Monday, August 23, 2021

Mitigating Audio Hum

My station wiring is extensive and complex. I try to keep it reasonably well documented and the mass of cables reasonably tidy. However that's difficult to do in practice. The antennas and control systems are constantly evolving, and a lot of my home brew devices are not as pretty as I'd like. In short, it's a mess.

While I do have plans to gradually make improvements there are issues that I must either live with or troubleshoot and solve. One common problem that plagues many stations is largely absent in mine: RFI. This is because most of the towers and antennas are far from the shack. Some, though not all of the control lines have RF chokes and bypass capacitors to shunt RF to ground.

One of my challenges is grounding. I have ground rods at the base of all the towers, the coax and cables are almost all underground until they are near the shack, and I try to follow best practices for grounding where it is possible and practical. It is good enough that a couple of lightning strikes this year did minimal damage. They may have been secondary strikes, but I was either not home or not looking out the windows at the time to say for sure.

The grounding issues have more to do with hum than safety. The connections among RF, AF, control line, PC and equipment grounds are haphazard. For example, operating one of the rotators induces hum in the receive audio of one of the rigs. It is enough to impair reception of weak signals on FT8. Unfortunately it doesn't stop there: hum and related noise can appear on my transmitted audio, whether digital modes or SSB.

It came to a head during this year's sporadic E season. As the season progressed I noticed odd behaviour of the transmitted signal. The audio level drifted up and down and there were momentary spikes on my FT8 signal. I didn't know what it was for sure until a fellow ham sent me a spectrogram of my signal. There were weak spurs across the audio spectrum, and there was little doubt these were coming from my transmitter. In an email exchange we eliminated other possibilities.

Using the rig monitor function I confirmed there were hum and crackling sounds. The levels were well below the FT8 audio so that only stations receiving me strongly would notice. I inspected the spectrogram and noticed that the spurs, though not actual harmonics of 60 Hz, were separated by multiple of 120 Hz. It was time to dig deeper.

The first task was to reproduce the problem. There is no easy way to monitor your own transmit audio and I needed to do that. The rig's monitor function can give you a false sense of security since it monitors the input to the RF transmitter stages and not the output of the transmitter, and certainly not that of an external amplifier.

Sampling the RF requires a separate receiver. Since I am configured for SO2R in contests this was not too difficult to set up. I made use of the PC's two sound cards to transmit using WSJT-X on one rig and to receive on the other using JTDX. A wire stuck in the antenna jack provided a sufficiently attenuated signal that didn't overload the receiver.

I performed two tests at different audio frequencies (DF). One was positioned close to that in the original report. The spectrograms confirm that there is a problem and that it is as reported. There are a few unrelated signals that happen to be within the pass band that are from other sources in the house. For example, the heat pump controller is a little noisy when it is in air conditioning mode. Since there are no spurs at 50.313 and 50.323 MHz it is not worth spending time on it.

Notice that the spurious signals are mostly at intervals of 60 Hz and its harmonics, and especially 120 Hz. They shift along with the DF since I use WSJT-X in "split" mode, which offsets the transmit frequency to keep the FT8 audio within the SSB pass band sweet spot.

It was not only my transmit signal that suffered. There have been several hum issues on receive that have annoyed me for some time. I left those unfixed since they were not serious and I was too busy with station building. Here are a couple of examples:

In the upper pane are hum harmonics that appear when I release the brake on a Tailtwister rotator. Notice that the audio frequencies are odd multiples of 60 Hz: 300, 420, 540, 660, 780, 900, etc. These line up with the hum harmonics on the lower pane. These persistent lines wax and wane with no discernible pattern. They are too weak to interfere with FT8 decoding. The rotator hum does interfere with received signals and also appears on the transmit audio. I was careful not to turn the 6 meter antenna during transmit periods.

Finding and resolving the root cause of the hum is daunting. As already mentioned, my station is extensive and complicated. There are endless possibilities to explore. However, there are several simple things to try before diving deeper. I tried all of the following common cures, without positive effect:

  • Checking and cleaning audio connectors, and then other connectors to the PC and rig
  • Moving the rotator controller and other equipment, in case transformer proximity is a cause
  • Moving power cords to different power bars and outlets
  • Testing outlet polarity to ensure that neutral and ground pins are correctly wired
  • Disconnecting and isolating equipment, including microphones, SM5000 monitor, headphones and PTT lines
  • Adding and improving ground busses between equipment, and the service ground

Despite those failed measure, there were indicators of where the problem might reside. Disconnecting the transmit audio cable from the PC the problem could be replicated by "shorting" with cable with my fingers. This suggests that the hum source could be the rig itself (FTdx5000) since my skin resistance coupled the ground to the signal pin. 

Another indicator was that it was possible to alter the amplitude of the received hum by jiggling the audio connections to the PC. But, frustratingly, not always or not by a lot. This suggests that the PC power supply or internal wiring has degraded, possibly oxidation at a ground connection or a leaky capacitor. The effects are inconsistent and not persistent.

I disconnected the many interconnection cables and hauled the the FTdx5000 onto the workbench and opened it up. I poked around the connectors and audio stages to look for anything amiss. All the connections seemed secure and checks with an ohmmeter uncovered no obvious defects. I put it back together and reconnected the cable. It was no surprise that the hum was still there.

The next candidate was the computer. Modern PCs are notorious for poor and defective power supplies and I've had past trouble with them in my commercial signal processing work. Here I balked since time was running and the sporadic E season was at its peak on 6 meters. Perhaps I'll pursue this during winter when I have more time for indoor jobs. I instead chose to pursue mitigation rather than a cure.

I rooted through my junk box and located a miniature audio transformer. I mounted it and connectors on a small breadboard. I put it in series with the transmit audio line (PC headphone jack and rig audio in jack). It was a struggle to fit it under the fan-out PTT connector without wires getting pulled out of the breadboard.

It worked. My transmit audio was free of hum and all the snaps, crackles and pops. I had two friends check my signal, to be absolutely certain. They gave me a clean bill of health. 

I operated in this fashion for the remainder of the sporadic E season, confident that my signal was finally clean despite my failure to locate the root cause. Hum on the received signal continued, but I could live with that.

The transformer works because the direct ground connection between the PC and rig is broken. Common mode hum cannot cross the transformer. It is for the same reason we use common mode chokes on transmission lines. For small signal levels, such as for audio signals and for my Beverage receive antennas, two-winding transformers are very effective. However, if the hum is differential mode -- on the audio signal and not just conducted over the ground connection -- the isolation transformer won't help.

I needed a something better to replace the flimsy breadboard, and for both the receive and transmit audio lines. Less than confident that I could find the root cause of the hum without a great deal of effort I opted for a permanent mitigation measure. I chose to build a transformer-based isolator for both audio lines. Since I had only the one audio transformer I went online to shop for parts.

My original intent was to order more of these miniature audio transformers, which are very inexpensive. Sites like Amazon have good deals on packs of 10. It doesn't hurt to have a few extras in the junk box. Flea markets are also good sources but those have been few and far between during the pandemic. I already had an enclosure and connectors, and I chopped a piece from a small prototype board to fit inside. The enclosure should be plastic unless the audio connector grounds can be isolated from a metal enclosure. My remote Beverage switch shows one way in which this can be done.

In the list of items from the Amazon search results there were many commercial audio isolators. One or two of those (they're almost all for stereo lines) will work if wired for mono operation. Although they cost more than building an isolator from discrete components many might prefer those.

Further down the list there was a fully populated PCB with transformers (for stereo). Since it would save me the trouble of soldering small parts I decided that for $11 it was worth taking a chance. When it eventually it arrived from China I installed it in my enclosure with the connectors.

All the connectors are stereo, as they typically must be for the PC and rig jacks. I bridged the two channels on all the jacks for mono operation. Thus one side of the isolator is for receive and the other for transmit. Grounds on each side of the PCB are common so one side is for the PC and the other for the rig. Otherwise the unit is symmetric and there is no need to differentiate which side is which. The wires support the board inside the enclosure.

Initial tests with the front headphone jack were promising other than signal attenuation. The 8 Ω impedance is likely a poor match for a transformer designed for high impedance circuits. Signal levels were good with the FTdx5000's high impedance back panel jacks. PC sound cards are even higher impedance, typically 47 kΩ. Frequency response appeared to be reasonably flat from 100 Hz to 3000 Hz. I did not test the unit beyond that range.

One point worth noting is that the isolator is DC coupled. That is, there are no capacitors in series with the 4 transformer windings. Sound card microphone ports have a permanent or software configurable DC bias for electret mics. Depending on the transformer this may pose a problem. These miniature transformers typically have a DC resistance in the range of 100 to 200 Ω. It is unlikely that more than 10 ma of DC will flow due to the electret mic bias and that is unlikely to be a problem. I recommend checking the winding resistances to be sure.

I made a 2" (5 cm) cable from twisted Cat5 wire pair to temporarily connect isolator to the phono jack on the rig. The other jack was wired with a commercial 3.5 mm stereo cable. I plan to make short shielded cables for both rig ports to keep the installation tidy and hum free. Short cables are better than long ones.

FT8 testing was successful. Levels were good and there was no evidence of hum on transmit. There is still hum was on receive when I operate the rotator brake, but it is much weaker than before. It may be due to the short unshielded cable or the plastic enclosure.

With that job done I declared the problem solved. Some cleaning up is required and I will do that in the not too distant future. It is unlikely that I'll use FT8 until the winter 160 meter season. 

Many modern rigs reduce the cable count by combining CAT, audio and other functions on a single USB cable. That reduces the opportunity for noise and hum to sneak into the audio paths. I hope that will be the case when I eventually upgrade the shack equipment, and I can set aside the isolator. If the problem source is the PC that may not work. On the other hand, since PCs age faster than rigs it is probable that by then I'll have a new computer running the shack.

Finally, I strongly recommend that you monitor your RF or ask a friend to do so. Use the buddy system to help each other to keep your signals clean. Most hams are too shy or polite to tell you, so don't rely on unsolicited reports. Not only that, even if you are don't know I can guarantee that most hams in the vicinity know that your signal is dirty. They are likely miffed and silently cursing you for your negligence. Should someone reach out with a negative report, thank them and move quickly to confirm and correct the problem.

Monday, August 16, 2021

Return to the Flea Market

During the pandemic almost all hamfests and flea markets were cancelled. Recently we've seen a gradual return to normalcy. This past weekend I attended my very first flea market since 2019. That it was a 75 km drive did not deter me. It is a small local event hosted in the village of Mayberly by the Lanark North Leeds ARES.

The only reason I've been in that area before was while driving through to go elsewhere or to enjoy cycling the back roads with groups of friends in years past. It's beautiful country but off the beaten track.

I doubt there were more than 50 hams present and the vendors numbered no more than 15. It was done open air, from car trunks and tables at the back of the sod parking area of the local community centre. The weather was perfect for it.

The picture shows the sum total of my purchases. A few connectors and a handful of Bourns multi-turn 10 kΩ linear pots that I use for prop pitch motor direction indicators. The prices were good although they hardly justified burning 150 km of fuel. I did better earlier this month while dumpster diving at a tower service company. I scored numerous LDF4 and LDF5 Heliax connectors and short lengths of Heliax and LMR400. And it was free.

The most important reason for the drive was not the flea market: it was to see people again. That was by far the most enjoyable part of the trip. Bumping into friends I hadn't seen for a couple of years was great. There were good conversations with a couple of fellow contesters who also made the drive. 

With everyone wearing masks I was slow to recognize some people that I knew well. One fellow contester was unrecognizable with his large mask, glasses and a baseball cap pulled low over his forehead. I was only able to identify him by his voice. 

Since larger events in the region have already been cancelled I may not get another opportunity to meet up with many hams until 2022. It is unlikely that I'll be inviting anyone to my station to participate in a multi-op this fall or winter, or that they'd be willing if I did. Caution reigns for the time being.

Wednesday, August 11, 2021

6 Meter E Season Wrap-up for 2021

For all practical purposes my 6 meter sporadic E season is over. Yes, there will be more openings from time to time. However, the likelihood of DX is low, and that is my primary motivation. For me this is as good a time as any to look back at the season that was while memories are fresh. Look back in the blog and you'll see that I do this every year.

One important observation is that activity is higher. Interest in 6 meters is increasing and that's a good thing. There is more QRM of course but that's a fair trade off for the increased opportunities that the activity engenders. There is a lot of spectrum available that, as a community, we have yet to exploit. Digital modes, especially FT8, tend to encourage the majority to crowd into one or two SSB 3 kHz watering holes. Eventually that will have to change.

With respect to the objectives I set at the beginning of the season this has been a very successful year. I surpassed by one my DXCC stretch objective of 110 countries on 6 meter digital modes. Of these, 103 are confirmed on LOTW. I do not intend to apply for the DXCC award since awards are unimportant to me. It is enough to know that I've done it.

Since early May my log has accumulated around 1000 DX contacts. The station improvements I made earlier this year have paid dividends.

Two of my close 6 meter buddies also passed the 100 confirmation mark this season. We notify each other of openings and happenings throughout the E season, and cheer each other's successes and commiserate when we are not so fortunate. With pandemic restrictions removed we are planning a get together to celebrate our achievements. 


As I've said numerous times on this blog, FT8 is not a low power mode. More precisely, it is no more a low power mode than any other. For example, CW is a low power mode yet QRO is a strong advantage whether you are DXing, contesting or simply having a conversation. 

During the first major opening to Europe on May 19 my country count jumped from 90 to 96. These were countries I've heard and called in the past but could not work. With power I did. Some would prefer to keep it challenging with low power, but for my tastes this is a welcome development. Sporadic E openings are mostly brief and marginal, and I see no reason to continue struggling.

One thing I find myself doing more often is to call CQ for long periods. The reason is that with a bigger signal I have the opportunity to "open" the band. That is, those monitoring a quiet band may hear me and start transmitting. We all like to passively monitor a dead or quiet band for those elusive DX openings, waiting for the "big guns" to break through. With QRO I can now make a contribution.

Yet there are many stations that still cannot hear me. Some have mentioned on chat groups and elsewhere that the local man-made noise is strong so signals must be very strong. One Middle East station said he has to shut down at dusk because the noise of LED lighting wipes out the band. This is a global problem that will only get worse. 

QRO on my end helps to be heard by those living with the plague of noise. Since I hear very well at my quiet rural QTH many stations I can hear don't hear me. It's frustrating, though a little less so now that I can run more power. The downside is that sporadic E occurs when the weather is warm and heat from the amp can make the shack uncomfortable.

Europe and Caribbean

During the peak weeks of the season it is rare to not decode at least one station in Europe or the Caribbean. That's why I've lumped them together. The hops to these areas are geographically favourable for transitory E-layer clouds almost daily. That does not mean that there is a workable opening. These are merely "teasers" that keep hams in the shack when they could be doing something more worthwhile.

That said, there are frequent openings to these areas. Activity is high enough that if there is a reflection there will be a station at either end of the path to decode the digital message. First you hear the big guns and then you wait (or you probe with your own CQs) for the next layer of stations to appear. In the best case the opening brings in the smallest stations. I have had more than a few stations in Europe tell me that I'm their first Canada or first North America on 6 meters.

While I do love these openings my priority is working new countries. Both of these areas are filled with DXCC entities that I need on 6, but where the activity is absent or the stations are small and therefore relatively rare. So I work the openings and keep an eye on all the decodes for that elusive new one. I interrupt the pile up to call them, sometimes successfully and sometimes not. 

The rare ones can accumulate quite the pile up. HV0A moved their pile ups from 50.313 MHz to 50.303 MHz to make it more managable. Other shift to 50.323, 50.333 or elsewhere. You must pay attention to the spotting networks or QSY frequently or you'll miss when this happens. When I worked OH0Z they chose an audio frequency (DF) of less than 200 Hz. It was necessary to shift the VFO lower to get a reliable decode. Digital modes are not as simple as many imagine! There are tactics to be learned to successfully work the DX that are different than for traditional modes.

The more northerly path to Scandinavia, the Baltic countries, Ukraine and Russia opened numerous times but were so marginal that contacts were difficult most of the time. New ones on that path included OH0, ES, YL and UA.

Far East

To my surprise there were many openings to Japan this year: 6 that I can recall. Some were so feeble that few stations could be worked. One remarkable case was discovered by accident. Around 2330Z one evening -- an hour later than the typical peak for a JA opening -- I checked PSK Reporter while I was working the Caribbean. I had a flag in JA8 (Hokkaido), off the back of the beam. 

I turned the yagi, half convinced it was a mistake of some kind, heard nothing and called CQ. I was immediately answered by JA8EPO. After our QSO we both CQ'd for quite some time and worked nothing. I gathered several flags in JA8 over the next 20 minutes but heard and worked no more stations. No one else nearby appeared to hear anything at all. That was quite the spotlight opening.

The path to the far east was otherwise disappointing. I heard one HL briefly, and that was it. The only success on that path was finally working KL7HBK for a new one on digital. I heard several more Alaskans that were not coming in for long enough to work. Stations to the south and west had more success, working BA, BV, HL and DU. Maybe next year.

Middle East and Central Asia

I had success though not as much as I had expected. Two 4X stations were worked and then I had a drought. There were many openings into the Arabian peninsula, with many enticing new countries, yet little resulted. While calling an A7 station I was called by two in 9K. That was nice but the others went unworked. Heard and not worked countries included: TA, OD, A7, 7Z, A9. 

As mentioned earlier, it could have been noise on their end. Others had similar difficulty getting through. Another problem is that we have to penetrate the European "wall" on this tenuous path and there is no good way to know whether our chosen frequency is clear. Calling on their frequency, which ought to have been fairly clear of QRM, was also unsuccessful. Of course there may have been other callers on that frequency, and due to the peculiarities of sporadic E propagation I wouldn't hear them. 

Those a short distance to the east in W1 had far better luck, as did those in VE1/VO1/VY2. The same goes for the openings to central Asia. Others were heard working UN and EY, which were not heard here at all. Last year I did hear a few of these stations but it was impossible to be heard without an amp. Hopefully my luck will improve next year.

Pacific and West Coast

There were numerous openings to W6/W7/VE7 this year. A handful were remarkable. One was so good that I heard many new stations. In an email, a California station told me he uses an indoor antenna and it is difficult for him to work my side of the continent. Portable operation from several rare grids were there for the taking for those on the hunt for grids. I worked a few of them despite that not being my interest.

Going further to the west, I worked two more stations in Hawaii. During one opening, NH6Y was heard for almost 30 minutes. That's impressive. Unfortunately most of the Pacific is devoid of land and hams so the propagation goes to waste. One exciting event was several in the northeast copying a ZL near 00Z one evening. I was on the great circle route aligned with those stations so I listened and CQ'd for some time. Unfortunately I heard nothing and I raised no flags far away. It would be a stunning achievement and you can be sure I'll try again next year.


The main difficulty working continental Africa is the low activity level. There are few hams and even fewer are active on 6 meters. Digital helps since it encourages more to make the attempt. Even if there were more activity it would be difficult to reach beyond northwest and west-central Africa with sporadic E. East, central and south Africa are particularly challenging. I have yet to hear any of those stations during my most recent years of activity. Yet I keep listening.

A few stations are well equipped and within reach. Good examples this year are TZ4AM in Mali and 5T5PA in Mauritania. Of these I've only worked the latter since Jeff TZ4AM has a high noise level and I have yet to catch him when signal levels are sufficiently strong. It is admirable that he keeps trying and many in North America got lucky this year. 

Other Africans I notched up this year include XT and 7X. These were difficult because they do not have big stations. I did not hear TT8SN this year, which is unfortunate since my uncertain QSO with him in 2020 did not make it into his log. I regrettably erased TT from my worked list. 6W1TA was worked again this year, while 9G5FI remained out of reach. 

With more activity I am sure I will put more Africans in my log next year. Other than hoping for exceptional openings there is little I can do until the current solar cycle peaks.

South America

Working the north coast of South America is becoming routine. There are a few well equipped stations in north Brazil (PV8) that are also frequently heard, and occasionally a few in HC and ZP. Crossing the equator to the countries further south is far more difficult. Sporadic E is not enough to reach the far south. Concurrent TEP is needed to complete the path. Conversely, this is a relatively easy path via the F-layer during solar maxima.

I heard one LU last year who could not hear my 150 watts. This year there was one great opening to LU and I worked 3 stations, including LU5FF on FT4. I'm glad he changed modes since FT4 is much faster and more stations can be worked during these brief opening. Yet few others do the same. I get few takers when I CQ on FT4 during strong openings.

In that opening and another, CE and CX stations were heard and worked by those not too far away from me. Unfortunately I copied none of them. These are two more countries to try for next year.

The wanderer

It is not only more hams that are showing up on 6 meters. As more and fancier digital technology invades our communities there are more noise sources. I am occasionally affected even though my closest neighbour is 250 meters from my 6 meter antenna.

The latest invader is sometimes called "the wanderer". It is showing up in numerous places. The signal takes the form of a carrier, either alone or with weaker companions, that wanders up and down the band in the vicinity of the digital watering holes above 50.3 MHz. An example spectrogram is shown to the right.

In my case it peaks to the northeast. This is odd since the distance to my nearest neighbour in that direction is 1.5 km. Others see the wanderer far stronger, including some VHFers that I know in the Toronto area. It hasn't affected my operating, yet, although others have been less fortunate. I am sure the responsible devices are known, just not by me.

There are other noises on the band that I can identify. One is my own heat pump that radiates a weak though narrow signal when it is in air conditioner mode. It is not causing me any difficulty so I'll let it be.

Signal quality

There are many hams who have no idea how to adjust their rigs and PCs for digital modes. The result is a lot of heavily distorted signals that cause grief to everyone. The worst offenders are not the newer hams. These more experienced hams ought to know better. We all make mistakes but some persist in their bad behaviour despite having been informed by their neighbours. 

I don't expect any improvement until there is a new generation of equipment that does not rely on the SSB mode of current generation rigs. There are too many ways to mess up our digital transmissions so that even the most careful of hams will run into problems. 

Below is an example of third audio harmonic distortion that may be due to over-driving the transmitter or amp, or forgetting to turn off the SSB compressor. Most distortion case are unintentional so they may need nothing more than a gentle reminder from someone they know. They may be remain unaware of the problem if others are too shy to tell them.

When a ham informed me of a signal quality problem this year I went to work on it immediately. Although the root cause remains elusive I was able to find a workaround to clean up my signal. I'll have more to say about this in a future article since it could prove useful to other digital operators. I am awaiting a few parts to make the solution permanent.

Remote confusion

Numerous 6 meter enthusiasts in locations less favourable for select DX paths are opting to operate remote. I see just the US side of this phenomenon, and I know it is also done elsewhere. The motivation is to improve results for DXCC, VUCC and other awards, or to simply have some fun. With many commercial "for rent" stations in the northeast US they are routinely heard here. 

The rules for DXCC credit remote operation from within the same country. Like Canada, the US is a large country, and with 6 meter propagation being what it is there is a strong temptation to take advantage of remotes thousands of kilometers away. It is not unusual to hear US 6th district call signs sporting W1 and W2 grid squares during openings to Europe, Africa and further afield.

None of this bothers me. I don't often bother working the US and Canada on 6 meters so it is easy to ignore. Besides, with US call sign regulations it is common to hear mismatched grids and call signs. However, there are some that are less observant of the regulations. A few Europeans have been heard on these remotes using their home grid squares and not signing portable. I can only shake my head at this absurd behaviour. A stable and strong signal with an east European call sign on 6 meters is suspicious when other signals from that area are weak or absent.

I know that the commercial station owners tend to take a dim view of this use of their facilities. How well they police their customers is unknown to me. I am not really affected other than to shake my head at the absence of operating ethics of a (hopefully) small number of hams.

Wrap up

I was so focussed on 6 meters that, on reviewing my log, I found that I made only 4 QSOs on HF in July. That is, other than 800 during the IARU contest. My HF activity continues to be low in August, so far, while I am busy with antenna construction and non-ham summer pursuits. That will change. It takes time for me to switch gears and get back into the HF mindset.

I continue to monitor the spotting nets for signs of 6 meter activity despite my absence from the band. Anything can happen at any time of year. I am not terribly interested in meteor work, such as the ongoing Perseids meteor shower, since it does not mesh well with my DX ambitions. Who knows, perhaps I'll try EME one day.

Overall, my 2021 season was a good one. I had fun and it kept me active during the months when my attention would otherwise wander to other things. Soon I will begin to consider my plan for the 2022 sporadic E season. From here on the difficulty of working new countries will increase quite a lot. Either I will have to get lucky or countries less distant will have to be active. There are quite a few in the Caribbean I have yet to work. I anticipate no changes to my 6 meter capabilities in 2022.

The coming winter E season is less compelling since my geomagnetic latitude is not favourable to generate DXing opportunities. Unlike last winter I will have my 6 meter antenna connected, so we'll see.

Wednesday, August 4, 2021

Skewed Vertical Arrays

Not long after my article on arbitrarily spaced driven verticals a reader posed an interesting question, one that was only briefly touched on in the article: can the array be steered by adjusting the element phases? The actual question wasn't exactly that so I am paraphrasing based on our exchange. Unfortunately the answer is no, not really.

With 2 elements in a driven array you can steer pattern nulls but not the main lobes. To steer a null you adjust the phasing so that at a selected direction (azimuth and elevation) the phase difference is 180°. In the general case there will be more than one null, but no more than two for the optimum spacing of ¼λ. This can be useful for attenuating local noise sources, but it is not useful for a transmit antenna.

With 3 or more elements there are improved steering options. The design can be complex since power splitting and phasing must be adjusted for all the elements, and the vertical elements cannot be collinear (in a line). Examples include triangle arrays and 4-squares. General steering isn't worthwhile since the patterns are broad enough that several fixed, switchable directions are sufficient.

Since there are ample designs and commercial product for 4-squares and other multi-element driven vertical arrays, I will focus this article on steering of 2-element end-fire driven arrays and 3-element reversible vertical yagis. 

The steering will be done by skewing the elements hung from a common catenary (rope) between non-conductive or non-resonant supports. The supports are thus excluded from the models. Skewing can be useful when the positions of the supports do not allow the catenary to be run in the desired direction. That is, we have a means to put arbitrarily positioned supports to good use.

I previously showed how to skew a horizontal wire yagi for the same catenary challenge. The design ideas in this article can be seen as complementary to that one. The examples are for 160 meters since the low bands are where these designs are likely to be attempted. It is easy to scale these antennas to other bands.

Modest skewing

I adapted this antenna from a 2-element 160 meter end-fire with optimal ¼λ element spacing and 90° phase shift. The base of each element has an orthogonal offset of 10 meters so that the angle to the catenary of the line connecting the element bases is about 26°.

For convenience, the model was done with perfect ground. This is acceptable since the pattern skew is not affected by ground quality. For a real antenna the elevation angle for optimum F/B is dependent on ground quality and element phasing.

The skew of the azimuth pattern is 20°. This is close to the value of the physical skew of the element bases. That's a good result. The bases are separated by 0.28λ because of how the skew was achieved. Despite that change the phase shift to preserve the F/B performance remains at 90°. As mentioned above, for real ground the phase shift should be adjusted to optimize F/B at a more realistic elevation angle.

Greater skewing

As you increase the skew angle the array performance deteriorates. Even so, you can push quite far and get a good result. In the example below the bases of the 2-element end-fire are skewed 45°. Unlike the previous example, the bases are rotated on a virtual circle so that they retain their ¼λ separation. The apex of the elements is lower due to the tilt.

Pattern skew is, again, almost the same as the physical skew: 40°. The phase shift was increased to 130° to get the best F/B. F/B is better with a smaller skew. 

I included the elevation plot since there is a significant change. The horizontally polarized radiation due to the greater element tilt fills the pattern at high angles. Depending on your operating interests this can be good or bad. For a DXer the high angle radiation is not useful in most cases. For a contester it can be beneficial to work closer stations.

Vertical yagi skew

For this antenna I took an existing 160 meter model with 3 wire elements and shifted the base positions of the director and reflector by 15 meters orthogonal to the catenary. Element spacing is equal (30 meters) since the antenna was designed to be reversible. As with the first end-fire the angle to the catenary of the line connecting the element bases is 26°.

Pattern skew of 20° is only slightly less than the base skew. That's better than what I achieved with the skewed horizontal yagi referenced earlier. It is interesting that the pattern skew is the same for the 2-element end-fire that also has a 26° physical skew.

Adjustment of the elements to optimize for the new configuration is recommended to get the best from this antenna. I skipped that step since it does not affect the skew angle.

Geometry of skewing

The reason why a skewed vertical array works is that the field strength of an antenna (or antenna element) is in proportion to the current. Since the current on a ¼λ vertical is greatest at the base and the height of the average current is low, the virtual position of the vertical is not far inboard of the base. Thus the pattern skew is only a little less than the physical skew angle.

While the horizontal polarization is increased with element tilt the impact is modest for low tilt angles. As discussed above this can be bring an operating advantage for some and an annoyance for others. Extreme skew is not recommended. It is possible to compensate by raising the catenary height and tying the tops of the wire elements to the catenary with ropes. But if the catenary must be lower the tilt and horizontally polarization radiation are increased and the elements will likely need to be loaded in some fashion.

The direction of the element base offset only slightly affects performance of a driven array since the elements are far enough apart that the mutual impedance is low. However, element phasing must be changed to accommodate the geometry. That is why keeping the element bases at the ideal separation for an end-fire by skewing them on a virtual circle is not critical. Yagis are different and the adjustment for large skews will require model experimentation.

Element tilt and spacing has an impact on the feed point impedance. Modelling is helpful but you should measure the impedance after building one of these arrays. Design the matching network for the measured impedance.

Ideas, not designs

Details for the models in this article are deliberately avoided. I have not delved deep into these skewed vertical arrays and I am reluctant to provide detail that might be read as recommendations. The ideas presented in this article are just that: ideas. Should you wish to further explore these antennas, I suggest that you model alternatives and choose ones that suits your operating objectives and circumstances.

A few ideas for more interesting skew verticals that come to mind include:

  • Pair of skewed end-fire arrays for 4 switchable directions
  • 4-square with skewed vertical wires
  • 3-element skewed vertical yagi, with 5 elements for 4 switchable directions

I have no intention of building a skewed vertical array so I have no real life experience to share. I can achieve my most urgent needs on 160 meters by shunt-feeding and driving both of my big towers.