How Not To Build a Gamma Match

As mentioned in my fall maintenance article, the upper 5-element 20 meter yagi was on the ground for maintenance. That's a big job. The antenna has a 42' (13 m) boom and weighs 120 lb (55 kg). There are guys and other obstacles to navigate while tramming the antenna up and down. It sits 40 meter above ground with a 5-element 15 meter yagi a few meters above it on the mast. The rotator is a prop pitch motor.

After becoming intermittent earlier this year, the antenna completely failed this summer. A group of friends came over a few weeks ago to help me take it down. Then they came back, twice, to put it back on the tower; the first lift had to be abandonned due to a rigging problem and then the wind became too strong to repeat the operation. 

After all that trouble I am pleased to report that the antenna is back on the air and working perfectly. In this article I'll discuss the problems and their resolution, all of which involved the yagi's gamma match. I may say more about the challenges of tramming large yagis like this in a separate article. I've discussed tramming yagis in the past but there are always new lessons to be learned.

Gamma matches are simple devices that are difficult to accurately characterize. I have had some success modelling gamma matches with NEC2 but not with NEC5. Gamma matches are often preferred for yagis because the driven element does not need to be split at the centre, enabling a design that can be mechanically simple and robust. It is allegedly (proof is elusive!) less susceptible to conducted common mode. However it is not true that the asymmetric feed significantly unbalances the antenna pattern, especially not in a yagi. That might be fuel for a future article.

Regardless of its pros and cons, the gamma match has its mechanical and electrical challenges. These are especially important on long boom HF yagis where the feed point is inaccessible from the tower. Smaller yagis usually have the feed point within reach which simplifies maintenance and repair of matching network faults, whether it be a gamma, beta, T or other network. A network of some kind is usually unavoidable to raise the low feed point impedance of conventional yagis to 50 Ω.

Let me take you through the flaws of the gamma match that I designed and built for the 20 meter yagi -- refer to that article for details. I used variations of the design for all of the yagis I've built for the 20, 15 and 10 meter stacks, and for 40 meters. The ones for 20 meters are most notable due to their relatively large size which magnifies the flaws. These lessons may prove useful to other yagi home brewers.

On the upper left, the proximate cause of the intermittency and failure is obvious (sorry for the blurry photo). The wire (#12 copper THHN) broke off the SO239 connector. That choice of wire was a mistake. Flexing of the gamma match in the wind (it's windy 40 meters above ground) fatigued the metal. I vaguely recall using solid wire to help stiffen the large and unwieldy wire lead and gamma capacitor. That's such an obvious misjudgment that I'm surprised that I did it. I only remember that I was in a rush at the time because it was November and I was running out of decent weather.

On the lower left is the primary cause of the flexing: the PVC pipe that suspends the inner end of the gamma rod insufficiently grips the element. The shorting strap at the other end does not have this defect. Also notice the faded. supposedly UV-resistant, black cable tie due to UV and the aluminum wire wound on for insurance. Being in a hurry carries a price.

The closeup on the right was more interesting. That is scrap RG8 with the jacket and braid removed. The polyethylene (LDPE) dielectric is a good choice for making the gamma capacitor (slides into the ½" aluminum gamma rod but its UV resistance is modest. The polyethylene developed numerous hairline cracks along its exposed length, due to either or both of UV and flexing in cold temperatures. Commercial gamma matches typically use acrylic or a similar polymer that is a low loss dielectric and UV resistant.

I found a sheen of oxidation on exposed length of wire when I cut it open. That isn't serious but it was at risk of further deterioration. The other end of the wire inside the gamma capacitor had popped off the caulk cap I put on, which allowed water to seep into the other end. There was water inside the gamma rod even though the inner end was taped. Water shouldn't have built up since the outside dips down, along with the element.

It didn't help that the gamma match bounced off one of the tower's top guys when it was first raised several years ago. That may have accelerated failure and contributed to what turned out to be a out of adjustment gamma capacitor that I had to deal with.

With the antenna on the ground I got to work. There was no point berating myself for all of these preventable mistakes. Consider this exercise a learning experience for your own antenna projects. I don't hide my mistakes so that you don't have to repeat them. And neither will I! Writing a blog does not make me perfect or blameless.

The new gamma match has several improvements:

• I fabricated a clamp out of sheet aluminum allow for the top of the PVC insulator and a hanger from the coax connector secures the open end of the wire to the gamma capacitor. Flex has been almost entirely eliminated.
• The solid vertical wire was replaced with #12 stranded wire. A new length of scrap RG8 was used for the wire which forms the inside of the capacitor.
• All wires are taped with Scotch 33+ for UV protection, and connections are sealed.
  
• Cable ties on the boom, coax choke and on the gamma match are covered with Scotch 33+ to protect against UV, even for supposedly UV-resistant cable ties. I saw a friend do it and it seemed like cheap insurance. It also doesn't hurt to coat rigid PVC even though its UV resistance is good.
  
• The open end of the gamma rod (not in the picture) has been sealed against most moisture.

In other words, I saw no need for a redesign, just incremental improvements. The coax choke tests good after 5 years; the winding diameter is within the bending radius spec for LMR400, but it doesn't hurt to check that it's still okay. One reason I use coax chokes rather than ferrite chokes on these antennas is to avoid excess heating and failure due to common mode (antenna) currents when the tower is shunt fed on 160 meters.

While I had the antenna on the ground, I did a complete inspection. Problems can become apparent after being on the high tower for 5 years (since 2019).

I didn't mention where I got my hardware when I built the antenna since it might have been taken as an endorsement. I can say more now that the antenna has been service for several years. The 5/16" galvanized saddle clamps on the left were bought from K2SSS on his eBay store. There is no corrosion on the bolts, saddles or nuts, and none of the nuts have slipped. I am happy with them. 

The ⅜" clamps on the right were purchased from DX Engineering. Cycle 24 galvanized clamps are on the mast and the two stainless clamps with solid aluminum saddles are on the boom. I abuse these clamps quite a lot when raising and lowering the yagi and they show no signs of wear. I lubricate the stainless threads before tightening them to reduce the risk of galling, especially when tightening and loosening the nuts while they're under heavy load.

As an example of heavy loading, notice the tape marks on the boom. The near one is at the CoG and the one centred on the mast is at the centre of the boom. They are 16" (40 cm) apart. The boom-to-mast clamp is moved to the former for tramming. Thus the antenna is heavier on one side when properly mounted. I have to move the boom after it's raised and before it's lowered. That puts extra stress on those stainless saddle clamps. I could have used a boom counterweight to place the CoG at boom centre but the antenna is already very heavy.

The galvanized ⅜" u-bolts holding the elements were acquired from a commercial tower service company and those fasteners are not sold retail by the Canadian manufacturer. They remain in excellent condition. Other unbranded plated and galvanized u-bolts fared less well. I cleaned and then sprayed them with cold galvanizing compound. I've had good luck with the Rustoleum brand in the past so I'll see how it performs in this case.

I skipped over adjustment of the gamma match to keep the mechanical information contiguous. So let's backup to cover that. I used rigging similar to when I originally adjusted this yagi. It's difficult to lift a 120 lb antenna in a manner that is safe, high enough to achieve a "free space" impedance, and that is not significantly affected by the near field environment. There are guys, towers, coax (for tuning) and even an aluminum ladder in the vicinity. I did not want to incur the time and trouble for elaborate rigging to put it in a more favourable area of the field.

A ½" rope runs between the guyed towers at about the 70' level, near guy stations -- the towers are 200' (60 m) apart -- and please don't try this with self-supporting towers. This rope is attached to another rope that runs through a pulley to a winch on the ground that is anchored to a tree. Ropes on both sides of the boom allow the yagi to be oriented in any direction, including upward. A chain and shackle at the centre of gravity (CoG) allow freedom of movement -- the rope freely passes through the shackle. 

Because it takes a lot of cranking to lift the yagi due to the winch's 5:1 winding ratio, this time I anchored the second rope to the tower and used a pulley on the winch cable to speed up the lifting and lowering of the yagi. The pulley functions as a reverse block and tackle to effectively lower the winch ratio to about 3.5:1.

The driven element side is tilted down to the ground for adjusting the gamma match by pulling on a rope. There is a long length of LMR400 coax to the analyzer, which is entered into TLW or similar tools to convert the measured impedance to that at the feed point.

I did the coarse tuning with the yagi level at about 2.5 meters height, where the gamma match was easily accessible from a step ladder. I then lifted it higher and tilted it down for adjustment. At 7.5 meters height, a ladder is needed to reach the gamma match (6.5' or 2 m from end of the boom) when it is tilted down.

As expected, the element tap point was approximately correct. By fine tuning it, I achieved a 50 Ω match at about 14.150 MHz which, for this antenna, keeps the SWR below 1.5 across the band. The bulk of the improvement was in the value of gamma capacitor. 

The impedance became unreliable when the antenna elements were approximately parallel to the guys, despite being segmented into non-resonant lengths, and drifted when the reflector was tilted downward. The reliable readings were with the antenna level and the elements at right angles to the tower guys at either side.

After all the fussing the result was perfect. The antenna SWR curve matches the EZNEC (NEC2) design, and it barely budged after it was lifted onto the tower. Several hours were required to dismantle the rigging for lifting and lowering the yagi, and then to remake the coax connections and thoroughly weatherproof them. There was no moisture incursion or corrosion on any of the connections so the original weatherproofing performed well.

Of course I was eager to power up the stacks after I descended for the final time. They are working great. One of my tasks on the way down was to pull off the compensating L-network and delay line for the previously misadjusted gamma match. They are happily no longer needed. The extra RG213 patch cable will come in handy.

I'll close with a view at the antenna looking due north. There's a beautiful view of a lake and the fall colours from 40 meters up. But I have had little luck persuading others to climb up and enjoy the view. Maybe they suspect that it's a trick to get them to help with the tower work, and they may be right! It was a perfect warm and sunny fall day for completing the tower work. Colder weather is approaching.

CQ WW SSB is this weekend. I'll do it as a single op in a category that I have yet to pick. The station isn't ready for another multi-op. Perhaps for the CW weekend.

Series Xc Antenna Tuning

Earlier this year I was helping a friend install and tune a 40 meter vertical that he had purchased at a flea market. It was made from large aluminum tubes of constant diameter and was therefore a fixed length (height). It was mechanically sound but required rope guys and a post for support.

He had prepared 16 radials of about 10 meters length -- about ¼λ -- which we stapled to the ground. It was directly fed with coax, without a matching network. The match was poor. The antenna resonated about 300 kHz too low, well outside the band. I suspected that the radials were too long, but cutting them was not an option.

Not being allowed to cut the radials or the vertical, there were still a few options. I studied the antenna with an analyzer for a few minutes to characterize its impedance. At resonance (outside the band) the impedance was approximately 37 Ω (I don't recall the exact value). This is typical for a vertical with low ground loss. However, as the frequency increased the R value also increased, along with the inductive reactance X. R was close to 50 Ω between 7.0 and 7.1 MHz (again, I forget the exact values).

This was a blessing and a curse. A blessing because only a series capacitor was needed to cancel the inductive reactance to provide a good SWR curve across most of the band, but a curse because I didn't have suitable capacitors on hand, fixed or variable. To my surprise, my friend had a large supply of ancient mica transmitting capacitors. All I needed to do was find the right one.

Rather than guess, we did the simple math to calculate the capacitor value that would equal the measured inductive reactance near the centre of the spectrum that of interest: 7.1 MHz. The value came to 400 pf. 

The equation, which all hams ought to know, is Xc = 1/(2πfC). Look carefully at that equation if you are unfamiliar with it: the smaller the capacitance, the greater the reactance. Large values that have a very low reactance (at the design frequency) can be found in lightning arresters and bias-T circuits to block DC while passing RF.

I rooted through the box until I found a capacitor that was suitable for 1000 watts and close to the desired value. That was a beefy 330 pf mica capacitor. I connected it in series and measured an excellent SWR curve. We made the connection more permanent and left my friend to add a weatherproof enclosure later. The antenna continues to work well.

This approach to antenna matching is similar to that for gamma matches where you find the tap point on the element where R is close to 50 Ω and then use a series capacitor to cancel the inductive reactance, resulting in a 50 + j0 Ω match at the selected centre of the operating bandwidth. There are other potential applications. 

Consider the SWR curves for two antennas resonant (X = 0) at 3600 kHz, for CW and digital modes. The vertical has a "perfect" ground, or one simulated with an extensive radial field, and the inverted vee is 30 meters above EZNEC medium ground.

Now suppose that you want to also have a low SWR for SSB high in the band, say 3900 kHz. You have several choices, and you can probably think of more:

• Make it a fan dipole/vertical, with the parallel element tuned for higher in the band.
• Cut the antenna for 3900 kHz and have a switchable coil at the base or partway along the element (each half-element of the inverted vee).
• Switched L-network or similar to match the antenna at 3900 kHz.
• Switched series capacitor to improve SWR in the SSB segment, if the R value is suitable.

Note that both antennas are not a perfect 50 Ω match for CW, though the SWR is close enough in most cases, especially when an antenna tuner is used. The vertical is more broadband than the inverted vee (or dipole), which is typical. Although the omni-directional mode of my 80 meter yagi (driven element as a simple vertical) has a reasonably low SWR up to 3800 kHz, I included a switched L-network to lower it further for SSB to "future proof" it in case I purchase a broadband solid state amplifier.

Getting back to those two example antennas, SWR curves are inadequate to determine whether it is possible to insert a series component to match the antenna for the SSB segment of 80 meters. We need to calculate or, better, measure R and X across the operating range. For reliable measurements you should use a modern single-port antenna analyzer or VNA of known accuracy, especially for large deviations from the nominal 50 + j0 Ω impedance. I use RigExpert but there are other excellent products on the market.

For this exercise I'll stick with calculations by EZNEC. Although I mostly used the NEC5 engine for the models in this article, NEC2 is perfectly good for these simple antennas, and it comes free with EZNEC. Below is a plot of the R and X values for both antenna models.

One striking difference is that the inverted vee's X (reactance) changes more rapidly with frequency. That's the reason for its narrower SWR bandwidth. Also, notice the slow change in R for both antennas, which increases with frequency. Finally, there is an excellent linear frequency relationship of both R and X. However, that is only true for small percentage frequency ranges. Other antenna types will have different curves.

The relationship scales: the chart is for 80 meters but the same is true for my friend's 40 meter antenna. It should be clear why I was inspired by the antenna feed point's measured R and X.

We can cancel the inductive reactance with a series capacitor to shift the SWR curve higher in the band. Of course it isn't quite that simple. First, since R will remain the same, that will determine the minimum SWR in a 50 Ω system. On the chart you can see that the vertical is more promising than the inverted vee. Second, the quality of the capacitor is critical. It must have a high Q so that very little power is dissipated by the devices ESR (equivalent series resistance) or it will fail with high power. Good transmitting capacitors (see the earlier article reference) should have a Q of at least 1000 so that the ESR is low enough for high power. Solve for R in Q = X / R and then use that in P = I²R to calculate the power dissipation. Unlike coils, capacitors are small so their construction and surface area to conduct heat away can be critical if the loss is more than a few watts.

For the vertical it is easy to find the correct capacitor value by calculation or trial and error in EZNEC. To bring X to zero at 3900 kHz the capacitor value is 835 pf. There are no commercial capacitors with that value so it would have to be done with a combination of capacitors or a variable capacitor, with or without a parallel fixed capacitor. EZNEC also helpfully calculates the power dissipation if you provide the ESR. For a capacitor with a Q of 1000 the calculated loss is almost exactly 1 watt for a transmitter power of 1000 watts.

We are not so lucky with the inverted vee due to that high R of about 94 Ω at 3900 kHz. This is a case where a two-component L-network is preferred in order to transform both R and X to achieve a better SWR. The same is true for an inverted vee tuned to resonance at 3900 kHz and brought down to 3600 kHz with coils.

It should also be noted that since the inverted vee is a balanced antenna, a series capacitor in each leg is required to preserve balance. In this case the capacitance reactance in each leg must be less because they are in series. That is achieved with a higher value capacitor of 550 pf versus about 280 pf if a single capacitor is used. You can use one capacitor but should not because the antenna becomes unbalanced and common mode current is more likely and a CMC choke with a higher impedance is needed to avoid excess heating.

At this point I'll reveal that I have an underlying motive other than what I've discussed. On my list for new projects is my longstanding desire to make my 80 meter 3-element wire yagi a yagi on SSB. It is only a yagi in the CW segment at present. A 4-square on 80 meters works from 3.5 to 3.8 MHz (the 80 meter segment of interest to me) while a yagi is too narrow band, only covering 3500 to 3650 kHz. Shifting the antenna upward 150 kHz would achieve my objective.

I won't get it done this year, so there is time to consider alternatives. A series capacitor in all 5 elements is one of the options. The approach has several advantages:

• High efficiency: High Q capacitors are easier than high Q coils.
• Small size: A capacitor and relay will fit inside the existing PVC electrical boxes.
• Switching: SSB relay lines to the parasitic elements is already installed. The SSB selector line at present is only used to modify the L-network for the driven element in omni-directional mode.
  

Until now my plan was to place two coils in the parasitic element switch boxes. With the element tuned as a director for SSB, one coil would shift resonance downward to make it a reflector (as is currently done) and the second to move resonance downward from SSB to CW.

As a CW reflector there would be two series coils. That would further reduce the already low radiation resistance (due to the T-shaped parasitic wire elements) and incur loss in the coils. Getting coil Q high enough to avoid significant loss would require new enclosures to fit two of them in a manner that avoids stray coupling.

By using a series capacitor these difficulties can be largely circumvented. The new difficulty is finding enough of the needed low loss, high RF current capacitors of the required value. But first, let's determine the capacitor value and its performance using an EZNEC model.

For yagi operation from 3500 to about 3650 kHz the director is tuned to 3680 kHz and the reflector to 3450 kHz. By opening the shorting relay, the series coil shifts resonance downward by 230 kHz. For use between 3650 and 3800 kHz, the parasitic resonances shift 150 kHz upward to 3600 and 3830 kHz. 

The height of the driven element (tower + stinger) is difficult to adjust so an L-network tunes the antenna for yagi mode (all 4 directions) and for both CW and SSB omni-directional modes. In any case, feed point R is quite low for yagi mode and below 35 Ω in omni-directional mode.

My first question was how much the parasitic element's R would change when inserting the appropriate value of series capacitor at the feed point. For the required 150 kHz upward shift the capacitor value is 1400 pf. R increases from 21.4 Ω to 23.8 Ω, or about 10%. That's for perfect ground. When ground loss is added the percentage change is less since it is in series with the feed point. 

The percentage change is less when it is made a reflector by switching in the 2.1 μH coil. R is 23.9 Ω at 3450 kHz (CW) and 25.8 Ω at 3600 kHz (SSB).

That's promising since the impedance is roughly the same for parasitic elements tuned to either CW or SSB by the series capacitor. If the same can be done for the driven element, a fixed L-network can be used for all yagi and omni-directional modes. That can now be tested in the model.

I pulled out my old EZNEC model of the completed 80 meter yagi. There were several design iterations before construction began, and this is the one that was built. In the EZNEC view, the antenna direction is to the right.

I used NEC2 since NEC5 introduced small differences that I didn't want to spend time on even though the result is certainly more accurate due to the acute angle on one side of the T-shaped parasitic elements. Continuing with NEC2 does not substantially affect the present study. I'll switch to NEC5 when I am ready to proceed with the project.

The L-network for the yagi modes was refined to make the SWR curve as good as it can be. When I built the antenna, I used the model as a guide but built the matching networks based on measurements. The two were pretty close. 

SWR curves for CW were calculated and then 1400 pf series capacitors were inserted at the base of the 3 active elements (the inactive elements are floated) to, hopefully, shift the array to the SSB contesting part of the band, which is roughly 3650 to 3800 kHz. 

The driven element reactance is not the same as the reflector and director so I manually adjusted the capacitor until the SWR curves were roughly alike. The capacitor for the driven element is 3000 pf (less inductive reactance to cancel).

The curves are almost identical. I expected them to be close but not this close. The impedance change for the 150 kHz upward shift is quite modest so the same L-network at the driven element feed point works very well for both CW and SSB. 

However, we have not yet demonstrated that the yagi's performance is similar. I did that next.

To my eyes they're identical. In fact, the SSB performance is marginally better. Performance lags in the top 50 kHz for both CW and SSB, which was already known from the original design. Yagis, which are high Q antennas, are challenged on 80 meters where the percentage span of the operating range is high, in this case over 4%. That's equivalent to 300 kHz on 40 meters and 600 kHz on 20 meters.

The low gain is due to near field and far field ground loss, typical of verticals. It's worse with yagis since the radiation resistance is low. 4-squares perform better. I have plans to improve antenna performance, which I hope to implement next year. 

Series capacitors to support SSB appear to be a good technique to apply to the current and future version of the 80 meter yagi. It's simple, efficient (with the right capacitor) and predictable. All I have to do now is scrounge those 5 capacitors.

Fall Maintenance

It should not be surprising that there is more maintenance for a large station there is for a small one. That means that I have a lot of work ahead of me this fall. I am prioritizing some jobs so that I am ready for the major contests that are rapidly approaching.

Despite all the problems, there are so many antennas that I have been able to continue operating. But that's for casual operating; in a contest I want all of the antennas to be available. That is especially important for multi-op and SO2R where the antennas must be shared among two stations.

In addition to repairs and other maintenance, I have new projects underway or planned. To give you an idea of what's involved to keep my moderately-sized "big gun" station going, I'll show you my to-do list for this fall. First the repairs and then the new projects.

Repairs

20 meter 5-element yagi: The upper rotatable yagi in the 20 meter stack began exhibiting intermittent behaviour in the spring. By midsummer the failure was complete and the antenna became unusable. There is very little that can go wrong in a simple, if large, antenna like this so I knew the repair would be easy. Unfortunately, after testing the entire antenna system in stages, the fault was determined to be at the feed point. It is unreachable from the mast so it had to come down. It is now sitting in the hay field. The repair was indeed simple and I hope to raise it soon. I'll have more to say about the faults and their repair in a future article.

80 meter wire yagi: Deer continue to molest the antenna. One enterprising individual tore apart the "temporary" protection on the southwest parasitic element and proceeding to chew and tug the wires until it pulled off the switch box. When other projects are out of the way I would like to build metal cages for the box and wires, and perhaps replace the bottom 2 meters of the wire element with tubing.

40 meter 3-element yagi: The capacitance hats need to be replaced. It's a complicated job since the antenna is so large and heavy. The replacements have been ready for quite some time. I haven't been in a rush since no more capacitance hat arms have broken and the antenna performs well. I may have to defer this job (again) to next spring.

Side mount rotator: Intermittent operation was found to be a cold solder joint on the Hy-Gain Ham M motor phasing capacitor. I have it mounted on the tower to eliminate loss and eliminate two wires. It currently turns an XM240 40 meter yagi. I had to inspect the capacitor on the tower, determine the fault, bring it down for soldering and then return it to service. Even a simple fix like this takes time due to the climbing. I took the opportunity to replace the enclosure with UV-resistant plastic.

Trees: Half a dozen large dead trees need to be taken down since they threaten Beverage antennas and, in one case, my workshop/garage. Beverages and feed lines will have to be temporarily moved since they're in the fall zone. There are no trees threatening the towers or guys at present, which are mostly well away from the trees. That was by design. Threatening trees are marked with blazes so that they can be identified this winter when all trees have no leaves.

Software: The 160 meter mode of the 80 meter vertical yagi can now be used. This had been a limitation of my antenna selection software that I delayed fixing due to its relative complexity. Along with that, several bugs have been resolved that are related to antennas that are multi-band or on the same port, with an auxiliary switch. Full SO2R and multi-op testing needs to be completed before CQ WW.

Beverages: Ants cut through the taped weep holes of the remote switch so I had to once again evict them. I caught them early so there was no damage. However there is an intermittent in the one or more of the RF paths that occasionally cuts the signal path. Switching appears to be fine. I suspect the RG6 connectors. I will have to open all of them to clean the conductors and ensure that all threads are coated with dielectric grease. Failure of the short east-west Beverage in September was due to the centre conductor of the RG6 breaking off inside the F connector.

Antenna interaction: The side mounted XM240 and TH6 have an interaction on 40 meters that impacts the XM240 when it is pointed approximately west. In that direction it is at right angles to the south pointing TH6. It is not often appreciated that a 3-element yagi has a "hidden" resonance at the next lower band, where it behaves like a short dipole with large capacitance hats (the parasitic elements). I will model the antennas and decide if I can reduce the interaction by raising the TH6 several feet.  It can't go much higher since it'll get too close to the next higher set of guys and the risk of increased interaction with the lower yagi of the 10 meter stack.

160 meters: My failed attempt to broaden the bandwidth of the shunt fed tower with a wire cage for the gamma rod was aggravating. I gave up when the weather got too cold for further attempts, especially as contests approached and the 160 meter season was well underway. I will try again this month once the 20 meter yagi is back on the tower. I don't roll out the radials while I have ground crew helping me with tower work since they are a safety risk. Breaks in the radials due to critters must also be mended -- wire nuts served as temporary repairs.

Prop pitch motor controller: There was no lightning damage this year but I diagnosed and repaired damage from last year. The motors turned slowly and the current draw was high. One motor was affected more than the other so I suspected a motor problem. The motors are fine. I mistakenly relied on the current measurement when I ought to have measured the voltage. The old controller I am currently using (it will be replaced) only produces 24 VDC under no load. Under load that drops 2 or 3 volts even with a large filter capacitor, and is lower still at the motor due to wire resistance. When I measured it this summer it was between 17 and 19 volts at the power supply. I discovered that the bridge rectifier was damaged by lightning. Semiconductor devices can partially fail when they are hit by a voltage spike. A new 50 amp bridge rectifier fixed the power supply. I ordered several; they're inexpensive.

New projects

Although repairs receive the highest priority, this station is constantly changing and growing. The changes are mostly incremental now that the station is mature. This is a list of new projects that I am working on. Most won't be completed this winter, but all are being worked on as time allows.

40 meter reversible Moxon: Mechanical construction is mostly complete. The half elements are too long to keep in the workshop so they've been moved outside along with the boom. Dimensions and component values have been fine tuned using NEC5. The elements are not yet mounted onto the boom and the switching system isn't built. With luck it'll go up in late fall.

Stubs: Although a simple addition to the station, I have yet to do it. This is a job that is easy to do during winter so I have deferred it. I really should have done it last winter. The easiest stubs are for 80 and 40 meters, to suppress harmonics on the second and third harmonics, because the antennas for those bands are connected to their own auxiliary switches instead of separate ports on the 2×8 switch.

Antenna selection software: The UI (user interface) has not stood the test of time. Operators select the wrong antenna, don't know which are available and, for SO2R and multi-op, one UI is difficult to use and confusing. Design for its replacement is well advanced, although development has yet to begin. It will feature separate UI windows for each station, which can be networked on different computers, and limit the display to the availability of the antennas for only the current band, including receive antennas. I plan to write the software over the winter. The Arduino switching system does not need to change, although I'd like to migrate PC communication form USB to wireless.

80 meter wire yagi: There are several electrical and mechanical improvements on my list. I've been deferring them as the solar maximum has waxed since 80 is less important than the high bands for the time being. I intend to add SSB yagi modes (it is currently only a yagi on CW), install concrete bases, replace the tower with a taller one (to remove the troublesome stinger), decrease ground loss, improve critter protection (see above), and a few other changes. I will do what I can this fall and winter as the weather and other projects allow. Most will wait until at least 2025.

New prop pitch motor controller: I am well along in the construction of an Arduino-based controller for the two prop pitch motor rotators. The first step is direction indication, followed later by rotation controls. The project has been idle for several months due to lack of time and some confusion over non-linearity in the op amp circuits. Eventually I will interface it to a PC for software control. An article will follow once the controller is complete.

6 meter Moxon: The Moxon is on the small tower bracketed to the house. There is no rotator or coax! I haven't yet decided how to proceed, whether to fix the direction or make it rotatable. My objective is rapid propagation checks in different directions.

Small is beautiful?

It should be obvious that a big station is not for everyone! There's always work to do so it has to be something you enjoy. I do, most hams do not and I can't fault them. Dreaming of a big station is far less stressful than owning one!

Between good DX conditions on 6 meters, DXpeditions and station maintenance, fall is a busy time. We've had unexpectedly mild weather which is very welcome to getting the work done. However, good weather is good for other outdoor activities competing for my time. Somehow I have to do both.

6 Meters Recap 2024

There is evidence that sporadic E incidence declines during solar maxima. I haven't looked into the research but I do know, from this part of North America, that last year's 6 meter sporadic E was poor and this year was worse. I delayed writing a season recap in the hope that fall equinox propagation would add some spice to a dull year but that hope is fading. 

Although there is a good chance of F-layer DX propagation this fall, now seems to be as good a time as any to summarize the season. Maybe by writing the season summary now the DX will subsequently start rolling in!

My hopes earlier this year for a significant increase in my DXCC count were entirely squashed. I expected at least 10 new ones and ended up with just two: E51EME and FR8UA. I heard a few others that I failed to work. Sometimes it was a matter of timing, such as when I was doing a chore when HD8M was worked by several locals. My stretch objective of 20 was absurd in retrospect. 

I was confident that an average sporadic E season combined with additional F-layer propagation due to the high solar flux would carry me to my DX objective. Although solar flux dramatically increased, boding well for the remainder of the current solar maximum, and 10 meters has been very good, it didn't carry to 50 MHz. It isn't easy for the MUF to bridge that frequency gap of close to an octave.

Those at lower geomagnetic latitudes did better. Although FN24 is almost exactly midway between the equator and north pole, the same is not true of our geomagnetic location. Follow the lines of constant magnetic inclination (isoclinics) and all of Europe below Scandinavia and northern Scotland are further "south". Since envy is not an effective strategy we can only do the best with what we get.

That is not to say it was all doom and gloom. We experienced periods of fascinating and tantalizing  propagation. That it didn't always translate to DX in the log does not diminish my interest. Fleeting propagation due to as yet only partially understood natural phenomena is one of the attractions of 6 meters.

• Propagation to Europe was well down. We had only one widespread opening, and the rest were marginal or to parts of west and south Europe that are routinely heard here. 
• Openings to South America were brief, and in any case I have pretty well worked out that continent. 
• Other than 7Q, which was in with surprising regularity, and the usual west African islands like EA8, Africa was nearly absent this year. 
• There were a couple of likely F-layer openings to the Indian Ocean during which I worked FR and heard 3B8 and 3B9 stations that I worked before.
• There were several marginal and brief openings to Japan which netted a total of 4 contacts along with several partials. The rest of east Asia was not heard, however I did hear at least one Maine station work DU.
• West and Central Asia were marginal several times, with stations in OD, TA, and UN heard. One tantalizing message from 9N is of uncertain veracity. More on this below.
• Pacific stations were absent other than a brief opening to Hawaii and regular appearances by E51EME (ZL1RS) during his two DXpeditions in June and September, along with 3D2 and FK. VK9DX was briefly and weakly heard late one evening.

A lot of the marginal openings are mostly notable due to being caused by the high level of activity. Without the prevalence of capable stations around the world and their willingness to periodically call CQ DX on 50.313 MHz (FT8) many (most?) openings would have been undiscovered. It is very interesting to see those orphan (single) messages from around the world when the band seems to be otherwise dead. True, they do not result in QSOs, but the possibilities excite the imagination.

I don't miss much on 6 meters. During the sporadic E season, and now beyond that with the improved propagation prospects, I usually monitor 50.313 MHz whenever I am not using the station. If there's an opening or one is likely (W1/VE1 hears DX, DX spots or occasional decodes) I will often CQ in the direction of the opening and then check for any flags on PSK Reporter.

The following are a few highlights of openings or at least near openings.

East Asia: There were quite a few openings to Japan though only occasionally good enough to work anyone. I worked a total of 4 JA stations on two separate openings. No other east Asia was heard.

Central Asia: UN (Kazakhstan) had numerous openings though none very workable from here. I called a few and worked none. Other central Asia were heard in northeast NA but not here. Examples include EX. 

On the same path (compass bearing) there were repeated marginal openings to Ukraine and Scandinavia. One time when eastern UN was heard, the following message appeared on my screen:

The path is the same and, on inquiring on ON4KST chat, 9N7AA was working Europe at the time. I did decode a few messages of Europeans working him. Out of curiosity I reached out to him by email to ask if this message was legitimate but he did not reply. It remains an intriguing mystery.

West Asia: Numerous countries were copied, including TA, OD and 4X. None of the openings was persistent enough to sustain a QSO. It takes at least 2 continuous minutes to have an FT8 QSO once the station is heard. On the other hand, hearing a station on CW or SSB during a fleeting opening is very unlikely. You accept the bad along with the good on the digital modes.

Arctic: There were a few workable openings to Scandinavia. QSB was deep with signals cycling from strong to unheard every several minutes. One interesting QSO was with LA in the far north that was in daylight while it was night further south. OX and TF were also heard and worked.

Europe: There are many openings to Europe that are easily noticed due to the high level of activity. Most openings were not widespread; they were brief, narrow in coverage and weak. One spotlight opening worth mentioning was to Greece in July. From the discussion on ON4KST chat, it seemed that I was just about only one on this side of the Atlantic to experience the opening. It took patience and some coordination on the chat to log several SV stations. The opening eventually faded without having extended outside the spotlight zones.

Aurora: There was one good aurora opening in May that netted many CW contacts including western Canada and the US. Other aurora sessions were not as far ranging. Aurora is more common during a solar maximum so we can expect more for the next two years. It isn't DX but I enjoy it nevertheless.

Central America: While not rare, it was nice to be able to work TI on both CW and SSB. These days I don't often bother with the traditional modes but when propagation is good these modes easily outperform digital. The QSOs are fast and they're fun. If F2 propagation really gets going, you can expect to find me on CW and SSB more often.

West: There were a surprisingly large number of openings to western NA, including one to Hawaii. I only worked one KH6 but a large number of W6, W7 and VE7 stations were worked this season. I don't think I've ever worked so many west coast stations in previous sporadic E seasons. It was great for grid hunters, which I am not, yet it was difficult to resist calling several of the rare ones.

South America: Every second or third day for the past few weeks we've heard a few weak SA stations in the late afternoon. This is typical equinox propagation. It was poorer than expected for the high solar flux. I enjoy working SA even though I've worked all the easy ones. As noted earlier, I missed HD8M. CB0ZA was never heard here.

The CY9C DXpedition was an easy shot from here. I worked them on a previous DXpedition so I stayed out of the pile ups. The path was more difficult for many others. Of course there are countries and DXpeditions that are difficult for us and relatively easy for others to work on 6 meters.

Arras, C. & Resende, Laysa & Kepkar, Ankur & Senevirathna, Gethmini & Wickert, Jens. (2022). Sporadic E layer characteristics at equatorial latitudes as observed by GNSS radio occultation measurements. Earth, Planets and Space. 74. 10.1186/s40623-022-01718-y.

Where do we go from here? What are the prospects for better DX? There are readers closer to the equator (the geomagnetic equator) who are already experiencing good propagation and may be wondering what I'm complaining about. It isn't just high-MUF but also sporadic E. Compare the above chart of global sporadic E incidence with the earlier one showing geomagnetic isoclines. Do you see the similarity?

My primary interest on 6 meters is DX. My DXCC total now stands at 139 worked and 128 confirmed (LoTW) since my return to the magic band in 2017, and I am reaching the point of diminishing returns. I want more, but it won't be easy.

As I write these words the solar flux is 275 and there was a suspected F2 opening to western Europe occurred earlier in the day. I will keep monitoring 50.313 MHz for signs of openings, turning the yagi throughout the day to the most likely directions for DX openings. October and November are excellent months for F2 propagation in the northern hemisphere, so I am hopeful. I recall the pattern from the 1989/90 solar maximum.

6 meter DX has been poor so far this year but there could be fireworks ahead.