. I have until next year to decide.
Surveying was similar to what I did for the first guyed tower. I'll refer you to that article rather than repeat myself.
Pretzel machine
Once again I opted to do my own rebar cages for the anchor and base. This time I had no outside help at all. I recruited material on hand to make the bending jigs and did a few tests to ensure each bend was exactly where I wanted them. I'm getting much better at this compared to the first time.I again used an LR20 tower section and side mount bracket to build the jig for bending the rebar ties. I call it my pretzel machine. The design is an improvement over what I used before. It worked very well. The main challenge was determining how far the rebar would advance to the left as the hickey was rotated counter-clockwise on the leftmost stud. With that known it was easy to achieve consistent and accurate bends.
The circular stirrups were more of a challenge. The trick was to exploit the natural bend radius the jib imparted and repeatedly advance the rebar when the correct arc for a 12" circle was achieved. A circular template was used to check progress and to correct errors. The resulting stirrups aren't pretty but they're perfectly good.
When all was done I had 12 square pretzels, 18" on a side, and 5 circular pretzels of 12" diameter. Straight lengths of 20M rebar were cut and then combined with the ties and stirrups to form the 3 anchor cages and base pillar cage. The base platform grid is comprised of straight lengths of 20M rebar.
To bend the 20M bars for the base pillar (equivalent to US #6 bars) I needed a heftier jig. As in the past I recruited a suitable tree and steel pipes. After looking at several dozen trees (I have thousands on my property) I found a birch that was perfect. With this jig the 8 bars for the pillar were given a 90° hook on the end for joining to the base platform grid.
Notice the construction of the completed anchor cage. There are extra bars on the top and front that assist with distributing the tension of 4 guys across the load bearing faces of the anchor. Without them there is a risk that the concrete could split in the middle under severe wind load.
The cage is 18" × 18" × 90". This leaves a minimum 3" of concrete on all sides for the 2' × 2' × 8' reinforced concrete anchors. This is standard procedure to ensure long term corrosion protection of the rebar.
Excavation
I had a chance to chat with the backhoe operator before the tower crew arrived. He looked and sounded familiar. I soon realized that he was the plumber who came to my rescue when the house pressure system failed soon after I moved in. Turns out he had been laid off and returned to his earlier job as a backhoe operator.
While this is an interesting story what was more important is that I admired the skill and meticulousness he demonstrated on the plumbing job. He brought the same attributes to this job. There are ways to use a backhoe that can greatly improve the excavations, if the operator cares enough and has the requisite skill. This was my lucky day.
Knowing that the anchor holes were to be 2' × 2' × 8' he brought a 2' bucket on the front. He was able to made these 3 excavations between 24" and 27" wide. That's excellent. This was so accurate that I had to get the crew to use their shovel to clear 3" around all sides of the rebar cages, including squaring the bottom corners. There was little margin for error with this quality of backhoe work.
The advantage is that the quantity of concrete was kept to a minimum, which saved me a few hundred dollars. While it is possible to build casings for the anchors it is more costly in labour and materials, and if the casing is to be removed it is necessary to bring back the backhoe a day or two later to backfill the holes. Using what they call "mud holes" is faster and cheaper. But to do it you need the right soil and soil conditions and a good backhoe operator. On this day everything went right. Casing was only used for the base.
Concrete
Readers may remember the fiasco with concrete delivery for the first big tower. The truck got stuck in the boggy November hay field. It and the concrete had to be rescued by backhoe. I had no intention of letting that happen again.When the driver arrived we did a walkabout to decide what to do. The backhoe has a big bucket (front end loader) for concrete delivery, if necessary.
The driver declared the ground just fine and drove onto the hay field. His judgment was good. Despite the 5 m³ of concrete onboard there were only light indentations left in the field.
Delivering the concrete direct to the excavation by chute is by far the superior method of delivery. It avoiding shifting of the steel when dropping concrete from the bucket and leaving time to push concrete into all the nooks and crannies to minimize air pockets. It is also much faster.
A handheld electric concrete vibrator made it easy to encourage the concrete to flow into all those spaces and level the surface. There is also less risk of shifting the rebar when shovels are used to pump the concrete.
Alignment
The crew did not spend time checking my surveying. There was no need. The crew leader aligned the anchor rods the old school way, with a string. In his experience it's the fastest and most reliable way of doing it. Too often he's found that transits are out of calibration or improperly used, but a string never lies.
When I did my surveying I measured the levelness of the ground. In one case I adjusted the distance to the anchor to account for the 18" drop in that direction. This ensures that the angle of all guys of each set come down from the tower at the same angle. My low tech method was to use a long level on a platform at the future position of the base pillar. Point it to a marked stake at the anchor site, ensure the level is level, then sight along it to measure the elevation difference.
More modern tools were used to set the 38° angle of the anchor rods. Every member of the crew would pull out their smart phones, lay them on rods and use inclinometer apps to adjust the angle. The angle was checked during and after the concrete pour.
The rule of thumb I was taught was that there are 30 minutes after the concrete is poured to move and align the anchor rods. Allow 2 hours before back filling over the exposed concrete, which allows it to firm up.
Back fill
When all but the back filling was complete the crew left, leaving me and the backhoe operator. While we waited for the concrete to firm up I had him move dirt around. This was the excess soil and subsoil from the excavations displaced by the concrete.
Some was left in small piles at the four excavations. I will use those to level the surface once the soil settles. That will take until spring. Since I forgot to leave extra soil at the excavations for the first big tower I also had him leave some at those four locations. I had done some wheelbarrow work in the spring but gave that up since it was tedious manual labour.
As the clock advanced we proceeded to back fill the three anchors. These were done in the same order they were filled with concrete and first poked to check firmness. He started slow with granular soil until the concrete was covered to 1' depth and the space under the anchor rods was filled. For the latter I used a shovel. This helped to prevent the weight of the back fill from pushing the rods downward to a lower than intended angle.
Over the next two days I spent a few hours raking and shovelling the extra soil. Large stones were removed by wheelbarrow. Last year I chose a spot within the bush to place the displaced soil and stones from the excavations.
Pier pin
The pier pin for the base section was embedded at the centre of the pillar soon after the concrete was poured. The pin in this case is a standard pipe with an OD ~1.3". The opening on the base section is 1.625". I may add a shim to fill the gap, however that is not really necessary.
One day later I filled the pipe with no-shrink grout and cleaned the pipe of stray grout and rust. It will be painted before the load bearing plate is slipped over the pin and grouted.
As you can see the 10' ground rod is already in. It was placed at a corner of the excavation then hammered down into the undisturbed soil. They crew would normally drive it below ground level and fill around it with gravel for future access. I prefer the ground rod to poke up a few inches. The difference in lightning protection is not large. I can drive it down later should I change my mind.
With that we're done! All that's left is final preparation of the tower sections and building upward. That stage of construction is scheduled after the CQ WW SSB contest. It should go faster than the first tower since the rigging can be reused and the lifting process has become routine. Hopefully I can get the same hams out to serve as ground crew. It's a race against winter.
Tuesday, October 9, 2018
3-element 40 Meter Yagi on a 40' (12 m) Boom
My recent article about long boom yagis reminded me of an omission in my blogging practice. The 15 meter and 20 meter yagis had references to earlier articles or elsewhere so that readers could learn the details of design and performance. I did not do the same for the 40 meter yagis on a 40' (12 meter) boom.
The designs were done some time ago, which is probably why I forgot about them until then. Not long before I wrote that article I sent the EZNEC files to a ham in Europe who was inquiring whether I had a design handy for a 12 meter boom. But in that article I only mentioned them in passing. It is worth writing about them because they do have interesting performance characteristics in comparison to the usual 48' (14.7 meter) boom length commonly used for 3-element 40 meter yagis, including those with a fourth element (coupled resonator, OWA design).
Before diving in it is worthwhile to briefly recap a few points about 3-element yagi design.
Overview of the yagis to be compared
The 3-element yagi on a 48' boom in the ARRL Antenna Book is a useful baseline for comparison because of its balance between gain and SWR bandwidth. If that antenna interests you, look there because I won't get into the details here. To summarize, its 2:1 SWR bandwidth is ~200 kHz, gain rises from ~7.8 dbi at 7.0 MHz to ~8.7 at 7.3 MHz, and F/R is 21 db at 7.0 MHz, rises to 27 db at 7.1 MHz then falls to 12 db at 7.3 MHz.
The tuning spread of the parasitic elements is 15%, or ±7.4% of the design midpoint. I will use the latter convention in this article. It is not half of 15% since the exponential mean must be used. You get this with the square root of the ratio between the reflector and director lengths. This is good enough for our purposes though not absolutely precise since the tubing taper schedule has an effect.
For comparison, the 3-element yagi I discussed in an earlier article has a tuning spread of 6.4% to increase gain by ~0.5 db. F/B continues to be very good, although 2:1 SWR bandwidth is a little less than 200 kHz. With a coupled resonator added the SWR bandwidth is low from 7.0 MHz to 7.3 MHz.
Because reducing the boom length to 40' also reduces achievable gain I further tightened element tuning to 5.3%. This recovers much of the gain while sacrificing SWR bandwidth, as we'll see. The addition of a coupled resonator helps with the latter.
As you likely noticed I have reverted to English units for these yagis. I do this because the tubes and pipes I use are measured in these units and so I model the yagis accordingly. The figures on the left are the distances along the boom the elements are placed and the lengths of each half element. The addition of a couple resonator only affects the length of the driven element. Its length without the coupled resonator is in any case dependent on the matching network: gamma, beta, L-network, etc.
Half element tubing schedule is: 144" of 1.9" pipe; 96" of 1.5" tube; 66" of 1" tube; 66" of ⅞" tube and a variable length of ¾" tube. This is not likely how I would construct the elements. It was an experiment to determine how I could put my stock of aluminum pipe to good use. The idea was spurred by reading Dave Leeson's Physical Design of Yagi Antennas -- it's out of print but the author kindly sent me a copy. For other tapering schedules it is necessary to carefully scale the elements.
For interest I show the 4-element yagi element currents at a higher frequency to highlight one aspect of how the coupled resonator broadens the SWR bandwidth. With the coupled resonator tuned to a higher frequency its current dominates that of the driven element at the high end of the band. In a sense it becomes the driven element despite not being attached to the transmission line. Since it is offset toward the front of the yagi the gain and F/B are slightly affected at higher frequencies.
Performance comparison
In the chart I used the same colour lines for both curves of each antenna -- gain and F/B -- to make it easy to compare yagis. Gain and F/B ought to be easy to distinguish!
I chopped the top of the chart to further improve readability since F/B figures well above 30 db are very difficult to achieve in real antennas due to the precise cancellation of element fields required. It is sufficient to state that F/B is excellent over a portion of the band.
Gains of the 40' boom yagis are about 7.8 dbi at 7.0 MHz and 8.4 dbi at 7.3 MHz. Gains of their 48' boom sisters is a fairly consistent 0.7 db higher. That isn't a large sacrifice to make considering the substantial construction differences for equal robustness.
F/B is significantly better for the 40' boom yagis even though I hadn't planned for that. It may be that further tuning of the 48' boom yagis would erase some or most of the difference. Certainly the yagi in the ARRL Antenna Book does a little better than these gain optimized yagis.
With a fixed matching network the 2:1 SWR bandwidth of the 3-element yagi on a 40' boom is 180 kHz. That's good but not great. With a switchable L-network at the feed point it is possible to achieve a low SWR up to 7.25 MHz. Getting all the way up to 7.3 MHz would require one more switch position. I wouldn't bother though some might want it. At least in the Americas where we have a 300 kHz wide 40 meter band.
The coupled resonator version of the 40' boom yagi can achieve better than 2:1 SWR across the entire band. However I was unsuccessful bringing down the SWR lower than 1.4. Further tuning of the driven element and coupled resonator might do it, but there are no guarantees. My difficulty was exacerbated by NEC2 which has some difficulty correctly modelling the impedance of closely spaced elements even when great care is taken with element segmentation, as I did.
Perhaps in practice it'll do better than the model and can be tweaked once on the tower -- the driven element and coupled resonator are within easy reach. Otherwise it may be necessary to loosen the tuning of the parasitic elements to improve the SWR, at the expense of some gain. I did not explore this path for the present study.
Further work
Despite my best intentions I will not construct and raise a full size 40 meter yagi this year. Maybe not even next year. There is therefore time to play with the models and explore further options. For example, to give up some gain to recover SWR bandwidth. No matter what I do there will be have to be compromises made.
I hope the information in this article spurs a few ideas of your own. These antennas are far more challenging than the 40 meters wire yagis that have been so popular among the readers of this blog.
The designs were done some time ago, which is probably why I forgot about them until then. Not long before I wrote that article I sent the EZNEC files to a ham in Europe who was inquiring whether I had a design handy for a 12 meter boom. But in that article I only mentioned them in passing. It is worth writing about them because they do have interesting performance characteristics in comparison to the usual 48' (14.7 meter) boom length commonly used for 3-element 40 meter yagis, including those with a fourth element (coupled resonator, OWA design).
Before diving in it is worthwhile to briefly recap a few points about 3-element yagi design.
- Optimizing for gain only modestly reduces F/B but will significantly reduce the SWR bandwidth. The latter is due to the low radiation resistance associated with maximum gain.
- Frequency of maximum gain is above the usable bandwidth, while F/B tends to peak towards the low end of the usable bandwidth. In practical terms, a 3-element yagi typically has maximum gain on SSB and maximum F/B on CW.
- Designs which maximize SWR bandwidth sacrifice up to 1 db of gain. However F/B can remain good.
- Gain is optimized by bringing the self resonance of the director and reflector closer together. The spread in percentage is a convenient metric, one that I originally learned about in the venerable Yagi Antenna Design book by W2PV. Tuning of the driven element affects the match (and matching network) while having negligible effect on gain, F/B and SWR bandwidth.
- Best performance typically has the driven element offset toward the reflector end of the antenna a small amount.
Overview of the yagis to be compared
The 3-element yagi on a 48' boom in the ARRL Antenna Book is a useful baseline for comparison because of its balance between gain and SWR bandwidth. If that antenna interests you, look there because I won't get into the details here. To summarize, its 2:1 SWR bandwidth is ~200 kHz, gain rises from ~7.8 dbi at 7.0 MHz to ~8.7 at 7.3 MHz, and F/R is 21 db at 7.0 MHz, rises to 27 db at 7.1 MHz then falls to 12 db at 7.3 MHz.
The tuning spread of the parasitic elements is 15%, or ±7.4% of the design midpoint. I will use the latter convention in this article. It is not half of 15% since the exponential mean must be used. You get this with the square root of the ratio between the reflector and director lengths. This is good enough for our purposes though not absolutely precise since the tubing taper schedule has an effect.
For comparison, the 3-element yagi I discussed in an earlier article has a tuning spread of 6.4% to increase gain by ~0.5 db. F/B continues to be very good, although 2:1 SWR bandwidth is a little less than 200 kHz. With a coupled resonator added the SWR bandwidth is low from 7.0 MHz to 7.3 MHz.
Because reducing the boom length to 40' also reduces achievable gain I further tightened element tuning to 5.3%. This recovers much of the gain while sacrificing SWR bandwidth, as we'll see. The addition of a coupled resonator helps with the latter.
As you likely noticed I have reverted to English units for these yagis. I do this because the tubes and pipes I use are measured in these units and so I model the yagis accordingly. The figures on the left are the distances along the boom the elements are placed and the lengths of each half element. The addition of a couple resonator only affects the length of the driven element. Its length without the coupled resonator is in any case dependent on the matching network: gamma, beta, L-network, etc.
Half element tubing schedule is: 144" of 1.9" pipe; 96" of 1.5" tube; 66" of 1" tube; 66" of ⅞" tube and a variable length of ¾" tube. This is not likely how I would construct the elements. It was an experiment to determine how I could put my stock of aluminum pipe to good use. The idea was spurred by reading Dave Leeson's Physical Design of Yagi Antennas -- it's out of print but the author kindly sent me a copy. For other tapering schedules it is necessary to carefully scale the elements.
For interest I show the 4-element yagi element currents at a higher frequency to highlight one aspect of how the coupled resonator broadens the SWR bandwidth. With the coupled resonator tuned to a higher frequency its current dominates that of the driven element at the high end of the band. In a sense it becomes the driven element despite not being attached to the transmission line. Since it is offset toward the front of the yagi the gain and F/B are slightly affected at higher frequencies.
Performance comparisonIn the chart I used the same colour lines for both curves of each antenna -- gain and F/B -- to make it easy to compare yagis. Gain and F/B ought to be easy to distinguish!
I chopped the top of the chart to further improve readability since F/B figures well above 30 db are very difficult to achieve in real antennas due to the precise cancellation of element fields required. It is sufficient to state that F/B is excellent over a portion of the band.
Gains of the 40' boom yagis are about 7.8 dbi at 7.0 MHz and 8.4 dbi at 7.3 MHz. Gains of their 48' boom sisters is a fairly consistent 0.7 db higher. That isn't a large sacrifice to make considering the substantial construction differences for equal robustness.
F/B is significantly better for the 40' boom yagis even though I hadn't planned for that. It may be that further tuning of the 48' boom yagis would erase some or most of the difference. Certainly the yagi in the ARRL Antenna Book does a little better than these gain optimized yagis.
With a fixed matching network the 2:1 SWR bandwidth of the 3-element yagi on a 40' boom is 180 kHz. That's good but not great. With a switchable L-network at the feed point it is possible to achieve a low SWR up to 7.25 MHz. Getting all the way up to 7.3 MHz would require one more switch position. I wouldn't bother though some might want it. At least in the Americas where we have a 300 kHz wide 40 meter band.
The coupled resonator version of the 40' boom yagi can achieve better than 2:1 SWR across the entire band. However I was unsuccessful bringing down the SWR lower than 1.4. Further tuning of the driven element and coupled resonator might do it, but there are no guarantees. My difficulty was exacerbated by NEC2 which has some difficulty correctly modelling the impedance of closely spaced elements even when great care is taken with element segmentation, as I did.
Perhaps in practice it'll do better than the model and can be tweaked once on the tower -- the driven element and coupled resonator are within easy reach. Otherwise it may be necessary to loosen the tuning of the parasitic elements to improve the SWR, at the expense of some gain. I did not explore this path for the present study.
Further work
Despite my best intentions I will not construct and raise a full size 40 meter yagi this year. Maybe not even next year. There is therefore time to play with the models and explore further options. For example, to give up some gain to recover SWR bandwidth. No matter what I do there will be have to be compromises made.
I hope the information in this article spurs a few ideas of your own. These antennas are far more challenging than the 40 meters wire yagis that have been so popular among the readers of this blog.
Sunday, September 30, 2018
80 Meter 3-element Vertical Yagi: First Light
Much to my surprise I have been making slow and steady progress on my 3-element vertical yagi for 80 meters. I have many projects competing for my attention. Although significant work remains to see this project to completion there is finally enough in place to give it a actual on the air test. It is time for an update.
When I last visited this antenna the central full size vertical was built, with enough radials (34, with 700 meters of wire) that it easily became my antenna of choice for DX on 80. During September I did the following:
A set of 8 radials for each parasite was laid down before the elements were raised. They are each 15 meters long except for the one that ties the radial hubs for the parasite and the driven element. In earlier articles I described my radial system topology as overlapping rather than connected at busses placed between the 5 elements in order to reduce the work of soldering radials to busses at the expense of more radial wire.
After the parasitic elements were installed the impedance was measured and the radials increased to 16. The impedance was again measured to determine the trend toward non-resonance in the radial system, which strongly depends on the ground's dielectric constant and thus the velocity factor.
The EZNEC medium ground model for 20 meter long radials is a very close fit to what I measured: ~40 kHz increase in resonant frequency when the radial count increased from 8 to 16. I can now adjust the elements confident that I can predict what will happen should I add more radials later. Apparently the velocity factor with on-ground and shallowly buried radials is substantially lower than in the model. This isn't surprising since it is difficult to accurately model radials of this type with NEC2. In part because they must be perched a fraction of a wavelength above ground, where less of the field flows through the ground.
Before proceeding with tuning I added 2 more radials to each parasitic element, for a total of 18. These are wires running the ~15 meters distance between each of the 4 parasitic element radial hubs. Although the change in impedance was negligible this should slightly reduce ground loss for the entire array, no matter the direction chosen, including the array's omni-directional mode.
I chose 15 meters as the radial length for two reasons: limit the overall area of the antenna to minimize the land taken from the haying operation, and; limit swings in parasite resonance as radials are added.
Parasitic wire elements
Designing the T-top wire elements was a challenge. This is an element topology that NEC2 is not able to model accurately. I knew this from the start, as I learned when I put up my 160 meter antenna last year. The second factor influencing resonance is the number and length of radials. The 8 radials in that antenna are 30 meters long, which is approximately the same as 15 meter radials on 80 meters, relative to wavelength. The resonant frequency is pulled downward.
For a single element antenna with a low feed point impedance the correction is as simple as an L-network. It doesn't matter that the antenna is not resonant since the network easily accommodates a non-zero reactance, and the efficiency is high if the resonant frequency isn't far off. For a yagi there is no forgiveness in tuning the elements; you must get it right.
As a guide I used the K3LR dimensions for a 160 meter version of this antenna which you'll find in ON4UN's Low-Band DXing book, version 5. With a bit of geometry and adjustment to fit the physical layout of my antenna I came up with dimensions for the T and the vertical. A little was then added to both to allow room to snip wire to reach resonance. The initial length of each leg of the T is 5.5 meters. The vertical is 12 meters, which includes an extra 0.5 meters for tuning purposes.
Two wire elements are visible in the photo above. Unfortunately you'll have to squint to see them. I didn't properly compensate for sag so the vertical segment drags on the ground. The centre junction is simply a stainless steel bolt which the wires wrap around and then snugged tight. It's lighter than an insulator and more secure than solder alone.
The ropes that form the top end of the catenaries for the wire elements were cut to length and installed when the stinger and top section were lifted. The elements were walked up the tower and connected and the bottom ropes tied to the anchors, located 25.5 meters from the tower. That's right at the edge of the radial system (10.5 meter element spacing plus 15 meter radial length) to minimize land use.
It took a couple of hours to adjust the tension of each rope to achieve the best compromise among element sag, force on the stinger and centering the stinger. Eventually I was done and ready to proceed to the next step: tuning the elements and lighting up the yagi.
Measure, measure, measure
As I said above, precision is of the utmost importance in getting a yagi working properly. To this end I was fastidious about measurements. A marked template was set up on the ground to ensure the wire for the 4 elements were cut to the exact same length. The wire elements are therefore identical. Exactly 3" of wire are wrapped around the insulator at each end of the T. When I tied the catenary ropes up the tower I made a mark on the tower where each T should terminate, which helped achieve symmetry. All element ground anchors are exactly the same distance from the tower.
Although opposite elements are, and must be 180° apart, adjacent elements are not 90° apart. This symmetry is necessary in a 4-square but not in the yagi. In yagi mode only two parasitic elements are in use. The other two are floated (disconnected from ground) making them non-resonant and effectively invisible. I used this feature to optimize array aiming for my geographic location. Floating works, as demonstrated by no change to driven element impedance when the parasitic elements were raised and left floating.
The feed point of each wire element is similarly identical with respect to radial hub and its support, switching system anchor, back plate and enclosure. Before tuning the elements I measured the resonant frequency of all 4 of them, once with 8 radials and again with 16 radials.
The resonant frequency was below the design objective of 3.680 MHz so that they can be cut to resonance. More important is that my fastidiousness resulted in a resonance spread among the 4 elements of only 20 kHz, or 0.6%. Notice that the resistance part of the impedance dropped 7 Ω with 16 radials. There is obviously more ground loss to be eliminated. I can probably bring the resistance closer to 20 Ω by doubling the radials. But that's another 1,000 meters of wire! Efficiency doesn't come easy.
To measure any element of the array, including the driven element (tower), all other elements must be floated. That is, the monopole and radial systems must be disconnected. Otherwise the mutual impedance will mask what is really going on. One of the jobs of the switching system will be to float elements that are neither directors nor reflectors for the selected direction. All parasitic elements are floated when the array is in its omni-directional mode.
Rough wiring the 3-element yagi
The next step is the fun part: lighting up the yagi. Since the most useful DX heading is towards Europe I rough wired the northeast element as a director and the southwest element as a reflector. Since I don't want to cut wire at this time I calculated the amount to shorten the element to resonate the director to 3.680 MHz and shaved the insulation of the wire at the appropriate position to expose a tap point. The ~40 cm of wire beyond the connection has negligible effect on element behaviour.
For the reflector I used a rough wound coil of AWG 14 wire from my junk box since it looked to be about the right size. I attached it and alternately squeezed and stretched the coil until it resonated at 3.450 MHz. This only took 30 seconds since the analyzer continuously recalculates the impedance. All I had to do was move my hands out of the way after each adjustment.
With the element tuned I temporarily completed the connections with wire nuts. I move the analyzer to the driven element and measured the impedance of my improvised 3-element yagi at 25 kHz intervals.
The resistance part of the impedance is about as expected. This clearly shows how important it is to achieve the lowest possible ground loss with the biggest radial system you can manage. Even with a ground loss as low as 5 Ω the loss can be -2 db. That's a lot.
The X value is not terribly important, provided its absolute value is not much higher than R. That helps to minimize matching network loss. However for now I am leaving the 4:1 SWR as is and correcting it with the rig's ATU. The estimated total transmission line loss is -2 db despite being almost 300' long. It isn't difficult to keep transmission line loss low at 3.5 MHz. Once the matching network is in place the loss should be better than -1 db.
Before going further it is worth a moment to talk about instrumentation. To achieve accurate and repeatable measurements it is important to have an analyzer with the requisite performance and to use it properly. The RigExpert AA-54 is quite good considering the price. There are better products on the market for a higher price.
I am not making any recommendation. Refer to detailed technical reviews such as those found in QST rather than rely on informal opinions of friends who may know even less than you.
The analyzer should be able to get the R and X values correct within a few ohms when the SWR is high, which most of the cheapest units cannot do. Not only is accuracy important but so is repeatability. That is, the values should be the same between readings, including readings made after the unit is turned off for a while and reconnected to the antenna under test.
Make sure your body is not influencing the measurement by moving around. Do the same for the analyzer itself, including when in your hand or supported elsewhere. Keep the test leads short or compensate for the length; better units can calibrate on the transmission line length, or use software such as TLW to convert the measured impedance to that present at the load.
Doing it right with a finicky antenna like this one can save you a lot of grief. Buy the best analyzer you can afford if you like experimenting with antennas. A 2-port VNA is favoured by those with a need to design and test more complex antennas or to analyze impedance transformation networks. A handheld unit like the RigExpert is perfect for me.
On the air
This article is being written after 3 evenings with the antenna in its hard wired direction to the northeast (Europe, North Africa and Indian Ocean). Not only has activity on 80 meters has perked up after the summertime lull there are several current DXpeditions roughly in that direction, including 9X0T and TO6OK. As always there are many Europeans active overnight and their sunrise.
When I first lit it up I was briefly disappointed. Switching from the inverted vee (now with an apex of 19 meters) to the vertical yagi the band noise dropped precipitously. It seemed that the antenna efficiency was low, so that the analyzer measurement might be hiding a deeper problem. Or, perhaps, the transmission line loss is higher than calculated. My worries dissipated when I tuned in a signal from Europe.
All European signals were stronger versus the inverted vee just as they were when the antenna was configured as an omni-directional vertical. But now the difference is substantially greater. I did extensive comparisons to ensure that Faraday rotation and other causes of QSB were accounted for by comparing through signal strength peaks and valleys. The improvement was consistent. However there is variation with different stations and path lengths. The variation -- elevation angle, polarization and skew -- demonstrates the value of having more than one antenna per band.
Signal differences were as little as 1 S-unit and as much as 4 to 5 S-units. That is promising. But what happened to the band noise? One hint was listening to W8 and W5 stations off the back of the yagi. The F/B is very good. Signals that were S-9 on the inverted vee would drop to S-3 or lower; as a vertical the difference was typically 2 S-units in favour of the inverted vee. What these differences are in decibels is hazardous to estimate since an S-meter is not a reliable instrument.
What appears to be happening is the attenuation of early fall atmospheric QRN from warmer locales south and southwest of VE3. The northern path to Europe is of course colder with less of the weather that contributes to noise. That is, the antenna has good directivity. I confirmed this by comparing reception against my 175 meter long northeast Beverage. The Beverage is still the better receive antenna, though by far less than with an omni-directional antenna.
Keep in mind that a well tuned 4-square can achieve similar or better F/B over a wider bandwidth than this yagi. I knew this before proceeding with this antenna. For me the ability to experiment and make a less expensive directive array of similar performance was a deciding factor.
I can see myself living with the yagi on 80 meters and reserving the Beverage and other planned receive antennas primarily for use on 160 meters. I have no plans for a directive transmit array for 160 meters, although that could change.
Up next
The switching units must now be assembled, installed and adjusted. The 4 parasitic element units must be identical to ensure identical performance, which is important when switching direction. This applies to the coils, relays, lengths and routing of internal wires. The unit at the driven element will contain the switching matrix, signal distribution and relays for the matching networks.
Most of this work can be done indoors. The only parts I have yet to order are the relays, which I have been researching. There are trade offs with respect to cost, power handling, RF isolation and current draw. A wrong choice is not a disaster since they are easy enough to access and replace. The switching matrix is built but not fully tested.
The driven element stinger may need to be replaced, if not this fall then next year. It is proving to be mechanically marginal when tension is put on the catenaries. I would like to take up more of the slack. Replacement would take a few hours and should only affect the L-network due to a change in the electrical length of the driven element.
I don't anticipate completion before November. There are too many other projects to be done this fall and this job can be done during the cold weather. I may even lay more radials before the snow flies.
With the rough wired yagi performing so well I am really looking forward to completing this project.
When I last visited this antenna the central full size vertical was built, with enough radials (34, with 700 meters of wire) that it easily became my antenna of choice for DX on 80. During September I did the following:
- Laid radials for the 4 parasitic elements.
- Designed, built and installed the T-loaded wire elements.
- Rough tuned the parasitic elements.
- Hard wired the northeast element as a director and the southwest element as a reflector.
- Put it on the air and compared it with the inverted vee.
A set of 8 radials for each parasite was laid down before the elements were raised. They are each 15 meters long except for the one that ties the radial hubs for the parasite and the driven element. In earlier articles I described my radial system topology as overlapping rather than connected at busses placed between the 5 elements in order to reduce the work of soldering radials to busses at the expense of more radial wire.
After the parasitic elements were installed the impedance was measured and the radials increased to 16. The impedance was again measured to determine the trend toward non-resonance in the radial system, which strongly depends on the ground's dielectric constant and thus the velocity factor.
The EZNEC medium ground model for 20 meter long radials is a very close fit to what I measured: ~40 kHz increase in resonant frequency when the radial count increased from 8 to 16. I can now adjust the elements confident that I can predict what will happen should I add more radials later. Apparently the velocity factor with on-ground and shallowly buried radials is substantially lower than in the model. This isn't surprising since it is difficult to accurately model radials of this type with NEC2. In part because they must be perched a fraction of a wavelength above ground, where less of the field flows through the ground.
Before proceeding with tuning I added 2 more radials to each parasitic element, for a total of 18. These are wires running the ~15 meters distance between each of the 4 parasitic element radial hubs. Although the change in impedance was negligible this should slightly reduce ground loss for the entire array, no matter the direction chosen, including the array's omni-directional mode.
I chose 15 meters as the radial length for two reasons: limit the overall area of the antenna to minimize the land taken from the haying operation, and; limit swings in parasite resonance as radials are added.
Parasitic wire elements
Designing the T-top wire elements was a challenge. This is an element topology that NEC2 is not able to model accurately. I knew this from the start, as I learned when I put up my 160 meter antenna last year. The second factor influencing resonance is the number and length of radials. The 8 radials in that antenna are 30 meters long, which is approximately the same as 15 meter radials on 80 meters, relative to wavelength. The resonant frequency is pulled downward.
For a single element antenna with a low feed point impedance the correction is as simple as an L-network. It doesn't matter that the antenna is not resonant since the network easily accommodates a non-zero reactance, and the efficiency is high if the resonant frequency isn't far off. For a yagi there is no forgiveness in tuning the elements; you must get it right.
As a guide I used the K3LR dimensions for a 160 meter version of this antenna which you'll find in ON4UN's Low-Band DXing book, version 5. With a bit of geometry and adjustment to fit the physical layout of my antenna I came up with dimensions for the T and the vertical. A little was then added to both to allow room to snip wire to reach resonance. The initial length of each leg of the T is 5.5 meters. The vertical is 12 meters, which includes an extra 0.5 meters for tuning purposes.
Two wire elements are visible in the photo above. Unfortunately you'll have to squint to see them. I didn't properly compensate for sag so the vertical segment drags on the ground. The centre junction is simply a stainless steel bolt which the wires wrap around and then snugged tight. It's lighter than an insulator and more secure than solder alone.The ropes that form the top end of the catenaries for the wire elements were cut to length and installed when the stinger and top section were lifted. The elements were walked up the tower and connected and the bottom ropes tied to the anchors, located 25.5 meters from the tower. That's right at the edge of the radial system (10.5 meter element spacing plus 15 meter radial length) to minimize land use.
It took a couple of hours to adjust the tension of each rope to achieve the best compromise among element sag, force on the stinger and centering the stinger. Eventually I was done and ready to proceed to the next step: tuning the elements and lighting up the yagi.
Measure, measure, measure
As I said above, precision is of the utmost importance in getting a yagi working properly. To this end I was fastidious about measurements. A marked template was set up on the ground to ensure the wire for the 4 elements were cut to the exact same length. The wire elements are therefore identical. Exactly 3" of wire are wrapped around the insulator at each end of the T. When I tied the catenary ropes up the tower I made a mark on the tower where each T should terminate, which helped achieve symmetry. All element ground anchors are exactly the same distance from the tower.Although opposite elements are, and must be 180° apart, adjacent elements are not 90° apart. This symmetry is necessary in a 4-square but not in the yagi. In yagi mode only two parasitic elements are in use. The other two are floated (disconnected from ground) making them non-resonant and effectively invisible. I used this feature to optimize array aiming for my geographic location. Floating works, as demonstrated by no change to driven element impedance when the parasitic elements were raised and left floating.
The feed point of each wire element is similarly identical with respect to radial hub and its support, switching system anchor, back plate and enclosure. Before tuning the elements I measured the resonant frequency of all 4 of them, once with 8 radials and again with 16 radials.
The resonant frequency was below the design objective of 3.680 MHz so that they can be cut to resonance. More important is that my fastidiousness resulted in a resonance spread among the 4 elements of only 20 kHz, or 0.6%. Notice that the resistance part of the impedance dropped 7 Ω with 16 radials. There is obviously more ground loss to be eliminated. I can probably bring the resistance closer to 20 Ω by doubling the radials. But that's another 1,000 meters of wire! Efficiency doesn't come easy.
To measure any element of the array, including the driven element (tower), all other elements must be floated. That is, the monopole and radial systems must be disconnected. Otherwise the mutual impedance will mask what is really going on. One of the jobs of the switching system will be to float elements that are neither directors nor reflectors for the selected direction. All parasitic elements are floated when the array is in its omni-directional mode.
Rough wiring the 3-element yagi
The next step is the fun part: lighting up the yagi. Since the most useful DX heading is towards Europe I rough wired the northeast element as a director and the southwest element as a reflector. Since I don't want to cut wire at this time I calculated the amount to shorten the element to resonate the director to 3.680 MHz and shaved the insulation of the wire at the appropriate position to expose a tap point. The ~40 cm of wire beyond the connection has negligible effect on element behaviour.
For the reflector I used a rough wound coil of AWG 14 wire from my junk box since it looked to be about the right size. I attached it and alternately squeezed and stretched the coil until it resonated at 3.450 MHz. This only took 30 seconds since the analyzer continuously recalculates the impedance. All I had to do was move my hands out of the way after each adjustment.
With the element tuned I temporarily completed the connections with wire nuts. I move the analyzer to the driven element and measured the impedance of my improvised 3-element yagi at 25 kHz intervals.The resistance part of the impedance is about as expected. This clearly shows how important it is to achieve the lowest possible ground loss with the biggest radial system you can manage. Even with a ground loss as low as 5 Ω the loss can be -2 db. That's a lot.
The X value is not terribly important, provided its absolute value is not much higher than R. That helps to minimize matching network loss. However for now I am leaving the 4:1 SWR as is and correcting it with the rig's ATU. The estimated total transmission line loss is -2 db despite being almost 300' long. It isn't difficult to keep transmission line loss low at 3.5 MHz. Once the matching network is in place the loss should be better than -1 db.
Before going further it is worth a moment to talk about instrumentation. To achieve accurate and repeatable measurements it is important to have an analyzer with the requisite performance and to use it properly. The RigExpert AA-54 is quite good considering the price. There are better products on the market for a higher price.
The analyzer should be able to get the R and X values correct within a few ohms when the SWR is high, which most of the cheapest units cannot do. Not only is accuracy important but so is repeatability. That is, the values should be the same between readings, including readings made after the unit is turned off for a while and reconnected to the antenna under test.
Make sure your body is not influencing the measurement by moving around. Do the same for the analyzer itself, including when in your hand or supported elsewhere. Keep the test leads short or compensate for the length; better units can calibrate on the transmission line length, or use software such as TLW to convert the measured impedance to that present at the load.
Doing it right with a finicky antenna like this one can save you a lot of grief. Buy the best analyzer you can afford if you like experimenting with antennas. A 2-port VNA is favoured by those with a need to design and test more complex antennas or to analyze impedance transformation networks. A handheld unit like the RigExpert is perfect for me.
On the air
This article is being written after 3 evenings with the antenna in its hard wired direction to the northeast (Europe, North Africa and Indian Ocean). Not only has activity on 80 meters has perked up after the summertime lull there are several current DXpeditions roughly in that direction, including 9X0T and TO6OK. As always there are many Europeans active overnight and their sunrise.
When I first lit it up I was briefly disappointed. Switching from the inverted vee (now with an apex of 19 meters) to the vertical yagi the band noise dropped precipitously. It seemed that the antenna efficiency was low, so that the analyzer measurement might be hiding a deeper problem. Or, perhaps, the transmission line loss is higher than calculated. My worries dissipated when I tuned in a signal from Europe.
All European signals were stronger versus the inverted vee just as they were when the antenna was configured as an omni-directional vertical. But now the difference is substantially greater. I did extensive comparisons to ensure that Faraday rotation and other causes of QSB were accounted for by comparing through signal strength peaks and valleys. The improvement was consistent. However there is variation with different stations and path lengths. The variation -- elevation angle, polarization and skew -- demonstrates the value of having more than one antenna per band.
Signal differences were as little as 1 S-unit and as much as 4 to 5 S-units. That is promising. But what happened to the band noise? One hint was listening to W8 and W5 stations off the back of the yagi. The F/B is very good. Signals that were S-9 on the inverted vee would drop to S-3 or lower; as a vertical the difference was typically 2 S-units in favour of the inverted vee. What these differences are in decibels is hazardous to estimate since an S-meter is not a reliable instrument.
What appears to be happening is the attenuation of early fall atmospheric QRN from warmer locales south and southwest of VE3. The northern path to Europe is of course colder with less of the weather that contributes to noise. That is, the antenna has good directivity. I confirmed this by comparing reception against my 175 meter long northeast Beverage. The Beverage is still the better receive antenna, though by far less than with an omni-directional antenna.
Keep in mind that a well tuned 4-square can achieve similar or better F/B over a wider bandwidth than this yagi. I knew this before proceeding with this antenna. For me the ability to experiment and make a less expensive directive array of similar performance was a deciding factor.
I can see myself living with the yagi on 80 meters and reserving the Beverage and other planned receive antennas primarily for use on 160 meters. I have no plans for a directive transmit array for 160 meters, although that could change.
Up next
The switching units must now be assembled, installed and adjusted. The 4 parasitic element units must be identical to ensure identical performance, which is important when switching direction. This applies to the coils, relays, lengths and routing of internal wires. The unit at the driven element will contain the switching matrix, signal distribution and relays for the matching networks.
 |
| QRP friends visiting the 80 meter array (Credit: VA3RKM) |
The driven element stinger may need to be replaced, if not this fall then next year. It is proving to be mechanically marginal when tension is put on the catenaries. I would like to take up more of the slack. Replacement would take a few hours and should only affect the L-network due to a change in the electrical length of the driven element.
I don't anticipate completion before November. There are too many other projects to be done this fall and this job can be done during the cold weather. I may even lay more radials before the snow flies.
With the rough wired yagi performing so well I am really looking forward to completing this project.
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