Monday, January 28, 2019

Short Beverage Antenna for 160 Meters

One of the many projects I did not get done in 2018 was putting up more receive antennas for the low bands. The delay is due to its relative priority being lower than transmit antennas, such as my still not quite complete 80 meter vertical yagi.

Up to now I have just the 175 meter long Beverage antenna pointed northeast at Europe. It's a wonderful antenna, although one that requires periodic maintenance. That's a common complaint about Beverages strung through bush and forest. The area was selected because it is far from sources of potential interference and it is only populated by wildlife. The farm fields are easier to work in but would require taking the Beverages down during spring and summer.

With the upcoming CQ 160 meter contest as motivation I spend some time last week putting up a temporary Beverage pointing west. It is shorter and simpler than what I have planned for a permanent antenna. What it therefore lacks in performance is compensated by the reusability of its components (even the wire) and ease of construction. By "ease" I mean relatively easy compared to alternatives.

The Beverage is ~89 meters long, about the shortest a Beverage for 160 meters can be and still deliver acceptable performance. That length is not randomly chosen. Like yagi booms there are lengths that exhibit peaks in F/B, and therefore directivity and noise attenuation. To demonstrate this I selected three lengths -- 70, 89 and 110 meters -- and modelled them with EZNEC. The impetus for the modelling comes from ON4UN's book Low-band DXing, in which optimum lengths are discussed.

Notice the differences. F/B is significantly better with an 89 meter length. However gain increases (beam width decreases) with length. There is a peak in F/B approximately every multiple of 89 meters; gain continuously increases as the length increases. Gain is not too critical since, if needed, it can be provided with a pre-amp. The length does not have to be precisely 89 meters. A few meters either way has little impact on performance. The small difference in F/B is likely swamped by other variables such as ground quality.

The gain difference is noticable. The modelled gain of the 175 meter Beverage on 160 meters is -10.5 dbi versus -15.1 dbi for the 89 meter Beverage, or -4.5 db worse on the shorter and lower antenna. About -0.5 db of that is due to the lower 1 meter height of this antenna. (There is another -1 db of coax loss, as we'll see later.) The additional loss is enough to make comparisons between the Beverages difficult. Of course the gain is not indicative of the antenna's directivity, and therefore its effect on copy of signals in the target direction.

Feed point

In the spirit of keeping it simple for this temporary antenna the feed point is built into a discarded plastic food container. The clear plastic helpfully shows all of the components, inside and outside, but does confuse which side each is on. The inside only contains the matching transformer. Stainless steel hardware provides studs to attach the Beverage wire and groung wire. I am using UHF connectors since I have them and I don't have type F bulkhead connectors.

The ferrite core and construction are the same as for the northeast Beverage. The turns ratio of 5:2 is a good match between RG6 (70 Ω) and 500 Ω for the antenna. This was tested with a 470 Ω resistor which measure 495 Ω. A better match is possible with a turns ratio of 8:3 but I got frustrated trying to thread more turns through those tiny holes in the BN73-202 binocular core. This is despite using thin AWG 24 insulated wire scrounged from old Cat5 cable.

With the cover on the container it is pretty well watertight when the lid faces up. Otherwise water could seep in around the studs and SO239 connector. Sealant is near useless due to the flexibility of the thin plastic.


Driving the ground rods into frozen ground is not fun. After a couple of weeks of extremely cold weather and thin snow cover the frost has penetrated deep. I used a pick axe to remove the top 10 cm of frozen soil. That was enough to hammer the rods through the remainder of the frozen soil into the warmer ground below. However I did encounter rocks that required repeating the process several times until I could get down the full 4'.

I did not use a 470 Ω resistor for the termination. After reviewing material on Beverage antenna construction I realized that I had to compensate for the serial resistance of the ground loss. With a single ground rod this can be exceed 100 Ω even in good soil. I opted for a 330 Ω carbon composition resistor that measure close to 350 Ω (carbon composition resistor increase in value with age). This worked out well when I measured 495 Ω at the feed point from 1.5 MHz through 7.5 MHz.

I kept the construction simple. The resistor is clamped directly to the ground rod. A wire nut connects it to the Beverage wire. Since the wire swings a bit in the breeze I dropped a piece of scrap lumber on it to avoid breakage due to metal fatigue.

The wire tensioner uses a thin nylon rope and a cleat made from a couple of nails pounded in a tree. The feed point end of the wire is secured to a wood fence rail with a nail driven through the insulator. It's simple, cheap and effective.

Beverage wire and siting

I used what was available and long enough: AWG 14 THHN solid copper wire. I have a 300 meter reel from which I've been building my wire antennas. When the Beverage is removed in the spring the wire will be reused for other wire antennas. The insulation allows the wire to sit directly on trees and wood fencing without risk of performance degradation.

The Beverage wire runs along the wood fence line about 1 meter off the ground. There is little to no risk of deer or humans tangling with the wire, other than yours truly. I climb the fence to get to work on the 80 meter array. Because the coax and control cable for the 80 meter antenna cross the fence the Beverage passes close to them. While the Beverage performance should not be affected by the proximity there is a risk 80 meter transmission into the Beverage when operating SO2R on 80 and 160 meters concurrently. I have not tested this yet.

The 150' tower is as close as 25 meters to the Beverage. The tower and antennas are not resonant on 160 meters and the separation should be enough to avoid Beverage pattern distortion even if the tower were resonant. The 80 meter array elements are closer but are not resonant on 160 meters. However if the Beverage is used on 80 meters there is a risk of interaction. First listening tests on 80 meters don't demonstrate cause for concern. The southwest radials get close to the Beverage, although those of the 160 meter vertical (gray circle to the south) are 20 meters from the feed point.

Coax for the northeast Beverage (feed point at the northeast corner of the site map) runs along the fence line on the ground, as far west as the Trylon tower in the house backyard. Therefore they overlap for ~30 meters. This is generally poor practice due to the potential for noise incursion but difficult to avoid in this instance. The RG6 coax for the west Beverage angles south into the hay field, running midway between the 160 meter radials and the Beverage.

Terminating the Beverage further west to reduce all these interaction issues was inadvisable because it would bring the antenna close to the power line that runs through my property (indicated by the gray line). The drop to the house runs underground along the forest of young tree south of the driveway.

These pictures illustrate how the fence is being employed for the west termination (left), supporting the wire and the east feed point. It's as simple as it looks. Laying the line on the fence rails took a couple of hours of walking through the undergrowth with a wire reel, cutting branches and thorns along the way. The deep snow and slush didn't help. The bush on the verges of the hay fields has grown thick over the years due to not being maintained. I am unlikely to change that.

Initial on air testing

I had one evening with the antenna before the CQ 160 contest. Testing was limited due to finding few stations far to the west to properly. I compared it to the vertical itself and the northeast Beverage. At least the large number of Europeans active in preparation for the contest made it easy to establish that the F/B of the west Beverage was reasonably good, perhaps as much as 20 db. That indicates the wire length is performing in accordance with the model.

Later in the evening I heard a W6 and a couple of W7's. The Beverage definitely improved the SNR on those stations. While promising, this was only a tentative assessment. I would have to wait for the contest to have lots of activity and a range of signal levels to better assess its performance. The directivity is better on 80 meters, but again there was a dearth of suitable stations available to get reliable comparison data.

Since I used the full 150 meter roll of RG6 there is an estimated transmission line loss of ~3 db. The extra length was coiled up outside -- it will later become a bidirectional Beverage. The loss is not a great inconvenience other than to make antenna comparisons more difficult. A lesser impact is that the periodic impedance variation with frequency is mostly smoothed away when measured in the shack.

Contest performance testing

Hundreds of stations audible at any time from all over North America and around the world is a fantastic environment in which to conduct an antenna test. Mediocre to poor DX conditions on Friday night were helpful in providing many weak signals for testing, although it was damaging to my score. Late in the evening when west coast activity peaked was the best time to test. It gave me something to do after largely working out the east coast and being unable to work many Europeans.

The TLDR version of its performance: meh! This is about the shortest Beverage you can have on 160 meters and get anything approaching good performance. Although I have not done a direct comparison it is visually apparent on looking at the far field patterns of this and a compact antenna such as a Flag or K9AY array that performance is comparable. One important difference is that the compact antennas require a pre-amp, which in some cases can create noise during SO2R and multi-op contesting.

Despite having a broad azimuth pattern the antenna performed best on VE7 and northern W7 and W0. Reception of W6 stations was slightly improved but very little on W5. I doubt that I would have missed any QSOs during the contest without this antenna but it made easier copy. No Pacific stations were heard. That test will have to wait.

One disadvantage of the overly broad pattern is that the F/S is poor. W2, W3 and W4 stations showed little improvement with this Beverage and were not notched as they are with the longer northeast Beverage. Removing QRM, not just noise, is desirable in a receive antenna. It did reject signals well off the back, but all I have off the back is Europe and, sadly, there was no QRM from that direction.

Initial tests on 80 meters are promising. Directivity is superior to that on 160 meters due to the antenna being twice as long relative to wavelength. It has been used just once in daily DXing, during a sunrise Pacific opening (I don't often wake up early enough for these!). It made a modest improvement on VK3 and E5 signals, which are more southwest than west from here. I suspect that the modest result is due to atmospheric QRN predominantly coming from the southwest. But I could be wrong.

There are upcoming contests where I expect it to assist with adding multipliers on 80 meters. As yet I have nothing conclusive to report about performance on 40 meters. Another reception tool would be welcome on 40 due to the poor directivity of the XM240.

Future plan

This experimental Beverage antenna will come down in the spring. As an experiment is has already proven fruitful and I expect to get more out of it for the rest of the winter. The wire and coax will be recycled into other antennas and the transformer will likely see service in another Beverage. The plastic container will be discarded (recycled) since it won't survive the weather for long.

Many low band enthusiasts have replaced their Beverages with switchable vertical arrays, which can achieve equal or better directivity with a smaller footprint. But they're more complex, requiring hybrid combiners, phasing harnesses and amplifiers among other specialized components. Most opt for commercial products. As I said earlier, these arrays need to be well separated from transmit antennas to avoid the potential for grief from the pre-amps.

I am on the fence regarding Beverages versus vertical arrays. This is a choice I'll have to made by the fall. Regardless of that decision I am very likely to twin the northeast Beverage to make it bi-directional. Ultimately that may be my only Beverage.

Tuesday, January 22, 2019

On Surviving a Solar Minimum Winter

VE3 winters are long and cold. This far north that is often true of the HF bands as well. Although my geographical latitude is not all that high at 45°, the auroral zone is nearby and is frequently responsible for partial radio blackouts on the most productive DX paths. It can be frustrating to hear stations only a few hundred kilometers south working Europeans and Asians I can barely copy, if at all.

Lack of sunspots makes it worse. The openings on 20 meters are short, limited to the brief hours of daylight. It gets even worse on 17 meters, and 15 meters doesn't open at all much of the time. On 10 meters there is feeble sporadic E and the occasional South American.

Going lower helps. However 30 and 40 meters close early as the MUF drops like a rock after sunset. As partial compensation the polar path, when the auroral absorption permits, does bring in workable stations over the pole from Asia and Europe for several hours every morning. But if you only have a simple antenna these weak ones are difficult to work. My high yagi helps, and high power would produce more reliable results.

The lowest bands are often good, which many hams embrace with enthusiasm. Although I enjoy DXing on 80 and 160 meters all that QRN gets to me. During the NAQP SSB contest this past weekend one ham remarked how nice it was to put a voice to my call since I am mostly on CW. I am avoiding most phone contests because my brain gets rattled by the noise and difficult copy due to the wide bandwidth needed for SSB.

Many days I avoid the bands entirely to recuperate from the strain of operating the low bands. Although this ought to increase time spent in the shop working on antenna projects I find that my enthusiasm is muted. Progress is being made but not at a pace that the available hours would allow.

The important thing is not to fret too much about it. Some downtime during the year can contribute to sustained interest over the long term. Soon the days will grow long and the weather will warm up. On a slightly longer trajectory the sunspots will return. Not much will change in 2019, so we must look ahead to 2020 when solar cycle 25 will flex its muscles. Before long the high bands will be hopping.

In the meantime I am learning to love 160 meter DXing. There is DX to be found every night, and less frequently there can be enhanced conditions. Several days ago I switched on the rig near midnight just before heading to bed and I heard a few strong Europeans. So I called CQ. To my delight the DX rolled in, to the tune of 22 Europeans logged over 40 minutes. The only problem being that I was so sleepy my CW fist was poor.

To mix things up I like to add challenges to my operating. One example, in tune with the low sunspots, I operated QRP for the Stew Perry TBDC contest a few weeks ago. During my brief operation I was able to put 12 Europeans in the log, including a best distance of over 8000 km. Not bad for 5 watts on top band! Achieving the highest point QSO in the contest by working 3V8SF (who operated low power) was icing on the cake.

It is little things like this that get me through a solar minimum winter. Other hams choose different tactics. VHF/UHF enthusiasts are so isolated from the solar cycle they don't see what all the fuss is about. For them every day is a challenge.

There is really no point to this article other than to emphasize that an ebb and flow of energy and enthusiasm for the hobby is normal and not a cause for concern. Shutting the shack down for awhile is okay. Socializing with your fellow hams is also anodyne, during which you can commiserate on the poor conditions and encourage each other on your respective projects.

The physical strain of digging out of the recent fierce snowstorm is also refreshing in its way, despite the frigid weather. It's -25° C midday as I write these words and the wind is howling at 40 kph. Brrr! I'm glad my rotators are greased for these conditions. Soon enough the sun will return. As evidence of this 20 meters is once again opening to Japan and UA0 late in the afternoon rather than going dead the moment the sun dips below the horizon.

With the CQ 160 contest coming up this weekend I am fighting the doldrums with a quick and easy project that will pay dividends: another Beverage antenna. Stomping through the frozen thorn bushes and snowdrifts stringing wire and coax with half numb hands in order to battle the elements and poor conditions, when followed by a hot mug of fresh-ground coffee is highly recommended for lifting one's spirits.

Tuesday, January 15, 2019

Bare Bones SO2R

Single-op two-radios (SO2R) must almost seem perverse to non-contesters. At least that's my experience when the subject comes up in conversation. For contesters with the ambition to compete at a high level it has become a necessity. It's a necessity because our competitors are doing SO2R and are significantly boosting their scores.

It isn't easy. Aside from the technical challenge it requires practice to become effective. It can be mentally gruelling. The truly talented are able to run on two bands simultaneously, and their results are impressive. Like any competitive event, be it sports or radio sports, winning is hard work. In other words, if you find contesting easy or comfortable you're leaving points on the table because you could be working harder. There's nothing wrong with taking it easy, provided you don't care about winning.

SO2R rookie

During this past weekend's NAQP CW contest I had my SO2R debut. In one important way it was the ideal contest to do this: all competitors are limited to 100 watts. Therefore I could measure myself against both my expectations and the results of better contesters, after accounting for station size and geographical advantage. I can definitely say that it helped, increasing my score at least 10% if not 20%. It is no surprise that contesters with well-honed SO2R skills ran circles around me.

Operating SO2R along with its advantages and disadvantages is a topic I must push off to the future. I am as yet unqualified to discuss it. In this article I will show how I added to and configured my station to be SO2R capable. This is about as simple an SO2R as you'll find anywhere. It is just enough to give it a try with minimal effort and expense. I'll go further when I'm ready to do so.

Operating position

The display is front and centre, right where I believe it ought to be. I remain entirely skeptical of contesters who put the rig in front and the display on top. As the station and operator improve the rate also improves, including near continuous running, requiring less attention to the rig. It's just type, type, and more typing.

You will fatigue far faster when you have to constantly lift your neck and eyes to that degree as your attention flits between display and keyboard. Most modern contest software enable keyboard control of common rig features. One of the most used is RIT as stations call off frequency and your filter is narrow to manage congested band conditions. Controlling that by keyboard is a tremendous stress reducer.

You will likely notice a few problems with placement of some items. Of this I am aware and they will be dealt with. Perfection is nice but not mandatory, so I went with what I had for this first outing. The FT950 is not a good contesting rig because the receiver performs poorly and the DSP filtering is several generation old. But it was there and just gathering dust as a backup rig. I'll get something better later.

Antenna switching

Station automation is lacking and remains on my lengthy task list. For the present a manual switch controls the remote 2 × 8 antenna switch. Left and right radios have their respective switches on the top row of the enclosure. Antenna positions are identical on both sides. Hardware interlock in the antenna switch prevents the disaster of one antenna being selected on both sides.

The rotary switch has 6 positions: 4 allocated to antennas and the extreme right and left positions select no antenna. Outside of contests the second radio is normally at the latter setting. The switch next to the knob selects between antennas 1-4 and 5-8. By careful placement of antenna ports a desired antenna for a given band is almost always one step or switch click away.

On the bottom row there are blanks. The rotary one on the left is reserved for selecting the direction of the 80 meter vertical yagi. The one on the right will eventually be used to select receive antenna direction. Both radios will share the receive antenna. That's okay since it will most often only be needed for 160 meters.

RF interactions and filters

Most of my antennas are not adjacent, and that helps manage fundamental and harmonic interference with the other radio's receiver. This is important since I do not use band pass filters. Many contesters will be shocked by this yet it was common many years ago. I fondly remember running two kilowatt stations side by side during multi-op contests and having to coordinate with the other operator to avoid having the lower band station's harmonic clobber the other operator.

Yes, sensitive receiver front ends can be damaged. Although it has happened to me the fix was to replace the small incandescent lamp used as a fuse in the antenna line when it took the brunt of the abuse. A spare transceiver was always on hand for swapping in when this happened, and so avoid more than a few minutes of down time.

With 100 watts the risk of receiver failure is quite low. The greatest risk is when yagis on the same mast are in use by each station. The fundamental and harmonics can be very strong. The higher end rigs used by contesters usually have low-Q front-end filters ahead of the pre-amp that apply enough attenuation of the fundamental signal from a transmitter on another band to avoid a catastrophe or fundamental overload. The FT950 on the right is more susceptible than I like.

Band pass filters help in two ways: attenuate harmonics from the transmitting rig and attenuate the fundamental energy on the receiving rig. If you use an amplifier it will happily regenerate harmonics that the filter removed since no amplifier is perfectly linear, and this is even more so with RF power amplifiers, especially solid state amplifiers. Amplifier harmonic reduction requires tuned stubs or high power (and expensive) band pass filters.

Before the contest I ran through every combination of antennas and bands on both rigs to test for harmonic energy. All was as I expected. The worst case was transmitting on the 40 meter yagi where the second (20 meters) and third (15 meters) harmonics were very strong on the TH6 3 meters below it, hindering effective use of segments of those bands. The easiest solution was to switch to the TH7 at half the height.

Even with the best filtering there will be band segments wiped out by harmonics. It helps to run at a higher frequency on the lower band so that the harmonics on the higher band are less likely to be encountered. I made this mistake numerous times during the contest.

Audio switch, and using it effectively

One week before the contest I built a manual switch to feed receiver audio to the headphones. The wiring is straight-forward and can be easily figured out by anyone wishing to build a similar unit. There are stereo 3.5 mm jacks on the back for the left and right radios and one in the centre for the headphones. A splitter on the headphone jack can direct headphone stereo audio to a recording device, which is strongly recommended for top competitors in major contests.

The SPDT switches on top correspond to the headphone earpieces: left for left ear and right for right ear. Both switches to the left puts audio from the left radio into both earpieces, and vice versa. When listening to both radios at once the typical switch positions are left rig on the left earpiece and right rig on the right earpiece (as shown above). To concentrate on one radio the audio can be temporarily switched to both earpieces.

I put the switches on top because this is the best ergonomic fit for me. They're a short reach for my fingers that are constantly hovering over the keyboard.

A lot of switching goes on during the contest! The best SO2R control boxes will, under software control, switch the audio for the rig in receive to both earpieces when the other is transmitting, with an option to blend the audio in various ways to accentuate, say, the run radio's audio or to monitor the transmission side tone (CW) at a reduced level.

The way I blend audio is with the AF Gain controls on the rigs. I set the rig side tone level as low as I can while still being able to copy it. The side tone let's me know the progress of memory transmission or for feedback when using the paddles. Experienced operators disable the side tone during memory playback. There is no provision for a microphone. Transmit audio switching is more complicated and my favourite contest mode is CW. The WinKeyer USB takes care of rig switching under control of N1MM Logger+. The software ensures that just one rig transmits at a time in compliance with the rules of virtually all contests for single op entrants.

Ordinarily both audio channels from HF transceivers are identical. For radios with two receivers the stereo wiring brings the benefit of dual receive with no added effort. Split operation is rare during contests but can happen, so you'll be prepared. More common is to use the second receiver to search for stations on the same band and antenna, either while running or to double your S & P potential. This can be useful when sunspots are absent, such as now, when only one band is consistently producing contacts, or for single band contests. I may try this in the upcoming CQ 160 contest.

Don't be surprised if you hear power line hum when the audio switch is connected to both radios. Make sure the interconnect cables are high quality and that there is a low RF impedance bond between radio chassis and other equipment powered by the mains. I had a low level of hum only in the FTdx5000 audio which I traced to the headphone jack and in particular the 3.5 mm to ¼" adapter. Replacing it with a high quality unit resolved the problem. You can learn much more about trouble-free audio interfacing from K9YC, starting at page 40 of the linked document.

In summary, the audio switch is simple and it works. For an investment of a few dollars and a couple of hours it gives me a good entry point to try out SO2R. When or if I go all-in for SO2R a more substantial investment on a control box will be warranted.


N1MM Logger+ software is smarter than I am. The SO2R features have been designed by contesters who have learned from their own long experience and feedback from the world's top competitors. The choices they have made are good ones. The challenge for an SO2R novice is to understand and use them effectively. I have much to learn.

The software chooses where next to transmit (left or right radio) and position the text cursor from context. It is not what you might expect or guess. It all makes sense once you get used to it. I wasn't used to it so I made many mistakes. As the contest progressed my error rate declined. You can learn a lot in just a few hours. There is nothing like a real contest to spur learning, far better than offline practice (which I also did).

The SO2R feature is well documented so I will simply point you there. Other popular contest software packages support SO2R as well, including interfacing with external control devices. I am obviously making use of the minimum set of features to get started with SO2R. This will change as I progress to phone SO2R, a superior audio switching system and more aggressive operating, including simultaneous running on two bands.

One feature I plan to make use of soonest is two keyboards, one for each rig. When done properly there is less fatigue and fewer typing/transmitting errors.


At first it can be difficult to concentrate on copying the signal heard in one ear and not be distracted by what's being heard in the other ear. A momentary lapse means requesting a repeat, resulting in lost time for you and the other station.

Other types of distractions I experienced include:
  • Sudden appearance of a noise burst or a loud signal in the other receiver.
  • A CW tone close to or equal to that of a signal in the other receiver can be disorienting.
  • Locking your attention on a weak caller takes longer when you're listening to both receivers.
  • Poor timing of transmissions can have you paying attention to the wrong side. For example, answering a CQ on one rig a second or two after your CQ on the other radio ends. You're focussed on making your call and fail to copy the station calling you.
Put in the time and you'll get better at dealing with these and other distractions. The danger is that you become so anxious about mistakes that you abandon SO2R entirely. Don't do that; don't be afraid to make mistakes. It's better to stick with it and climb to the top of the learning curve. I know that I have more climbing to do, and I will surely make many more mistakes.


It sure was nice when the contest ended and I could get a proper rest from SO2R. Several times during the contest I retreated to a single radio to reduce the stress level. It is not necessary to use both rigs all the time, especially in a long contest. As proficiency improves the stress will become managable. That's when you can challenge yourself to accomplish even more with SO2R.

I am considering a follow up article on the the nuances of SO2R and how some (not me!) push themselves to the maximum effort, and score. NAQP is a contest where SO2R makes a difference unlike most other contests. For once it was nice not to have the lowest score among my more exalted team members, which includes two WRTC competitors. I salute them.

Now it's on to practice, practice, practice. I intend to do SO2R again, though hopefully in a contest not quite so intense. My bare bones SO2R setup will transition to one more sophisticated as my schedule permits. Most of what is built for SO2R is needed for multi-op contests --filters, switching, automation and software -- and that I intend to do by the end of 2019. For now I am happy that I can achieve some of the potential score boost due to SO2R.

I hope I have inspired others to try SO2R. The thing is you don't have to do SO2R 100% of the time. Like beginning runners, you can alternate walking and running until your body is tough enough to go the distance. Pick your places and you can increase your contest score from a modest effort. With the availability of off-the-shelf software and hardware to take care of SO2R mechanics it's never been easier. Others are doing it so why not you.

Wednesday, January 9, 2019

Permanent 160 Meter Antennas Under Consideration

When you have a tall tower it is quite easy to put up a high performance wire antenna for the low bands. My 160 meter antenna is a good example: a catenary tied off at the 40 meter level support a slanted T-top vertical that performs remarkably well. In the most recent Stew Perry TBDC in which I operated QRP I was able to work numerous Europeans, with my best distance slightly over 8000 km. Imagine if I had more than the present 8 × 30 meter radials.

Because it's a temporary antenna it will not see further improvement. I would like to do better on top band with a better antenna. For almost all of my ham career I had no antenna for 160 meter so I am now making up for lost time. My contest scores depend on it, as does my pursuit of DX.

My antenna is temporary because it has to be taken down from mid-spring to late summer -- a minimum of about 4 months -- due to the incompatibility of radials and hay harvesting. It is not only a better antenna I need but preferably one that is permanent. These two requirements -- better and permanent -- are not easily accomplished. I will be happy to have a better part-time antenna and a modest though permanent one.

To this end I am actively investigating options. In this article I'll run through what are, so far, the best of them. I think it is worth taking the time to blog about it because there are sure to be others in a similar situation. The ideas may be of wider interest. But to be clear, this is primarily about my station, my operating objectives and my constraints.

Independent full size vertical

This may be the ideal solution. It requires a new tower of at least 30 meters height, well separated from the two big towers and receive antennas. The former requirement is to ensure enough structural strength for a physical ¼λ vertical, which is 40 meters high. The latter is to avoid destructive interactions and coupling which would distort the radiation patterns of the vertical and the receive antennas.

Separation ought to be at least 1λ, which is 160 meters (500'). That's a lot! Fortunately I have the space. Otherwise it may be necessary to dynamically de-tune towers when operating on 160 meters. Some do this on transmit, but if the array is directive you need to do it on receive as well; that is, full time.

My neighbour would likely be annoyed by this antenna since it takes at least 1 acre out of hay production unless I undertake the herculean effort to bury 2000 meters of radials. The area is trebled or quadrupled should I go further and make a 4 direction, 3 element vertical yagi out of it of the same type as my 80 meter array, just as K3LR originally designed. Again, I do have the space were I crazy enough to go for it.

Limiting the tower to 30 meters height would keep the guy stations out of the forested areas at the east side of my property. A 10 meter high stinger makes completes the monopole. The radials can extend into the forest, with some difficulty. The difficulty is multiplied for a yagi.

The areas where it can go (see the site map) are to the semi-enclosed areas east and southeast of the 150' tower or north of the 80 meter array. Elsewhere are swamp, forest, power lines or other towers and antennas. Feed lines would be very long, which is expensive and inconvenient though not a significant loss risk at 1.8 MHz. Many hams with the land put their 160 meter antennas far away to avoid all these problems. My receive antenna field is close, probably too close, to the east area.

Then there's the expense and maintenance for a tower. In sum, I really dislike this option. My ambitions for 160 meters are not grand enough to justify it.

Shared radial system

The 80 meter array has a large and connected radial system that covers a full acre. The radius is ~25 meters. Although this is a little short for 160 meters there is a lot of copper on the ground. Sharing the 80 meter antenna is an option I've discussed before and tentatively rejected because of the challenge of preserving performance on 80 meters.

There is one more option to consider now that the antenna is up and I know what I have to work with. By placing a switchable coil at the top of the tower, electrically inserted into the stinger, there would be negligible degradation of 80 meter performance and 160 meter performance may be acceptable.

The stinger will need to be electrically isolated from the tower. A thick wall fibreglass tube or solid rod would have the necessary strength. There are enough wires in the control cable to accommodate a signal to switch in a matching network and to operate a vacuum relay to switch in a coil at the top of the tower. A vacuum relay is mandatory due to the high voltage that high up the monopole.

According to the model the coil will have a substantial inductance of 105 μH to be electrically equivalent to a ¼λ. The higher up a monopole the inductor is placed the higher its value needs to be. It is important to design the coil with the greatest feasible Q to minimize loss. The inductor has a reactance of 1200 Ω at 1.825 MHz, giving an ESR (equivalent series resistance) of 6 Ω for a Q of 200, or 3 Ω for a Q of 400. Recall that R = X / Q. Since the higher Q can be difficult to achieve for a coil this size I will assume with the lower value.

A reasonable assumption of 5 Ω ground loss for the full 80 meter array's radial system at 1.8 MHz the loss antenna loss is -2.5 db. The additional coil loss is -1 db. These values are rough estimates. The pattern shows the impact of these losses. The capacitance hat in the model has negligible affect on the required coil inductance due to its small size. A larger hat affects 80 meter performance because it comes too close to the parasitic elements. It may be best to remove them entirely.

It is no surprise that the SWR bandwidth is poor. There is a span of 35 kHz with an SWR below 2. An L-network in the model optimizes SWR at 1.825 MHz, which is close to the centre of the band segment of most importance to me.

It is entirely possible to place the coil lower or entirely forego it by adjusting for the low impedance in the matching network at the base. In either case the antenna efficiency will be lower due to the coil and network loss, and the effectiveness will be lowered due to most of the antenna current being near the ground. A coil up higher put more of the current up higher. It's just that the latter is more difficult to build and switch.

Of course the antenna cannot be concurrently used on 80 and 160 meters. This is a problem in contests were there are no other antennas for these bands. But for the benefit of a year round 160 meter antenna it is of interest to me despite this constraint, the poor bandwidth and the loss.

Between two towers

I have written previously about the presence of an interaction between my current 160 meter antenna and the 150' tower from which it hangs. The physical height of the tower and mast is ~47 meters. The electrical length will be substantially more due to the top loading of the yagis, at least 55 meters. Although not resonant at 1.8 MHz it does distort the pattern a small amount by acting as a weakly active reflector. The estimated gain reduction towards Europe is approximately 2 db.

This is a significant amount for working stations in that direction, and there is little recompense in gain towards the opposite (southwest) direction. I would like to correct the problem. Regardless of what I do the antenna must be temporary due to haying during the spring and summer. But I'd rather have a good temporary antenna than a mediocre one.

To begin this exercise I placed a wire vertical centred between the two towers, which are 60 meters apart. The 30 meter spacing is ~0.18λ, a little more than is ideal for yagi spacing. The towers are modelled as 50 meters high with poor grounds of 25 Ω, representing the lightning ground with no radials. The resistance lightning sees is lower, but the near field of a 160 meter antenna involves a large area of lossy soil.

The antenna radial ground loss is 10 Ω, representative of a mediocre radial system, on the order of what I have on my current antenna: 8 × 30 meter radials. Using MININEC ground simplifies modelling of ground loss.

With this configuration the loss in the tower grounds is -0.7 db  and -1.0 db in the antenna ground, for a net gain of 1.4 dbi. The azimuth pattern is almost perfectly omni-directional. Improved tower grounds increase efficiency while the azimuth pattern becomes slightly asymmetric, with a broadside gain ~0.5 db better than in end fire. My towers are aligned approximately northeast towards Europe to facilitate wire yagis should I choose to do so at some future date.

With the electrical length increased to 55 meters the gain increases ~0.15 db as interaction decreases. This is negligible. The 2:1 SWR bandwidth in both cases is 100 kHz, without a matching network. With a better radial system the impedance would fall and require a simple L-network. However that does not change the SWR bandwidth.

This antenna is simpler and has somewhat better performance than my existing T-top wire vertical. All it requires is a catenary rope between the 40 meter levels of the towers. It would in actuality have to be at least 1 meter lower to avoid the rotation loops for the yagis on the 140 meter tower.

With sag in the centre of the span the true height would be around 36 to 37 meters, requiring a short capacitance hat suspended from the rope or dealt with at the feed point matching network. Gain loss for the slight length reduction is negligible. Were I to have a catenary rope to support a low band yagi it would be at a lower height and therefore require a longer capacitance hat for the 160 meter vertical.

Exploiting interactions

I am pleased that placing a wire vertical between the towers produces a better omni-directional pattern than with just the one tower. This is cause less by the symmetry of being between two towers than the increased distance (30 m) between antenna and tower. The base of my 160 meter antenna is only 20 meters from the 150' tower and the upper arm of the T-top gets to within ~10 meters. Modelling confirms the distance sensitive interaction.

With a 0.18λ spacing it is natural to think about a 3 element yagi switchable northeast and southwest, along with the omni-directional mode. It would require putting radials, switches and loading elements on the towers. For an antenna that requires the radials to be rolled up each spring that's a lot of work. Further, the antenna may preclude using the antennas on both towers while operating in yagi mode on 160 meters.

Is it worth it? Maybe. At the very least a model is justified to explore what is possible. Several decibels on top band can go a long way to improved contest scores. Implementation, if it occurs, won't happen until at least 2020. I have more than enough to do in 2019.

Saturday, January 5, 2019

What Tuners Match

I am reaching the end of a long delayed project to rewire all the coax and control cables coming into the house and shack. One task was to dig a trench from the nearest tower -- where all the transmission lines and control lines from the antennas terminate -- to the house. All cables but one are now underground.

The coax runs from the 2×8 antenna switch have been drastically improved. The underground sections are now Andrew LDF5 Heliax, which is burial grade, with LMR400 jumpers to the switch and the runs through the house into the shack. Once the burial grade control lines were run and jumpers made I was happy to find that everything worked; I had been QRT for 5 days after cutting and removing all the overhead runs of ancient and not outdoor rated cables.

Although I ought not to have been surprised, when I got on the air that night on the low bands I discovered that the SWR on a few of the antennas was inordinately high, as much as 3:1. Yet they all received well and showed appropriate directivity. After several minutes of puzzlement I had to kick myself for not seeing the obvious. There was in truth absolutely nothing amiss.

The clue was that the antennas displaying the anomalous SWR were those that have a significant mismatch at one or all band segments. The antennas that already have a low SWR continued to have a low measured SWR with the new set of transmission lines.

The problem is directly related to a previous article I wrote on the importance of low SWR antennas to contesters. Included with that article was the following Smith chart. We'll use it to help understand what I was experiencing. If you haven't read that article you may want to do so now.

My 80 meter 3-element vertical yagi currently has an SWR in excess of 3 at the feed point because I have not yet built the switching system for the array which will contain the switchable L-networks to transform the low impedance to 50 Ω. Mismatch loss due to the high SWR over the long transmission line (LMR400 and LDF4) is acceptable for now due to the low frequency and the good quality coax.

The mismatch is dealt with in the shack with the rig's internal ATU. In each of the tuner's "steps" of 10 kHz across the band of interest to me -- in this case 3.500 MHz to 3.580 MHz -- the ATU finds the correct match and stores it in its memory. During normal operation and especially during contests I can roam across the band and be assured of a perfect match. When I switch to the inverted vee, which has an excellent SWR across the CW segment of 80 meters, the ATU is disabled.

Tuners transform impedance, not SWR

For an antenna with a perfect match -- Z = 50 + 0j Ω -- no matter the length of transmission line the SWR remains exactly 1. For all other impedances the impedance at the shack end of the transmission line is sensitive to the length of the transmission line. As the Smith chart makes clear there are infinite R and X combinations for every SWR greater than 1. Every electrical ½λ of transmission line (multiply physical length by the transmission line's velocity factor) makes one complete circle of the Smith chart circle for that SWR.

The Smith chart is in this case normalized to 50 Ω so that R and X values must be multiplied by 50. Capacitive reactance is negative and inductive reactance is positive. The higher the SWR the greater the circle diameter. The outer diameter of the chart represents an infinite SWR. There are no closed circles on real transmission lines; attenuation causes the circular path to spiral inward, at a slow rate for low loss transmission line and faster when the loss is high. Interesting fact: a sufficiently long transmission line is equivalent to a dummy load.

The SWR in the shack for this antenna is approximately 3, a little lower than at the feed point. It is the same before and after I changed the coax configuration. It was the impedance that changed due to the shorter length of coax. However the ATU was set to transform the previous impedance. This is why the SWR seen by the transceiver after the change was high.

Solution 1

By now you may have guessed the solution to the problem: reprogram the ATU. It was just that simple. I did the same for the XM240 at the bottom of the 40 meter CW segment for the same reason. Problem solved. Antennas with matches close to 50 Ω exhibit a low SWR do not require the ATU and therefore the measured SWR remained the same.

Those with vacuum tube amplifiers might not even register the existence of a problem since changing antennas and frequency always require adjustment of plate and load capacitors to the transform the amplifier's high impedance output to 50 Ω. Contesters have a habit of defacing amplifiers with stickers on which they pen or pencil marks for each band, band segment and even antenna to speed up tuning after band and frequency changes. Had I been using an amplifier the marks for high SWR antennas would have needed to be redrawn.

Solution 2

As that earlier article on SWR and contests demonstrated the ideal solution is antennas with broad SWR bandwidths or feed point matching networks. Once I complete the 80 meter yagi the SWR will be low and the transmission line length irrelevant. The XM240 will always require solution 1, and therefore ATU or amplifier tuning whenever the transmission line changes. But that is a rare event in most stations.

Even with these solutions danger still lurks, waiting for a chance to manifest. Solid state amplifiers with broadband output networks are not so easy to match to high SWR antennas. Kilowatt rated tuners are expensive and require RF sensing circuits or communication between tuner and rig to adjust the match to the antenna and frequency. It is better to avoid this level of complexity with improved antenna matching.

Another problem to consider is that as the SWR increases you may find that the tuner is incapable of obtaining a match. The extreme values of R and X with a minority of transmission line lengths can exceed the range of the tuner. Replacing the tuner or altering the transmission line length are not reasonable options.

Strive for the best match obtainable at the feed point and all these problems vanish. Avid contesters have learned this lesson. Others can benefit as well. As you have seen, I became complacent, almost forgetting the implications of the operational transparency of how I dealt with high SWR antennas. Had I been using an amplifier I risked arcing or worse.