Reflection on the Sweepstakes Contest

With the year's premier event -- CQ WW CW -- rapidly approaching I thought it worthwhile to say a few brief words about ARRL Sweepstakes. I have some warm feelings about these contests because of the central role they played in my early contesting career going back 45 years ago when I was a teenager and a new ham. I don't feel so enthusiastic about it now. Times change.

Once again I entered the CW weekend in the QRP category. I do this for the experience of using skill over brawn to put contacts in the log. In contrast I will be burning up the watts in CQ WW. I resurrected the 3 db attenuator so that the FTdx5000 could be used at 5 watts. Luckily the resistor bundle was still around, having been stored for just such an eventuality. I soldered it back into the since repurposed box and it was ready to go.

Sunday can be a drag in Sweepstakes because there are a limited number of stations to work. It is less so with QRP since, due to the lower rate, there are still stations to work, mostly those that haven't yet been able to pull my tiny signal out of the noise. Chasing rare multipliers is more thrilling with a power handicap. I am one of those contesters who likes to play both ends of the power range -- QRP and QRO -- each with its unique challenges and benefits.

I operated SO2R as before to maximize the use of my many antennas. QRP is a good introduction to SO2R since the rates are lower. Stress is minimized as you learn the ropes. Despite this it does get quite boring by Sunday evening when I can be CQ'ing on two bands and the QSOs still come several minutes apart. Indeed, I quit a little early because my rate had slowed so much that I probably only sacrificed 3 or 4 contacts.

New this year was the SO2R Mini to switch rig audio. Keyboard control of receiver audio was a great convenience compared to the manual switch I used for my first foray into SO2R. The kit is inexpensive and takes care of the most important switching responsibilities, while eschewing sophisticated features you might never use. I recommend it.

Although I did 15% better this year than the last two years I was squashed by the QRP big guns. Last year it was N0NI in Iowa. Unfortunately that super-station was flattened by a major storm and was absent this year. From reports they are rebuilding and will be back in action before too long.

This year I was outgunned by W2GD and VY2ZM despite a capable station. As with real estate the secret is location, location, location; rospects in Sweepstakes are very location dependent. For example, as I type these words I am hearing W2 stations working Europeans on 10 meters that I cannot hear. Even without an ongoing geomagnetic storm, 500 km further north it is a different world with respect to propagation. 

Of course W2GD is a top notch contester and, to my knowledge, has good antennas. I have no way of knowing whether the problem was me, my northerly locale or antennas. A few decibels can make a big difference at the QRP level. It just seemed there weren't any more contacts to be had. Would a different strategy have helped? I am doubtful. It is more likely that I am a victim of circumstance.

The over 1000 QSO log from VY2ZM is spectacular. Here we have a top notch station and operator in a location well placed to work the large midwest population on 20 meters, where many casual operators congregate, and from a section that, for the first time, is a new multiplier and he had little competition. Back in the beginning I had a similar advantage from VE4. However there were no assisted classes in or the supporting technology in the 70s so I still had to work hard to attract attention.

I did have technical difficulties leading up to the start of Sweepstakes. Since I hadn't done SO2R in a while I was unaware that the remove antenna switch had a problem. Relays were misbehaving on the second radio/operating position. Less than 1 hour before the contest started I discovered that the problem was earwigs building a nest inside the DB25 connectors to the switch. Moist eggs are a conductance path between the connector pins. Once they were evicted the problem was eliminated. 

Earwigs have been a big problem this year in all my close to the ground electronics at the towers, antennas and control systems. It takes a very small hole to permit them entry. They, of course, love weatherproof enclosures.

Unlike the CW weekend I had no interest in the SSB version of the contest. I got on 80 meters briefly Sunday evening and made 28 contacts in 13 minutes. When stations stopped calling I quit. The motivation to continue "for fun" wasn't there. Phone contests don't attract me the way they once did unless I do it as part of a multi-op. But that's me and not the fault of the contest.

As everyone knows Sweepstakes is approaching a crisis. Participants are old and the contest risks passing as they pass. There are more new hams to be found on SSB than CW though not enough to keep the contest going for the long term. That's a shame. 

Sweepstakes is not an indicator that this is the end of contesting as a global sport. Contests will be around for as long as amateur radio is around. But those contests won't be Sweepstakes. 

 It'll be a very different story in CQ WW CW this weekend. For this contest I will be running a kilowatt and the new 15 and 20 meter stacks are online and working. And, boy, do they work! More about that in a future article.

Small Pile Ups

Many hams have noted that activity on the bands changed as the pandemic continued and lock downs came in waves in countries around the world. My own antenna plans were altered in the spring when it became impossible to bring a crew together. Eventually we did resume but the lost time could not be recovered. Work on my new antennas has extended into the cold of late autumn.

Travel restrictions put a brake on almost all DXpeditions. By mid-spring there were almost no new countries to be had by ardent DXers. That seemed to bring a lull to the HF bands that is unusual. Ordinary person-to-person QSOs continued as before, for the most part, so that non-DXers didn't see much that was different. For non-DXers it was an opportunity to be more active, on the air or concentrating on projects indoors.

Despite the increased leisure time there has been a psychological toll. We have the time but we may not have the same degree of motivation. With the worries over family, income and life as we've known it we haven't used the time as productively as we might. I noticed a similar effect after I retired: I have all the time in the world, which removes urgency and often causes a loss of focus on doing things now. An external spur is needed, whether it be an upcoming contest or a DXpedition to finish antenna projects.

The lack of DXpeditions removed a major spur. Outside of the summer sporadic E season on 6 meters my own on-air activity has lagged. Summer is also the low season for major contests. I did what I could on the ground to progress antenna projects but for the most part my attention was diverted to other pursuits.

When several DXpeditions appeared in recent weeks I was surprised at the small the pile ups. You would think that after months of no rare DX the pile ups would be fierce. Lethargy does not evaporate instantly. For a time I could get through the pile ups very quickly running low power since there was little competition. 

The small pile ups are becoming bigger as DXers are drawn back to the shack. There is a stark change between the number of callers to 7Q6M than to the more recent 7Q7RU DXpedition. The first was easy to work and the latter more difficult. The pile ups are quite a bit bigger and the competition more fierce. That and their QRN made working them on 80 and 160 a challenge.

Although DX chasing has been subdued this year it has not been difficult for me to drum up activity with just a CQ. With cycle 25 beginning to flex its muscles I find it quite easy to draw a lot of callers on 15 meters even without high power. Contests have also seen plenty of action. Contest organizers have noticed a sharp year over year increase in entries. Small contests have also been the beneficiaries.

Clearly there are things that will spur activity and overcome our pandemic lethargy. Perhaps it's the novelty of a higher MUF, the lure of contest competition or DX on 6 meters. Whatever it is I am enjoying the activity when it occurs. After all, what's the point of building all these towers and antennas if I can't put them to good use? So I get on when I can. 

Soon I'll have more time to operate. The weather is turning cold and the year's antenna projects are coming to an end, and mostly to a successful end. With the end of the pandemic in sight we should enjoy the winter season and the coming major contests. DXpeditions will not be common until well into 2021 so jump in and pursue the ones that do appear during the interim.

A little luck with the weather in the coming days should see me well equipped for CQ WW CW next weekend. The new 15 and 20 meter stacks should be largely operational and the new 160 meter antenna appears to be working very well. 

Helped by new sunspots expect the largest turnout ever for this major contest. Let's see some big pile ups on the DX that is able to get on and pursue those points, multipliers and, for the casual contester, new band-countries. It should be a lot of fun. It'll also help us to shake free of the pandemic blues.

160 Meter Shunt Fed Tower

I am trying something different for 160 meters this winter. The T-top wire vertical hung from the 150' tower the past few years is a great antenna but not without its negatives attributes. These include:

• Potential for interactions with yagis, of which I now have more
• Tower interactions affecting directivity and efficiency, up to 3 or 5 db in some directions and down to -2 db, respectively
  
• Low radiation resistance that reduces efficiency by, perhaps, -1 db
  

A few possible alternatives were reviewed in an article last month. My intention is to do the best I can within the constraints I have. My constraints are atypical in that I have two towers that are approximately λ/4 tall on 160 meters, and that makes many things possible that are unattainable for most hams.

After more analysis, research and modelling I decided to shunt feed the 140' tower. Shunt feeding a tower with yagis on top has long been a popular choice for hams with limited space and height since it exploits the modest height tower they have, very often with relatively efficient top loading provided by a tri-band yagi on top. 

In my case the electrical length of the tower is far greater than λ/4 and while that's impressive and potentially very effective it does introduce a few unique problems. These I knew in advance because they are covered in depth in ON4UN's Low-Band DXing book. 

This is a timely reflection on the book and John DeVoldere's remarkable legacy since he died on November 9. If you have an interest in the low bands you must have this book on your bookshelf. The antenna described in this article behaves almost exactly according to the chart and equations to be found in that book. It is the marriage of theory with the practical that makes the book a treasure.

A shunt fed tower is pretty simple: run a wire parallel to the tower, attach it to the tower where the resistance part of the impedance is 50 Ω and use one (gamma match) or two (omega match) capacitors to tune out the net inductive reactance at the base of the gamma rod (or wire). 

It is straight-forward to model the antenna in NEC2 (I use EZNEC), with a few cautions:

• Align the segments of the tower and gamma rod (wire)
• Use MININEC ground and place resistance loads in a one segment wire connected to ground to emulate the loss due to the tower ground and radial system
  
• Rather than include yagis in the model it is easier and equally effective to measure the electrical length of the tower and make the tower that height in the model
• The short wires connecting the tower and gamma rod should be one segment
• Put the gamma capacitor and source at the bottom of the gamma rod
• Connect the bottoms of the gamma rod and tower with a one segment wire, and do connect them in the built antenna
  

The guidelines on how to proceed are addressed in ON4UN's book. Recall that I measured the resonant frequency of the tower to be in the vicinity of 1200 kHz. This is an electrical length of about 62 meters, which is 135° or ⅜λ at the low end of top band. Although this is quite a bit more than 90° (λ/4) the pattern does not sprout any lobes at high elevation angles.

I was successful replicate the tabulated data from the book with the model I developed in EZNEC. The initial height estimate for tapping the tower with a wire spaced 1.5 meters is about 25 meters. Perhaps the largest uncertainty is the diameter of the tower which, as a lattice structure, is typically equivalent to a wire somewhat less than the tower face dimension and depends on the structural details. Gamma wire diameter and insulation are other variables with an effect.

For simplicity in getting to a first measurement I used the boom of the lower 5-element 20 meter yagi that is ~22 meters high. A clamp holds the wire in position along the boom and the wire is bonded to the tower metal by scraping away the paint around a hole in the adjacent tower girt. I did not rely on continuity between boom and tower because there's a layer of paint between them. I scraped the paint off the galvanizing at the attachment point.

It was no fun to lean out from the tower on a face with no climbing horizontals to clamp the wire out 1.5 meters (5') from the tower centre. I couldn't get it quite that far without additional acrobatics, an unwarranted effort since the tap would almost certainly have to be moved.

That was indeed the case. After cancelling the inductive reactance with a capacitor (low voltage capacitors are suitable for analyzer measurement) the resistance, at 122 Ω it was far wide of the mark. Part of that was due to the mess of clip leads but no where near 150% error's worth. Apart from the high impedance the antenna seemed to work okay. I am using the same set of 8 × 30 meter radials from my earlier antenna.

It was a windy during the first trials and the periodic billowing of the long gamma wire during the analyzer's scan made for peculiarly wavy SWR curves. It is worthwhile to place insulating arms at several points on the tower to hold the wire in place to avoid impedance swings and wire fatigue. I have not yet done so since with the antenna incomplete the positions were subject to change.

I returned to the computer to re-calibrate the model based on what I learned. It turned out that the error was not as bad as I feared. I estimated that the 50 Ω tap could be found 3 to 5 meters lower. I split the difference and used the available tower girt about 3.5 meters lower (~60' above ground).

I built an extendible arm to suspend the gamma wire from the tap point. A length of angle steel and an ABS pipe are joined with hose clamps. The outer end of the ABS pipe is notched to hold the wire in place. The bolt that connects the arm to the tower doubles as the electrical bond to the tower. The end of the wire is a tinned loop that fits on the bolt and minimizes galvanic corrosion when sandwiched within the galvanized hardware.

Minimal acrobatics are required to adjust the telescoping arm. To change the distance I disconnect the wire on the ground, loosen the hose clamps and slide the pipe to its new position. A retractable steel tape measure can be extended out to the end of the pipe to set the wire separation.

The separation between the gamma wire and tower was not constant. The wire was farther at the bottom than at the top. Although this is not ordinarily discussed in the literature there is no reason for the two to be exactly parallel. All that does is improve predictability. The effect of the angled wire is that of a parallel wire with a separation between those of the top and bottom.

The reasons for the non-parallel wire were to avoid more tower acrobatics and because the radial hub is not easily moved. I only moved the radial hub, along with all 8 radials, when the antenna was approaching completion. The general layout of the antenna base is shown in the photo below.

Pictured are the final positions of the components, after all the experiments and final adjustment. A wood stake has a wood platform for the plastic container with the gamma capacitor and an insulator for the gamma wire.  This keeps the capacitor and feed point off the ground and safe from snow, puddles and even small animals.

This is a high voltage point so beware of the presence of incidental conductors. Insulated wire is recommended for the vertical gamma rod (above the capacitor). A wire snakes along the ground between the tower lightning ground rod and the radial hub (ABS pipe next to the stake) to prevent the high loss of a return path via the soil. A short length of RG213 runs from the main Heliax transmission line to the feed point adjacent to the capacitor. The Heliax is buried in a trench along with all the other transmission lines and control cables.

It is important to check for continuity between the gamma wire and the tower ground. Despite the many splice bolts between tower sections it is possible for paint to insulate tower sections. A friend in the business once explained that the metal ridges I found on several of my used commercial tower sections are evidence of the tower having been the radiator of an AM broadcast station. After installation all the legs at each section splice are spot welded to ensure continuity and no resistance loss due to high RF currents.

Returning to the tuning discussion I have to say that we got lucky with the second trial using the lower tower tap. After tuning out the inductive reactance with the capacitor the impedance was almost exactly 50 Ω. This is what I call hitting the bullseye! Unfortunately after tidying the site -- changing connecting wire lengths and location of the radial hub -- the impedance dropped to 38 Ω. Further adjustment of the gamma wire got us back to 50 Ω.

I drew a diagram of the adjustment process for the gamma wire. Coarse tuning to get to 50 Ω is done by changing the height of the tower tap. Higher is higher impedance and lower is lower impedance. Once you're close -- 35 Ω to 65 Ω range -- you can fine tune the impedance by changing the separation of the wire and tower. Closer is lower and farther is higher impedance. There is an effect on bandwidth in different combinations of the two, however it is small enough that I solely focussed on achieving a match.

Since the radials are difficult to move you can either run a wire from the bottom to the radial hub or fix the gamma wire position at the bottom and extend or retract the tower arm. I performed trials using both methods. Do whatever works best in your situation. The extra wire on the ground for the former method changes the tuning and that can be tuned out with the gamma capacitor.

I centred the match at 1840 kHz. This is 10 kHz higher than for general DXing, for which most top band operators aim for 1830 kHz. Because contests are a primary interest of mine and the activity in top band contests can spread quite a lot higher in the band I centred the antenna higher. Alternatively the antenna centre can be moved higher just for contests, easily accomplished in a few minutes by adjusting the gamma capacitor.

The 2:1 SWR bandwidth is a little more than 75 kHz, as predicted in ON4UN's book and in the software model. This is narrow though typical of an electrically long shunt fed tower. Better than 100 kHz bandwidth can be had with a wire cage for the gamma wire. I'll consider doing that next year if I decide to keep this antenna.

With the gamma capacitor value and range determined once the 50 Ω impedance was found for the final antenna layout I proceeded to select a gamma capacitor from my ample junk box. The gamma capacitor has a high voltage across it due to the large inductive reactance it must cancel. By large I mean thousands of volts. The greater the inductive reactance the smaller the capacitor value required to cancel it and the higher the voltage it must withstand. For the 145 pf capacitor measured and modelled it is more than 2500 volts for 1000 watts.

A variable capacitor with the required range and voltage rating is large. It is better and cheaper to use a small value variable capacitor in parallel with a high voltage fixed capacitor. The smaller range of the variable capacitor is also easier to tune and this is important because the capacitor value is critical: a tiny change has a large impact on the feed point impedance.

My first attempt was a split stator capacitor with 50 pf per section in parallel with a 100 pf ceramic doorknob capacitor. The approximate range is 100 to 200 pf, plus stray capacitance in the wires connecting it to the gamma wire and feed point. 

The plate spacing is not enough to withstand 3000 volts, which is the minimum recommended in this application. Air requires at least 0.12" to survive 3000 volts, and that is for dry air with no margin for humidity and particulate contaminants. To determine the actual flash over voltage I followed the advice from an old joke:

To determine the load rating of a bridge drive heavier and heavier trucks over it until the bridge collapses. Rebuild the bridge as before and put up a sign with the load limit as the weight of the last truck that made it safely across.

I gradually increased power until the capacitor arced. This occurred around 650 watts. I had no difficulty operating at 600 watts. The load data in EZNEC tells the story.

Load #3 is the capacitor. At 600 watts it sees a little over 2000 volts. It is reasonable to assume from this (and a measurement of the plate spacing) that the capacitor is rated for 2000 volts. The box the capacitor comes in does not specify the voltage rating.

I rebuilt the capacitor by adding a 30 pf ceramic doorknob and wiring the split stators in series. The range of the assembly is now 130 to 155 pf. Recall that series capacitors of equal value result in a capacitance half that of each, which is 25 pf for the two 50 pf section. These act as a voltage divider with a combined rating of 4000 volts. Should you use different value capacitors in series the voltage division will be unequal and you may not eliminate arcing.

I added less than 10 pf to the range with a few inches of scrap RG213, which is 2.1 pf/inch and has a voltage rating of at least 3000 volts. The braid is trimmed near the edges to prevent arcing through the air.

For weather protection I put the capacitor in a margarine container. There are holes for the external connections and bottom holes to weep water and moisture. A scrap piece of wood on top reduces UV damage and, with a stone, keeps it from blowing away in a high wind!

Returning to the load data you'll see the 3 resistance loads for the radial system and the lightning grounds of the shunt fed tower and the similar tower 60 meters away. Ground loss has been reduced compared to my previous wire vertical and that of a wire vertical adjacent to one tower or between the two towers. 

It is difficult to know whether the efficiency increase is true in practice. For now all I can say is that the antenna is working very well and is certainly at least the equal of my previous winter 160 meter antenna. Cumulative experience over the coming winter's DXing and contests will provide additional performance data.

I'll close with noting a couple of issues, one that I ran into and one that may arise. After tuning the antenna and testing it in the shack I found that the resonant frequency shifted from 1840 to 1855 kHz. That may not seem a lot but for a narrow bandwidth antenna on 160 meters it is an almost 1% change that pushed the SWR over 2 at the bottom of the band. Scale this to 20 meters and it's equivalent to shifting resonance from 14.100 MHz to 14.220 MHz. Most hams would notice that!

The cause was the connection to the main transmission line. It is buried 20 cm below grade and behaves as an additional radial, one that is longer than the other 8. There is no common mode choke on the transmission line to defeat this behaviour. The gamma match provides a modest amount of common mode attenuation and the ground around the Heliax provides a degree of common mode choking because, by being buried, the common mode field loses strength along the way. However this choking effect is not enough to prevent it acting as a radial. With a small radial count there can be a current imbalance due to its different length and depth but imbalance is almost certain in any case with just 8 radials.

To compensate for the shift I tuned the antenna to resonance at 1825 kHz. With the transmission line attached the resonance shifted 15 kHz to 1840 kHz, which is where I want it.

The other concern, one common with shunt fed towers, is RF into electronics on the tower and heating of common mode chokes on yagis. At a minimum all control lines requires bypass capacitor or RF chokes, and even then there may be effects. I will be watching for problems with my home brew stack switches when they are installed in the next week or two. Since I use air core coax chokes there are no ferrite cores to overheat and damage. At least that's the theory. Again, I will have to see what happens.

Most often these problems do not manifest themselves. When they do occur they can be difficult to cure. Opting for a wire vertical adjacent to the tower rather than shunt feeding the tower itself can help but not as much as you might think since the coupled energy is almost as great as in the wire itself. More separation is needed to lower the risk.

There is no easy way to predict which installations will suffer from these problems. I will try it and see and take action if necessary. One reason I chose the tower with the 15 and 20 meter stacks is that it less likely I'll be on those bands at the same time as 160 meters than 40 or 80 meters.

160 Meter Antenna Arcing

A few weeks ago my "small" 160 meter antenna malfunctioned. At first it was only with a kilowatt, then it deteriorated until I was only able to run QRP without the problem occurring. It pretty well took me off top band other than playing around as a QRP entry in the Stew Perry contest in October.

The antenna is the 160 meter mode of my 80 meter vertical yagi. It's base matched by an L-network that is switched in when 160 meters is selected. Although only half height the antenna exploits the extensive radial system of the 80 meter array. In comparative testing it appears to be -6 db relative to my usual full size wire vertical. While not a wonderful antenna it allows me to operate year-round on top band. The full size wire vertical must be removed in spring to keep radial wires are out of the way of farm equipment used for haying. 

The first symptom of trouble was erratic SWR changes while transmitting with high power. At lower power, although the SWR was more steady, the rig detected a problem and reduced power. A low volume sizzle was heard in the headphones. This was my first hint of arcing.

Troubleshooting the antenna was . Since it is so far from the shack I could not do a transmit test while also being present at the antenna. Visual inspections uncovered nothing amiss.

My suspicion first fell on the L-network capacitors. There is a 2000 pf vintage transmitting mica in parallel with several 100 pf 1 kV low loss capacitors. Old style mica high current capacitors are known to occasionally suffer internal connection failures after several decades. Although the small ceramic capacitors are calculated (current, voltage, Q) as more than adequate to the application and have not failed in other networks I've built, well, you never know.

I first substituted an identical 2000 pf mica capacitor. The problem persisted. Cutting the 100 pf ceramic capacitors out of the circuit again had no effect. I turned elsewhere to find the problem.

The DPDT relay that switches the tower connection between the 80 meter L-networks and the 160 meter L-network has its 8 A contacts wired in parallel for greater current capacity. I disconnected the 80 meter connection and shorted the relay contacts with a wire. Again, no change. I didn't really expect the problem to be the relay since it continued to work properly on receive and low power which would not be the case had the contacts been ablated by arcing.

My attention next shifted to the L-network coil. It is large, to maximize Q, and is exposed to the weather. It is wound with weathered THHN wire I scavenged from an old antenna. The high voltage across its terminals could possibly arc through the weathered wire insulation to an adjacent turn or to a nearby conductor. A close inspection showed no evidence of arcing.

Having failed to diagnose the problem visually or by component substitution and bypass I asked a friend to help. We communicated by handheld. He transmitted at power just high enough to elicit the arcing while I poked around the antenna. Despite the audible sizzle of arcing it took a few minutes to pinpoint the location. It can be difficult to localize a quiet sizzle outdoors with components of the antenna bound together and hidden by weather covers.

The problem was not at all what I expected. The arc was from the tower to a few of the 12 VDC control wires. There is a bundle of Cat5 cables that connect the central control box to the 80 meter parasitic elements and to the shack. The cables are buried and are only exposed at the tower base.

 
When I completed the 80 meter array, long before adding the 160 meter L-network, I made a temporary weather cover for the control cables. There's a lot of them! I bundled and wrapped them in a black polyethylene sheet that was handy. I taped the wrap closed and taped that to the lowest tower brace.

On 80 meters this isn't a problem because the tower base is at a low RF potential, where current is maximum and voltage is minimum. The base of a vertical is like the centre of a dipole. This is not the case on 160 meters where the relatively large transformation ratio of the 160 meter L-network is a pussycat at the 50 Ω port but a monster with bloody fangs where it connects to the antenna.

TLW shows 1200 volts across the coil, and therefore on the antenna port, with 1000 watts applied. The control cables were an easily accessible path to RF ground through the inadequate layers of thin plastic. It punched a hole through the polyethylene sheet (left side, above) and then burned through the thin plastic covers on the two crimp connectors closest to the tower brace.

Therein lies the problem with temporary solutions: you fail to follow up to replace it with a permanent solution. This is a lesson I never seem to learn. For those following the blog you'll know I have far too many projects on the go. I forget or I choose to focus on other things. Small maintenance items like this tend to be put off and finally forgotten. Sometimes these oversights come back to bite me.

A more robust weather cover for the control cables is now in place. It's simply a short length of PVC pipe with the cable bundles stuffed inside and taped top and bottom to protect against rain and insects, respectively. I cleaned and painted over the scorched area of the tower brace (visible in the picture). This time it ought to last.

RF is weird. You might expect that high RF power leaking into the control wires would damage the control system components. It didn't. All the 80 and 160 meter modes of the array continue to perform as before. It probably helped that all the control lines entering and exiting the central control box have RF chokes. However the parasitic element boxes do not have chokes on their end of the control lines since they did not appear to be necessary. Exactly where the RF decided to travel is unclear. 

Soon I'll have my winter 160 meter antenna ready and this lesser antenna will lie idle until next summer. Among the alternatives available to me, I'm trying something different this year for 160 meters. Its RF arc potential is even greater than for the antenna just discussed. More on the new antenna in a future article.

15 Meter Stack Switch

The 15 meter stack switch that I recently completed is almost a duplicate of the one for 20 meters. Both are single band, utilizing an L-network. There are a few differences that I'll describe in this article. For background on the design, design objectives, construction and testing you must read that article.

The L-network is very similar, only the L and C value are different. As before it is a low pass design. For 15 and 10 meters a high pass design may be preferable in a multi-operator or SO2R station, however I took this route for convenience in the choice of components. In any case, adjacent band attenuation is modest (no better than -10 db), so the benefit is not critical.

The major change to the 15 meter version is the layout of the input port and relays surrounding the L-network. There was stray inductance in the 20 meter stack switch that required a significant reduction of the coil inductance. The effectively longer lead length -- wire distance from port to port via the relays -- was responsible. At a higher frequency and lower inductance a better layout is required.

To arrive at the optimum layout I spent an hour with pen and paper to see how different component positions affected the lengths and paths of interconnecting wires. For the layout I settled on the two ports and relays for the yagis are unchanged. The input port was moved to the side of the box with the L-network relays beside it, between the yagi port relays and the barrier connector for the control wires. As before the L-network is situated above the other components, supported by conductive spacers and a terminal strip. This style of layering keeps wires short.

For comparison the 20 meter stack switch is shown on the left. On the right is the complete 15 meter stack and in the centre it is shown without the L-network so that the layout is clearly visible. The L-network connects between the NC (normally closed) pin of the input port SPDT relay and the common pin of the other. 

The (unpowered) default position is BIP (both in phase) so the L-network is in the circuit and connected to both yagi ports. For upper and lower yagi selections the L-network is bypassed and the input port is directly connected to the upper or lower port.

The L-network has a 150 pf shunt on the 50 Ω (input) port and a series 0.19 μH coil to the 25 Ω port. The output port connects the two nominal 50 Ω antennas in parallel. After testing with a thin wire coil I wound the permanent coil from AWG 12 wire. Its inductance is calculated as approximately 0.14 μH, which implies 0.05 μH of stray inductance. The stray inductance is equivalent to ~2" (5 cm) leads, and that visually corresponds well with the layout. The revised layout proved its effectiveness by halving the stray inductance.

Testing was done with my VNWA3 by DG8SAQ. With this instrument I could accurately measure insertion loss, port imbalance and input SWR. The final smoke test with a kilowatt is done only after the insertion loss is determined to be acceptably low at no more than -0.05 db. This is achieved with high Q coils and capacitors to minimize ESR (equivalent series resistance). 

The VNA was recalibrated before measurements were done since I discovered that insertion loss (S21) was at least 0.04 db better than expected. The drift from the original calibration, tiny as it is, is enough to make the stack switch appear to have unity or better gain, and that's impossible. Accuracy is worth the few minutes it takes to re-calibrate.

Let's start with the default BIP position. There was little difficulty adjusting the coil to centre the pass band. The excellent match is indicative of the capacitance value being correct. As for the 20 meter unit one yagi port was connected to the VNA to measure the insertion loss (S21) and the other had a precise 50 Ω load.

There is a small imbalance between the ports. The insertion loss with the yagi ports reversed is -3.08 db. Since the exact value per port should be -3.01 db for a perfect and lossless power division the net loss is very good. As tuned the BIP position is still not too bad on 20 meters despite no attempt to make this a multi-band unit. When selecting either the upper or lower yagi the L-network is bypassed so that the unit can be used on any band.

The insertion loss is effectively nil when one yagi is selected. It shows -0.01 db but that is variable with the measurement trial and port and other times shows as 0 db. If it is -0.01 db that is only 2 watts of loss when transmitting at 1000 watts. As the frequency climbs conductor loss increases due to skin effect. This is evident in the slight upward slope of the blue trace. The stack switch uses a mix of AWG 12 and 18 copper wire, and the relay internal wires are smaller. However, as we'll see later in the "smoke test" none of these parts exhibited measurable heating.

Another frequency effect is the input port SWR. As the frequency climbs the internal wire lengths are a larger fraction of a wavelength and increasingly exhibit transmission line effects. The "dead bug" wiring method I use is beginning to show its limits at 21 MHz. A similar unit for 10 meters would be worse though probably still acceptable. Different techniques are required at VHF and above.

An SWR of 1.07 is quite good and is typically dominated by the yagi impedance which is higher over most of the 15 meter band. To alleviate the problem it is necessary to use coax for the internal connection or PCB with parallel conductors (one at ground potential) to maintain the internal connection at 50 Ω and thereby lower the SWR. This is typical of the construction method in commercial stack switches.

Of course the final step is the smoke test, just as it was for the 20 meter unit. For this test a legal limit signal is passed through the stack switch in BIP mode to determine how much power is dissipated, which is the true indication of the insertion loss. This is done in the shack with both sides of the 2 8 switch connected to the yagi ports and each connected to different 15 meter antennas.

Since the new stacks are not yet connected I use the TH6 and TH7, the same as I did for the 20 meter test. I chose a time when the band was dead so there is no inconvenience to others. I picked a frequency on 15 meters where both have a low and near equal SWR.

Driving the two yagis at full power the coil got warm. Everything else stayed cool to the touch. With one minute at a kilowatt the coil was uncomfortable to touch for more than a second but there was no danger of a burn. Coil Q is not as high as I'd prefer: it is calculated by K6STI's Coil to be ~300. This isn't great but neither is it bad. A higher Q coil would be wider and difficult to fit in the space without causing other proble.

With the smoke test completed I am confident that the 15 and 20 meter stack switches are ready to be installed on the tower. That could happen as soon as a week from now. The weather is improving so there is time to catch up on tower work. 

I am looking forward to having 15 and 20 meter stacks fully operational later this month. All 4 yagis are on the tower, and that is a major step forward. More on that in a future article (or two).

Prop Pitch Motor: Motor Repair

For your Halloween treat we're going to disembowel a prop pitch motor. Don't worry, it won't be too gory! We begin with the emergence of trouble atop the high tower one dark and stormy night...

When the prop pitch motor was first installed on the new tower with the 15/20 meter stacks I mentioned that it turned slowly. After doing resistance checks on the cable and the motor there appeared to be a faulty internal electrical connection. The problem was dirty contacts between the motor contacts and the receptacles on top of the gearbox. This I was able to fix with contact cleaner, tiny swabs and correctly torquing the bolts on the motor retaining ring.

A guide to the motor wiring can be found on K7NV's web site. There should be lettering on the motor housing denotes the motor as right hand or left hand, and the motor voltage.

Trouble signs

Unfortunately the trouble didn't end there. After several minutes of bench testing with a 13.8 VDC supply the motor noise I had already been aware of became worse and the motor repeatedly bogged down. When I connected it to the 24 VDC controller the deterioration accelerated and within two minutes the motor pretty well ground to a halt. This was accompanied by loud squeaking coming from the housing. For a motor running at close to 10,000 rpm any mechanical resistance can be catastrophic.

The failure was accompanied by excess current draw from the controller which, I discovered, is inadequately fused. The audible sizzling from the overheating was so apparent that I shut it down before the power supply failed. The ham who built the controller back in the deeps of time must have been an optimist.

With no backup on hand I had to take on the unwanted task of pulling the motor apart. I had some trepidation because these motors are becoming increasingly rare and expensive and I was unsure whether I'd be able to diagnose and repair it. With no readily available alternative I went to work.

Disassembly and testing

The prop pitch motors used as rotators were designed decades ago, with the originals dating to WW II. They were used on USAF bombers and other aircraft. The motor typically runs on 24 VDC, which is the aviation standard. We call it a motor but it is a motor plus a gearbox. It is the gearbox that enables it to be used as a heavy duty rotator.

DC motors with commutators and brushes are no longer common and parts are not always easy to find. Some hams have replaced it with an AC motor of similar RPM and power. Commutator motors will operate at lower voltage, but not too low or the motor can bog down and draw excess current. Luckily my motor is in good condition with none of the unique components requiring replacement.

The first stage of disassembly is to separate the motor and gearbox. The motor can be powered using the pins on its base. I used a high current 13.8 VDC supply on the workbench for testing during the repair process.

Removing the 3 bolts that hold together the two halves of the motor housing is not enough to pull them apart. The bearings at each end of the motor shaft are press fit into the housing halves. Axial force is needed to separate them. Levering too forcefully from one side can damage the shaft. Without a specialized tool for the job I used two pries between the upper housing and the shaft end to achieve a net axial (vertical) force. I moved the pries around the shaft in small steps as I worked the housing apart. Once separated the drive end of the shaft can be pushed out of the housing with a few taps of a cushioned mallet. Don't lose the thin shims that come tumbling out.

That done you have the armature and bearings removed and you can access to the brushes and field coils. Inspect the commutator and brushes for excess wear. If the brushes are excessively worn replacements can be had from a good quality motor repair shop. If the commutator is worn you may have no alternative other than to replace the motor.

The armature and field coil surfaces were pitted and coated with debris but otherwise sound. I cleaned them up to make myself feel better although it doesn't really accomplish much. Have a look at K7NV's web site to see what a pristine restoration looks like. Very pretty.

The brushes were inspected and found to have lots of life. I removed the easily dislodged debris (mostly carbon dust from the brushes) with a soft brush to avoid damaging the coils. The sides of the armature were cleaned with 400x sandpaper and then carefully brushed away the fine particles. Keep the motor interior clean of metal dust.

The brushes are bypassed with ceramic capacitor on bottom of the housing (not shown) which largely eliminate RFI generated by the rapid circuit interruption as the commutator rotates over the brushes. I cleaned and checked them. All were good.

The input shaft of the gearbox should turn easily by hand. Use a wide blade screwdriver to make testing easier. With a suitable coupler that doesn't damage the splines you can perform a higher speed test with a drill. I was satisfied by a hand test alone.

Bearings

Now we come to the crux of the fault: bearings. In the picture above you can see the non-drive side bearing and in the picture below is the drive side bearing below the commutator. The upper bearing is a shielded (not sealed) 3201 (if I remember correctly) and the lower bearing is an open 6200.

Both bearings ought to be sealed. There is a lot of carbon dust and other particulate debris inside the motor. The shielded bearing tests good so I'll leave it there. The open bearing was dry and pitted and took force to turn. A little machine oil freed it but could not repair the pitting. 

This is not the original bearing and whoever put it in there made a poor choice. Sealed bearings cost only a few dollars more. It pays to check the specs since the RPM rating decreases going from open to shielded to sealed. The rating of 6200 shielded bearings from reputable manufacturers exceed 10,000 RPM, which is the minimum rating for this motor. Check the low temperature rating if, like me, you have cold winters.

Within days I had a new 6200 sealed and cold weather rated bearing for less than $10, including tax and shipping from an Ebay merchant located in VE2. The old bearing was given a shot of penetrating oil and pulled off without trouble. A little more oil and the new one was pressed on.

I should mention that both the 6200 and 3201 are shown with metric dimensions in all the catalogues I checked. This can be deceptive since they often round those with English dimensions to the nearest millimeter. A friend checked his US military parts list for the small prop pitch motor, dated 1944, to check the dimensions before I placed my order. I suspected an unsuitable substitution. It is very unlikely that the USAF specified a metric and Japanese bearing during WW II! Unfortunately the specified bearings were only listed with proprietary part numbers from long gone manufacturers. Further research into the bearings was not practical.

I reassembled the motor and powered it up. It spun nicely with 13.8 VDC and the current draw was 2 amps lower than with the bad bearing. With this positive sign I did another and longer test in the shack with the 24 VDC controller. Motor heating was nominal and the current draw was very good. Back on the gearbox the motor hummed along at a more typical 7.5 amps. The gearbox resistance (mechanical loss) increases motor current.

I have some concern about the grease in the gearbox despite it testing well in the cold and not having excess mechanical resistance. I may tear it apart next year if only to ease my mind. There is no time for this preventative maintenance before winter.

Current draw

Commutator DC motors are interesting devices. Their theory of operation is well outside of my areas of knowledge. For example, I hadn't realized that the starting current is quite high at around 20 A. It is a bad idea to operate the motor by switching high current DC, whether by manual switch or relay. The high starting current can and do weld together relay contacts. That can cause a lot of grief up the tower because the motor will not stop.

The controller I use switches the AC line, which is safer. The CW or CCW direction is selected by switch before activating the rotation lever which turns on the power supply. Commercial controllers designed for prop pitch motors use other means to deal with the starting current. I will have to keep this in mind when I design or purchase a better controller for my two prop pitch motor rotators.

As with any motor there is a kind of torque curve. The motor will operate quite well with less than 24 VDC, and even a little more if you're careful, but not at peak efficiency. The field coils and commutator are optimized for a smaller range of speeds. The current draw is not very different when driven with 13.8 or 24 VDC. Driving a load at the lower voltage will further decrease efficiency and increase motor heating. 

I suspect the greatest risk is to the bearing lubrication, brushes and commutator, though perhaps not in actual usage since on periods are typically under a minute. Risking motor failure is inadvisable unless you have a ready supply of spare parts or spare motors. They haven't been manufactured for decades.

One way to limit excess current draw is to not use the largest wire gauge you can afford. A modest amount of extra resistance puts a ceiling on the current draw even in the event of a dead short. I am using 125 meters of AWG 10 wire for the motor (3 conductors). The DC resistance of the 250 meter long return circuit is 0.8 Ω (confirmed with an ohmmeter). 

With a dead short at the motor the current draw at 24 VDC is limited to 30 A. This drops to 19 A for the 1.25 Ω of AWG 12 wire. These figures assume the power supply voltage doesn't drop under the high current draw. If it does the power supply can overheat and fail due to its internal resistance unless there is over current protection. Of course with greater wire resistance the voltage will drop at the motor terminals and mast rotation will be slower. 

There is no one correct answer to the system design. There are several parameters to consider.

Weather delay

It's cold, really cold. We are setting record lows. This is not weather in which I want to do tower work at great heights. Once the weather warms up again I will remount the prop pitch motor on the tower. That is also when I will deal with the upper 20 meter yagi of the new stack. Yes, it's up and mechanically secure though not tested because I had to remove an element during the lift. 

The weather is delaying a lot of work that needs to be done. I want the new stacks operational for CQ WW CW at the end of November. There is little chance they'll be ready much earlier. 

Being ready includes a working prop pitch motor for the rotator. At least it's working, and that's something. I would have preferred this lesson in prop pitch motor repair in warmer weather. However, when it comes to maintenance you rarely have a choice and most repairs are done in winter when the station is stressed by the activity spurred by the cold keeping hams indoors and by the schedule of major contests.

More Thoughts on SSB Contests

When I got my phone license at 16 years of age I was understandably mic shy. Most everyone I spoke to was an adult and that was an unusual experience for a teenager. DXing and contests made it easier since there was no expectation of holding a conversation with all those "old" folks. As my comfort with the mic improved I quite enjoyed the ease of conversing on the air, even with the old folks. 

The popularity of SSB contests is in part due to that ease: almost every ham is able to speak. With short and often fixed exchanges language is a minor barrier for contests. And humans sure do like to talk!

Unfortunately SSB is a victim of its own popularity. With a 2.7 kHz bandwidth and thousands of stations piling into limited spectrum a popular SSB contest can cause quite a mess. CQ WW SSB, the most popular contest of all, is especially difficult. There's an endless number of stations to work but most are very difficult to hear, and the ones you hear often can't copy you. It is frustrating.

When you operate in CQ WW SSB with less than legal limit power and excellent antennas success can be elusive. This is not the case with CW and digital modes. Narrower modes allow some elbow room for less dominant signals to be heard well. You can even run with QRP. The same is only true of SSB during solar maxima when there enough open bands to allow everyone to spread out. Of course this is only partially true since you must eventually squeeze onto every band to work more stations and multipliers.

I have written about SSB contests before, more than just once, especially years ago when I did it with QRP.  Although I have two world #1 plaques for QRP in CQ WW SSB I gave it up because it was so difficult and because declining sunspot numbers forced me onto the low bands where SSB QRP is quite painful. Even during my winning years I spent very little time on 40, 80 and 160, only spending enough time to gather what multipliers I could and largely limited to trying my luck with the biggest of the big guns. It was futile to attempt anything more.

With this dismal introduction and another CQ WW SSB in the bag let's look at a few things to consider for those of us who are not the biggest of the big guns.

SNR

Power has an outsize impact on SSB. When you run low power you may be no more than 10 to 13 db below the high power stations yet it will seem far worse. Because the QRM and QRN are so fierce with the wide bandwidth of SSB the received SNR (signal to noise ratio) can be very poor with 100 watts. Solid copy with a kilowatt may be no copy at all with 10 db less power.

This is a threshold effect that I previously discussed with respect to QRP where the challenge is far greater. It can take a brave ham to venture into an SSB contest with QRP! Low power contest entries -- typically 100 watt maximum -- are somewhere in, what I've termed, the muddy middle. Many are surprised at how difficult SSB contests can be with low power when it can be very successful in daily use. Look at the QSO and multipliers of the top high and low power stations in a major SSB contest and the difference is stark. For the same power categories the spread is less in CW contests.

At least with QRP you know SSB contests will be difficult and slow going. Low power is deceptive. I am surprised by how many experienced contesters are surprised by their poor results with low power. Of course you can use big towers and antennas to compensate, and it does help to a degree. It isn't easy to boost your signal 10 to 13 db with antennas alone. An amplifier is far easier and cheaper.

Accents

This is another topic I've written about before. On SSB there are language and accent differences that can make copy difficult. Although English is in many respect the universal language on SSB many hams have only a rudimentary grasp of it. Their English may be limited to phonetics and a handful of useful phrases. It is perfectly possible for a non-English speaker to be successful in an SSB contest, especially CQ WW with its simple and (to be honest) predictable exchange.

For English speakers like myself -- which probably includes you if you are reading this -- there is an obligation to make it easier for others. Use standard phonetics or common variations that in your experience are successfully understood by all. Learn the numerals of several common languages and you'll complete contest contest exchanges faster and more accurately. 

Spanish is the one I find most useful, and there are others. Don't be afraid to experiment with others! There are only 10 numerals to learn and your effort will be appreciated by other hams. Try not to be too glib with more words and phrases or the other operator may believe you speak their language and will reply with full sentences and then you'll be lost. Stick to numbers and you'll do just fine.

Phonetic usage

Months ago I shortened one of my standard voice messages. If you're familiar with N1MM Logger+, this is the message that goes in F3 when you run using ESM (enter sends message). This is the message that logs the QSO, confirms completion to the other station, and solicits the next contact.

"Thanks! Victor Echo Three Victor Norway"

Simple, short and it does the job exceptionally well. All I had done was to change "Victor Echo" to "V E". It caused me a lot of grief. The problem was due to using high power and a good antenna. When you do this the runs continue without a break. As a result I rarely sent a CQ. The CQ uses complete phonetics for my call.

Some of those who tuned across me heard "V A". They sound much alike on SSB where fidelity is less than perfect and is worsened by QRM and poor SNR. Indeed, that's why we use phonetics. The miscopied call was occasionally spotted and I would get a run of dupes. My temporary workaround was to interrupt F3 and speak my call with full phonetics.

My reasoning for the shortening was to save time by cutting two syllables. While running low power it worked well since my runs frequently dried up and I'd CQ with full phonetics. Time was saved and there was little risk of a misunderstanding. I'll have to revert to using full phonetics. Becoming a big gun requires a different approach to SSB.

Vocal endurance

Many hams in their eighties have no difficulty sending CW at high speed. A modest loss of manual dexterity is compensated by decades of practice. With the extensive contest use of software generated CW even that may not be necessary. The same cannot be said of SSB, and that's a problem because as we age it can be difficult to impossible to keep our voices going for 48 hours.

Voice memories reduce the need for vocal endurance. Unlike CW, unfortunately, speaking into the mic is difficult to avoid. In CQ WW there is the need to speak the other person's call. In other contests there are serial numbers and other exchange information that is not constant throughout the contest. When a repeat is requested alternative phonetics and syllabic emphasis are helpful, as is using the other operator's language for critical items, especially numerals as mentioned earlier.

For those who have lost their vocal endurance the alternatives are multi-ops, so that they operate fewer hours, or to use technology to voice serial number and call signs. The latter is improving and no longer has to sound like a freaky robot. Expect to hear more of it in future. 

Although I've not reached the age of lost vocal endurance I am beginning to think about the aids I'll eventually need. It is funny to realize that as a little pistol I could operate CQ WW without using the mic for long stretches. In search and pounce (S & P) you can get by without the mic by recording just two messages: call sign and exchange. You rarely need to speak other than to vary phonetics or syllabic emphasis for difficult contacts.

40 meters

The globally common portion of the band is only 75 kHz: 7.125 to 7.200 MHz. That's a problem. With a 2.7 kHz bandwidth only 30 or so SSB signals (and clean ones at that!) can coexist without overlap. Yet there are thousands active in CQ WW. When the sun sets this band segment is a wall of QRM. Big guns are rattling out a constant stream of CQs and answering almost no one because only the strongest signals can be reliably copied. Other CQers are deep inside the noise, mostly unheard.

I have worked DX multipliers in CQ WW SSB with QRP, although not many. I would wait for the second evening when rates declined and I had less competition. Even so I needed excellent propagation to have a chance with a wire dipole or loop for an antenna. At sunrise, if I got lucky, I'd work a KH6 and a W6/7 in zone 3 and that would be it.

To deal with the narrow spectrum there are ways for a Canadian to do better. One is to operate below 7.125 MHz where there are no Americans; our mode permissions are less strict than in the US. This allows us to work more DX with less QRM. To work American stations and other North and South American countries you operate above 7.200 MHz. Americans and Europeans will often work split, with Americans calling above 7.2 MHz and announcing a listening frequency below 7.1 MHz. Europeans do the reverse.

Compared to years past when broadcasters outside the Americas were to be found down to 7.1 MHz and sometimes lower (remember Radio Tiranha?) it's actually better today! That isn't saying much.

160 meters

This band is like 40 meters for SSB, except worse. All modes must coexist so when there's a major SSB contest on 160 it can be impossible to have non-contest QSOs on CW, digital and SSB. Antennas are often narrow bandwidth because they're small and that restricts operating frequency. Many sponsors of SSB contests exclude 160 meters because of these problems.

Amateur radio does not have exclusive access from 1.8 to 2.0 MHz in many parts of the world. Although not as restrictive as in the past due to LORAN and other services moving away it is still helpful to be aware of the restrictions some countries face. A notable example is Japan which, until recently, had strictly limited access. Now it's a little better and JA stations have allocations where we like to operate in the lower part of the band so that we don't have to work them split.

The high atmospheric noise on 160 meters makes high RDF receive antennas almost mandatory on SSB. You can only narrow your receiver bandwidth so much before phone signals become unintelligible. The only resort is a directional receive antenna to improve SNR. SSB DXing on 160 with an omni-directional antenna is neither enjoyable nor productive. 

Yet the big guns keep CQing, as they must, to make all the contacts they can. The rest of us can at least work them if nothing else.

Casual operators

There are more casual contest operators to be found on SSB than on CW. Make an effort to sound welcoming on the bands and at the times when many hams habitually turn on their rigs and they will call you. They may not know the contest or the exchange but they are happy to oblige you with a brief QSO. 

Succinctly explain what information they need to exchange and you'll both benefit from the experience. However you will need to know enough to help them out. For example, when a ham can only tell you they're in Ohio, do you know whether they're in CQ zone 4 or 5? If you can't tell them the correct zone they can't tell you, and that means you don't have a valid QSO. Be prepared.

Another advantage of giving a quick lesson on the contest exchange is that there are often lurkers listening. It is quite common that I get a few casual operators calling me after I explain the exchange to someone. A helpful and friendly SSB contester is a successful SSB contester.

Opting out

Although I don't dislike SSB contests they are not favourites. With my summer antenna work incomplete and major tower work in the immediately preceding days the CQ WW SSB contest was far from a priority despite its importance on the contest calendar. I was too tired and my score potential too poor to be bothered.

I took it easy and got on when I was so inclined. A geomagnetic disturbance made the contest a challenge on the low bands. For me the contest was an opportunity to practice running and observe propagation under unusual conditions. Openings on 15 meters were spectacular and running Europe was quite easy. Even 10 meters made itself felt. In contrast 80 and 160 were poor, and without a 160 meter antenna at present the latter band was irrelevant to me even had conditions been good.

It isn't necessary to operate every major contest or to do so competitively just because contests are one's primary interest in amateur radio. If you do it because you feel you must it becomes more of a job than a hobby. That's a recipe for losing interest in what you love to do. When the feeling isn't there, there is no shame in stepping back and being a spectator rather than a competitor. 

For me SSB contests are best enjoyed with others as part of a multi-op team, something that is difficult to impossible at present. As my station evolves I plan to host multi-ops for contests like these. By then the pandemic will be over and we can once again gather with friends for a weekend of SSB fun.

Presentation: DX'ing on 6 Meters With FT8

Those of you who have followed this blog for a while will know that I have a special passion for 6 meters. It has been so for many decades. Nowadays my primary focus is on 6 meter DX. When sporadic E season rolls around each year you'll find me on 6 meters, and not on HF.

In early 2019 I did a presentation about 6 meter DX'ing using FT8 to a local group of contesters and DX enthusiasts. I was subsequently invited to repeat the presentation to several local clubs. If you've heard more 6 meter activity from FN25 and surrounding grids I may be partly responsible.

For the RAC AGM this fall they took the advantage of it being done by video conference to organize a few hours of presentations preceding the business segment of the AGM. It was a learning experience for all and for the most part it went well. There were a few technical problems related to running several concurrent webinars using Zoom. My webinar was abruptly interrupted halfway through.

I recorded the audio of the second half of the presentation which was coordinated with the slides by one of RAC's technical gurus and spliced onto the first half video. It is now available for viewing on YouTube. For those interested it is embedded below, or you can find it on the RAC YouTube channel. It's just over 1 hour long.

Since I rarely put my picture anywhere on this blog it is an opportunity to see what I look like, if you care. I deliberately avoid including pictures of myself on the blog so that the focus is on the topics being discussed and not on myself. Too many people, hams and others, turn blogs and their social media channels into vanity projects. That I disdain.

Be sure to watch some of the other interesting presentations from the conference. One in particular that is especially interesting to me is by my friend Chris VE3FU/VO2AC about their DXpedition to VO2 for the CQ WW 160 meter contest. That was quite the adventure, and they didn't do it just once. Expect to hear them on again, if not this season then perhaps next.

The Zoom conference was open to all and there were participants from at least several countries outside Canada. A benefit of virtual conferences, because there is no travel required, is that every conference can be global. Most are of course of local interest only, such as the virtual meetings by a large number of clubs. 

I see no reason why the trend won't continue when the pandemic is over and hamfests return. The one thing I miss from hamfests are the flea markets and those don't work well virtually. Online swap shops are poor venues for buying and selling small items and browsing for the unexpected gem that you absolutely must have.

With regard to 6 meters, we are approaching peak sporadic E season in the southern hemisphere. Don't spurn the small winter peak north of the equator since, although DX opportunities are uncommon, the possibility of TEP to connect to southern stations is ever present. You should at least watch the DX spots for signs if you prefer not to monitor 50.313 MHz. You may be surprised.

80 & 160 Meter Verticals and the Tower Forest

An antenna farm is replete with interactions. Most are unwanted and detrimental. It isn't enough to deal with harmonically related bands since non-resonant antennas, guys, coax, control cables, utility lines and building metals will affect antennas when they are an appreciable fraction of a wavelength or longer, or if they are short and close.

Interactions can be eliminated if the offending conductors are within your control. Unfortunately the effort and expense may not always be worth it. Many hams are unaware of interaction problems or, unless it is especially serious, live with it. A few choose to pretend they doesn't exist. 

 

For those of us invested in high performance antennas those interactions can remove a lot of that performance and therefore require attention. It may not be possible to eliminate every problem but that is not an excuse to do nothing. The answer is to focus our efforts on the worst of the lot and, perhaps, deal with the rest later.

 

This article is about vertical antennas for 80 and 160 meters since the best for DX are verticals and towers are also verticals. That is, towers are inevitably a part of the antenna system unless they are exceptionally distant. Recall that "distant" is with respect to wavelength and a wavelength on these bands is larger than the vast majority of hams' properties.

 

There are several common methods for dealing with tower interactions: 

• Locate the vertical antennas as far as possible from towers. 
• Place verticals arrays and towers so that no tower is in the direction a directional vertical array is pointing.
• Have more than one vertical antenna for the low bands so that the directional deficit of one is covered by another.
• Detune towers so that they don't resonate on 80 or 160 meters.

Methods can be combined when helpful. For my antennas I placed the 80 meter array far but not too far from the towers. I wanted to keep the array close for unrelated reasons and the placement only disfavours one direction (southeast) which is not the most productive for DX paths in contests. Other directions are unaffected.

 

The situation on 160 meters is more problematic. The towers are supports for 160 meter antennas for the foreseeable future so the interactions must be dealt with in a manner that is most advantageous or, failing that, least deleterious. That can be difficult to achieve due to their large electrical length. As we'll see detuning is not always necessary.

 

You will not find many satisfying conclusions in this article. It's all part of my learning process. Expect food for thought rather than clearly defined antenna ideas.

 

Site plan

 

For this exercise I will use my own antenna farm since that's my immediate interest. Lessons should be applicable to other stations, both existing and planned. For those who cannot change what they have, whether due to lot size or other reasons, there is an opportunity to understand what is going on and to use methods such as tower detuning to deal with the most severe interactions.

The 80 meter 3-element vertical yagi is in the north field and the two big towers are in the field to the east and south. The northernmost is 150' and the other is 140'. The heights are nominal due to section overlap and masts. Actual heights to the top of the mast are approximately 46 meters and 43.5 meters, respectively. The Trylon tower near the house is 24 meters to the top of the mast.

The 140' tower is marked with a red dot since the Google Maps image predates it. The distance from the 80 meter central tower and driven element to the 150' tower and Trylon is ~60 meters, as is the distant between the big towers. 

 

Model notes

 

Since the Beverage antennas to the northeast of the image appear to suffer no pattern distortion due to these towers and antennas they will be omitted from the models. That is not always true, especially with vertical receive arrays, and those interactions must also be dealt with.

 

For the 80 meter case the 140' tower and Trylon will also be omitted, the first due to the distance and the second due its not being directly in one the array's four directions. That is not to say they have no effect but the effect is small enough that I am not unduly concerned. For the 160 meter case the Trylon and 80 meter array will be ignored due to their short heights.

The big towers will be modelled as 40 meter high thick wires with 2 capacitance hat arms at the top representing the top yagis. This is not exact and is in fact not really even very close to reality. The side mount yagis and the mess of control wires and coax are difficult to model and so they aren't. 

 

To see what the impedance might really be I plotted the R and X of both towers with an antenna analyzer, placing it in line with the wire to the ground rod. The galvanized ground rods are ⅝" × 10' and are located just beyond the subsurface reinforced concrete platform. The tower and pier pin are not bonded to the the re-rod so the bases do not behave as Ufer grounds.

 

 

As you can see it's a bit of a puzzle. The only recognizable resonance is around 1.2 MHz, which is not out of line with expectations. Overall the impedance is dominated by the ground resistance. All I can say is that the ground resistance (loss) at these frequencies is probably in the range 25 Ω to 40 Ω. The other tower has a similar profile.

 

At 1.83 MHz the impedance is 79 + j20 Ω, which is equivalent to a reflector with a lot of ground loss. This is not too unlike the model of an electrically long wire on 160 meter, and is an approximation I've used before. However the impedance is about the same at 3.5 MHz. Who knows, had I inserted the analyzer on a feed line or control cable the result could be very different. 

 

Modelling the tower as a simple thick conductor with yagis as capacitance hats and a resistance load (ground loss) at the bottom has no resemblance to the real world measurement. There is no simple model that mimics the measurement and I decided it would be foolhardy to make further attempts.

 

As a consequence, what a distant antenna "sees" is exceedingly difficult to know. This complexity limits what I can say about interactions, more so on 80 than on 160 meters. At least on 160 meters the measured impedance is likely closer to what a 160 meter vertical antenna would see.

MININEC ground is specified in the model with resistance loads at the bases of the towers and vertical antenna elements. These can be set to values approximating the ground rods and radial systems. We don't need to be very accurate for this overly rough analysis.

 

80 meter array

 

From the foregoing model discussion it should be evident that modelling the interaction is quite a challenge! So I won't try. What I did was try various electrical lengths of the 150' tower that is 60 meters distance.

Regardless of tower tuning the SWR of the 80 meter array does not measurably change. This is not surprising. Feed point impedance is the last thing to be affected by interactions. In order, the effects are felt in directivity and gain. It takes a far tighter interaction to alter the SWR.

Depending on tower tuning, with the 80 meter array pointed at the tower (southeast) gain varies by ±1 db and F/B is reduced by 3 to 10 db. Yes, the tower can act as a wide spaced director and increase gain. From my measurements, however, that is unlikely. From on air use I know there is gain southeast and a small degradation in directivity. That is, there is interaction but nothing too concerning.

When the tower is placed to the side of the 80 meter array, as it would be for northeast and southwest directions, the influence of the tower is small. Recall from the pattern charts for the 80 meter array the F/S is less than 10 db so there is just enough radiation towards the tower to have some effect. Pointed northwest, where the tower is behind the array, there is no interaction, and that is expected.

A more detailed analysis is pointless because of the discussed uncertainty of the tower's true effect on 80 meters. I feel confident that I can ignore it, just as I intended when I chose the location for the array. When directivity is insufficient to copy a weak station I can listen on the Beverages.

 

160 vertical centred between the towers

 
For the model I adjusted the towers to assign them the approximate measured impedance. This may not be representative of the situation at other stations. Despite that there are qualitative results that are broadly applicable. 

Assume a rope catenary from tower top to tower top supporting a vertical wire. Were I to build it that is how it would be done. This is not arbitrary since I planned to use this method to build a reversible 3-element vertical yagi by tuning the towers (LC networks) to act as directors and reflectors (see below for references). However in this case we take the towers as they are with their measured resonance and ground rods. This is an antenna I've looked at before but without the tower impedance data known.

The current magnitude and phase on the towers are equal when their impedances are equal, and that should result in a symmetric azimuth pattern. In other cases expect the pattern to be asymmetric. The feed point impedance at resonance is 28 Ω assuming a radial system with an equivalent ground resistance of 10 Ω, typical of no more than 8 radials. With a matching network the 2:1 SWR bandwidth is 70 kHz.

 

Bandwidth is not great and neither is the efficiency. Both towers together have about the same ground loss as the antenna itself. To improve efficiency you'd have to put radials on the towers since adding radials to the vertical won't fix the tower loss. The pattern is a problem if you have no other 160 meter antenna to cover the broadside directions.

This is not a very good antenna. It would help to detune the towers, not only to reduce tower currents and loss, but also to circularize the azimuth pattern. 

 

You may not know you have a problem unless you measure the impedance and resonance of nearby tall towers. Ignorance is not bliss.

160 bent vertical closer to one tower than the other

This antenna requires just one tower for the upper support. A rope from the bend is anchored on the ground to give the antenna its shape. The configuration of the towers is identical, electrically and physically, to what is described above. The vertical is 20 meters from one tower and 40 meters from the other. 

 

The antenna is a little like an inverted-L but with efficiency and bandwidth closer to that of a straight vertical. The angle of the bend is 45°. The radiation resistance is higher than the T wire vertical I've used for the past few years.

As you can gather from the EZNEC antenna view, including currents, the left tower's induced current is lower than for the centred vertical wire. Loss in that tower's ground is therefore lower. Current and loss in the right tower is about the same as for the centred vertical wire. Overall loss is lower so the antenna is more efficient. Rather than resulting in higher gain the power appears in the broadside directions so that the pattern is more omni-directional.

 

As you would expect from the asymmetric currents and the wire being closer to one of the towers the pattern is asymmetric. Before the second tower was built I knew from models and from operating that the pattern of the T wire vertical was directional by a few decibels, with the tower acting as a reflector. The result was a small deficit towards Europe. Even so it worked well in that direction.

With the second tower on the scene the deficit in that direction is reduced (on the plot left is northeast). Compared to the centred wire vertical the broadside deficit is reduced and is acceptable. The modelled 2:1 SWR bandwidth is 80 kHz, which while not great is good enough for my operating interests.

Here I have to use the term "good enough" since this is almost certainly the antenna configuration I will use this winter. It's simple and effective despite its imperfections. 

 

Actually the wire will be offset a few meters to the east so that two of the radials don't run into the stone wall separating the yard and the hay field (see satellite view above). That will skew the pattern so that the east (up) and west (down) directions will differ by about 2 db.

Efficiency of the antenna can be improved with a few radials on just the right tower. That is a feature I will consider. The antenna is simple enough that I could put up another to better cover the east and west directions. That is not a feature I am considering for this winter. I have the 160 meter mode on the 80 meter array available to fill pattern holes since it is more omni-directional although it may be as much as -6 db worse than the full size wire vertical.

160 vertical alongside the tower

A quite common style of wire vertical is to run it alongside a tall tower. It is given its own radial system so that there is no direct connection to the tower and lightning ground rod. Of course the wire couples strongly to the tower and its many cables, and ultimately the ground rod as well. This is not a shunt fed tower. Many report low to no deleterious RFI to antennas and connected equipment while others report severe problems. It seems to depend on details of cabling and yagi feed systems and the resonances therein.

I used the previously measured impedance of the tower at 1.830 MHz to model a grounded thick wire model of the tower and put a vertical AWG 14 wire separated by 2 meters, which seems to be a popular choice among hams who have tried this antenna. Again I use a MININEC ground with resistance loads at the base of the wire and vertical to mimic the loss of radials and ground rods.

The feed point impedance is around 25 Ω and with a 2:1 transformer (another popular choice) has an SWR 2:1 bandwidth of 80 kHz (say, from 1810 to 1890). That's pretty good. The pattern is skewed somewhat and the efficiency is poor. Current in the tower is high (as you can see in the plot at right) so even with a good radial system for the vertical wire about 40% of the power is dissipated in the tower's ground resistance via the ground rod.

Despite the gross simplification of the model this appears to be a risky design. Some of the loss can be mitigated by tying the radial system to the ground rod at the further risk of more serious RFI. It may be little better than a shunt fed tower, if at all. But, again, there is a lot of uncertainty in the model due to the unpredictable behaviour of the many cables on the tower and running toward the shack, whether over or under the ground.

 

Future 160 meter directional antennas

 

In an earlier article I explored recruiting the (unavoidable) towers as parasitic elements to make a reversible 3-element vertical yagi. Tuning the elements appropriately will be more difficult than in the simple models (again, all those cables) but it does get useful work out of towers interactions. Radials on the towers reduce the loss due to coupled current on the towers and, to a degree, may reduce the impact of the cables on the tower.

That only provides two directions since, as shown earlier, when the towers are somehow detuned or decoupled they are still present as non-resonant elements that will distort the otherwise omni-directional pattern of the driven element alone. Switchable detuning networks are needed to have an omni-directional mode.

In the future I will explore this antenna further and perhaps attempt an experimental tuning of the towers to see how well they can be adjusted to give the desired effect. I am less hopeful now than I was when I wrote the article that it will work well in practice.

 

Final notes on mitigation

 

Towers with resonances on bands with nearby antennas is a problem, even if you aren't fully aware of it in your operating. Some mitigation strategies were discussed but not analyzed in depth. For me these can be summarized as follows:

• Detune towers: This can be more difficult than it sounds. The problem lies with all the various cables alongside the tower. Placing an analyzer at the tower base can be misleading. A field strength measurement may be necessary to confirm that the pattern is circularized.
  
• Improve tower ground: Towers with substantial induced current and a lightning ground will decrease vertical antenna efficiency. Although it won't stop the interaction, lowering the ground resistance will improve efficiency. Several radials attached to the tower base may be all that's needed. The specifics are not described in this article but were confirmed in the model.
  
• Recruit the tower: Tall towers often act as reflectors quite naturally. Place your vertical antennas to take advantage of that and thereby improve your signal. Unfortunately you will then need at least one more wire verticals to cover all compass directions. With more effort the tower can be tuned as a director or reflector and that can be a great antenna.
  

Another technique that can work well in many circumstances is to disconnect the tower from the ground rod and replace it with a high value resistor and spark gap. Think of it as a more radical method of detuning the tower. This technique is typically only used on tower verticals that must be isolated from ground. Its value for a tower supporting multiple yagis and cables is less certain and introduces serious safety concerns. To be complete I want to mention it even though I recommend against it.

 

This is not the final word. My hope is that this limited analysis of potentially destructive interactions for low band vertical antennas will open eyes. Only then can corrective action be taken. It's food for thought that I will consider for my future 160 meter antenna plans.

160 meter antenna for this winter

As I write this I am not able to operate 160 meters. There is a fault in the 160 meter mode of the 80 meter vertical yagi. I have had little time to work on the problem due to more important tasks. The full size wire vertical can't be deployed until work on the 15 and 20 meter stacks is complete.

I will use a bent vertical described above rather than the sloped T used for the past few years. Interactions with the stacked yagis has not yet been modelled but I expect it to be minimized by locating the wire directly ahead of the lower, fixed yagis. 

 

Next year I may try something different. I'm out of energy and time to be creative with a 160 meter antenna for this winter. Unravelling those tower interactions is an intriguing puzzle that I am sure to return to.