Side Mount for a Limited Rotation Yagi

For the past few years I have had a Hy-Gain TH6 side mounted at ~72' (22 m) on the 150' tower, fixed south to W4/W5, the Caribbean, Central and South America. It has been used as a multiplier antenna in contests, and it has proven to be very useful in the intended application. That said, having it fixed is less than ideal. I would to use it to cover more of North America to earn more contest points working the US when my bigger antennas are pointed to more distant DX locales.

I have written previously about different methods of side mounting yagis on towers for partial compass coverage. This year I decided to do it for the TH6. A rotation of a little more than 120° allows coverage from 150° (Brazil) to 285° (VE7). That's perfect for my purposes.

I have more to say about the TH6 that will be deferred to a future article. It had to come down for reasons other than the new side mount system: to permanently repair a wire bond that could not be done on the tower, and to flip the boom to mast clamp since the rotatable side mount is on the opposite side of the tower from the fixed side mount bracket.

It is amusing to note that the antenna and rotator were manufactured not long after I was licensed almost 50 years ago. I acquired them secondhand in 1985 when I bought a house and could put up a tower after moving Ottawa as a young man several years earlier. Both went into storage when the tower came down in 1992, where they remained for over 20 years. 

The rotator, a CDE Ham-M, was refurbished and used when I returned to the hobby and put up a tower and tri-bander in 2014. In 2016 they went back into storage.

Looking around at my stock of metal and hardware I formulated a plan. I have a large stock of scavenged material that tends to find its way into projects or gets passed on to others. Nothing needed to be purchased for this project other than a few bolts. 

The tasks to be accomplished included:

• Take down the TH6 and its side mount fixture for service
• Service the rotator
• Select a mounting geometry that would achieve the desired rotation and not interfere with climbing and the numerous cables affixed to the tower
• Build a side mount system that is sturdy, servicable and meets the objectives
• Design the cabling system (about 230' long) to use the minimum amount of new cable and provide adequate current capacity
• Raise the refurbished TH6 and test the system

Getting the TH6 down was straight-forward. For simplicity I used my lawn tractor as the tram line anchor. You back up until the rope is taut, then block the wheels. I can do this for antennas up to around 70 lb, and more if the slope of the tram is low. For heavier antennas and the requisite greater tram line tension, the wheels lift off the ground. Lawn tractors aren't very heavy.

There is some difficulty rigging the antenna for proper balance since, unlike going up, you really only get one chance. The TH6 was a little unbalanced and a couple of tubing clamps snagged a guy. Jiggling was enough to free the snags. The entire job was quickly done with the help of just one friend as the ground crew. Less muscle is needed to tram antennas down, and is further helped by the shallow slope (under 25°) of the 200' long tram line and a height of 75'.

The new side mount went up the same day that the TH6 and the old fixed side mount bracket came down. It had been fabricated over the previous weeks in my workshop where I have a spare tower section to use as a jig. At 10' tall the tower section rests against a roof rafter. I use a step ladder to comfortably work at the top of it.

Laying the tower section horizontally makes it easier to for work on it in some respects. The negatives are that floor clearance is needed for tower projections, visualization is more difficult and levelling and supports can behave unexpectedly. Keeping it vertical help with visualization, and levelling and alignment are the same as when it is on the tower. I shim the wood plate under the tower section to make it level and vertical. Garage floors are sloped for drainage.

On the left is the basic structure. The angle aluminum (⅜" × 3") attaches to the tower girt with two grade 5 ½" bolts. Although A325 hardware is a better choice, the shear force in this application is well within the rating of bolt, nut and tower girt. Large fender washers provide a larger bearing surface for the bolt heads, which helps to reduce point stress on the tower girt and aluminum arm. The aluminum angle was cut to a length that is long enough to mount the rotator, and not too long for excess bending stress due to the weight of antenna, rotator and mast balanced at the end of the arm. 

Not seen in this picture is a vertical support cable for the arm, running from next to the rotator to a tower strut. You can see it below after it was installed on the tower. The cable reduces stress and the turnbuckle allows for exact levelling of the system when it is under full load. Even without the cable the support easily handles my weight when I stand where the rotator is located.

That 3" width of the aluminum angle is a tight fit for the Ham-M bolt pattern so I attached a short length of steel angle to the aluminum. The rotator is centred on the joint between the two to keep it in line with the tower face. Levels were used to keep everything aligned. On the right a pipe (mast) goes from the rotator through the upper support arm affixed to the next higher girt. Detail can be seen in the picture below.

The multitude of holes in the aluminum angle were already there. There are a couple of holes directly under the rotator that are used to fish the 8-wire cable to a terminal strip on the angle, where it is partly sheltered from the weather. The aluminum angle was rescued from a dumpster for free. I had no particular project in mind when I claimed it, but I was sure that it would find a use. There is more in my stock for future projects.

The support girt is at the 75' level, which is 5' above the second set of guys. The upper support arm is at 80'. These are nominal figures that ignore tower section overlap, and the actual values are closer to 72' (22 m) and 75' (23 m). This is a good height to minimize guy interactions and to match the elevation angles needed for the intended coverage area.

On the left you see the support cable and the level used to adjust the turnbuckle. It has to be tightened a tad when the antenna is mounted. The rotator cable and terminal strip are visible below the level.

The steel angle arm supports a mast bushing. A bearing is not really necessary for horizontal wind thrust when there is no vertical force. Also, a bushing is cheap to fabricate. For the 1.9" diameter of the mast the bushing is a short length of 2" schedule 80 aluminum pipe with an ID of 1.939". The fit is so close that the bushing must be carefully aligned. A burr present on the mast had to be filed flush to the pipe surface so that it would slide through the bushing. The mast diameter is probably closer to 1.91" due to the galvanizing for an even closer fit. 

Time will tell how the bushing wears in service; it is aluminum so that it will wear rather then the steel mast. The bushing is easy to replace if necessary.

The thrust arm is steel angle (⅛" × 1-½"). It pivots on the rear bolt to the girt for one degree of adjustment (there are 2 bolt holes on girt that can be selected) and another degree of adjustment is made by moving the nuts on the ⅜" threaded rod between the arm a short and heavy steel angle bolted to the girt face (not shown). The adjustment range was tested on the jig and determined to be sufficient.

Once everything is tightened the arm is very stiff. It will be periodically inspected it to check that it doesn't shift. I will add lock washers and other hardware if the need arises.

Hy-Gain rotator clamps are not very adjustable and a mast has to be about 2.1" diameter to be properly centred. The 1.9" OD pipe can be shimmed to meet that spec. I don't see the need since the distance to the bushing is far enough and the restricted rotation angle small enough that mast misalignment is unlikely to cause binding at the bushing.

After the TH6 was repaired it was trammed to the new side mount. The picture contains several items worth noting. First, notice that the mast clamp is low on the mast, close to the rotator. Although the bushing prevents bending stress on the rotator, an extreme wind can "bow" the mast. That increases bending stress and it is maximum at the midpoint of the mast. It's not a major concern but why take chances. A second benefit is that a shorter mast can be used to secure the boom truss. In this case the mast clamp for the boom truss is just below the bushing.

For a swing arm you must use thrust bearings above and below the swing arm for support and to protect the rotator. In my side mount article the diagram I drew of the swing arm is incorrect; I know better but the mistake crept in anyway.

Geometry and utilization of the tower faces dictated that the side mount would be placed on the tower's one climbing face. One of the other faces is dedicated to cables, which excluded it from consideration, and the other face was not ideal for the desired compass coverage and there is the risk of the antenna boom striking the cables. Putting it on the climbing face raised the problem of having to climb over the wide aluminum strut (see above). In practice the 3" projection from the tower face turned out not to be a problem. Not only do I not accidentally bump into it, it is comfortable to stand on when I'm working at that level.

The pulley for the haul rope is suspended directly above the mast with an arm attached to the tower. Depending on the geometry of the tram line this may be necessary to ensure the mast clamp aligns with the mast when the tram line is slacked. It is easier to bolt together the clamp halves without having to use muscle to align them to insert and secure the long bolts. Alternatively, have a friend join you on the tower. Yagi wrestling isn't fun.

The longer the side mount the further the rotator is offset from the tower. This can be tempting since you can eke a few more degrees of rotation. With my mount I have approximately 135° of rotation available. Placing the boom on the outside of the mast adds another couple of degrees. However, go too far with most antennas there will be a problem: the elements on either side of the mast can strike the tower. That's a bad idea.

Rubber cushions will be put on the boom so that it softly strikes the tower at the rotation limits. The Hy-Gain rotators have too little torque to do any damage and the motor will halt when contact is made.

Side mount rotation, whether a fixed mast or a larger-rotation swing arm, requires an antenna with elements spaced far enough from the centre so that it is the boom and not the elements that limit rotation. Smaller yagis and those for higher frequencies are more problematic. 

The Hy-Gain Explorer 14 that I recently sold is not compatible with a side mount because the driven element is close to the mast (boom centre). The TH6 has adequate space for this system (see diagram, above, copied from the TH6 manual). I opted to use the TH6 rather than the TH7 because there is inadequate space between the two driven elements of the newer antenna. The mono-band yagis I built for 10, 15 and 20 meters are compatible with rotatable side mounts, should I choose to do that in the future.

In addition to mechanical clearance there is electrical interaction of the innermost elements and the tower as they come into proximity during rotation. In most cases it is minor, and when it's the driven element the effect is mostly on the feed point impedance (SWR) and not the antenna pattern. The benefits of rotation typically far outweigh the negatives of pattern distortion. I ran several models to judge the potential magnitude of the interaction for the side mount article, and I reported my general findings. Exact determination of pattern distortion is difficult to do in a software model.

In a future article I'll say a little more about the side mount rotator and rotation. As of this writing the rotator is not wired back to the shack. Indeed, the TH6 is oriented so that the tram can remain in place to lift and adjust the 10 meter yagis that are now built. I should have everything working by early October.

Fighting Flora and Fauna

This is not the first time I've written about my troubles with wildlife. While a rural QTH is great for antenna farms, the majority of animals are not accustomed to seeing or dealing with humans. Unlike they behaviour changes they exhibit in and near urban areas, they proceed as if in the wild. 

They come close and satisfy their curiosity by chewing or walking on cables, dig in the loose soil of recent excavations and make their homes in shelters built for antenna and cable switches and junctions, and inside tubes and pipes. Deer and their predators follow the trails I make through the foliage and snow. The predators are intelligent enough to respect humans, and their firearms, and keep their distance.

Dealing with animals, vegetation and insects is an unavoidable part of regular station maintenance. Sometimes it is damage I must prevent or repair, and other times nature must be tackled in pursuit of my antenna farm projects. Read on for my latest adventures.

Many insects like dark enclosed spaces in which to build their nests and to store food and eggs over the winter. To their delight, all of my outdoors enclosures for matching networks, switching and cable junctions have weep holes to allow moisture (rain or condensation) to exit. It seems that no matter how small I make the holes there is an insect that is smaller yet. I can't make the holes too small or the surface tension of water will prevent drainage.

Even so, when I built the Beverage antenna remote switch early in 2020 (see article for pics) I made the weep holes smaller than usual and the hole for the Cat5 control cable a snug fit. In early summer the switch exhibited intermittent short behaviour (excess current to the relay coils). A few weeks later when the hay was harvested and I could safely access the switch.

As I slid the cover off after removing the screws an enormous number of ants came scurrying out. They crawled around the enclosure, over my hands and up my arms, with most jumping off when they realized they were on an animal (me). In the 30 seconds or so that it took me to pull my phone out and take a picture only about half the ants were left inside.

You can see the cocoons under the ant mass. These had to be scraped off after the the ants were cleaned out. The funny thing is that the ants were not responsible for the switch failure. After bench testing in my workshop the likely culprit is a secondary lightning strike. Long Beverage wires are notorious for building up large induced voltages from nearby strikes, and in this case the integrated suppression diodes in the relays had failed. 

Unfortunately, as I discovered in a similar case, the diodes fail to a low resistance value (not a complete short) when their PIV rating is exceeded. I was further irritated that the specs for these Littlefuse reed relays do not state the PIV rating of the suppressor diodes. I didn't notice that when I selected them. For the interim I have more of these in my stock so I will be installing them shortly, in time for the fall 160 meter season. I would like to replace them with relays that use my choice of suppressor diodes.

Despite the diagnosis the ants are not innocent. They brought a lot of moisture into the small enclosure that left its mark. Notice that all the bare copper wires are heavily corroded (green). Tinned wire and hardware is unaffected. When I rebuild the switch the bare copper will be replaced by tinned wire. Wire that than cannot be easily replaced (e.g. transformer windings) will be coated to inhibit corrosion.

It is interesting that one of the two styles of coax jacks corroded (on the left) and the other did not. Application of dielectric grease to the threads should inhibit further deterioration.

The ants were a surprise since it's earwigs I typically have to deal with. Earwigs will climb at least several feet to find a nice comfortable hole to lay their eggs in late summer. At last count there are 6 enclosures with earwig infestations (including every one in the 80 meter vertical yagi). I am not yet able to reach the Beverage antennas which each have two enclosures (head end and reflection transformer) to be inspected.

The picture shows the 80 meter yagi switch box with the largest earwig infestation. It is the one at the base of the southwest parasitic element. All the covers were removed and the units left open for a few days until the eggs dried and could be cleaned out. Try it when they're fresh and you will only smear the black goo everywhere. 

A bit of rainwater while they're uncovered won't damage the relays and coil. Neither will a water rinse. Sealed relays can put up with a lot of environmental abuse.

Before winter I plan to deer-proof the cables and support ropes in the 80 meter yagi. They do like to chew things, much to my surprise. In my station they are far worse than rodents. Squirrels, mice and their kin have molested none of the on-ground cables. Sometimes a chipmunk will dig a home along a trench line but they have not damaged anything. Perhaps they favour recently disturbed soil.

In the picture above you may be wondering what the problem might be. It is an after picture, once the problem was resolved. When I put up my first big tower in 2017 the ideal location for one of the guy anchors was behind a short spruce tree. It was not really in the way so I ignored it. Little trees grow into big trees and that's when the trouble begins. 

First it gobbled up the lowest guy. I trimmed branches to avoid contact with the guy. The tree continued to grow and soon gobbled up the second guy and was well on its way to the third. I like trees so I avoid cutting them down when possible, especially an attractive tree in a pleasant setting like this one. 

My patience was exhausted when climbing vines that infest trees grew over the guys. Vegetation in contact with steel, including galvanized steel, promotes rust. With the help of a friend the tree was dispatched and roots cut out below ground. They guys are now free and ground levelled where the tree once stood.

There is a ham I know (call withheld to protect the guilty party) who installed a guy anchor near a seedling many years ago. The tree grew and grew until the anchor and equalizer plate were embedded in the trunk of the now large tree. Neither the tree nor the anchor seemed to suffer from the experience, or at least not yet. I would have loved to take a picture but did not to avoid offending the ham in question. It would have made a great picture, and an instructive one.

Speaking of anchors and trees, there is one last item that is a little different. In this case the tree in question is very much wanted.

A few years ago I opened a path in the bush at the east end of the hay field to use a tree as an anchor for tramming yagis up and down the 150' tower. This worked well. I want to do the same this fall when I decommission the TH7 and bring down the experimental 40 meter yagi element. 

If the latter passes inspection for its mechanical soundness it will become the driven element of a 3-element 40 meter yagi. That project is proceeding and if all goes well it will be built and raised to 150' later this fall. The yagi will weight close to 300 lb (135 kg) and will require a tram line that is equal to the challenge.

There is a large and healthy tree deeper in the bush that appears to be ideal. Equally important is that it is directly opposite the guy anchor discussed earlier. The guy anchor, which has a spare eyelet for this purpose, will hold a back stay cable to the mast to balance the large force of the tram line tension and the yagi's weight.

Clearing of the bush to access the tree and make a path for the skyward pointing tram line is ongoing. The above picture shows the current progress. The tree itself is hidden in shade at the centre of the frame. I'll have more to say about it when it is ready. As a trial run the tree will be used as an anchor to lower the TH7 and 40 meter yagi.

I'll close on a more amusing note. Wild turkeys are common in the area. They roam the lawns and harvested fields almost daily this time of year. They step around guys and over radials and, so far, have done no damage. I leave them alone.

The big birds are shy and run (or fly) when they see me. This one was taken through the window. One day earlier this year there were more than 20 of them in the driveway.

Correcting the Mismatch of the Upper 20 Meter Yagi

To summarize a long story, after the upper 5-element 20 meter yagi of the stack was raised I discovered that the gamma match had somehow slipped out of adjustment after being tuned. This probably happened while weatherproofing the gamma capacitor. Since the antenna is very large and heavy I decided to correct the mismatch and not to take the antenna down for repair. Taking the antenna down, adjusting it and raising it again would take 3 full days with the help of several friends. Correction is the easier and safer alternative.

I developed models to determine the effect of a matching network. A simple L-network is all that is required, and it can be made very efficient. For convenience my plan was to mount the network at the stack switch. Since the network and the gamma mismatch both shift the phase of the upper yagi it is also necessary to bring the yagis back into phase. The existing phasing lines assume that the yagis are identical, per the design of the antennas and stack.

Although the problem I am solving is specifically for my antenna system, the techniques and tools are applicable to other antenna challenges. Since these may be of use to readers, it is worthwhile to describe the resolution in depth.

Danger of calculation versus measurement

I keep so busy with my many projects that I don't always remember what I've done and my notes may be missing or difficult to understand. I had a set of impedance values across the band for the upper yagi in my notes and I assumed they were measurements. It turned out that they were calculated for the length of the phasing line to the stack switch based on measurements at the coax joint on the boom where it connects to the rotation loop.

The impedance is determined by the electrical length of the transmission line. The phasing harness lengths were calculated from the physical lengths and the VF (velocity factor) of the coax. For the upper yagi that includes 11' of RG213 (rotation loop) and 30' of LMR400 (tower run). This is approximately equivalent to 44' of LMR400. The total length is 66' including the 22' length of LMR400 from the feed point to the tower.

Physical lengths are easy to measure and mine were done with great accuracy. Unfortunately the published VF of coax is not always exact for a variety of reasons. When the phasing harness segments are from the same coax reel the VF is usually equal. In other cases, the VF can differ and the yagis will not be properly phased.

Under the misconception that the recorded values were measurements I used TLW to design the L-network. It turned out to be a degenerate case where the network reduced to a single component: a series inductor. 

I dutifully built it (see above) and tested it with an analyzer (at right). The box must be closed since the inductance is reduced by the aluminum enclosure. To compensate, the coil is designed with a higher inductance. The required 31 μH of series inductance is what I got after adjusting the coil turns.

I discovered my mistake at 110'. Thoroughly confused and out of time that day I descended the tower.

Measurements

Several days later I went back up the tower with an antenna analyzer to measure the upper yagi impedance at the stack switch. It was a windy day so I had to visually integrate the readings as the elements wiggled and waggled above me. A few ohms either way is not a serious issue since the L-network can be fine tuned once it is installed.

Taking care not to lose the piece of paper with the numbers in the brisk wind I came down and ran them through TLW. With a bit of experimentation the measurements and calculations matched for a 40.5' physical length of LMR400. That's an error of 8%! This implies a VF of 0.78, far less than the specified 0.85. This is so surprising that I plan to take a tape measure up the tower to recheck the lengths, despite having triple-checked them on the ground.

At right are the measurements, taken at every 50 kHz across the 20 meter band. From a cursory examination of the impedance values it might appear to be impossible for a fixed network to properly transform the SWR across the band. Appearances can be deceiving.

Accounting for frequency, one network can transform a disparate set of impedances to a fixed target impedance. That is approximately true in this case where one network restores the designed SWR curve for the 5-element yagi: about 1.5 at the 20 meter band edges and 1 in the vicinity of 14.1 MHz.

Achieving a perfect 50 Ω impedance is not possible nor is it desirable. Careful design should result in a close match to the lower yagi's SWR, and therefore equal power division and near equal SWR when switching among upper, low and both yagis in the stack. There are software tools to ease the design process. Having one antenna exactly 50 Ω across the band does not achieve either objective.

Designing and testing the L-network

An L-network consists of a capacitor and a coil, one in series and the other a shunt on either the 50 Ω or the antenna port. There are two optional configurations, usually called low pass or high pass since they also behave as filters. Its filter performance is unimportant for this application so I chose a low pass network because the calculated L and C values were easy to work with. By this I mean a low value for L (small coil and low loss) and for C close to a capacitor value and power rating in my junk box.

As for the gamma match, I designed a network to transform the impedance to 50 Ω at the same frequency, a little above 14.1 MHz. For the gamma match that gave an SWR below 1.5 across the 20 meter band. It is a little more complicated for the mismatched upper yagi. Some experimentation was required.

I used a combination of TLW and SimSmith. Using the actual impedance measurements, I designed an L-network for 14.150 MHz. I plugged the network into SimSmith and checked how it performed against the measured values across the band. The SWR curve was good but not great. For the best SWR the L-network was set to match at 14.100 MHz. The result was an SWR of 1.3 at 14 MHz and 1.7 at 14.350 MHz.

I picked a vintage 100 pf transmitting mica capacitor from my junk box for the network. These capacitors are old and require testing, but I have had good success with them. A modern transmitting ceramic doorknob is a better choice. A variable capacitor can be used but you'll need a larger box and adjustment will require extra work. It really isn't worth the trouble for this application. But if you choose to use a variable capacitor, pay attention to the voltage calculated by TLW. The variable capacitor must meet the requirement for your maximum power, plus a safety margin.

Since the capacitor measured as 102 pf versus the required 96 pf it was necessary to return to SimSmith to check the network performance across the band with the larger capacitance. The capacitance may be even higher due to stray capacitance within the enclosure.

It is no surprise that a perfect SWR of 1 cannot be achieved at the design frequency. The best I got was the depicted 1.1. That is not really a problem since it has negligible effect at the band edges where the SWR is highest. This is typical since the mismatch at the band edges is dominated by deviations of R and X from 50 and 0 Ω, respectively, of the load's complex impedance rather than the small deviation due to the capacitor being off by a few percent. With this network SimSmith calculates the SWR as 1.4 at 14 MHz and 1.8 at 14.350 MHz.

The inductor was designed with Coil by K6STI. It is 7 turns of AWG 12 bare copper wire, with a diameter of around 0.8" (2 cm) and 1.25" long (3 cm). To wind the coil I used a ½" PVC pipe that has an OD of 0.84". The calculated Q is about 350, which is quite good. TLW predicts very little power will be dissipated. I took the old coil out of the enclosure and substituted the new one. A 50 Ω load was connected to the antenna port (the same setup as was shown earlier) and measured by an antenna analyzer at 14.1 MHz. 

To adjust the coil I opened the enclosure to squeeze or spread turns. The measurement must be done with the enclosure closed since the aluminum reduces the inductance. For this reason the coil design was for an inductance of a little over 0.5 μH. Once the measured inductance was 0.46 μH the shunt capacitor was installed. It's a tight fit but that's okay; the coil and capacitor can be close, or even touch, and the only effects might be slight increases of C and L. The coil can be adjusted during final turning of the network.

For tuning the network a simulated complex load is helpful. It is not really required if you enjoy doing this work 110' up the tower! My preference is to minimize the tower work by simulating the load in my workshop. For the measured impedance of 82-j9 Ω I put a 75 Ω resistor in series with a 1000 pf capacitor. Although 75-j11 is not exact it is close enough to test and coarse tune the network.

The simulated load only permits adjustment of the network at the 14.1 MHz design frequency. You would need to build loads to simulate the impedance at other frequencies to fully bench test the network. I didn't do that since it isn't strictly necessary. If the measurements are correct the software calculations for its behaviour over the rest of the band should also be correct.

Testing of the completed network is shown at right. The SWR is a little high because the enclosure is open for the purpose of taking a picture. With the enclosure closed the SWR is 1.1, which is quite good for the inexact simulated load.

The network was further examined with SimSmith by substituting the simulated load and seeing what the measured impedance would be. The impedance measured by the analyzer was within 1 Ω for both R and X. That's less than the accuracy of the analyzer so we can't expect to do any better. 

I do have a better instrument (VNWA3) but that degree of accuracy is overkill for what this project requires.

On a final note, look above at the image from TLW. Notice the RF voltage across the shunt capacitor. It is not much higher than for a matched load at a kilowatt. The transformation ratio is small so there are no high impedance points in the network and therefore no especially high voltages.

A physically smaller capacitor than the one selected is not advised. The current is high and you want a capacitor rated for high power RF so that the loss is low and within the physical heat dissipation rating of the component. 

The low risk of flash over to the aluminum enclosure permits a tight fit, and that will come in handy during installation on the stack switch. The high power test would have to wait for installation since there is no easy way to simulate a high power complex impedance load for bench testing.

The time had come to go for a climb.

Installation of the network

Through the miracle of software and bench simulation the work on the tower was brief and successful. I plugged the coax to the upper yagi into the antenna port of the network and the analyzer to the other port. Take care because the network is not symmetrical. Label the ports if that help you to remember.

I fiddled with the coil to see if I could do better. For reasons described earlier, it was not to be. The match was near perfect at 14.1 MHz and behaved as calculated by SimSmith elsewhere across the band. It is a little high at the top end of the SSB segment, a place I only venture during popular SSB contests with heavy activity. I can live with it.

The enclosure I chose for the L-network was no accident. It fits very nicely onto the stack switch antenna port with a male UHF barrel connector without striking the connector for the other (lower) antenna port. Weatherproofing is a challenge since there is little space between the upper and lower yagi ports to wind tape. I will have to improve the temporary job before autumn's cool, wet weather.

The enclosure is oriented to allow water to leak out the bottom edges. The bottom two screws were not installed to help with that. Tape placed across the top edges limits water incursion. There are better enclosures available but I used what I had on hand, and it really is good enough. It's 110' in the air and no one will see it but me.

Back in the shack the SWR of the upper yagi was nearly identical to what I measured on the tower. Some reduction of SWR can be expected and is not unusual due to the very lengthy transmission line. The LDF5 Heliax is doing its job well. 

When in lower + upper stack mode (BIP) the parallel SWR via the stack switch L-network is even better (see picture to the right). 

I tested the completed system with a kilowatt to be sure there are no weak components or poor arc tolerance. All is well.

Phase compensation

The misadjusted gamma match and the upper yagi's matching network both exhibit a phase shift. In this case they are in the same direction so they add. A delay line for the lower yagi is required. Should I ever fix the gamma match on the upper yagi the network and delay line must be removed.

Measuring the phase of the antennas is impractical, so I rely on calculation. Unfortunately, it is easier to calculate the delay line length in software than in reality. On the other hand, forward gain is not overly sensitive to modest phase error. Where we can lose is with the size of minor forward lobes, as shown in the previous article on this topic.

Phase shift in the L-network can be accurately calculated. You can see this (above) for both TLW and SimSmith. The phase shift in the mis-tuned gamma match is more difficult to ascertain. Modelling of the net reactance at the feed point is the best bet, and what I previously did with a model. That is what I will use: varying between 10° to 20° across the 20 meter band. 

The L-network phase shift (before substituting a 100 pf capacitor) is 39° at 14.1 MHz, and it, too, varies with frequency. Since this network is almost identical to that in the modelling exercise, and I have had difficulty developing a model that corresponds well with the real antenna measurements, I estimate the phase shift ranges between 49° and 58° across the band, including that of the gamma match. 

They add because both phase shifts have the same sign, which is to advance the signal to the upper yagi. Correction therefore requires a delay line of around 54° to the lower yagi. This is a almost exactly what was found for the earlier modelling exercise, and that is not surprising. Software modelling works and it can save a lot of time.

For the average phase shift of 54° the length of the delay line is 0.15λ, or 3.2 meters in free space at 14.1 MHz. That must be multiplied by the VF of the coax used for the delay line. For example, 2.1 meters (6.9') for RG213 and 2.7 meters (8.9') for LMR400. All that said, the length is not critical since the phase shift is frequency dependent. No fixed length can be a perfect solution, and an average value is good enough in this application.

My plan is to use RG213 and insert it at the tail from the lower yagi's feed point at the tower. Should I not repair the gamma match on the upper yagi and the delay line continues to be used, the RG213 will eventually do double duty as a rotation loop. I hope to make the lower yagi rotatable in the next year or two. It is currently fixed on Europe.

This is easy to implement, and yet I haven't done so yet. The degradation of the stack pattern without the delay line is small, but with careful A-B testing on the air it is noticable. The modelled deficit is about 1 db of gain and the appearance of a higher angle minor forward lobe.

Good performance without the delay line may seem odd but when you add in the larger uncertainty of terrain on the yagi patterns the phase error is not a major concern. SWR is the more important concern since amplifier tuning can be a problem when switching among the stack's 3 modes. Correcting the mismatch also restores the equal power division required for optimum stack performance.

Time is a concern now that autumn is fast approaching and my many antenna projects require my attention. Those are the priority now that the SWR of the 20 meter stack has been corrected. The delay line can wait a few more weeks.

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.

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.

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. 

Power

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.

Africa

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.

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.