Logging errors in contests can exact a steep penalty. Not only will the sponsor remove QSOs containing errors they also assess penalties. On average a removed QSO will reduce your score by at least double that amount. If the removed QSOs are multipliers the cost can become very expensive indeed.
With the advent of computer logging, log submission and log checking the wages of sin will always be paid. In the olden days logs had to be manually checked. This was such a labourious process that logs with scores not high within their entry classes were rarely checked. Carelessness that was once penalty-free for 90% of contesters has evolved and is now a guarantee of score reduction. This is not only embarrassing it can also keep you out of contention for awards.
Is it possible to submit an error-free log? Yes, but it takes a combination of diligence and luck. I'll show you what I mean by luck in a moment, but let's first cover the errors that diligence can prevent. Computer logging is both a blessing and a curse in this regard. Software makes it easy to avoid some mistakes and easier to make others.
Call sign and exchange errors
These are the easiest errors to make and often can be completely eliminated by taking appropriate care. Errors include copying mistakes, typing mistakes and pre-fill oversights. Here are some of the ones I am most familiar with, along with ideas on how reduce mistakes.
Busted calls: This can happen on both SSB and CW. In the former case it is usually due to QRM or difficulty understanding a non-native English speaker. In the latter case the causes of copying errors are more numerous. A sequence of short letters (e.g. E, I, T) or characters with 3 or 4 dot sequences (e.g. B, V, 4, 6) at high speeds will often do it. Although there are some contesters with poor CW skills who get by due the short exchanges, everyone is at risk.
If you're running the other station will most often correct your error since you are sending their call to them. However if you're sending at 30 wpm or faster the other guy may not notice the error. I'm surprised how often I hear this happening while waiting to call someone. Worse, they may not care since in the majority of contests they are not penalized for the other guy's copying errors!
Some stations while in S & P mode make a point of sending the running station's call just to be sure they've correctly copied it. But this can be expensive in time if it is done on every QSO. I would only recommend doing this when there is some doubt about the other's call.
Some logging software will flag calls that are suspect by dint of not being known as having appeared in previous contests -- a so-called master database. Flagged calls should be double-checked, just in case. Be particularly wary of partial call databases, used by you or the other station, that will attempt to pick a likely call from the master database if the call is suspect or incomplete. It is often wrong. I am a regular victim of this feature since the other station often has difficulty copying my QRP signal.
Exchanges: In most contests the exchange is fixed and often predictable from the call. For example, in this past weekend's ARRL DX CW contest my exchange was "599 ON". The RST is of course routinely sent as 599 in every contest exchange. The state/province is a constant and in the case of Canadian calls is strongly correlated with the call sign prefix. Most logging software will analyze the call and pre-fill the exchange field for you, saving you time and potential for a typo. This can also be done for CQ and ITU zones in contests where those are part of the exchange.
US locations in particular are less predictable. It has been many years since a call sign prefix correlated to a state or zone. Logging software makes a best guess but it is up to you to confirm that what the other station sends is what the software pre-fills. It is too easy to get lazy, especially when you're tired, and not confirm the fill before logging the QSO. I can only say that you must be diligent. This is the cause of some of my errors.
If you are uncertain of your copy in contests with a more complex exchange (e.g. Sweepstakes) you should immediately ask the other station for confirmation or a repeat.
Some logging software allows you to use a history file built from previous contest logs (your own or by importing one) to more accurately pre-fill the exchange. The percentage of mistakes will be reduced, but you must still be diligent and confirm what is sent matches what is pre-filled.
Correcting errors on the fly: When I note an error and make a correction on the fly it is not always possible to record the correction in the log. Even if you're highly effective at manipulating the logging software this can take several seconds, during which the other station is wondering what's going on while others waiting for you (if you're running) may QSY. I keep a pen and paper handy to jot down the needed correction since it is sometimes the fastest way to move onward. The log can be updated even just a minute later while your memory keyer or DVM is playing a CQ.
Another technique during S & P is to stick around a few seconds to hear for a second time their call and/or exchange. The call can be quickly corrected this way. However there is a danger if the error is in the exchange. If the running station has a poor rate you could be waiting a while for their next QSO to hear the needed information. Rather than getting into this undesirable situation you should not be shy about asking for a repeat during the QSO.
Not-in-log errors (NIL)
NIL errors are unlike the errors discussed above in that they are not entirely under your control. That is, you cannot be certain that the other operator logged your QSO. You can reduce NIL errors but not eliminate them entirely. This is a topic I previously discussed so you can reference that article for background. What I want to address now is some of the "why" NIL errors are so difficult to eliminate.
I will use a real example. Although the results are not out I am one of the participants in last fall's (November 2014) CQWW CW contest sent a preview log check report (LCR) for review. My error rate is comfortably under 1% so there is little risk of losing my provisional #1 North America position in the SOAB (single op, all band, unassisted) QRP category.
Apart from a small number of busted calls and improperly recorded exchanges there were 3 NIL errors. In trying to understand what might have happened, despite my effort to eradicate NIL during the contest, Randy K5ZD suggested I look through the public logs. He seemed sufficiently confident in their log checking software and processes to punt the question back at me. So I did what he suggested.
Case #1: This occurred while I was running on 15 meters. Getting an NIL while running is odd since the other station would seem to have obviously copied me or would not have called. I have assumed, perhaps mistakenly, that the majority of NIL errors occur while S & P. This is an ongoing risk to those of us operating QRP, and especially so on low bands. Unfortunately the other station's log in this case is uninformative. He was indeed on 15 at the time but his log does not provide the frequency for each QSO, just the band (21000).
Case #2: This one was also while I was running, this time on 20 meters. The other station was multi-single so the log contains the interleaved QSOs of two operating positions. One of those was on 20 at the right time, however that station was running and positioned far from my frequency.
Case #3: Unlike the previous two cases this is one that is easily determined. It was a European on 80 where all of my DX QSOs are marginal. His log confirms he was there and running, and I have some recollection of the QSO. I recall that he did copy my call, with difficulty, though he seemed uncertain and may not have copied my exchange. After a while he moved on, though he first gave me some indication that the QSO was complete. Usually this is a "TU" or something similar before soliciting the next QSO, although I don't remember what it was in this case that decided the case for me that I should log the QSO. I may have been unduly rash since it was a multiplier, something that is very precious to me on 80!
Resolution: As Randy noted confusion often reigns during a contest and some NIL of the sort I had are not uncommon. It is entirely possible for an adjacent QSO (of which you might only hear only one side) can have just the right timing to make it seem that it was with you. This may have occurred in case #1. I have no idea what might have happened in case #2. The call was that of a big gun and not likely to be a copying error on my part, and even if so the log checking software would most likely have determined the correct call from scanning other submitted logs. On this basis there is little I could have done to avoid these two NIL errors.
Case #3 is a dilemma. When there is uncertainty in a situation like this there is no best choice. If I log the QSO and it is not logged by the other station I lose the QSO and multiplier and get assessed a further penalty. If I don't log it not only I will lose the QSO and multiplier, which the other station might have logged, I could cause the other station to suffer an NIL. That would be inconsiderate of me.
This comes back to suggestions above regarding getting as much confirmation of critical data during the QSO to eliminate these doubts about whether to log it. On low bands where the other station is barely able to copy me this is difficult. That does not rate as a justifiable excuse. You just do the best you can.
Hole-in-One
Getting to a 0% error rate is difficult, as I hope my experience has shown. It is not purely a matter of chance: if you are sloppy I can guarantee you will never achieve 0% errors. Yet even if you are extremely diligent I cannot guarantee you will eliminate all errors. The reason is that what the other operators do, the hundreds or even thousands of them you work in a contest weekend, is out of your control.
At its fundamentals the error rate is a stochastic process, where there are one or more random variables. We can draw an analogy from the game of golf. The top players can never guarantee getting a hole-in-one, not in any particular match and perhaps not in their lifetimes. What they have is a higher probability of doing so than everyone else who has ever picked up a golf club. This is because they can more often hit their tee shots onto the green. If you can't do that, or do it often enough, you will never score a hole-in-one. Unless you get very, very lucky.
Operating a contest is much the same. You may never score a 0% error rate but your chance of doing so dramatically rises when you make the effort to reduce errors. Even if you don't get to 0% you will see a big improvement in the difference between your claimed and published scores, and that will push you up the leader board past those who don't make the effort.
Wednesday, February 25, 2015
Friday, February 13, 2015
2-element Parasitic Ground Plane for 40 Meters
As the solar cycle declines my attention to the low bands increases. This means I have an increased interest in vertical antennas, even though "serious" low-band antennas are impractical on my suburban property. So I instead plan and model in the hope that one day I can start building large antennas.
Experimenting with 40 meters is in some respects easier than doing so on 80 and 160. Antennas are easier to successfully model and prototype at the shorter wavelengths, and then compared to existing antennas. Antennas that work out can then be scaled to the longer wavelengths with predictable results. There are also some things you can do that may be too mechanically challenging on lower bands. The antenna in this article is one of those.
Concept antenna, not a final design
Please keep in mind that this is purely a concept antenna. It is perhaps worthy of prototyping but should not be seriously considered without further work. I did not aim to fully optimize the design. My intention is to play with it to see it if has good DX performance with regard to gain, F/B and match. As we will see there are design aspects that require more work before committing to construction.
Another motivation is to see what can be accomplished with a relatively simple vertical array in comparison to well-tuned, switchable 4-square antennas that many big guns use on 80 and 160. Although this design is for 40 the antenna can be scaled, with some construction effort and expense.
My concern with the 4-square and similar directive arrays is the intricacy of the feed and switching networks. This invites the potential for failure when one or more elements is affected by weather (e.g. snow and ice) or a component drifts in value or fails. That is why 4-squares often have a "dump" resistor and a warning system. The design lacks a degree of robustness.
This is not meant to demean recent efforts at optimum phasing and power division, which can be very impressive. Designs such as those you'll find in chapter 11 of ON4UN's fifth edition of Low-band DXing are so bizarre because the elements are often so closely spaced that mutual coupling dominates. To my mind it is better to use judo rather than brute strength to tackle the problem. That is, to accept mutual coupling as a design partner rather than having to coerce it to behave in a prescribed manner. I try to do that in this article.
Copy and spin
There are many ways to make a parasitic array. You can even do it with λ/4 monopoles with ground planes, if you're careful. Consider the simple 4-radial ground plane mentioned near the end of my recent article on vertical modelling experiments. It is broadband, with low-angle radiation (good for DX), and is a good match to 50 Ω coax.
I proceed in the usual fashion of making a parasitic (reflector) array by copying a resonant single-element antenna and offsetting the copy in the desired direction. To avoid tangling the radials, which are about as long as the inter-element spacing, I spin the radials of one element by 45°.
With the elements mounted 10 meters above ground they a maximum height of about 20 meters. The bases can be light-duty television towers or masts made from aluminum or steel. I prefer the former so that the feed point is easily accessible for assembly and maintenance. Guying is necessary but there is no need for concrete. The radials can do double duty as guys, if you use something stronger than aluminum or pure copper wire.
With a bit of open space this should be an inexpensive and not too challenging antenna to construct. The minimum required area is 500 m² (25 x 20 meters). Even though mounted above ground it is recommended that there be no other structures within 1λ (40 meters) radius, and even farther from towers or other large conductors.
It's a Moxon!
Okay, it doesn't look like a typical (or even atypical) Moxon but it does have the same attributes. The reason is those radials: the way they intermingle causes near critical coupling between elements. Even with the relatively wide spacing between monopoles of 10 meters (close to 0.25λ) those radials keep the coupling high.
You can see this most clearly in the radial currents. Rather than the current in each of the 4 radials being ¼ that of the monopole it varies a lot, depending on the radial's position. One implication is that the parasite must be configured as a reflector. Well, you can try to make it a director but you'll find that task quite difficult unless you can find a way to reduce the coupling.
In the driven element (wires 6 to 10 in the current plot above) the radial currents are 6% and 43% that of the monopole in the rearward and forward radials, respectively. In the reflector (wires 1 to 5) the radial currents are 53%, 34% and 40% that in the monopole in the forward, rearward and side radials, respectively. These values are at 7.1 MHz, near where gain is maximum. No only are the radial currents unequal their sum only equals the monopole current in driven element. The sum far exceeds the monopole current in the reflector element.
The current in the reflector monopole ranges from 60% to 70% that of the driven element across the band. This is typical of a Moxon and higher than in a conventional 2-element parasitic array. As we'll see, gain, F/B and SWR vary less than a 2-element yagi across the entire 40 meters band.
Tuning for optimum performance
Performance is sensitive to element separation (equivalent to boom length in a conventional yagi or Moxon rectangle) and radial arrangement. The thing I found annoying is that although gain would vary a lot when these are adjusted a little, the feed point impedance (and thus SWR) and F/B were far more stable. It's annoying because the latter two are far easier to measure, and would simplify the tuning of this array.
In the model I settled on monopoles 9.95 meters tall and made from 25 mm (1") aluminum tubing. This is an approximation to a real antenna that would use telescoping, tapered tubes. The monopoles are 10 meters apart with bases 10 meters (~λ/4) above medium ground. The radials are 16 AWG aluminum wire, such as the often used (and inexpensive) aluminum fence wire. All radials are 10.525 meters long and slope downward 30°.
I²R loss in the aluminum monopoles and radials is around -0.1 db. The pattern plots are with zero loss conductors, including for the reference single ground plane. The performance chart below includes the loss. Ground loss is calculated by EZNEC to be about -5 db over medium ground.
Considering how peculiar an antenna this is its performance is quite good. Not only is it 5 db better than a single ground plane at 7.1 MHz (comparison in the elevation plot above) the gain varies little up through 7.2 MHz. The F/B, while not exceptional, is adequate to my needs. The SWR is particularly nice, staying below 2 across the band.
Compared to various single element and 2-element antennas the 10° elevation gain is very good. For example, it equals an inverted vee (broadside) 25 meters high and even a 2-element yagi up 15 meters. If you don't have a high tower but do have some open land this could be an attractive antenna choice. Don't expect this performance on a suburban lot since vertically-polarized antennas can under-perform the models.
As I stated at the beginning, I did not really design this antenna with the objective of putting in on 40 meters. If I eventually have higher towers there are superior alternatives. This experiment is about getting a handle on antennas for 80 and 160 where, often, towers cannot be high enough to make a horizontal antenna competitive. When scaled to 80 meters the the required towers for comparable horizontal antennas must be twice as high. Scaled verticals for 80 lose relatively little gain at low height (though half as high in wavelengths) but may suffer from additional ground loss and environmental interaction.
Although the monopoles are the same height the reflector element has a base loading coil. It is a very small coil with an inductance of 0.4 μH. Although small this value is critical. Even if only 0.1 μH higher or lower the SWR and gain will noticably suffer. F/B is less sensitive to inductance changes. Small changes to the radials will affect the required value of this coil since their length and position affect mutual coupling between elements.
To give an idea of the dimensions involved, a suitable 0.4 μH coil would be 5 turns with a length and diameter of 1" (2.5 cm). The equivalent shorted 300 Ω open wire stub would be 16" (40 cm) long at 7.1 MHz. The stub is easier to tune (with a sliding shorting bar) but will be exposed to the weather which can alter its reactance.
Direction switching
It is always helpful in a fixed element array to be able to change the direction of the beam. This antenna is amenable to such an arrangement, though with some stringent construction and tuning criteria. This, too, is typical of Moxon (critically-coupled) arrays.
The switching method I describe here has significant differences to the one I used for the various styles of 40 meter wire yagis I described over a year ago. I am assuming that the support masts for the elements allow convenient access to the feed points which are 10 meters above ground. This is why I recommend light duty television towers for the supports.
The switching system requires 2 plastic enclosures, 3 DPDT relays, 2 loading coils, DC switching circuitry and 50 Ω coax for the transmission line and running between the element feed points. One element will be connected through to the transmission line while the other will be isolated from the transmission line and a coil connected between monopole and radials. Relay DC power can be run by separate cable or on the transmission line. In the latter case a DC cable is still needed between the 2 enclosures at the bases of the monopoles.
The recommended arrangement has the transmission line terminate at the enclosure at the base of one of the monopoles. Make it the one closest to the shack to keep the total length of coaxial cable to a minimum. The length of coax between that enclosure and the one at the base of the other monopole is non-critical, except that it must (of course) be at least 10 meters long, the element separation. That section of coax will be fully isolated on both ends when the second element is a reflector. Similarly the transmission line will be fully isolated from the first element when it is a reflector. The outer conductor of the both lengths of coax must not be connected together or to the radials, except when connecting to the driven element. This is why the enclosure cannot be metal. Metal will also alter the coil's inductance if it is inside the enclosure.
One relay selects the element to connect both conductors of the transmission line. The other two relays switch each element between the coax feed and the loading coil. The coil provides the inductance to configure that element as a reflector. A shorted stub can be used in lieu of the coil. Obviously when one element is connected to the transmission line it becomes the driven element and the other is a reflector. The normally-off position of the relays should point the array in the most important or commonly used direction.
The transmission line outer conductor will act as a radial when the first element is driven. To avoid asymmetry and mistuning in that direction it is best to run the transmission line along one of the radials and choke it where the radial terminates, making them the same electrical length and at the same potential. A coax coil choke can be used if tuned to be effective on 40 meters. There should also be a choke where the coax enters the second enclosure to ensure it also does not become a radial when the second element is driven.
The two supporting masts and the isolated connecting coax are λ/4 long and so should not interact with the array. The supporting masts should be isolated from ground to make them non-resonant.
Broadside
It is possible in many vertical arrays to create a feed arrangement (power division and phase) to convert an end fire array to broadside. The idea is that it's often more convenient to come up with an elaborate feed than put up more elements, whether two independent 2-element arrays or a 4-square. With the antenna described in this article this is not possible.
Pattern flexibility requires that the factors under one's control (phase, power division, element tuning) are sufficient to sculpt the desired result. With a near-critically coupled antenna like this one the mutual coupling tends to make any effort in that pursuit moot: the mutual coupling dominates. Coupling can be reduced by moving the elements farther apart, but that would negate the parasitic benefits of the array. More elements can be added, but that too has significant costs.
The best that can be achieved is an omnidirectional pattern by splitting the feed in the centre and running equal lengths of coax to both elements. The resulting feed point impedance is 15 Ω, which would require a 3:1 unun. In the broadside configuration here is less than 1 db of gain in comparison to a single ground plane.
I believe it is better to leave the array as is and use another antenna, even just an inverted vee, to fill the holes in the array's end fire pattern.
Next steps
This is an experimental design that I do not recommend be built by anyone. Because if you do you'll have to deal with its various idiosyncrasies either in your own modelling effort or (literally) in the field.
Before I would undertake construction of this antenna I would model variations in radial deployment to modify coupling in a way that preserves the array's best attributes while making it less sensitive to minor variations in tuning. Another thing I'd like is to find an easily-measured quantity that correlates well with antenna performance. For example, in the various 2-element switchable 40 meter antennas I've discussed in the past this metric was the frequency of maximum F/B.
Of course all of this modelling and planning is contingent on having the space to build it. That is tentatively in my long term plans, although for the present I can only design, plan and model. It's time well spent.
Experimenting with 40 meters is in some respects easier than doing so on 80 and 160. Antennas are easier to successfully model and prototype at the shorter wavelengths, and then compared to existing antennas. Antennas that work out can then be scaled to the longer wavelengths with predictable results. There are also some things you can do that may be too mechanically challenging on lower bands. The antenna in this article is one of those.
Concept antenna, not a final design
Please keep in mind that this is purely a concept antenna. It is perhaps worthy of prototyping but should not be seriously considered without further work. I did not aim to fully optimize the design. My intention is to play with it to see it if has good DX performance with regard to gain, F/B and match. As we will see there are design aspects that require more work before committing to construction.
Another motivation is to see what can be accomplished with a relatively simple vertical array in comparison to well-tuned, switchable 4-square antennas that many big guns use on 80 and 160. Although this design is for 40 the antenna can be scaled, with some construction effort and expense.
My concern with the 4-square and similar directive arrays is the intricacy of the feed and switching networks. This invites the potential for failure when one or more elements is affected by weather (e.g. snow and ice) or a component drifts in value or fails. That is why 4-squares often have a "dump" resistor and a warning system. The design lacks a degree of robustness.
This is not meant to demean recent efforts at optimum phasing and power division, which can be very impressive. Designs such as those you'll find in chapter 11 of ON4UN's fifth edition of Low-band DXing are so bizarre because the elements are often so closely spaced that mutual coupling dominates. To my mind it is better to use judo rather than brute strength to tackle the problem. That is, to accept mutual coupling as a design partner rather than having to coerce it to behave in a prescribed manner. I try to do that in this article.
Copy and spin
There are many ways to make a parasitic array. You can even do it with λ/4 monopoles with ground planes, if you're careful. Consider the simple 4-radial ground plane mentioned near the end of my recent article on vertical modelling experiments. It is broadband, with low-angle radiation (good for DX), and is a good match to 50 Ω coax.
I proceed in the usual fashion of making a parasitic (reflector) array by copying a resonant single-element antenna and offsetting the copy in the desired direction. To avoid tangling the radials, which are about as long as the inter-element spacing, I spin the radials of one element by 45°.
With the elements mounted 10 meters above ground they a maximum height of about 20 meters. The bases can be light-duty television towers or masts made from aluminum or steel. I prefer the former so that the feed point is easily accessible for assembly and maintenance. Guying is necessary but there is no need for concrete. The radials can do double duty as guys, if you use something stronger than aluminum or pure copper wire.
With a bit of open space this should be an inexpensive and not too challenging antenna to construct. The minimum required area is 500 m² (25 x 20 meters). Even though mounted above ground it is recommended that there be no other structures within 1λ (40 meters) radius, and even farther from towers or other large conductors.
It's a Moxon!
Okay, it doesn't look like a typical (or even atypical) Moxon but it does have the same attributes. The reason is those radials: the way they intermingle causes near critical coupling between elements. Even with the relatively wide spacing between monopoles of 10 meters (close to 0.25λ) those radials keep the coupling high.
You can see this most clearly in the radial currents. Rather than the current in each of the 4 radials being ¼ that of the monopole it varies a lot, depending on the radial's position. One implication is that the parasite must be configured as a reflector. Well, you can try to make it a director but you'll find that task quite difficult unless you can find a way to reduce the coupling.
In the driven element (wires 6 to 10 in the current plot above) the radial currents are 6% and 43% that of the monopole in the rearward and forward radials, respectively. In the reflector (wires 1 to 5) the radial currents are 53%, 34% and 40% that in the monopole in the forward, rearward and side radials, respectively. These values are at 7.1 MHz, near where gain is maximum. No only are the radial currents unequal their sum only equals the monopole current in driven element. The sum far exceeds the monopole current in the reflector element.
The current in the reflector monopole ranges from 60% to 70% that of the driven element across the band. This is typical of a Moxon and higher than in a conventional 2-element parasitic array. As we'll see, gain, F/B and SWR vary less than a 2-element yagi across the entire 40 meters band.Tuning for optimum performance
Performance is sensitive to element separation (equivalent to boom length in a conventional yagi or Moxon rectangle) and radial arrangement. The thing I found annoying is that although gain would vary a lot when these are adjusted a little, the feed point impedance (and thus SWR) and F/B were far more stable. It's annoying because the latter two are far easier to measure, and would simplify the tuning of this array.
In the model I settled on monopoles 9.95 meters tall and made from 25 mm (1") aluminum tubing. This is an approximation to a real antenna that would use telescoping, tapered tubes. The monopoles are 10 meters apart with bases 10 meters (~λ/4) above medium ground. The radials are 16 AWG aluminum wire, such as the often used (and inexpensive) aluminum fence wire. All radials are 10.525 meters long and slope downward 30°.I²R loss in the aluminum monopoles and radials is around -0.1 db. The pattern plots are with zero loss conductors, including for the reference single ground plane. The performance chart below includes the loss. Ground loss is calculated by EZNEC to be about -5 db over medium ground.
Compared to various single element and 2-element antennas the 10° elevation gain is very good. For example, it equals an inverted vee (broadside) 25 meters high and even a 2-element yagi up 15 meters. If you don't have a high tower but do have some open land this could be an attractive antenna choice. Don't expect this performance on a suburban lot since vertically-polarized antennas can under-perform the models.
As I stated at the beginning, I did not really design this antenna with the objective of putting in on 40 meters. If I eventually have higher towers there are superior alternatives. This experiment is about getting a handle on antennas for 80 and 160 where, often, towers cannot be high enough to make a horizontal antenna competitive. When scaled to 80 meters the the required towers for comparable horizontal antennas must be twice as high. Scaled verticals for 80 lose relatively little gain at low height (though half as high in wavelengths) but may suffer from additional ground loss and environmental interaction.
Although the monopoles are the same height the reflector element has a base loading coil. It is a very small coil with an inductance of 0.4 μH. Although small this value is critical. Even if only 0.1 μH higher or lower the SWR and gain will noticably suffer. F/B is less sensitive to inductance changes. Small changes to the radials will affect the required value of this coil since their length and position affect mutual coupling between elements.
To give an idea of the dimensions involved, a suitable 0.4 μH coil would be 5 turns with a length and diameter of 1" (2.5 cm). The equivalent shorted 300 Ω open wire stub would be 16" (40 cm) long at 7.1 MHz. The stub is easier to tune (with a sliding shorting bar) but will be exposed to the weather which can alter its reactance.
Direction switching
It is always helpful in a fixed element array to be able to change the direction of the beam. This antenna is amenable to such an arrangement, though with some stringent construction and tuning criteria. This, too, is typical of Moxon (critically-coupled) arrays.
The switching method I describe here has significant differences to the one I used for the various styles of 40 meter wire yagis I described over a year ago. I am assuming that the support masts for the elements allow convenient access to the feed points which are 10 meters above ground. This is why I recommend light duty television towers for the supports.
The switching system requires 2 plastic enclosures, 3 DPDT relays, 2 loading coils, DC switching circuitry and 50 Ω coax for the transmission line and running between the element feed points. One element will be connected through to the transmission line while the other will be isolated from the transmission line and a coil connected between monopole and radials. Relay DC power can be run by separate cable or on the transmission line. In the latter case a DC cable is still needed between the 2 enclosures at the bases of the monopoles.
The recommended arrangement has the transmission line terminate at the enclosure at the base of one of the monopoles. Make it the one closest to the shack to keep the total length of coaxial cable to a minimum. The length of coax between that enclosure and the one at the base of the other monopole is non-critical, except that it must (of course) be at least 10 meters long, the element separation. That section of coax will be fully isolated on both ends when the second element is a reflector. Similarly the transmission line will be fully isolated from the first element when it is a reflector. The outer conductor of the both lengths of coax must not be connected together or to the radials, except when connecting to the driven element. This is why the enclosure cannot be metal. Metal will also alter the coil's inductance if it is inside the enclosure.
One relay selects the element to connect both conductors of the transmission line. The other two relays switch each element between the coax feed and the loading coil. The coil provides the inductance to configure that element as a reflector. A shorted stub can be used in lieu of the coil. Obviously when one element is connected to the transmission line it becomes the driven element and the other is a reflector. The normally-off position of the relays should point the array in the most important or commonly used direction.
The transmission line outer conductor will act as a radial when the first element is driven. To avoid asymmetry and mistuning in that direction it is best to run the transmission line along one of the radials and choke it where the radial terminates, making them the same electrical length and at the same potential. A coax coil choke can be used if tuned to be effective on 40 meters. There should also be a choke where the coax enters the second enclosure to ensure it also does not become a radial when the second element is driven.
The two supporting masts and the isolated connecting coax are λ/4 long and so should not interact with the array. The supporting masts should be isolated from ground to make them non-resonant.
Broadside
It is possible in many vertical arrays to create a feed arrangement (power division and phase) to convert an end fire array to broadside. The idea is that it's often more convenient to come up with an elaborate feed than put up more elements, whether two independent 2-element arrays or a 4-square. With the antenna described in this article this is not possible.
Pattern flexibility requires that the factors under one's control (phase, power division, element tuning) are sufficient to sculpt the desired result. With a near-critically coupled antenna like this one the mutual coupling tends to make any effort in that pursuit moot: the mutual coupling dominates. Coupling can be reduced by moving the elements farther apart, but that would negate the parasitic benefits of the array. More elements can be added, but that too has significant costs.
The best that can be achieved is an omnidirectional pattern by splitting the feed in the centre and running equal lengths of coax to both elements. The resulting feed point impedance is 15 Ω, which would require a 3:1 unun. In the broadside configuration here is less than 1 db of gain in comparison to a single ground plane.
I believe it is better to leave the array as is and use another antenna, even just an inverted vee, to fill the holes in the array's end fire pattern.
Next steps
This is an experimental design that I do not recommend be built by anyone. Because if you do you'll have to deal with its various idiosyncrasies either in your own modelling effort or (literally) in the field.
Before I would undertake construction of this antenna I would model variations in radial deployment to modify coupling in a way that preserves the array's best attributes while making it less sensitive to minor variations in tuning. Another thing I'd like is to find an easily-measured quantity that correlates well with antenna performance. For example, in the various 2-element switchable 40 meter antennas I've discussed in the past this metric was the frequency of maximum F/B.
Of course all of this modelling and planning is contingent on having the space to build it. That is tentatively in my long term plans, although for the present I can only design, plan and model. It's time well spent.
Monday, February 9, 2015
KX3 Review by a QRP DXer and Contester
I've been using an Elecraft KX3 as my main station rig for 2 years, ever since returning to ham radio after over 20 years of being QRT. I purchased it since it met my needs at the time: high performance, and; low-impact operation. Now that I've added a FT-1000MP to my shack it seems a good time to review how the rig performs, and how it meets my primary interests of DXing and contesting. The latter activity was not in consideration when I bought the KX3 since I didn't realize that I'd return to contesting.
There are ample reviews of the KX3 so there is no need for me to do the same. In any case I do not have the test equipment needed to do a proper technical review. You can find those elsewhere, such as the QST review and user feedback on eHam. My intent is to give an operator's impression of the rig, both its high points and lows, as applied to DXing and contesting.
My review is in some degree going to be unfair to the rig. It was not designed to primarily serve as a base station, or for the most demanding applications. Take this perspective into account as you read onward. For its intended use the KX3 is a superior product. I mean that whole-heartedly.
Overload
The receiver front end is fragile. There are two significant categories of signals that overload the receiver: strong signals within the roofing filter; strong signals farther away, even very far away. This is with the optional KXFL3 roofing filter installed, which I ordered with the rig and is factory calibrated.
My impression from regular use is that the roofing filter does the intended job of reducing IMD from strong adjacent signals. However when very strong signals fall within the roofing filter the rig may turn off the pre-amp. This is reasonable when that signal is from the ham who lives a couple of blocks away, but less so when the signal is from W8. There is a brief message on the display when this happens which I have rarely noticed while tuning across these signals. A minute later I'm wondering why the band is suddenly quiet. When the rig was new I was always puzzled as to why I would occasionally notice that the pre-amp was off. Eventually I discovered what was going on.
The other problem is fundamental overload where a strong signal into the front-end, even if well outside the ham bands, is detected regardless of VFO tuning. This can be very inconvenient when it occurs. For example, there is a shortwave broadcaster in the US with an exceptionally strong signal here. Even with just a dipole that station can push its way through the receiver and be AM-detected no matter where the rig is tuned in the 20 and 17 meter bands. A narrow bandwidth on CW reduces the interference though not enough in many cases. Turning off the pre-amp or using the attenuator will usually cure the problem, but at the cost of sensitivity.
The better your antennas the worse the overload problems since signals presented to the front-end are going to be stronger.
Receiver DSP
As with all electronics the speed and capacity of DSP hardware has remarkably improved over the years. When coupled with effective software there is the potential for superior performance. In my experience the KX3 does very well in this regard.
The continuously variable receiver filter bandwidth (50 Hz steps) is a delight to use. At all settings the audio signals come through very clearly. Even at the narrowest bandwidth (50 Hz) ringing is low. It is also convenient that the roofing filter automatically adjusts in response to the filter setting.
There are limits to what the DSP filtering can accomplish in this direct conversion receiver. Filter skirts are shallow. For example, I typically set the filter to 200 Hz on CW and yet can hear well outside that narrow range. It is how I compromise between noise reduction (local QRN) and not missing much as I tune across the bands. During contests I often narrow the filter to 100 Hz for S & P (search and pounce) and only need to open it up to 300 Hz when calling CQ, and I don't miss much. The APF is pretty much superfluous on this rig.
Multi-pole crystal IF filters are needed to get the steep skirts needed for best QRM and noise rejection. This is not only impossible in a direct conversion design these filters could not fit inside the KX3's small cabinet.
A bigger issue is opposite sideband rejection for single-signal reception. This is another case where the shallow filter skirts limit performance. Elecraft is well aware of the issue but their suggested solution is one that has side effects I don't care for. So I live with it. It is a particular problem in popular CW contests where stations are packed close together. Even middling strong signals the other side of zero beat interfere with the desired signal. It can also be confusing in that a seemingly interfering signal is in fact 1 or more kHz away. I find it necessary at times to jog the VFO to determine whether the signal is really within the pass band.
Noise Blanker (NB) and Noise Reduction (NR)
I have a lot of noise to contend with throughout the day when neighbours are awake. Most seems to come from LED lighting power supplies, which is added to by various appliances and computers. The worst band is 80, followed by 30, and lesser noise on 20 through 10 which varies with the yagi's direction. For some reason 40 is mostly quiet.
Since I can't change the world or hope to track down every noise source and convince my neighbours to fix the problems the receiver must have effective noise control features. NB and NR are important features.
The NB in the KX3 sometimes works well and sometimes makes matters worse. The NB was not adjustable until a firmware version that came out in (I believe) 2013, after I'd owned the rig for a while. Unfortunately the variability helped little so I typically keep it at or near maximum (15).
The major problem with the NB is its susceptibility to signals outside the filter bandwidth and within or near the range of the roofing filter. Even if those signals are of middling strength the NB is heavily modulated and pretty much renders the desired signal unreadable. This appears to be a case of where the DSP filtering is unable to make up for the limitations of the basic receiver design.
The NR sometimes works, though as with most rigs with NR it typically works best on SSB, and not so well on CW. This is especially true with weak CW signals, where the NR is of no benefit. In my experience adjusting the NR doesn't help on CW.
When the noise is making a CW QSO difficult I often try the NB first. In the majority of cases I get a better result by tightening up the filter to 50 or 100 Hz. In contests where most of my QSOs are S & P (search and pounce) I use a narrow filter of 100 to 200 Hz to contend with the noise and QRM while ensuring I miss few signals as I tune across the band.
VFO Attributes Memory
Every rig associates a variety of controls with each VFO-band pairing, though not always the same ones. On balance I feel that the KX3 does better at this than some other rigs I've used. For example, the KX3 remembers these important settings with the VFO-band pair: attenuator, pre-amp, NB, NR, mode, frequency, and perhaps some others. Since noise and signal levels are band and antenna dependent the first four of those are very welcome. Other rigs often don't associate these with the VFO-band pair, requiring some button pushing on every band change.
What I wish the KX3 would remember is the filter bandwidth. It associates this setting with the mode but not the VFO-band pair. Yet like the items mentioned above the filter is also a control I set differently per band, for reasons of noise and activity level. At least that's how I operate.
VFO, RIT and XIT tuning rates
These features work pretty well aside from the small size of the controls. The problem I have is one of tuning rate. It can take many turns of the knob to effect the desired offset.
The VFO rate is less of a concern to me than RIT and XIT. When I am scanning the band, either in a contest or in daily operation, the VFO tuning rate is fine. For larger frequency excursions it is too slow. Tuning rate can be sped up with a long press of a button, but then the steps are quite large and unsuitable for tuning in a station. Alternative rate settings in the menu are less than ideal to my style of operating. It's easier to use the rig control pane of logging software for large QSY steps.
RIT and XIT tune so slowly that they are very cumbersome for use in split operation. It is almost always better to use both VFOs for split and leave the RIT and XIT for minor adjustments on ordinary QSOs.
QSK and VOX
The QSK (CW break in) and VOX (SSB) work very well. I have heard some complaints about the rig's QSK though that is the opposite of my experience. I use it full time on CW, and I use CW for over 95% of my QSOs. At well over 30 wpm I can hear clearly between dots. There are no annoying switching transients.
When I decided to enter a SSB contest last year I had planned to use PTT with a foot switch, just as I did years ago. I ran into some difficulty wiring in a foot switch and time was pressing, so I decided to try VOX. It worked so well that now I only use VOX when operating SSB with this rig. It was easy to adjust, reasonably immune to inadvertent or extraneous sound, and never cut enough of the first syllable to cause copy errors at the other end in rapid-fire contest exchanges.
ATU-free operation
I did not purchase the optional ATU (automatic tuner). This could have been added later if I got tired of manually adjusting an external tuner. But once I transitioned from my eaves trough antenna to resonant outdoor antennas I found that tuning was not necessary.
At 10 watts output I rarely triggered the protection circuitry even when the SWR got as high as 4. The only serious problem I encountered was common mode from my eaves trough antenna that was easily cured with a coax choke. It similarly was happy putting out 5 watts on 160 meters when feeding the coax centre pin of my 80 meters half sloper. In this case the measured SWR was close to 5.
Buttons and ergonomics
The KX3 is really small and lightweight. This makes it an ideal portable rig, it's designed purpose. As a base station -- how I any many others use it -- size is a problem. When I describe the rig to others I like to say that I can cover the entire face plate with one hand. It's no exaggeration.
The majority of controls are on one of the main circuit boards, which is mounted directly underneath the face plate. When you press a button you are pressing on the circuit board. Although the physical support for the board is quite good I worry that it is prone to eventual failure. If a button breaks or the board cracks the repair implication can be dire. Further, even with my relatively light touch (I'm not physically abusive with my rigs!) the entire rig will slide backward. The rubber feet don't help since the KX3 is very light.
Another problem with its small size is the overlaying of features on the available controls. In addition to a primary use each button or knob can access (presumably less-used) features by long press, pushing knobs, or by pressing another button first. While necessary in a compact design it does cause operating grief. For example, I have several times managed to QRM a DXpedition when trying to operate split since the A=B key is also a split selector on a long press. Playing back a CW memory requires 2 button pushes making it almost useless due to the delay involved between action and result, and the potential for error.
For some reason the normal CW mode operates on the lower sideband (LSB). This is opposite to most other rigs, requiring that I set the mode to CW-R (reverse, or USB) to suit my operating style. In N1MM Logger+ I had to locate the option to use CW-R rather than the default CW mode, otherwise every clicked (self-)spot reverses my preferred mode. It's a solvable problem though not one I find convenient.
Microphone flexibility and SSB
As originally designed the microphone gain could not be set to accommodate a dynamic microphone element. For some reason Elecraft was reluctant to change this despite numerous requests. I was surprised since, as it turned out, it was correctable with firmware alone. To their credit they did relent and I was able to use my venerable Heil headset with the KX3.
Despite the company's protestations about noise and hum that can come with high gain I have experienced no such problem. Ultimately I am happy with the outcome and the KX3's flexibility in regard to the variety of mic elements and handheld controls they support.
After adjusting the gain and ALC in accord with the manual I also added compression for more SSB talk power. The feature itself is standard on every rig on the market although not always done well. From numerous solicited requests on the air I feel confident in saying that when properly adjusted the KX3 produces a high quality, easily-copied SSB signal. This is with the Heil element that emphasizes the mid-range; I set the KX3's mic equalization to flat.
Computer integration
This was trivially easy: just plug one end of the supplied cable to the rig and the other to a USB port. When I first purchased the KX3 not all popular software supported it since it was relatively new, a lack that has since been filled. I have no issues with any of the standard and contest logging software. At least not since setting communication speed to its highest setting of 38,400 bps. Otherwise the logging software was slow to track mode and frequency changes.
One thing I particularly like is that only the one interface is needed for contesting since it can be used to send CW and play rig-resident message memories. That is, no additional serial port is needed for PC-generated CW. However when used in this way there are some things to be kept in mind.
In N1MM Logger+ a macro can be used in the function keys to tell the KX3 to send CW. For example,
closes off one QSO and invites others to call. The KX3's KY command converts the following text to CW, delimited by the ';'. CW speed is determined by the setting on the KX3.
A problem arises because once the macro is executed and the command sent to the rig the software does not know the ongoing progress of the message since there is no feedback from the rig. In N1MM Logger+ (to give a particular example) the following must be kept in mind:
Wrap-up
There are other things I like and don't like about the KX3, though those are relatively minor items that I won't spend time writing up. Features I don't use I can't report on at all, including everything related to digital modes and battery operation.
I plan to continue using the KX3 for contests in the coming months. Although I have the FT-1000MP it requires some work to be ready for the demanding requirements for contesting (CW filter and various mods), and I do not want to risk neighbourhood RFI. That is, my contesting will remain QRP.
Every rig has its problems, including the KX3, so the negative points I've made should be kept in context. There is also the matter of personal preference, where my preferences can be very different from that of others. The KX3 is well regarded in the ham community, a reputation it deserves. Be sure it meets your needs if you are thinking of getting one.
There are ample reviews of the KX3 so there is no need for me to do the same. In any case I do not have the test equipment needed to do a proper technical review. You can find those elsewhere, such as the QST review and user feedback on eHam. My intent is to give an operator's impression of the rig, both its high points and lows, as applied to DXing and contesting.
My review is in some degree going to be unfair to the rig. It was not designed to primarily serve as a base station, or for the most demanding applications. Take this perspective into account as you read onward. For its intended use the KX3 is a superior product. I mean that whole-heartedly.
Overload
The receiver front end is fragile. There are two significant categories of signals that overload the receiver: strong signals within the roofing filter; strong signals farther away, even very far away. This is with the optional KXFL3 roofing filter installed, which I ordered with the rig and is factory calibrated.
My impression from regular use is that the roofing filter does the intended job of reducing IMD from strong adjacent signals. However when very strong signals fall within the roofing filter the rig may turn off the pre-amp. This is reasonable when that signal is from the ham who lives a couple of blocks away, but less so when the signal is from W8. There is a brief message on the display when this happens which I have rarely noticed while tuning across these signals. A minute later I'm wondering why the band is suddenly quiet. When the rig was new I was always puzzled as to why I would occasionally notice that the pre-amp was off. Eventually I discovered what was going on.
The other problem is fundamental overload where a strong signal into the front-end, even if well outside the ham bands, is detected regardless of VFO tuning. This can be very inconvenient when it occurs. For example, there is a shortwave broadcaster in the US with an exceptionally strong signal here. Even with just a dipole that station can push its way through the receiver and be AM-detected no matter where the rig is tuned in the 20 and 17 meter bands. A narrow bandwidth on CW reduces the interference though not enough in many cases. Turning off the pre-amp or using the attenuator will usually cure the problem, but at the cost of sensitivity.
The better your antennas the worse the overload problems since signals presented to the front-end are going to be stronger.
Receiver DSP
As with all electronics the speed and capacity of DSP hardware has remarkably improved over the years. When coupled with effective software there is the potential for superior performance. In my experience the KX3 does very well in this regard.
The continuously variable receiver filter bandwidth (50 Hz steps) is a delight to use. At all settings the audio signals come through very clearly. Even at the narrowest bandwidth (50 Hz) ringing is low. It is also convenient that the roofing filter automatically adjusts in response to the filter setting.
There are limits to what the DSP filtering can accomplish in this direct conversion receiver. Filter skirts are shallow. For example, I typically set the filter to 200 Hz on CW and yet can hear well outside that narrow range. It is how I compromise between noise reduction (local QRN) and not missing much as I tune across the bands. During contests I often narrow the filter to 100 Hz for S & P (search and pounce) and only need to open it up to 300 Hz when calling CQ, and I don't miss much. The APF is pretty much superfluous on this rig.
Multi-pole crystal IF filters are needed to get the steep skirts needed for best QRM and noise rejection. This is not only impossible in a direct conversion design these filters could not fit inside the KX3's small cabinet.
A bigger issue is opposite sideband rejection for single-signal reception. This is another case where the shallow filter skirts limit performance. Elecraft is well aware of the issue but their suggested solution is one that has side effects I don't care for. So I live with it. It is a particular problem in popular CW contests where stations are packed close together. Even middling strong signals the other side of zero beat interfere with the desired signal. It can also be confusing in that a seemingly interfering signal is in fact 1 or more kHz away. I find it necessary at times to jog the VFO to determine whether the signal is really within the pass band.
Noise Blanker (NB) and Noise Reduction (NR)
I have a lot of noise to contend with throughout the day when neighbours are awake. Most seems to come from LED lighting power supplies, which is added to by various appliances and computers. The worst band is 80, followed by 30, and lesser noise on 20 through 10 which varies with the yagi's direction. For some reason 40 is mostly quiet.
Since I can't change the world or hope to track down every noise source and convince my neighbours to fix the problems the receiver must have effective noise control features. NB and NR are important features.
The NB in the KX3 sometimes works well and sometimes makes matters worse. The NB was not adjustable until a firmware version that came out in (I believe) 2013, after I'd owned the rig for a while. Unfortunately the variability helped little so I typically keep it at or near maximum (15).
The major problem with the NB is its susceptibility to signals outside the filter bandwidth and within or near the range of the roofing filter. Even if those signals are of middling strength the NB is heavily modulated and pretty much renders the desired signal unreadable. This appears to be a case of where the DSP filtering is unable to make up for the limitations of the basic receiver design.
The NR sometimes works, though as with most rigs with NR it typically works best on SSB, and not so well on CW. This is especially true with weak CW signals, where the NR is of no benefit. In my experience adjusting the NR doesn't help on CW.
When the noise is making a CW QSO difficult I often try the NB first. In the majority of cases I get a better result by tightening up the filter to 50 or 100 Hz. In contests where most of my QSOs are S & P (search and pounce) I use a narrow filter of 100 to 200 Hz to contend with the noise and QRM while ensuring I miss few signals as I tune across the band.
VFO Attributes Memory
Every rig associates a variety of controls with each VFO-band pairing, though not always the same ones. On balance I feel that the KX3 does better at this than some other rigs I've used. For example, the KX3 remembers these important settings with the VFO-band pair: attenuator, pre-amp, NB, NR, mode, frequency, and perhaps some others. Since noise and signal levels are band and antenna dependent the first four of those are very welcome. Other rigs often don't associate these with the VFO-band pair, requiring some button pushing on every band change.
What I wish the KX3 would remember is the filter bandwidth. It associates this setting with the mode but not the VFO-band pair. Yet like the items mentioned above the filter is also a control I set differently per band, for reasons of noise and activity level. At least that's how I operate.
VFO, RIT and XIT tuning rates
These features work pretty well aside from the small size of the controls. The problem I have is one of tuning rate. It can take many turns of the knob to effect the desired offset.
The VFO rate is less of a concern to me than RIT and XIT. When I am scanning the band, either in a contest or in daily operation, the VFO tuning rate is fine. For larger frequency excursions it is too slow. Tuning rate can be sped up with a long press of a button, but then the steps are quite large and unsuitable for tuning in a station. Alternative rate settings in the menu are less than ideal to my style of operating. It's easier to use the rig control pane of logging software for large QSY steps.
RIT and XIT tune so slowly that they are very cumbersome for use in split operation. It is almost always better to use both VFOs for split and leave the RIT and XIT for minor adjustments on ordinary QSOs.
QSK and VOX
The QSK (CW break in) and VOX (SSB) work very well. I have heard some complaints about the rig's QSK though that is the opposite of my experience. I use it full time on CW, and I use CW for over 95% of my QSOs. At well over 30 wpm I can hear clearly between dots. There are no annoying switching transients.
When I decided to enter a SSB contest last year I had planned to use PTT with a foot switch, just as I did years ago. I ran into some difficulty wiring in a foot switch and time was pressing, so I decided to try VOX. It worked so well that now I only use VOX when operating SSB with this rig. It was easy to adjust, reasonably immune to inadvertent or extraneous sound, and never cut enough of the first syllable to cause copy errors at the other end in rapid-fire contest exchanges.
ATU-free operation
I did not purchase the optional ATU (automatic tuner). This could have been added later if I got tired of manually adjusting an external tuner. But once I transitioned from my eaves trough antenna to resonant outdoor antennas I found that tuning was not necessary.
At 10 watts output I rarely triggered the protection circuitry even when the SWR got as high as 4. The only serious problem I encountered was common mode from my eaves trough antenna that was easily cured with a coax choke. It similarly was happy putting out 5 watts on 160 meters when feeding the coax centre pin of my 80 meters half sloper. In this case the measured SWR was close to 5.
Buttons and ergonomics
The KX3 is really small and lightweight. This makes it an ideal portable rig, it's designed purpose. As a base station -- how I any many others use it -- size is a problem. When I describe the rig to others I like to say that I can cover the entire face plate with one hand. It's no exaggeration.
The majority of controls are on one of the main circuit boards, which is mounted directly underneath the face plate. When you press a button you are pressing on the circuit board. Although the physical support for the board is quite good I worry that it is prone to eventual failure. If a button breaks or the board cracks the repair implication can be dire. Further, even with my relatively light touch (I'm not physically abusive with my rigs!) the entire rig will slide backward. The rubber feet don't help since the KX3 is very light.
Another problem with its small size is the overlaying of features on the available controls. In addition to a primary use each button or knob can access (presumably less-used) features by long press, pushing knobs, or by pressing another button first. While necessary in a compact design it does cause operating grief. For example, I have several times managed to QRM a DXpedition when trying to operate split since the A=B key is also a split selector on a long press. Playing back a CW memory requires 2 button pushes making it almost useless due to the delay involved between action and result, and the potential for error.
For some reason the normal CW mode operates on the lower sideband (LSB). This is opposite to most other rigs, requiring that I set the mode to CW-R (reverse, or USB) to suit my operating style. In N1MM Logger+ I had to locate the option to use CW-R rather than the default CW mode, otherwise every clicked (self-)spot reverses my preferred mode. It's a solvable problem though not one I find convenient.
Microphone flexibility and SSB
As originally designed the microphone gain could not be set to accommodate a dynamic microphone element. For some reason Elecraft was reluctant to change this despite numerous requests. I was surprised since, as it turned out, it was correctable with firmware alone. To their credit they did relent and I was able to use my venerable Heil headset with the KX3.
Despite the company's protestations about noise and hum that can come with high gain I have experienced no such problem. Ultimately I am happy with the outcome and the KX3's flexibility in regard to the variety of mic elements and handheld controls they support.
After adjusting the gain and ALC in accord with the manual I also added compression for more SSB talk power. The feature itself is standard on every rig on the market although not always done well. From numerous solicited requests on the air I feel confident in saying that when properly adjusted the KX3 produces a high quality, easily-copied SSB signal. This is with the Heil element that emphasizes the mid-range; I set the KX3's mic equalization to flat.
Computer integration
This was trivially easy: just plug one end of the supplied cable to the rig and the other to a USB port. When I first purchased the KX3 not all popular software supported it since it was relatively new, a lack that has since been filled. I have no issues with any of the standard and contest logging software. At least not since setting communication speed to its highest setting of 38,400 bps. Otherwise the logging software was slow to track mode and frequency changes.
One thing I particularly like is that only the one interface is needed for contesting since it can be used to send CW and play rig-resident message memories. That is, no additional serial port is needed for PC-generated CW. However when used in this way there are some things to be kept in mind.
In N1MM Logger+ a macro can be used in the function keys to tell the KX3 to send CW. For example,
{CATA1ASC KY tu {MYCALL};}
closes off one QSO and invites others to call. The KX3's KY command converts the following text to CW, delimited by the ';'. CW speed is determined by the setting on the KX3.
A problem arises because once the macro is executed and the command sent to the rig the software does not know the ongoing progress of the message since there is no feedback from the rig. In N1MM Logger+ (to give a particular example) the following must be kept in mind:
- ESC can't be used to interrupt transmission. You must tap the paddles.
- CQ auto-repeat interval is from when the command is sent to the KX3, not from end of the transmission. It is best to disable this feature and press F1 as needed.
- Sending speed cannot be easily adjusted from the software. For example, the "<" and ">" speed change commands don't work, nor do the PageUp and PageDown keys.
- If you operate SO2R or switch rigs the CATAASC macros must be swapped out. I have this problem now that I have a FT-1000MP, as soon as I start using it in a contest.
Wrap-up
There are other things I like and don't like about the KX3, though those are relatively minor items that I won't spend time writing up. Features I don't use I can't report on at all, including everything related to digital modes and battery operation.
I plan to continue using the KX3 for contests in the coming months. Although I have the FT-1000MP it requires some work to be ready for the demanding requirements for contesting (CW filter and various mods), and I do not want to risk neighbourhood RFI. That is, my contesting will remain QRP.
Every rig has its problems, including the KX3, so the negative points I've made should be kept in context. There is also the matter of personal preference, where my preferences can be very different from that of others. The KX3 is well regarded in the ham community, a reputation it deserves. Be sure it meets your needs if you are thinking of getting one.
Wednesday, January 28, 2015
Exploring Verticals with a 4-radial Ground Plane Model
Vertical antennas is a subject that currently interests me since I feel the pain of a poorly-performing antenna for 80 meters. It is noteworthy now that I'm running 100 watts in the DX pile-ups. For example, I quickly cut through the pile-ups to work C5X on 40 meters and above yet ran head first into a brick wall on 80. It isn't all bad since I have had a few notable DX successes on 80 with the loaded half sloper, and I did even better years ago with a full-sized half sloper. They will do if nothing better is available.
The EZNEC (NEC2 engine) modelled loss of my present antenna over medium ground is about -6 db. This understates the reality since the ground in my yard is worse than that, and there are many housing-related long conductors in the antenna's near field. I am, in effect, dialling down my recently-acquired 100 watt rig to QRP. What it does when I operate with my KX3 is dreadful to contemplate. Yet that's how I currently operate on 80: very, very poorly. I had similarly poor results with my experimental and vertically-polarized loaded sloper on 40.
Verticals are nice but radials and interactions with obstructions are a problem in suburbia. I have therefore avoided them over the years even though I know how well than can perform on the low bands. Software modelling of verticals is tricky due to their strong interaction with ground, regardless of the number of radials or high-conductance ground screen. Horizontally-polarized antenna are more predictable.
Motivation: use my tower as a ground-mounted vertical
To address the problem it is helpful to step back and consider what radials do and don't do in various antennas. If I want to load my tower as a monopole on 80 it would be helpful to choose the length and number of radials that minimize the loss without creating a backyard tangle of wires. However, first let me place this in context by presenting my thoughts on how I might utilize my tower on 80.
The first thing is to determine the electrical length of the tower. It is loaded by a tri-band yagi 15 meters above ground, which is the very top of the structure. ON4UN presented a simple formula for estimating this important datum in his book Low-band DXing. (Note: I am using the 1987 version which may have since updated this item.)
Using that formula the electrical length of my tower plus tri-band yagi is 100° at 3.6 MHz, or about 10% longer than λ/4. I then added 4 radials to my EZNEC model of the tower and yagi. ON4UN's formula was surprisingly accurate, with the antenna resonating at 3.3 MHz. Since the feed point resistance was a good match to 50 Ω I only needed to add a series capacitor of 900 pf to get a good match that can cover the entire band (500 kHz).
That sounds good, if it were only that simple. First, this feed requires that the tower be electrically isolated from ground so that the radials only need connect to the coax -- use the braid for the radial connection so that the coax outer surface can serve as a radial, if it isn't buried, and it's choked before entering the house.
While my tower is sitting on a wood platform and the guys are isolated with insulators there will still be conduction from tower to ground. The wood base is not a high-quality dielectric, especially when wet, and it has 1 m² contact area with the soil. Last, the half sloper must be removed, strapped to the tower or isolated or it becomes an active part of the vertical, and not in a good way. All the other coax and rotator cable will also affect performance unless radically reconfigured. Thus a more reliable approach to feeding the tower is to connect the radials to the tower and build an omega match. It is then also easier to adjust the match.
The modelled ground loss is -5 db and the radiation at 10° elevation is -2 dbi. The loss is 1 db better and the low angle gain is 3.5 db better than the loaded half sloper. Thus 1 db of increased low angle gain comes from the lower loss and the other 2.5 db from excising the excess high angle radiation of the half sloper.
Both models push NEC2 far enough that the reported ground losses are inaccurate. When adjusted in the manner recommended by W7EL the relative difference in loss (and gain) is lower by ~0.7 db. So the adjusted losses are comparable, though the vertical still excels at low elevation angles. However questions remain regarding loss in the model.
When modelled over poor ground (as in my case) the (adjusted) losses are -7.2 and -8 db for the half sloper and vertical, respectively. If this seems surprising note that the average current height is higher on the half sloper, and therefore is less negatively impacted by ground. You can easily add radials to the vertical for lower loss, but not for the half sloper.
The loss in both antennas perversely contributes to their excellent SWR since ground is a broadband resistor in series with the radiation resistance. I mentioned this very thing when I commented on the unexpectedly good match of the loaded half sloper, which the model did not fully anticipate. My especially poor ground (not medium) is likely to blame.
Despite the uncertainties this approach may be worth an experiment this winter, if I have the time. Direct A-B comparison with the half sloper is not possible due to the previously mentioned requirement of putting it out of the way. I recently found a large roll of 22 AWG insulated wire lurking deep in my junk box which can serve for radial experiments. After 20 years of inactivity I am frequently surprised at all the gems I am discovering I already own. I don't remember half the stuff I keep finding.
Basic model: 40 meters ground plane with 4 horizontal radials
Now that you see my motivation I will switch over to a simpler model to demonstrate a few attributes of verticals and how they affect performance. By performance I mean efficiency: getting as close to 0 db ground loss as possible. With 4 or more radials, a monopole height near to λ/4 and no obstacles in the near field the far field pattern will be omnidirectional with a single low-angle lobe. That is, the pattern is unaffected by antenna height, radial number and length, ground quality or match.
I am using a model for 40 meters since it is easier to visualize. Lots of hams use ground planes on 40, but on 80 almost all verticals are ground mounted with surface or buried radials: the mechanical requirements of a raised base on 80 are considerable. The 4-radial ground plane is perhaps the simplest of the breed since 4 is the minimum number of radials to achieve an omnidirectional azimuth pattern. It's a good place to start the exploration of radials and verticals.
A further reason is to enable a comparison to the extensive data in a 2-part QEX magazine article by N6LF: part 1; part 2. My simpler treatment of the subject is intended to narrowly focus on a few aspects of these antennas' relationship to ground, especially as it relates to my particular needs and interests.
Questions to be considered:
In NEC2 (the engine use by EZNEC and EZNEC+) radials cannot be placed on or in the ground. That requires NEC4 (available with EZNEC Pro), which is expensive. However as W7EL recommends it is possible to model surface radials by lifting the antenna slightly above ground, by at least 0.001λ. In my models I make this distance 10 cm on 80 and 5 cm on 40, slightly above the minimum. This seems to work pretty well.
Free space
To start I will place the antenna in free space to discover its properties in the absence of ground effects. That will be our baseline for comparison. To be resonant at 7.1 MHz in free space the wires are zero loss 16 AWG bare wire, with each radial and the monopole 10.525 meters long. While not fully realistic it is a good place to start since we avoid several confounding variables. Feed point impedance is 22.2 Ω.
Notice anything odd about the free space elevation pattern at right? Despite its asymmetric structure the ground plane radiates equally above and below the plane of the radials. The radiation from the radials cancels so that there is no net horizontally-polarized radiation in the far field. All of the far-field pattern comes from the λ/4 monopole. At this point it should be clear that the radials are not behaving in the manner that many hams would guess or expect. Keep this in mind since we'll later see how this impacts performance.
Performance vs. height above ground
Now let's bring ground into the picture. I'll start by placing it 10 meters above medium ground and lower it down to ground from there, measuring change in resonance, feed resistance, loss and low-angle radiation. I did the plot in a manner that might look odd since I scaled some variables to improve presentation on a single chart.
At 10 meters height the resonant frequency is already shifting upward, until is dives sharply lower as the ground is approached. The feed resistance at resonance gradually increases as the antenna drops lower. Loss is surprisingly stable, remaining in a tight 1 db range.
The antenna's interaction with ground is interesting, and perhaps not what many would expect. An increasing proportion of the near field is penetrating the ground as the height is lowered. Go back and look at the free space elevation pattern as we review a few points.
A ground plane antenna that is well above ground level is notable as a good DX performer. Not only does it get above at least some obstructions (houses, etc.) it has good low-angle radiation. That performance does not come from lower ground loss (as should be clear from the chart above), but from the far field pattern change due to ground reflections.
Look again at the free space pattern above and then the adjacent elevation pattern. Like a horizontal antenna a vertical antenna benefits from being higher. This holds true whether it is a ground plane or a "no-radial" vertical dipole.
What radials do
Not all radials are alike. There was a time when I (like many) was confused by some verticals requiring different length radials than others. For some the radials must be λ/4, with a λ/4 vertical monopole. Other styles of vertical can have non-resonant radials that can be shorter or longer than λ/4, yet still with a λ/4 vertical monopole. What is going on here? Can both be right?
Let's hear it from W7EL, as stated in his EZNEC user manual:
Both the radials and the ground provide a return path to the feed point (generator). However for the ground to do so there must be a direct ground connection of some sort, such as a ground rod or metal stubs in concrete (Ufer ground). In effect the radials and ground act as a set of parallel conductors, where the radials are low resistance and the ground is high resistance. As more of the return path is via the radials the lower the ground loss in the near field. Longer radials can capture more of the near field at the cost of often undesired effects on loss and pattern, due to the radials becoming self resonant.
Pounding a ground rod into the ground does provide a return path in the absence of radials. However even with good quality (high conductivity) soil all you`re doing is building a high quality connector to a big resistor. Other than dipping a ground wire into salt water radials always provide the least lossy return path.
When the antenna base is above ground you should only use radials, and not make a direct ground connection. The wire from the antenna base to the ground connection has a radiation resistance and will degrade antenna behaviour.
Radial length sensitivity analysis
If you've ever researched or experimented with verticals you'll likely know that there is a great deal of flexibility in their permitted length. That is, the antenna doesn't change much until the radials are shortened or lengthened by more than you might expect. Let's look at this behaviour in the case of the model 4-radial ground plane for 40 meters with its equal length radials and monopole.
What I did was to vary the radial lengths by 2% and measure the change in resonant frequency, and I did so at base heights from 0 to 10 meters. Then I did the same for the monopole. The idea is to numerically discover the derivative (rate of change, from calculus) of frequency with respect to length, for this particular scenario, and thus tuning behaviour of radials and the monopole. The derivative will be different (not a constant) at other base values, though we don't need to deal with that right now.
I usually would present a chart at this point but that isn't necessary. The rates are constant (within modelling precision) within the chosen height range of 0 to 10 meters. For a 2% change in length the resonant frequency changes by 0.4% and 1.6% for the radial length and monopole length, respectively. If they had contributed equally both values would be ~1%.
This tells us that there is no need to fuss over the radial lengths, within reason. Conversely the monopole is more sensitive to length change than expected. Therefore a reasonable tuning procedure would be to cut the radials first and then adjust the monopole length to resonance. If you shorten the radials a lot you would compensate by lengthening the monopole ¼ as much. Just keep in mind that this only addresses resonance, since large changes in radial length impact ground loss (longer is usually better). But when approaching an electrical λ/2 (watch that ground dielectric constant) can cause significant misbehaviour. See the N6LF references given above.
That is for 4 radials, which is a reasonable number for a ground plane mounted above ground. Mounted on the ground and with more radials the situation is different. I won't get into that, or at least not in this article. My modelling experiments so far make me suspect that NEC2 is misreporting ground loss for large numbers of radials even though I have not (yet) found any obvious error in my approach. However I do feel safe in stating that for more radials their length can be shorter without significant additional loss, though probably not less than λ/8.
As one final exercise on this topic, let's assume the above rates of change are linear -- that isn't really true but is good enough for a first-order estimate. Then the 3% lowering of the resonant frequency at 0 meters height is equivalent to a velocity factor of 0.85; that is, radials lying on the ground. There are experimental results out there that measure self-resonance of surface radials in the 0.4λ to 0.45λ interval so this appears to be consistent. Another way of saying this is that λ/4 surface radials would have to be cut to a physical length of about ~0.2λ. Off the ground by more than ~0.1λ the velocity factor is close to 1, so the electrical and physical lengths are equal.
Matching
I earlier showed how the ground-mounted vertical can be directly fed by coax. The typical feed resistance at resonance is 30 to 35 Ω, or higher with ground loss added in, which is a good match to 50 Ω. On 80 meters you can have low SWR across most of the band, and certainly correctable with a typical transceiver ATU. The modelled 4-radial vertical made from my tower and yagi has a feed point resistance of 34 Ω.
If you are loading a tower plus yagi (as I would be) the direct feed method would most times require a series adjustable reactance (coil or capacitor) to bring resonance where you want it. For more flexibility an omega match is recommended. If the tower is grounded, or even if anchored in concrete (see Ufer ground) you should connect the radials to the tower and use an omega match.
When independently constructed and mounted above ground a ground plane antenna is easier to match. With the several radials sloping downward (and often doubling as guy wires) the feed point resistance can be very close to 50 Ω. This is useful to know. If nothing else, the common lore regarding feed point resistance of various vertical antenna styles is correct.
Conclusions and next steps
For a brief foray into the wide world of vertical antennas I am learning quite a lot. Although preliminary there are a few conclusions I would hazard to make. I also have some ideas on where I need to go from here.
Regardless of what I physically build, I do plan to explore software models of verticals using more radials of various lengths to gain additional insight into lowering ground loss and increasing low-angle performance. The literature is clear that more and shorter radials can work well. Shorter radials would be a great advantage in my yard which is 15 meters wide and where the tower is set back 15 meters from the house.
The EZNEC (NEC2 engine) modelled loss of my present antenna over medium ground is about -6 db. This understates the reality since the ground in my yard is worse than that, and there are many housing-related long conductors in the antenna's near field. I am, in effect, dialling down my recently-acquired 100 watt rig to QRP. What it does when I operate with my KX3 is dreadful to contemplate. Yet that's how I currently operate on 80: very, very poorly. I had similarly poor results with my experimental and vertically-polarized loaded sloper on 40.
Verticals are nice but radials and interactions with obstructions are a problem in suburbia. I have therefore avoided them over the years even though I know how well than can perform on the low bands. Software modelling of verticals is tricky due to their strong interaction with ground, regardless of the number of radials or high-conductance ground screen. Horizontally-polarized antenna are more predictable.
Motivation: use my tower as a ground-mounted vertical
To address the problem it is helpful to step back and consider what radials do and don't do in various antennas. If I want to load my tower as a monopole on 80 it would be helpful to choose the length and number of radials that minimize the loss without creating a backyard tangle of wires. However, first let me place this in context by presenting my thoughts on how I might utilize my tower on 80.
The first thing is to determine the electrical length of the tower. It is loaded by a tri-band yagi 15 meters above ground, which is the very top of the structure. ON4UN presented a simple formula for estimating this important datum in his book Low-band DXing. (Note: I am using the 1987 version which may have since updated this item.)
Using that formula the electrical length of my tower plus tri-band yagi is 100° at 3.6 MHz, or about 10% longer than λ/4. I then added 4 radials to my EZNEC model of the tower and yagi. ON4UN's formula was surprisingly accurate, with the antenna resonating at 3.3 MHz. Since the feed point resistance was a good match to 50 Ω I only needed to add a series capacitor of 900 pf to get a good match that can cover the entire band (500 kHz).
That sounds good, if it were only that simple. First, this feed requires that the tower be electrically isolated from ground so that the radials only need connect to the coax -- use the braid for the radial connection so that the coax outer surface can serve as a radial, if it isn't buried, and it's choked before entering the house.
While my tower is sitting on a wood platform and the guys are isolated with insulators there will still be conduction from tower to ground. The wood base is not a high-quality dielectric, especially when wet, and it has 1 m² contact area with the soil. Last, the half sloper must be removed, strapped to the tower or isolated or it becomes an active part of the vertical, and not in a good way. All the other coax and rotator cable will also affect performance unless radically reconfigured. Thus a more reliable approach to feeding the tower is to connect the radials to the tower and build an omega match. It is then also easier to adjust the match.
The modelled ground loss is -5 db and the radiation at 10° elevation is -2 dbi. The loss is 1 db better and the low angle gain is 3.5 db better than the loaded half sloper. Thus 1 db of increased low angle gain comes from the lower loss and the other 2.5 db from excising the excess high angle radiation of the half sloper.
Both models push NEC2 far enough that the reported ground losses are inaccurate. When adjusted in the manner recommended by W7EL the relative difference in loss (and gain) is lower by ~0.7 db. So the adjusted losses are comparable, though the vertical still excels at low elevation angles. However questions remain regarding loss in the model.
When modelled over poor ground (as in my case) the (adjusted) losses are -7.2 and -8 db for the half sloper and vertical, respectively. If this seems surprising note that the average current height is higher on the half sloper, and therefore is less negatively impacted by ground. You can easily add radials to the vertical for lower loss, but not for the half sloper.
The loss in both antennas perversely contributes to their excellent SWR since ground is a broadband resistor in series with the radiation resistance. I mentioned this very thing when I commented on the unexpectedly good match of the loaded half sloper, which the model did not fully anticipate. My especially poor ground (not medium) is likely to blame.
Despite the uncertainties this approach may be worth an experiment this winter, if I have the time. Direct A-B comparison with the half sloper is not possible due to the previously mentioned requirement of putting it out of the way. I recently found a large roll of 22 AWG insulated wire lurking deep in my junk box which can serve for radial experiments. After 20 years of inactivity I am frequently surprised at all the gems I am discovering I already own. I don't remember half the stuff I keep finding.Basic model: 40 meters ground plane with 4 horizontal radials
Now that you see my motivation I will switch over to a simpler model to demonstrate a few attributes of verticals and how they affect performance. By performance I mean efficiency: getting as close to 0 db ground loss as possible. With 4 or more radials, a monopole height near to λ/4 and no obstacles in the near field the far field pattern will be omnidirectional with a single low-angle lobe. That is, the pattern is unaffected by antenna height, radial number and length, ground quality or match.
I am using a model for 40 meters since it is easier to visualize. Lots of hams use ground planes on 40, but on 80 almost all verticals are ground mounted with surface or buried radials: the mechanical requirements of a raised base on 80 are considerable. The 4-radial ground plane is perhaps the simplest of the breed since 4 is the minimum number of radials to achieve an omnidirectional azimuth pattern. It's a good place to start the exploration of radials and verticals.
A further reason is to enable a comparison to the extensive data in a 2-part QEX magazine article by N6LF: part 1; part 2. My simpler treatment of the subject is intended to narrowly focus on a few aspects of these antennas' relationship to ground, especially as it relates to my particular needs and interests.
Questions to be considered:
- How does height of the antenna above ground affect radial behaviour?
- How long should the radials be?
- How much does the impedance change with radial configuration and height?
- How much does the ground loss change with radial configuration and height?
In NEC2 (the engine use by EZNEC and EZNEC+) radials cannot be placed on or in the ground. That requires NEC4 (available with EZNEC Pro), which is expensive. However as W7EL recommends it is possible to model surface radials by lifting the antenna slightly above ground, by at least 0.001λ. In my models I make this distance 10 cm on 80 and 5 cm on 40, slightly above the minimum. This seems to work pretty well.
Free space
To start I will place the antenna in free space to discover its properties in the absence of ground effects. That will be our baseline for comparison. To be resonant at 7.1 MHz in free space the wires are zero loss 16 AWG bare wire, with each radial and the monopole 10.525 meters long. While not fully realistic it is a good place to start since we avoid several confounding variables. Feed point impedance is 22.2 Ω.Notice anything odd about the free space elevation pattern at right? Despite its asymmetric structure the ground plane radiates equally above and below the plane of the radials. The radiation from the radials cancels so that there is no net horizontally-polarized radiation in the far field. All of the far-field pattern comes from the λ/4 monopole. At this point it should be clear that the radials are not behaving in the manner that many hams would guess or expect. Keep this in mind since we'll later see how this impacts performance.
Performance vs. height above ground
Now let's bring ground into the picture. I'll start by placing it 10 meters above medium ground and lower it down to ground from there, measuring change in resonance, feed resistance, loss and low-angle radiation. I did the plot in a manner that might look odd since I scaled some variables to improve presentation on a single chart.
At 10 meters height the resonant frequency is already shifting upward, until is dives sharply lower as the ground is approached. The feed resistance at resonance gradually increases as the antenna drops lower. Loss is surprisingly stable, remaining in a tight 1 db range.
The antenna's interaction with ground is interesting, and perhaps not what many would expect. An increasing proportion of the near field is penetrating the ground as the height is lowered. Go back and look at the free space elevation pattern as we review a few points.
- The velocity factor of the radials declines as ground is approached, pulling resonance to a lower frequency. Each radial is like an insulated wire where the thick, lossy ground is the insulator. The ground parameters -- conductivity and dielectric constant -- determine the effect. Every part of the antenna, radials and monopole, has its own contribution to the near field, and it is strong within λ/4. Much of the energy associated with the radials and monopole is flowing in the ground, not on the conductors.
- Feed point resistance steadily increases as ground is approached. This is likely due to the series resistance of the ground coming increasingly into play.
- Ground loss is not much different over this range of heights. Indeed it only starts to substantially drop as the antenna is raised to unrealistic heights. The "ripple" is partly due to NEC2 inaccuracy at the lowest heights, though I did adjust the values using techniques suggested by W7EL. A confounding effect is from the monopole's ground interaction and affect on the far field pattern. I did not attempt to determine how much each factor contributes to the loss.
- Low-angle radiation shows a remarkable change with height. Higher is better. I don't often see this discussed in other articles about this type of antenna..
 |
| 7.1 MHz 4-radial ground plane at 0 and 10 meters height |
Look again at the free space pattern above and then the adjacent elevation pattern. Like a horizontal antenna a vertical antenna benefits from being higher. This holds true whether it is a ground plane or a "no-radial" vertical dipole.
What radials do
Not all radials are alike. There was a time when I (like many) was confused by some verticals requiring different length radials than others. For some the radials must be λ/4, with a λ/4 vertical monopole. Other styles of vertical can have non-resonant radials that can be shorter or longer than λ/4, yet still with a λ/4 vertical monopole. What is going on here? Can both be right?
Let's hear it from W7EL, as stated in his EZNEC user manual:
The effect of radials and other buried ground systems is widely misunderstood. In a typical quarter wavelength high vertical antenna, the ground has two distinct and somewhat independent effects. One is that the current flowing into the base of the antenna is matched by an equal current flowing from the ground to the other feedline conductor. This current flows through the ground and incurs loss in the process. The primary purpose of a buried ground system is to reduce this loss by increasing the conductivity of the ground near the antenna. The effect of a poor ground system is to reduce the antenna efficiency. This reduces the strength of the radiated field, but doesn't change the antenna pattern.The other purpose of ground (as he goes on to describe) is as a reflector to form the far-field pattern. Since that is not done with radials I will skip over that for now to briefly consider the near field, under and near the antenna.
Both the radials and the ground provide a return path to the feed point (generator). However for the ground to do so there must be a direct ground connection of some sort, such as a ground rod or metal stubs in concrete (Ufer ground). In effect the radials and ground act as a set of parallel conductors, where the radials are low resistance and the ground is high resistance. As more of the return path is via the radials the lower the ground loss in the near field. Longer radials can capture more of the near field at the cost of often undesired effects on loss and pattern, due to the radials becoming self resonant.
Pounding a ground rod into the ground does provide a return path in the absence of radials. However even with good quality (high conductivity) soil all you`re doing is building a high quality connector to a big resistor. Other than dipping a ground wire into salt water radials always provide the least lossy return path.
When the antenna base is above ground you should only use radials, and not make a direct ground connection. The wire from the antenna base to the ground connection has a radiation resistance and will degrade antenna behaviour.
Radial length sensitivity analysis
If you've ever researched or experimented with verticals you'll likely know that there is a great deal of flexibility in their permitted length. That is, the antenna doesn't change much until the radials are shortened or lengthened by more than you might expect. Let's look at this behaviour in the case of the model 4-radial ground plane for 40 meters with its equal length radials and monopole.
What I did was to vary the radial lengths by 2% and measure the change in resonant frequency, and I did so at base heights from 0 to 10 meters. Then I did the same for the monopole. The idea is to numerically discover the derivative (rate of change, from calculus) of frequency with respect to length, for this particular scenario, and thus tuning behaviour of radials and the monopole. The derivative will be different (not a constant) at other base values, though we don't need to deal with that right now.
I usually would present a chart at this point but that isn't necessary. The rates are constant (within modelling precision) within the chosen height range of 0 to 10 meters. For a 2% change in length the resonant frequency changes by 0.4% and 1.6% for the radial length and monopole length, respectively. If they had contributed equally both values would be ~1%.
This tells us that there is no need to fuss over the radial lengths, within reason. Conversely the monopole is more sensitive to length change than expected. Therefore a reasonable tuning procedure would be to cut the radials first and then adjust the monopole length to resonance. If you shorten the radials a lot you would compensate by lengthening the monopole ¼ as much. Just keep in mind that this only addresses resonance, since large changes in radial length impact ground loss (longer is usually better). But when approaching an electrical λ/2 (watch that ground dielectric constant) can cause significant misbehaviour. See the N6LF references given above.
That is for 4 radials, which is a reasonable number for a ground plane mounted above ground. Mounted on the ground and with more radials the situation is different. I won't get into that, or at least not in this article. My modelling experiments so far make me suspect that NEC2 is misreporting ground loss for large numbers of radials even though I have not (yet) found any obvious error in my approach. However I do feel safe in stating that for more radials their length can be shorter without significant additional loss, though probably not less than λ/8.
As one final exercise on this topic, let's assume the above rates of change are linear -- that isn't really true but is good enough for a first-order estimate. Then the 3% lowering of the resonant frequency at 0 meters height is equivalent to a velocity factor of 0.85; that is, radials lying on the ground. There are experimental results out there that measure self-resonance of surface radials in the 0.4λ to 0.45λ interval so this appears to be consistent. Another way of saying this is that λ/4 surface radials would have to be cut to a physical length of about ~0.2λ. Off the ground by more than ~0.1λ the velocity factor is close to 1, so the electrical and physical lengths are equal.
Matching
I earlier showed how the ground-mounted vertical can be directly fed by coax. The typical feed resistance at resonance is 30 to 35 Ω, or higher with ground loss added in, which is a good match to 50 Ω. On 80 meters you can have low SWR across most of the band, and certainly correctable with a typical transceiver ATU. The modelled 4-radial vertical made from my tower and yagi has a feed point resistance of 34 Ω.
If you are loading a tower plus yagi (as I would be) the direct feed method would most times require a series adjustable reactance (coil or capacitor) to bring resonance where you want it. For more flexibility an omega match is recommended. If the tower is grounded, or even if anchored in concrete (see Ufer ground) you should connect the radials to the tower and use an omega match.When independently constructed and mounted above ground a ground plane antenna is easier to match. With the several radials sloping downward (and often doubling as guy wires) the feed point resistance can be very close to 50 Ω. This is useful to know. If nothing else, the common lore regarding feed point resistance of various vertical antenna styles is correct.
Conclusions and next steps
For a brief foray into the wide world of vertical antennas I am learning quite a lot. Although preliminary there are a few conclusions I would hazard to make. I also have some ideas on where I need to go from here.
- Rather than run a large number of radials to reduce ground loss it can be easier to improve low-angle DX performance the same amount (1 to 3 db) by raising the vertical`s base. This can also reduce interference from and interaction with nearby conductive obstacles. The near field on the low band extends quite far.
- An omega match, while not always required, is worth the trouble to ease adjustment of the vertical`s resonance and impedance. Turning a knob is easier than trimming 32 radials or moving a yagi up or down a tower!
- On 40 meters you can probably get equal or better low-angle performance by using the monopole as a support for an inverted vee. Compare the gain charted above to other antennas for 40. Even so many do use verticals in 4-square 40 meter arrays to achieve 5 to 6 db of broadband gain. However on 80 and 160 it is usually easier to get good low-angle performance and array gain from λ/4 verticals than from a horizontally-polarized antenna. It`s often too difficult to get a horizontal antenna up high enough for it to be the superior choice.
Regardless of what I physically build, I do plan to explore software models of verticals using more radials of various lengths to gain additional insight into lowering ground loss and increasing low-angle performance. The literature is clear that more and shorter radials can work well. Shorter radials would be a great advantage in my yard which is 15 meters wide and where the tower is set back 15 meters from the house.
Wednesday, January 14, 2015
Whither QRP?
My very first transmitter in 1972 used an 807 final, managing perhaps 40 watts. That was as close to QRP I got since, like many, I believed that bigger was better. Provided my budget and
living arrangements permitted it, every station change since then was a step upward. That is, until 1992 when I abandoned the hobby for other things.
When I returned to air in 2013 after 20 years on inactivity I decided to do so in the smallest way possible: low power and no outdoor antennas. Since my venerable FT-102 was not working I chose to purchase a KX3. QRP fit the bill at the time since I could play around and test my renewed interest in the hobby, and do so without any risk of EMI at home or in the neighbourhood. The first antenna was the aluminum eaves trough winding around the roof of my two-story house.
After a few months with the eaves trough antenna I went on to build better antennas and (necessarily) reintroduce neighbours to my old hobby. Despite subsequent antenna size increases I stuck with QRP because I came to enjoy the idea of doing big things with little power. That is, the challenge motivated me to stay active.
More importantly it kept amateur radio as a hobby, one where I was no longer obsessed with "bigger is better" and feeling obliged to do well at DX and contests. The pressure was off. The old imperatives don't take hold of my mind as they once did. If I up my power I don't think it'll corrupt my thinking. Thus I firmly set the acquisition of a new rig and more power in my 2015 plan.
I have accomplished quite a bit with QRP and a small antenna farm
over the past nearly-two years. My updated DXCC totals as of early January are posted at right. Compare these with my results at the time I dismantled my station in preparation for the new tower and yagi.
My contest results have also been good, and can be found by a search at 3830. All my results are with QRP, 10 watts for daily operating and 5 watts in contests.
What's driving me away from QRP is the plateau I'm experiencing. I've reached the point of diminishing returns, especially in my primary interests of DXing and contesting. Even with the tri-band yagi my DXCC count only increased 20 entities over the past several months. I can eke out more with my current setup but I have to admit it is becoming fatiguing. My predicament has gotten worse with my foray onto 80 meters where working much within North America with QRP is difficult, let alone DX. A better antenna would help but I can't do much more with for low band antennas at this QTH.
With the inevitable decline of sunspots, increased geomagnetic activity and a renewed emphasis on low bands the limits of QRP are evident. Further, I don't believe that I have anything to prove by persisting with QRP. Consequently the following box has found a home in my shack this week.
This is the Yaesu FT-1000MP Mark V Field. According to the serial number it is 13 years old. It should be obvious that I purchased it used. It needs some cabling and modification to integrate well into my station and meet my operating needs. I have put it on the air for several QSOs and proved what a 10 db power boost can accomplish. I muscled through a 40 meters pile-up and worked a weak UA0 on 15 meters that I otherwise would not attempt with 10 watts.
Getting this rig is about more than power. The KX3, wonderful though it is, has its limits. Most of these are in the receiver. There is only so much performance you can get with direct conversion and DSP filtering. I plan to write a comparison of the KX3 as a base station and DX/contest rig versus the FT-1000MP in a future article, and why I selected this particular transceiver.
I can now also enjoy SSB, which is not often possible with QRP. In retrospect it's a shame I chopped off the Yaesu 8-pin connector from my Heil headset. I will have to make an adaptor so that I can use the 3.5 mm mic plug on the headset with both radios.
The KX3 is not going anywhere! I like it, so it stays. I will now have two rigs in my shack. This also does not mean that I am done with QRP. I remain uncertain whether it is a good idea to run 100 watts at all times. I lean towards staying with QRP for the remainder of this season's contests. I might use the KX3 in contests or the FT-1000MP with the power turned down to 5 watts.
Once I have the new rig sufficiently integrated with station hardware and software I intend to push my DX progress. I will not separately catalogue my DXCC count as QRP. Therefore the table above is my final tally for purely QRP DXCC. What I will do is stick with the count starting with my return to the hobby in 2013. This is more meaningful to me than sorting through mounds of records and QSL cards from the distant past. I enjoy DXing, not the collection of certificates. I have in fact never applied for the DXCC award.
While I proceed to enjoy the power boost I will wait and see if any of my neighbours notices.
When I returned to air in 2013 after 20 years on inactivity I decided to do so in the smallest way possible: low power and no outdoor antennas. Since my venerable FT-102 was not working I chose to purchase a KX3. QRP fit the bill at the time since I could play around and test my renewed interest in the hobby, and do so without any risk of EMI at home or in the neighbourhood. The first antenna was the aluminum eaves trough winding around the roof of my two-story house.
After a few months with the eaves trough antenna I went on to build better antennas and (necessarily) reintroduce neighbours to my old hobby. Despite subsequent antenna size increases I stuck with QRP because I came to enjoy the idea of doing big things with little power. That is, the challenge motivated me to stay active.
More importantly it kept amateur radio as a hobby, one where I was no longer obsessed with "bigger is better" and feeling obliged to do well at DX and contests. The pressure was off. The old imperatives don't take hold of my mind as they once did. If I up my power I don't think it'll corrupt my thinking. Thus I firmly set the acquisition of a new rig and more power in my 2015 plan.
I have accomplished quite a bit with QRP and a small antenna farm
over the past nearly-two years. My updated DXCC totals as of early January are posted at right. Compare these with my results at the time I dismantled my station in preparation for the new tower and yagi.My contest results have also been good, and can be found by a search at 3830. All my results are with QRP, 10 watts for daily operating and 5 watts in contests.
What's driving me away from QRP is the plateau I'm experiencing. I've reached the point of diminishing returns, especially in my primary interests of DXing and contesting. Even with the tri-band yagi my DXCC count only increased 20 entities over the past several months. I can eke out more with my current setup but I have to admit it is becoming fatiguing. My predicament has gotten worse with my foray onto 80 meters where working much within North America with QRP is difficult, let alone DX. A better antenna would help but I can't do much more with for low band antennas at this QTH.
With the inevitable decline of sunspots, increased geomagnetic activity and a renewed emphasis on low bands the limits of QRP are evident. Further, I don't believe that I have anything to prove by persisting with QRP. Consequently the following box has found a home in my shack this week.
This is the Yaesu FT-1000MP Mark V Field. According to the serial number it is 13 years old. It should be obvious that I purchased it used. It needs some cabling and modification to integrate well into my station and meet my operating needs. I have put it on the air for several QSOs and proved what a 10 db power boost can accomplish. I muscled through a 40 meters pile-up and worked a weak UA0 on 15 meters that I otherwise would not attempt with 10 watts.
Getting this rig is about more than power. The KX3, wonderful though it is, has its limits. Most of these are in the receiver. There is only so much performance you can get with direct conversion and DSP filtering. I plan to write a comparison of the KX3 as a base station and DX/contest rig versus the FT-1000MP in a future article, and why I selected this particular transceiver.
I can now also enjoy SSB, which is not often possible with QRP. In retrospect it's a shame I chopped off the Yaesu 8-pin connector from my Heil headset. I will have to make an adaptor so that I can use the 3.5 mm mic plug on the headset with both radios.
The KX3 is not going anywhere! I like it, so it stays. I will now have two rigs in my shack. This also does not mean that I am done with QRP. I remain uncertain whether it is a good idea to run 100 watts at all times. I lean towards staying with QRP for the remainder of this season's contests. I might use the KX3 in contests or the FT-1000MP with the power turned down to 5 watts.
Once I have the new rig sufficiently integrated with station hardware and software I intend to push my DX progress. I will not separately catalogue my DXCC count as QRP. Therefore the table above is my final tally for purely QRP DXCC. What I will do is stick with the count starting with my return to the hobby in 2013. This is more meaningful to me than sorting through mounds of records and QSL cards from the distant past. I enjoy DXing, not the collection of certificates. I have in fact never applied for the DXCC award.
While I proceed to enjoy the power boost I will wait and see if any of my neighbours notices.
Wednesday, January 7, 2015
Ice and the Geostrophic Wind
There are worse areas to experience freezing rain that where I live, though we do experience it several times every winter. Below Lake Ontario (New York) is the snow belt and above the lake, where I am, is an ice belt. As the weather systems proceed toward the east these seem to combine and deliver a double whammy of ice and snow to Quebec (VE2), New England (W1), the Maritimes (VE1, VE9, VY2) and Newfoundland (VO1). Hams along the eastern seaboard of North America know this all too well.
Ice loading is hard on antennas and their support structures. Ice not only adds substantial weight it also increases wind load. When the ice melts or fractures it can come off unevenly which can twist yagi elements and break wire and rope. Of course the weather conditions can make it hazardous to effect repairs, often for the remainder of the winter. Unfortunately this is prime contest and DX season. It is therefore important to build antennas and towers to survive winter.
All this came to mind when we were hit with consecutive snow and ice storms this past weekend. Happily it wasn't bad as these things go. Hardened as we are to the weather in this part of the world it was no more than a minor inconvenience.
In the photos above and below you can see some of the ice and its effects. The ice isn't thick, just a few millimeters. It is enough to make a ⅛" guy wire grow to a little over ¼". The same coating went on the wire antennas and yagi yet little adhered to the towers. The weight of the ice lowered the limbs of the large spruce tree to the ground. In bad storms they're completely flattened.
This is not enough ice to cause damage except in the most flimsy of antenna installations. The trees will rebound and the antennas will continue on as normal. The only problem was that the resonant frequency of the wire antennas dropped about 6%. Ice is a dielectric that lowers the velocity factor of the wire, increasing its effective length and so lowering the resonant frequency. The yagi experienced a smaller change. Rain's impact is different in that there is not enough water to appreciably lower the velocity factor but can cause end effects which similarly lower resonance. That is probably happening here as well since ice (fresh water plus impurities) coats the insulators.
Tower manufacturers should and mostly do specify load capacity under ice conditions. When the wind blows the ice-laden tower can carry less load. Since the tower must first be able to support itself at the rated wind speed, this means a lower capacity for antennas.
First, ice lowers wind load capacity by increasing the static load (dead weight). Bending stress increases due to the weight. That is, the tower will fail with less lateral load. Second, the ice increases the wind surface area of the tower itself, lowering the wind speed at which the tower itself will fail. This is why there is less capacity for the antenna load. Third, ice increases antenna weight and wind surface area.
Consider the following tables published by Trylon (a manufacturer whose towers are commonly used by amateurs in Canada and by some in the US) for their Titan series of self-supporting towers. The first is for wind alone, and the second is for a select example of severe icing.
Trylon provides a calculator so that you can determine tower capacity due to wind and antennas alone. The calculator does not take ice into account, which is a complicating factor not easily integrated into a general formula. That Trylon excludes ice as a factor in its calculator should not be taken as license to ignore it. They would rather you consult them or hire an engineer.
Too many hams in this climate who otherwise properly engineer their antenna systems for the maximum winds they should expect to experience (wind zones) fail to take ice into account. A typical reason is they don't expect severe wind and ice to occur at the same time, thinking that is too improbable an event. I, too, have been guilty of this oversight.
Unfortunately wind and ice are not statistically independent variables. The two are often causally connected. To understand this we must detour to review some meteorology. That should illuminate the danger of ignoring ice load.
In this part of the world the typical weather pattern is for a succession of high and low pressure systems (anti-cyclones and cyclones) travelling west to east. Air moves from high to low pressure areas, and circulating vertically from the warm low to the cold high. This is obviously a simplistic description but still useful. The coriolis effect mediates the air flow (wind) such that lows circulate counter-clockwise and highs circulate clockwise in the northern hemisphere. The 3-O's mnemonic aid: a low rotates counter-clockwise in the north.
Wind speed increases as the pressure gradient increases (isobars closer together) with low and high system intensities and proximity. Air spiral outward from the high and finally spirals inward to the low. Balanced in between, parallel to the isobars and approximately on a line connecting system centres lies the geostrophic wind. The diagram at right illustrates this, though you may find it helpful to mentally rotate it 90° clockwise so that north is at the top.
Under suitable conditions the approaching low draws a warm, moisture-laden wind from the southwest, which cools as it flows north and causes precipitation. In our scenario it begins as snow accompanied by high winds, becomes rain as the cyclone centre approaches, and a decrease in wind in the eye of the cyclone. If the warm air is pushed up over the cooler air what begins as rain at altitude freezes on contact with the ground, or antennas. That is a common way to get freezing rain occurs in this region.
As the low continues eastward the winds shift to the west then the northwest as the geostrophic wind asserts itself. This wind is colder, coming as it is from a high and from the northwest. The amount of ice and speed of the wind are related since both are related to system intensity.
Therein lies the danger: the worse the icing the worse the following cold geostrophic wind. Unless the systems are moving slowly the ice doesn't melt but is fixed in place by the cold. Now you should begin to see why Trylon's ice load chart above is so important.
While it is rare for extreme winds in these weather conditions it doesn't have to be. Look very closely at those reductions in capacity. Even as I type these words 3 days following the storm the ice is still encasing the antennas, the temperature is -20° C and the wind gusts are topping 60 kph. If the ice had been thicker the risk of tower failure would be a concern. This combination of weather events can and has brought down many towers over the years, both amateur and commercial.
I had a particularly bad case of ice loading on my tower and yagi stack back in the 1980s. I was lucky that most of the ice fractured and fell off before the wind arrived. It was a tense 24 hours.
There is a reason why Maritimers tend to shorter towers and smaller antennas. It gets expensive to replace them every few years. Of course living on the Atlantic shore you can do very well indeed with less antenna. Not so here.
All this came to mind when we were hit with consecutive snow and ice storms this past weekend. Happily it wasn't bad as these things go. Hardened as we are to the weather in this part of the world it was no more than a minor inconvenience.
In the photos above and below you can see some of the ice and its effects. The ice isn't thick, just a few millimeters. It is enough to make a ⅛" guy wire grow to a little over ¼". The same coating went on the wire antennas and yagi yet little adhered to the towers. The weight of the ice lowered the limbs of the large spruce tree to the ground. In bad storms they're completely flattened.This is not enough ice to cause damage except in the most flimsy of antenna installations. The trees will rebound and the antennas will continue on as normal. The only problem was that the resonant frequency of the wire antennas dropped about 6%. Ice is a dielectric that lowers the velocity factor of the wire, increasing its effective length and so lowering the resonant frequency. The yagi experienced a smaller change. Rain's impact is different in that there is not enough water to appreciably lower the velocity factor but can cause end effects which similarly lower resonance. That is probably happening here as well since ice (fresh water plus impurities) coats the insulators.
Tower manufacturers should and mostly do specify load capacity under ice conditions. When the wind blows the ice-laden tower can carry less load. Since the tower must first be able to support itself at the rated wind speed, this means a lower capacity for antennas.
First, ice lowers wind load capacity by increasing the static load (dead weight). Bending stress increases due to the weight. That is, the tower will fail with less lateral load. Second, the ice increases the wind surface area of the tower itself, lowering the wind speed at which the tower itself will fail. This is why there is less capacity for the antenna load. Third, ice increases antenna weight and wind surface area.
Consider the following tables published by Trylon (a manufacturer whose towers are commonly used by amateurs in Canada and by some in the US) for their Titan series of self-supporting towers. The first is for wind alone, and the second is for a select example of severe icing.
Trylon provides a calculator so that you can determine tower capacity due to wind and antennas alone. The calculator does not take ice into account, which is a complicating factor not easily integrated into a general formula. That Trylon excludes ice as a factor in its calculator should not be taken as license to ignore it. They would rather you consult them or hire an engineer.
Too many hams in this climate who otherwise properly engineer their antenna systems for the maximum winds they should expect to experience (wind zones) fail to take ice into account. A typical reason is they don't expect severe wind and ice to occur at the same time, thinking that is too improbable an event. I, too, have been guilty of this oversight.
Unfortunately wind and ice are not statistically independent variables. The two are often causally connected. To understand this we must detour to review some meteorology. That should illuminate the danger of ignoring ice load.
In this part of the world the typical weather pattern is for a succession of high and low pressure systems (anti-cyclones and cyclones) travelling west to east. Air moves from high to low pressure areas, and circulating vertically from the warm low to the cold high. This is obviously a simplistic description but still useful. The coriolis effect mediates the air flow (wind) such that lows circulate counter-clockwise and highs circulate clockwise in the northern hemisphere. The 3-O's mnemonic aid: a low rotates counter-clockwise in the north.
 |
| Geostropic wind |
Wind speed increases as the pressure gradient increases (isobars closer together) with low and high system intensities and proximity. Air spiral outward from the high and finally spirals inward to the low. Balanced in between, parallel to the isobars and approximately on a line connecting system centres lies the geostrophic wind. The diagram at right illustrates this, though you may find it helpful to mentally rotate it 90° clockwise so that north is at the top.
Under suitable conditions the approaching low draws a warm, moisture-laden wind from the southwest, which cools as it flows north and causes precipitation. In our scenario it begins as snow accompanied by high winds, becomes rain as the cyclone centre approaches, and a decrease in wind in the eye of the cyclone. If the warm air is pushed up over the cooler air what begins as rain at altitude freezes on contact with the ground, or antennas. That is a common way to get freezing rain occurs in this region.
As the low continues eastward the winds shift to the west then the northwest as the geostrophic wind asserts itself. This wind is colder, coming as it is from a high and from the northwest. The amount of ice and speed of the wind are related since both are related to system intensity.
Therein lies the danger: the worse the icing the worse the following cold geostrophic wind. Unless the systems are moving slowly the ice doesn't melt but is fixed in place by the cold. Now you should begin to see why Trylon's ice load chart above is so important.
While it is rare for extreme winds in these weather conditions it doesn't have to be. Look very closely at those reductions in capacity. Even as I type these words 3 days following the storm the ice is still encasing the antennas, the temperature is -20° C and the wind gusts are topping 60 kph. If the ice had been thicker the risk of tower failure would be a concern. This combination of weather events can and has brought down many towers over the years, both amateur and commercial.
I had a particularly bad case of ice loading on my tower and yagi stack back in the 1980s. I was lucky that most of the ice fractured and fell off before the wind arrived. It was a tense 24 hours.
There is a reason why Maritimers tend to shorter towers and smaller antennas. It gets expensive to replace them every few years. Of course living on the Atlantic shore you can do very well indeed with less antenna. Not so here.
Sunday, January 4, 2015
2015 - Challenges Ahead
2014 has now come and gone, so it's time to check back with my plan for the year to see how well I measured up. Then it's on to my amateur radio objectives for 2015.
One thing I've learned from decades in the business world is the value of stating objectives up front, making firm plans and then to measure performance against those plans. This isn't for everyone, nor should it be. For many this hobby is simply a casual pastime. Even then there is value to accepting some structure. If you can clearly express what you want to do you can articulate, and follow, the steps necessary to make those things happen. When done right it can lead to a satisfying result. Even for a hobby that's important.
2014 retrospective
My stated plan for 2014 was largely fulfilled. Not entirely of course, but enough to give myself an A or B+. Let's look at the key misses first: more power and 40 meters.
With the delay into early fall for getting the tri-band yagi raised I did not want the additional pressure from have to search for and purchase a new transceiver. Therefore I kept operating with QRP right through 2014. I was also more interested in testing my ability to score well in the fall contests with QRP than transitioning sooner to higher power.
My hopes for a gain antenna on 40 were dashed. Destructive interactions to the tri-band yagi pretty much ruled out a switchable wire yagi on the tower. With the yagi up only 15 meters there was no way to get sufficient separation from a 40 meters yagi and yet keep the wire yagi high enough to deliver better results than the inverted vee on 40. My attempt to create a sloper array just to Europe was shelved when my single sloper experiment didn't work out. I learned a lot but my station didn't end up any further ahead.
With the yagi in place and a poorly-performing 80 meters antenna, plus some great conditions, I was able to place high in the QRP global rankings in both the CW and SSB weekends of CQ WW. Although this remains to be confirmed after log checking I don't have to wait to declare success. The power and antennas delivered results. Any remaining problems would be in the operator, not the equipment.
Despite what I said above about my failure to build a better antenna for 40 I have come to believe the 40 meters inverted vee is doing better than expected. Although I cannot compare them directly, on the basis of results I now think it does better, broadside at least, in comparison to the delta loop that was taken down earlier in the year. It just goes to show how local ground and suburban clutter can negatively affect the DX performance of vertically-polarized antennas.
Since the yagi went up my DXCC total increased to 226, an increase of 20. Even on 80 I have managed to eke out 30 countries. My LOTW confirmations are now over 100 on 40, 20, 15 and 10 meters, and just shy of the mark on 17 meters. That's good for less than 2 years with QRP and modest antennas, antennas which up until 3 months ago were single element and no gain.
I do not have an antenna for 160 nor do I seriously plan one for this QTH. An antenna can surely be built but it would have to be a poor one. Nevertheless I decided to enter the ARRL 160 meters contest in early December for a laugh, just to see what I could do with 5 watts and no antenna. By "no antenna" I mean unscrewing the outer ring of the PL-259 of the 80 meters half sloper. It's an old trick that I've used before.
The surprise was making over 100 QSOs with this ridiculous setup. I could hear some DX, but though I worked none of it I did get as far as Oklahoma. Most QSOs were a struggle to complete, which is no surprise. Of course I was amply assisted by the big antennas and good ears of other operators. It was unexpected fun, and educational.
2015 plan and constraints
My plans for the VE3VN antenna farm in 2015 are more modest than they were for the previous year. Back then I was starting from very little so there was ample room for improvements. That is less so now, and I am running straight into several constraints on what I can or should do at this location.
First, the constraints:
Longer-term outlook
I have a decision coming up if I intend to have better and bigger antennas: build a large tower on this property or move. Both alternatives have their pros and cons, plus large impacts on non-amateur radio aspects of my life. As someone looking to retire early I do have the flexibility to consider another QTH, one removed from my current personal and business networks. That is, if I decide that amateur radio will be a large part of my post-career life.
Like everyone, I'm not getting younger. If I want it and can do it, it is better to do it soon and enjoy up to 20 to 30 years of playing with towers and antennas and pursuing operating objectives. This might be the year I choose.
This blog
In my travels around the internet I find that most hams with an online presence choose to organize their web sites by topic or project. Those with blogs, either alone or with an accompanying a web site, seem to quickly abandon them.
I seem unusual in that I do everything in a blog. There are advantages and disadvantages to this approach. For example, if I update my experience or further research on an antenna I do so in a new article, not by modifying the earlier one. Of course I link to earlier articles where it is informative, but if you come to my blog by way of searching out the original article you might not discover the updates. As to typos...well, they happen and are rarely worth the effort to fix in already-published articles.
Despite that deficiency I have a strong reason for sticking with a blog. That reason is narrative. I believe that any passionate pursuit, be it amateur radio or anything else, contains a story. The story is often more compelling than any individual milestone or set of milestones. From what I've seen I can assume that many others would disagree, and they do so by documenting various technical or construction projects rather than why they do what they do. Typically these pages are not updated. In fact you get little insight into who these hams are or even if they're still alive!
So I will continue to focus on narrative, for which a blog is best. I recommend the use of the search function provided by Google at the top of the page to find articles relevant to specific topics. That way the blog can still be useful to those who want to find articles on specific areas of interest and care not at all about the narrative.
Dark corners of the internet
For the vast majority of my audience the following message can be skipped. It is for the small number of bad actors lurking in the darker corners of the internet.
Copies of a number of my articles can be found elsewhere with authorship removed or no links to the source material. This is unethical at best and is illegal in most jurisdictions. I spent many years of my career dealing with intellectual property matters so I am no naif. I know it happens. I am disappointed to see hams do it to other hams.
Dealing with it not always easy, so I continue to observe and consider the matter. The internet which creates this problem also makes it easy to discover that it is occurring. That is, I know where you lurk.
On the brighter side, I do welcome fully-attributed references to my articles. In return I make every effort to attribute both online and offline sources I use or extract from. That's only right.
One thing I've learned from decades in the business world is the value of stating objectives up front, making firm plans and then to measure performance against those plans. This isn't for everyone, nor should it be. For many this hobby is simply a casual pastime. Even then there is value to accepting some structure. If you can clearly express what you want to do you can articulate, and follow, the steps necessary to make those things happen. When done right it can lead to a satisfying result. Even for a hobby that's important.
2014 retrospective
My stated plan for 2014 was largely fulfilled. Not entirely of course, but enough to give myself an A or B+. Let's look at the key misses first: more power and 40 meters.
With the delay into early fall for getting the tri-band yagi raised I did not want the additional pressure from have to search for and purchase a new transceiver. Therefore I kept operating with QRP right through 2014. I was also more interested in testing my ability to score well in the fall contests with QRP than transitioning sooner to higher power.
My hopes for a gain antenna on 40 were dashed. Destructive interactions to the tri-band yagi pretty much ruled out a switchable wire yagi on the tower. With the yagi up only 15 meters there was no way to get sufficient separation from a 40 meters yagi and yet keep the wire yagi high enough to deliver better results than the inverted vee on 40. My attempt to create a sloper array just to Europe was shelved when my single sloper experiment didn't work out. I learned a lot but my station didn't end up any further ahead.
With the yagi in place and a poorly-performing 80 meters antenna, plus some great conditions, I was able to place high in the QRP global rankings in both the CW and SSB weekends of CQ WW. Although this remains to be confirmed after log checking I don't have to wait to declare success. The power and antennas delivered results. Any remaining problems would be in the operator, not the equipment.
Despite what I said above about my failure to build a better antenna for 40 I have come to believe the 40 meters inverted vee is doing better than expected. Although I cannot compare them directly, on the basis of results I now think it does better, broadside at least, in comparison to the delta loop that was taken down earlier in the year. It just goes to show how local ground and suburban clutter can negatively affect the DX performance of vertically-polarized antennas.
Since the yagi went up my DXCC total increased to 226, an increase of 20. Even on 80 I have managed to eke out 30 countries. My LOTW confirmations are now over 100 on 40, 20, 15 and 10 meters, and just shy of the mark on 17 meters. That's good for less than 2 years with QRP and modest antennas, antennas which up until 3 months ago were single element and no gain.
I do not have an antenna for 160 nor do I seriously plan one for this QTH. An antenna can surely be built but it would have to be a poor one. Nevertheless I decided to enter the ARRL 160 meters contest in early December for a laugh, just to see what I could do with 5 watts and no antenna. By "no antenna" I mean unscrewing the outer ring of the PL-259 of the 80 meters half sloper. It's an old trick that I've used before.
The surprise was making over 100 QSOs with this ridiculous setup. I could hear some DX, but though I worked none of it I did get as far as Oklahoma. Most QSOs were a struggle to complete, which is no surprise. Of course I was amply assisted by the big antennas and good ears of other operators. It was unexpected fun, and educational.
2015 plan and constraints
My plans for the VE3VN antenna farm in 2015 are more modest than they were for the previous year. Back then I was starting from very little so there was ample room for improvements. That is less so now, and I am running straight into several constraints on what I can or should do at this location.
First, the constraints:
- Radials: These are not compatible with the use of my yard, nor is there really a lot of room on the east-west axis to run radials. Yet I need radials if I am to increase the efficiency of low-band antennas, and even venture down to 160 meters. My present 15 meter high tower models well on 80 and 160 as a vertical, but only with a good radial system.
- Power: I can increase power to 100 watts but no further. I know from experience that going above this will lead to neighbourhood EMI problems on 20 and above. It could work if only used occasionally, such as to break a pile-up, but is out of the question for regular use and certainly not in a contest.
- Noise: My immediate neighbourhood is full of noise sources. Most sound like LED light systems, but there are many more that are harder to identify. It isn't a solvable problem. Most hams face the same situation. Poor reception is acceptable for QRP since the noise mostly covers up the weak stations that would never hear me anyway. Increasing power and a large antenna investment would show a poor return. Overnight to early morning are best since that is when lights and appliances are mostly turned off. Evenings can be quite bad, especially in winter when the sun sets soon after 4 PM.
- Tower: A permanent tower requires a concrete base. From my original site plan this could only go at site B or D due to the location of the septic system tile bed. (Site C is where my tower and yagi are currently located, right on top of the tile bed.) Site D is preferred due to the municipal tower policy and setback requirements. Going above 15 meters height also requires "consultation" with all of my immediate neighbours for the same reason. That is more of an inconvenience than a significant problem. Even so a large tower may be a poor investment at this QTH due to my growing ambitions. Why spend all that money and still have physical limits on what I can get in the air, power limit and reception difficulties due to noise?
- 100 watt transceiver: I am already shopping, so it will happen. I am not only motivated by power but by the need for a better receiver. The Elecraft KX3 is a great little rig though one with serious receiver deficiencies in comparison to the best. I may detail my KX3 experience in a future article.
- 80 meters: The ground in my yard is dreadful, far worse than the "medium" ground I typically use in my models. Although permanent radials are out of the question there is the possibility of a winter-only antenna using the 15 meters tower and yagi as a monopole on 80. Initial modelling shows promise. It is worth the experiment, once I dig up a large quantity of cheap radial wire.
- 6 meters: This lowest VHF band used to be one of my favourites. I want to explore putting up a small 3-element yagi on one of the towers so that I can at least play around a bit during this summer's sporadic-E season. First I will have to address antenna interactions and mechanical barriers.
- Computerization: Inside the shack there is a lot I can do to improve operator performance and flexibility with an investment into software and hardware. The present ergonomics are barely passable for contest operating.
Longer-term outlook
I have a decision coming up if I intend to have better and bigger antennas: build a large tower on this property or move. Both alternatives have their pros and cons, plus large impacts on non-amateur radio aspects of my life. As someone looking to retire early I do have the flexibility to consider another QTH, one removed from my current personal and business networks. That is, if I decide that amateur radio will be a large part of my post-career life.
Like everyone, I'm not getting younger. If I want it and can do it, it is better to do it soon and enjoy up to 20 to 30 years of playing with towers and antennas and pursuing operating objectives. This might be the year I choose.
This blog
In my travels around the internet I find that most hams with an online presence choose to organize their web sites by topic or project. Those with blogs, either alone or with an accompanying a web site, seem to quickly abandon them.
I seem unusual in that I do everything in a blog. There are advantages and disadvantages to this approach. For example, if I update my experience or further research on an antenna I do so in a new article, not by modifying the earlier one. Of course I link to earlier articles where it is informative, but if you come to my blog by way of searching out the original article you might not discover the updates. As to typos...well, they happen and are rarely worth the effort to fix in already-published articles.
Despite that deficiency I have a strong reason for sticking with a blog. That reason is narrative. I believe that any passionate pursuit, be it amateur radio or anything else, contains a story. The story is often more compelling than any individual milestone or set of milestones. From what I've seen I can assume that many others would disagree, and they do so by documenting various technical or construction projects rather than why they do what they do. Typically these pages are not updated. In fact you get little insight into who these hams are or even if they're still alive!
So I will continue to focus on narrative, for which a blog is best. I recommend the use of the search function provided by Google at the top of the page to find articles relevant to specific topics. That way the blog can still be useful to those who want to find articles on specific areas of interest and care not at all about the narrative.
Dark corners of the internet
For the vast majority of my audience the following message can be skipped. It is for the small number of bad actors lurking in the darker corners of the internet.
Copies of a number of my articles can be found elsewhere with authorship removed or no links to the source material. This is unethical at best and is illegal in most jurisdictions. I spent many years of my career dealing with intellectual property matters so I am no naif. I know it happens. I am disappointed to see hams do it to other hams.
Dealing with it not always easy, so I continue to observe and consider the matter. The internet which creates this problem also makes it easy to discover that it is occurring. That is, I know where you lurk.
On the brighter side, I do welcome fully-attributed references to my articles. In return I make every effort to attribute both online and offline sources I use or extract from. That's only right.
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