Saturday, December 31, 2022

Anniversary and a Peek Ahead

The anniversary snuck up on me. It was almost exactly 10 years ago that I returned to amateur radio after being away from it for 20 years. I gave a few hints about how that happened in the very first article in this blog, which was published in February of 2013. There was more to it than what I wrote. No matter the circumstances, I am happy that I did come back.

The Elecraft KX3 that I assembled exactly 10 years ago, between Christmas and New Year's Day, was sold a few years ago. I had moved on and it no longer fit my operating style. Were you to peruse those early articles you'd notice how focussed I was on small stations and antennas, and how to get the most out of both. That's just who I am. Soon the DXCC countries piled up and then the reentry to contests.

With the resurgence of my radio ambitions, QRP no longer satisfied my appetite. I increased power and the antennas got bigger. A few years later I quit city life and moved to a rural QTH to give full rein to my ambitions. Although I certainly have gone far beyond what most hams would ever want to do, it filled a need in my soul. 

I am learning new things and achieving objectives I only dreamed about when I first ventured onto the air in 1972. I try to share that knowledge and enthusiasm in this blog. More importantly, I'm having tremendous fun. This is despite the many challenges of building and maintaining a station of this size. I continue to enjoy blogging so expect the pace of articles to be maintained.

The 530 blog articles (rate of one per week) since then follow my path and progression. That was my intent. Many hams make their sites a technical reference, updating and adding pages as they go. Mine is about the narrative: this is the story of my return and journey through the hobby. I let readers rely on the search function to find specific projects and other items of interest. The narrative doesn't end until I do.

I thought I'd end 2022 with an overview of what's in my station work pipeline. All of us have projects we're working on, and for me, at this time of year, most are indoors activities. Not all, but most. Many of these projects will get their own articles in the new year. This preview may be of interest to regular readers, or not. Whatever the case, here we go.

Station automation: first light

After several weeks delay I returned to software development for my home brew station automation system just before Christmas. This time I could put it to the test since I had the first phase of the switching system hardware assembled. For this first time the system would select antennas on band changes and alternative antennas for each band. I called this achievement "first light" in the same way a new telescope is put into service.

It's ugly but perfectly functional. Keep in mind that the switching system will be placed under the operating desk, out of sight. You'll hear relays clacking but that's all. In this picture the 20 meter stack is selected on radio 1. The second radio was not connected for the first test, and testing for that, and contention between radios was successfully tested shortly thereafter.

The first layer of relays controls the remote 2×8 antenna switch. I went with the same cabling as the manual switch for easy fallback in case of disasters. Since the picture was taken another layer of relays was added and is working. Despite the software being incomplete, the system is functional. The manual controller (seen in the background) handles functions not yet transferred to the new system. 

Cabling and connectors are a challenge but not nearly so bad as for the aborted design. The openness of the hardware eases maintenance and configuration changes. I hope to have the full system operational by mid-January. After it's complete and with at least one contest's worth of experience, expect an article on the project.

Operating desk

My current operating desk is very nice but not suited to effective multi-op contesting. Since that's my objective I built a new desk. This project was put on ice for quite some time when the pandemic ruled out multi-op contests. I am hoping to get to do one of those, with the new desk, later this winter.

The frame with the top removed (for painting) is shown at right. There's lots of legroom and shelving for peripheral equipment. The main support is at the rear where the heavy equipment, like the amplifiers, will be placed.

Installation was planned for the holidays but has been delayed until January. With so much progress on the automation system I didn't want to interrupt that project with several days of cabling and wiring work during the transition.

Related to this project is the purchase of PC for the second multi-op station. Only one PC is used for SO2R. It's a small desktop PC with an SSD and just 3 USB ports. It's lightweight, physically small and ideal for running N1MM. It has been set aside until the new desk is ready.

Beverage maintenance

The weather has been severe of late, with winds of 100 kph, heavy snowfall and ice. Add deer to the mix and the Beverage antennas are severely stressed. The northeast-southwest Beverage was bent out of shape by snow and ice laden trees and deer had chewed through a support rope. It was a mess. I spent a few hours repairing what I could. It works again but another round of maintenance is required.

The east-west Beverage is still unidirectional to the west since I ran out of parts to rebuild the lightning damaged head end. I hope to have that done in January. Other than that the Beverage system is working. With so much ongoing maintenance I have become more serious about considering a commercial vertical array. Perhaps not in 2023 but we'll see. I have other measures on my plan to reduce the system's susceptibility to lightning.

Prop pitch motor controllers

I have one old Hy-Gain controller that I will convert to a prop pitch motor controller. The transformers in the controller are not particularly suitable to making an op amp power supply so I will likely use the old controller's power supply. That and relays to remotely switch motor current from the Hy-Gain controller's levers will make a nice commercial looking solution. 

The project will wait until after the operating desk is replaced so that I don't have to do the wiring twice. For now I will, unfortunately, stick with the interim breadboard direction indicators.

40 meter antennas

The severe weather has taken another bite out of the big 3-element yagi. There are now two capacitance hat arms that have broken off, the latest one from the reflector element. The antenna continues to perform well but the problem must be dealt with. I have a couple of candidate designs to replace my poor choice for clamping the capacitance hats to the elements. 

I would also like to replace or complement the XM240 with a 2-element reversible and rotatable Moxon. I am at a preliminary stage of the design process to characterize the critical design elements. One objective is to eliminate all loads and their losses.

The elements must be symmetric for it to be conveniently reversible. That puts constraints on the mechanical design and switching electronics. I am unsatisfied by reversing methods that my brief research located, and I am working on alternatives. My initial model is similar in appearance to the Optibeam 40 meter Moxon.

The reason for making it reversible is to get 240° of coverage (2 × 120° of rotation) with a simple side mount rotator. I would like to avoid a swing gate for 300° coverage because the wind torque of a large antenna with an offset centre requires a more robust rotator. In particular, braking strength. I will most likely put this antenna where the TH6 currently resides and use the same Hy-Gain rotator.

No trap tri-band yagi

Following from above, the TH6 may go on the Trylon tower so that I have a rapidly rotating tri-bander for chasing multipliers. My longer term objective is to replace the TH6 with a trap-less yagi. I am looking at candidate designs. As time goes on I am increasingly unhappy with the unavoidable loss of traps. The Hy-Gain traps are pretty good but the design trade-offs are clearly noticable in comparison to my mono-band yagis.

Auxiliary antenna switches

The automation software has provision for up to 8 auxiliary antenna switches, and even for a 40 meter stack should I ever decide to do that. The immediate application is for 40 and 80 meters. I have two 40 meter antennas and I want to use a single port on the 2×8 switch plus an auxiliary switch to select between the XM240 and the 3-element yagi. I will do the same for 80 meters, using my old inverted vee for the second antenna. It's intended for short path contacts that are better served by a horizontally polarized antenna.

Using a switching hierarchy like this is common for contest stations. It makes the use of high power BPF (band pass filters) convenient and avoids over-subscription to the N×M antenna switch. The relays work fine on the low bands and may need compensation on 15 and 10 meters to keep the through impedance at 50 Ω. 

I hope to have these in place before spring, and when I do the 80 meter inverted vee will be installed on partway up the 150' tower. The feed line is already there. I need to buy enclosures for the switches, mount UHF jacks and install one SPDT relay in each. One of the existing Cat5 cables will be recruited to bring the control lines to the automated switch.

DX chasing

Yes, I occasionally get on the air! Although I sometimes wonder how I find the time. With one very rare entity currently active -- Crozet Island -- and another on the way -- Bouvet Island -- and improving propagation, this is a good time for DXCC chasers looking to reach the top of the Honor Roll. Rare DX is in my pipeline of things to do in early 2023.

It's karma that the Crozet call sign prefix is the same as the mode with the vast majority of the contacts to date. I hope that changes. The WSJT-X screenshot above was for my QSO with him on 30 meters. I have since done the same on 20. With these two contacts I now have a lifetime total of 3 digital contacts on HF. Until now I've restricted my use of digital modes to VHF and 160 meters.

I made the effort as insurance. If he has equipment failure or weather takes out the station I want to be sure I have Crozet in the log. With these insurance contacts in hand I was less anxious about working him on CW and SSB. He'll be active for some time and I expect to get what I want, eventually. (Note: Shortly after writing the above, I worked him on 20 meters CW. I'm happy.)

Soon we'll be bidding bon voyage to the Bouvet DXpeditioners and I wish them good fortune, for their sake and for ours. This one feels different because one of the team members, VE3LYC, is a friend. Although I worked Bouvet over 30 years ago, I restarted my DXCC count when I returned to the air 10 years ago. I don't believe in lifetime achievement awards.

Formal 2023 plan

2022 was a year when I took a break from building and installing large antennas. Expect a return to antenna work in 2023. I'll be setting project priorities for the year in the waning months of winter and be ready to go in the spring. As in previous years I'll have an article on my 2023 plan along with how well I kept to my 2022 plan.

Have a happy new year and I'll see you on the other side.

Monday, December 26, 2022

CW Contest Sending Speed

The speed of the CW we send in a contest is strongly correlated to our CW skill level. It's true even though we rarely use the paddles, by relying on computer software to do the sending for us. Is this sensible or is another strategy more effective? In a contest, effective means a higher score, and we score higher by having more QSOs, and that typically involves completing each QSO as quickly as possible. High speed CW depends on the skill and tactics of both stations in each QSO.

This is an important question since in a contest it is routine for highly skilled CW contesters to work less skilled operators. Indeed, many operators in this era of no-code licenses only learn the code in order to contest. There is often a wide discrepancy of ability that everyone needs to understand and deal with.

Since many CW contesters are old timers who learned the code decades ago, the difficulty newcomers face learning the code, and especially at the high speeds common in a contest, is not always appreciated. It takes time and practice, sometimes quite a lot. Few of us became proficient overnight! We forget that and become impatient when we are forced to QRS or are delayed by slow sending and repeats.

Hams with a natural talent for CW are fairly rare. I am not a member of that select group. Even today I sometimes struggle to send and receive at high contest speeds, and more when I take to the paddles. Years ago, memory keyers helped and today computer software takes over much of the effort. I built my first contest keyer in my teen years soon after I gravitated to contests. What a pleasure that was for a clumsy CW hack like myself!

Contests are not about having conversations. It is very possible to score well with modest CW skill. The computer does almost all the sending and copy is easier since the format is predictable and short. Although the sending speed you ought to select should be intuitive after spending an hour or two in a contest, I am always surprised by how many make choices that impair their results. 

Many casual operators do not care, and that's okay. Those that do want to increase score potential should reflect on the points I raise in this article.

For those who can't copy at contest speeds

A prevalent "mistake" by casual CW contesters is to send no faster than they can copy. When I ask why, they tell me that's what they're comfortable with. If that's 20 wpm, well, that's what they set the computer to send. This is odd because a large majority of contesters can copy much faster. Both operators are delayed and it isn't necessary. Go ahead and crank the speed up to 30 or 35 wpm when you call someone. They'll copy you just fine.

Consider S & P (search and pounce): You already know the call of the station being called, and that's probably the hardest information to copy. The exchange may be fixed (e.g. CQ WW) and if you use the call history feature of your logging software, the exchange may be pre-filled, or you already have it from their previous QSO. You need only verify that it is correct and make changes where necessary. 

For variable exchanges such as serial numbers, well, that you have to copy. But, again, you may already know what to expect based on their previously sent number. In any case, numerals are long characters (5 elements) and there are rarely more than 4 of them in a serial number. That isn't too challenging. Cut numbers are another matter which I won't get into (e.g. A for 1, E for 5, T for 0, etc.).

One thing you can be certain of is that the running station will not QRS to your sending speed. Not only does it throw off their rhythm and require extra work, they won't see the point since you obviously copied their call sign before calling them. Also, you probably already copied all or most of the exchange. Sending slowly does not help anyone in this most common circumstance. Be more aggressive; that is, be a contester and get out of the slow lane.

I know CW contesters who are not very competent at high speeds. They may use a CW reader application on their computers as an operating aid. They'll glance at the display to confirm what they copied or to fill in the gaps. A glance at the super check partial (SCP) window of known contester call signs is also useful as a sanity check: if it isn't in there you may want to listen again or request a repeat. 

There's no shame is using these aids as you climb up the lower slope of the learning curve. Check the contest rules since your entry class may be affected by the use of code readers.

Competition in the pile up

Another danger of sending slowly is that you will lose to the faster competition when other stations are calling. I deal with this quite often. Let's say that I am running at a good clip, sending ~35 wpm, with 2, 3 or more stations calling at a time. That's contest heaven: lots of callers but not so many that I can't pull one full call sign out of the bunch. 

I don't always pick the loudest or the one who starts sending first. Often it is the fastest that goes into the log. The reason is that I can copy it easily in a second or two. Time is of the essence. When I am operating SO2R it is critical that call sign reception take no longer than my transmission on the other radio or I will find myself having to copy on both radios at the same time, and that isn't easy. I pick the fastest since it is to my advantage.

Slow sending and long call signs upset my rhythm. It slows everything down and puts more burden on my short term memory, where your call resides until I type it in. When I pick the slower station, the subsequent delay discourages other callers since they don't want to wait the extra 10 seconds. They click on another spot and disappear. I not only lower my immediate rate and I might never hear that other station again. In my experience, slow stations don't immediately QSY when I answer a faster caller.

If you're not a contester, this reluctance to wait a few seconds might seem ridiculous. It is the reality we deal with and it affects scores. Send faster and you will become more competitive. If you have a weak signal or there is QRM or QRN the station you're calling will request a repeat. That may be a good time to QRS a little, but only then.

Help the other station by being fast. Unnecessary repetition of a call sign or exchange halves the effective speed. If you're already at 20 wpm, that takes you down to 10 wpm. That's breeds impatience and you may not get through at all. 

When there's QSB, QRQ is recommended because when it takes several seconds to send your call or exchange there is a strong possibility that one or more characters will be missed during a signal dip.

Running? QRQ could be a problem

Your speed does matter if you are running to attract callers. Many will QRS a few wpm. This is about more than courtesy: they want to move on quickly and if you ask for a repeat because they're sending too fast for you to copy the QSO takes more time. 

Of course there are those that never QRS, and that's a problem for both parties. Valuable time is wasted on repeats. I hear this all the time, and it's only funny because I am not one of the parties in the QSO. Operators who persist in calling slower stations at high speed often fail to rank high in the contest standings. That's not a surprise! The smart operator will QRS to get you in the log quickly so they can move on to the next contact.

Let's say you have to ask for a repeat of the QRQ stations' call sign or exchange. The effective speed of their sending is less than half of their actual sending speed. After all, the information is being communicated twice (or more) plus the time for the request to be made and the multiple turnovers in transmission and reception. 

Unrelenting QRQ slows the QSO rate for everyone. The slow runner is perfectly justified to ignore the persistently crazy fast caller.

Effective speed

The common method for calculating sending speed is by measuring the duration of character elements (dots and dashes). Character and word spaces are included in the calculation, using assumptions for character mix and average word length. A machine can do it easily, and they do.

CW Skimmer software measures speed quite well. Turn on skimmer spots on your favourite DX spotting network and soon your band map will be filled with skimmer spots. Watch the data in the Telnet window or (easier) hover your mouse over the call in the band map. The screen shot shows how it's done in N1MM Logger+.

That's only half the story. We are not machines and context matters. What we measure as CW speed (wpm or words per minute) is actually bit length: the time to send a dit. However, the true information rate is that of characters and words, and there are important variations.

Let me give an example of two call signs I worked in a recent contest: EE5X and OM0M. Despite both being 4 characters long there is an obvious difference between them. Using the common specification for CW keying, the number of dit lengths in the first call sign is 31 versus 53 in the second. That is, one of those calls takes almost twice as long to send at the same speed.

For many contesters, the one that is faster to send may seem attractive since it saves time. But therein lies a problem. The operator copying the call must work at twice the mental speed since the 4 characters come in half the time of the other call. That is the cause of many copying errors, and errors spawn repeats and busted calls and exchanges.

The Morse character set is deliberately optimized this way, similar to Huffman coding, by assigning short codes to letters that appear more frequently in typical English language text. Being less common, numerals and punctuation are given longer codes. Thus E is the shortest letter, at one bit, and J and Q are the longest, at 13 bits. It is no coincidence that E is worth 1 point and J and Q are worth 10 points in English version of the game Scrabble.

To bring us back to the point of all this, when you send at contest speeds, the message content matters. For call signs with short characters it can be very worthwhile to send more slowly. Conversely, call signs with long characters can be sent more quickly. It is quite easy to do so in most contest logging applications by altering the speed before and after call signs and to insert padding between characters.

Dealing with dits (again)

Following from the previous discussion, it is no surprise that strings of dits cause problems despite our best intentions. Ears and brains must work more quickly than for other element sequences. If your call sign has one or more of these strings, it is worthwhile giving some thought to how fast you send it.

This is a subject I've mentioned before, and more than just once. As much as I like my call sign it is a problem on CW. The VE3 prefix may seem to be a problem with its strings of dits, yet it rarely is. The prefix is so common that almost everyone recognizes the sound of it and can copy it correctly, no matter how fast it is sent. A few mistake it for VE2. For me the trouble lies with the second V in my call. 

My solution (first link in the previous paragraph) is to program a function key that sends the suffix slowly and with extra spacing. When the inevitable occurs I can correct the other operator with minimum effort and time. Unfortunately this only works for S & P; when running, few operators send my call sign and I can't correct them. If one of them spots me as VE3UN (the most common error) I am inundated with dupes. 

The error is so common that VE3UN not only appears in the SCP database, it usually appears above my correct call. When an operator "yanks" a call sign from the database it is often the wrong one. Thus the error persists, perhaps forever. Yet I have never heard VE3UN in a contest. Too many operator trust SCP without reservation. If you make use of SCP to cope with fast CW, be suspicious of what it recommends.

CW Skimmers don't often make this mistake, but they do make mistakes that are uncommon to human operators and apply to all call signs regardless of speed or content. Smart operator treat skimmer spots with extreme caution.

I envy other VE3 contesters with suffixes that are more easily copied because they're not full of dits. Perhaps one day we will be allowed 2×1 contest call signs. Until then I'll have to live with the problem. It is unusual to hear me sending faster than about 34 wpm in a contest because of this, even though I am comfortable at higher speeds. Meanwhile my friends can send closer to 40 wpm and be copied incorrectly less often.

Is there a speed limit?

A few contesters speed recklessly. They rely of spotting networks to distribute their call sign, or are blatantly unconcerned with whether others copy them correctly. All they want is your call in their log. What goes into others' logs, right or wrong, doesn't impact their scores. There are exceptions in a few contests where both parties must copy correctly but they are not the most popular events.

For those in rare multipliers, QRQ works to their advantage. For everyone else it often does not. Don't emulate them. Many operators will be scared off because they are unable to copy north of 40 wpm. How fast the speed demon can copy is irrelevant. The objective should be to be correctly copied without repetition. Moderating the speed delivers results even though each QSO, considered individually, may on average be quicker with extreme QRQ.

There is a tenet of effective communication that applies to all writing, and applies equally well to CW contests:

There are two ways to write. One is to write in a manner that is convenient to the writer. The other is to write so as to be read and understood. To be successful, be the second kind of writer.

When too many potential callers can't copy you or copy you correctly, whether in good conditions or bad, everyone pays the price. As in driving: speed kills; drive according to the prevailing conditions.

I find it both sad and amusing when an operator persists in sending at 40 wpm to a station sending at 18 wpm. There are endless repetitions and frustration on both sides of the QSO. I see it in contests and in everyday DXing. The keyer has a speed control and it's there to be used.

Enjoy the holidays. I can't say whether I'll have time to complete another article before January, so I may end December with one less article than is typical for me.

Tuesday, December 13, 2022

Overhead Cable Run: Version 2

I bury cables every time it is practical. This includes both transmission lines and control lines. I have thousands of feet of buried cable. This keeps cables safe from farm machinery, yard work, antenna maintenance, most critters (including human!) and other mishaps. Of course the cables must be suitable for direct burial. I do not use conduit.

There are several places where I run cables overground. For the Beverage system in particular there are long runs of RG6 that lie directly on the ground. I can get away with that in the bush where no one goes but me. Tree roots and other obstructions can be major impediments to burial, but it is convenient to go overground for long runs where it is not unsightly and the risk of damage is low.

The most important overhead cable run is from the edge of the hay field adjacent to the house yard to the Trylon tower where most of the switching and cable interconnections is located. The overhead run was a temporary measure until I had time to bury them. Since then I have come to realize that overhead is better. Maintenance and changes are easier. The mat of tree roots a few inches below grade make burial a formidable challenge.

The original overhead run was not sufficiently robust to survive for many years. Construction was admittedly rushed to leave more time for major tower and antenna projects. This year that had to change. Sagging and anchor woes coupled with the addition of more cables spurred me to act. The first step was to replace the ground anchor with one that is better able to support the messenger cable and the weight of the many cables. Once the concrete cured I got to work.

It is helpful to describe the problem and the underlying theory before diving into its construction. Let's do that using the following diagram.

The messenger cable is anchored to the tower and the ground. The post outside the stone wall keeps it at a safe height to walk beneath. Tension is needed to resist sag due the weight of the messenger cable and the cables it supports. The greater the tension the less the sag. This is a critical design parameter since there is stress due to tension on the tower and on the ground anchor. 

As we'll see, it takes a lot of tension to reduce sag to an acceptable amount. Even with high tension, sag is unavoidable. Consider the picture at right of the top guy on the 150' tower. The static tension (pre-load) is more than 1000 lb, yet it sags a foot or two. The guy is ~200' of 5/16" EHS guy strand. We won't come anywhere near that tension on the messenger cable!

This brings us to the catenary. It is a common subject in the ham literature since our antennas bend and sag due to wind and gravity, affecting performance and survival. Catenaries are more discussed with respect to wire antennas where the effect is particularly noticable. The physics and mathematics of catenaries is deceptively complex, and that is annoying when we want a quick answer to what appears to be a simple problem.

My "simple" catenary question: how much tension is required to have no more than 2' of sag in a 60' horizontal messenger cable and its cable load? Finding the equations that provide a reasonably accurate answer wasn't quick. I found the answer first by measuring the tension and the sag. The required tension is more than I can tolerate for the constraints I am faced with. 

Before diving into the mathematics I'll describe my practical approach. I ran the new ¼" EHS messenger cable above the existing overhead run, anchoring it to the tower with galvanized chain, to a replacement 10' steel post, and down to the recently installed ground anchor. I used several rubber tie-down straps to tie the cable bundle to the new messenger cable. A come-along at the tower anchor was used to increase the tension and measure the sag. As tension increased, the old messenger cable went slack and the cable load was taken up by the new messenger cable.

The old ⅛" aircraft cable messenger and aluminum post remain tied to the cable bundle. Had there been a mishap it would be there to retake the load. The old cable was temporarily transferred to the new ground anchor.

At right you can see a yellow rope that runs from the old post to the 150' tower 100' behind the photographer. I did that when the screw anchor failed. There is a steel peg under the post that provides good lateral support, but that is not reliable enough on its own. 

That peg gave me the time I needed to install the rope support. Whenever possible never have a single point of failure in a critical system.

My Loos cable tension gauge was mounted on the new messenger cable to monitor the tension during construction. I did not do this for the original cable, relying on "feel" to keep the tension within reason. 

To meet my sag target on the original system I had to install two intermediate 8' posts. They divide the span into 3 approximately equal sections which greatly reduced the sag for the amount of tension I was comfortable putting on the messenger cable, post and anchors. My hope was to eliminate the intermediate posts with the improved messenger cable. They can be a nuisance.

The top picture immediately above shows detail of the old and new posts during the project. The one on the bottom shows the Trylon anchors, old and new, with grips for the messenger cable and for attachment of the come-along. Look closely and you'll see that that plated chain for the old tower anchor is rusted. 

Galvanized hardware is more durable than plated hardware. This is especially important on smaller hardware since there is less base metal. I recommend spraying metal (rust) or cold galvanizing paint on plated hardware every couple of years. Galvanized hardware will eventually wear and also need to be painted.

When I increased tension to 700 lb tension (measured tension includes the weight of the cables) there was still too much sag. I couldn't safely walk beneath the cable. The cable and ground anchor can handle that tension but I am not so sure about the Trylon tower. Increasing the tension was out of the question since it rose alarmingly for little reduction in the sag. I lowered the tension and hit the internet to dig deeper into catenary mathematics.

Catenary theory is fascinating. For a mathematically minded person like myself it is easy to slip into the depths. Easy but unwise since I had an immediate problem to solve. Much of the material I encountered was far too general and required effort to simplify the equations to fit my project. More digging was required before I found what I needed.

There are many resources on the internet and I am sure there are better ones that what I found during the time I spent on researching the question. There are also spreadsheets to do the calculations Here is the link to the page that I found most helpful. It isn't perfect but it gets to the heart of the matter: the relationship between sag, tension and weight for a uniform horizontal catenary.

S = (WL²)/(8H)

S is the sag, W is the unit weight of the catenary (including the cable) and H is the tension. Any units can be used but they must be used consistently. I'll use English units in this discussion: feet and pounds. The only difficult variable to determine is W, which is the weight of the messenger cable per foot. From the known weights of the EHS, Heliax and heavy control lines that comprise a large majority of the weight, W is estimated to be 5 lb/ft. That comes to 300 lb for the 60' span.

For a tension of 700 lb the calculated sag is 3' at the midpoint of the 60' span. Since the ends are about 9.5' above ground and the bottom of the cable bundle hangs about 6" below the messenger cable, the ground clearance at the midpoint is 6'. This is surprisingly close to what I measured; it brushed the top of my head. Either I did the calculation correctly or I was lucky.

As I said, 700 lb of tension is too high, so the sag must increase. That is unacceptable. Even were higher tension permissible, the required tension rises rapidly. Notice that sag is inversely proportional to the tension. For example, to halve the sag to 1.5' (which would meet my objective) the tension is 1400 lb.

I concluded that the intermediate posts must remain. That makes 3 spans of 20' each. If I cut the tension in half to 350 lb the calculated sag for the shorter span is less than 1'. Since the posts are 8' high the bottom of the cable bundle at each of span midpoints should be almost 7'. And, indeed, that is what I measured. I think I'm getting the hang of catenaries!

In this picture the tension is less than 300 lb. Lots of rubber straps have been installed to hang the cable bundle; more were added after the picture was taken. I didn't use them for the old messenger cable, opting for plastic cable ties each time cables were added to the bundle. Although I no longer need the ties they might as well be left there until cables need to be removed. It's messy but not a problem that needs fixing.

Notice that straps are not placed close to the posts. When I tried, the cables were pressed hard against the post. It is possibly that could damage the more fragile cables over the coming years. By the time I was done there were about 15 rubber straps spaced an average of 4' apart. They're cheap and effective. I've heard that the rubber is prone to UV damage but the ones I've had outdoors for a few years do not show signs of deterioration. They'll be inspected at regular intervals.

There is one last item to discuss: lateral stability. The overhead run present a large surface area for the wind to press against. For a 60' run witha 4" cylindrical cross section, the total projected surface is 20 ft². That's a lot! For our wind zone it is recommended to build for a wind speed of 135 kph (85 mph). At that speed the wind load is 20 lb/ft², which adds up to a total force of 400 lb on the overhead run.

The actual force will be much lower. The overhead run is close to the ground and there are many obstacles that block wind that is orthogonal to the cables. The overhead run does lean to the leeward in high winds but not enough to be at risk. 

Snow and ice increase the unit weight but, again, it hasn't proven to be a problem. What is a problem is snow on the ground which reduces walking clearance by a foot or more in late winter. I am not too concerned by that since few people other than myself are likely to be walking there when that happens.

There are a few more steps left to complete the project. Now that the strength and reliability of the new structure is confirmed, the old messenger cable, post and tower anchor will be removed. After that is done, the new post will be fitted to the ground peg the old post still occupies. The new post leans a bit since it had to be placed several inches from the old post. I should be done by Christmas.

Monday, December 5, 2022

Prop Pitch Direction Pot Updates

When I raised the first of my big towers in 2017 there was no direction indicator for the chain-driven prop pitch motor rotator. I made one using a Bourns 10 kΩ 10-turn potentiometer, a device used by other hams of my acquaintance. 

These components are not hardened for outdoor use and require protection. I built a plastic enclosure on a bracket dangling below the motor platform and hoped for the best. It lasted 5 years, far longer than I expected.

It was time to replace the pot on that prop pitch rotator. The pot had water damage and there might also be internal mechanical wear. The resistance jumped around a lot during rotation and there is evidence of bald spots on the resistance wire.

I went through at least two plastic "hoods" for the pot. The container seen above replaced the original, which was too small to adequately protect against wind driven rain. I repurposed food containers to save cost for what I expected to be a temporary measure . The work great when they're new. Of course they are not resistant to UV and thermal cycling also takes its toll.

As the plastic cracked the silicone sealant around the gaps couldn't block water incursion. Notice the rust at the base of the pot shaft. It was always a danger of this design because the pot shaft points upward, and open to rain and snow without excellent water protection.

An underappreciated problem with ordinary pots in rotator service is wear due to rocking of the mast and antenna system. This is directly coupled to the direction pot, with the pot wiper moving back and forth over the resistance wire where it is resting. 

The wire in a typical pot is not designed for this amount of abuse. They have a limited service life in this application. In contrast, the pot in a Hy-Gain rotator (photo credit: MFJ) is much larger with thicker wire and a wide wiper. It may help to vary the direction of the yagis when they are not in use.

The multi-turn linear pot has its advantages and it is not too much of a burden to replace them every 5 years or so. To better protect the Bourns pot from the elements I undertook a redesign. I had planned this for some time but put it off until the pot failed.

The chain-driven drive shaft is 2" OD with a wall thickness of about ¼". I projects less than 1" below the bottom of the housing that sits on the side of the tower. There is just enough room to fit the Bourns pot. So that's what I did. As you can see it's completely enclosed and well isolated from the elements. There is no opening above the drive shaft where water can enter.

The difficulty with this design, and the reason I didn't do it this to begin with, is that with the pot fixed in place it is the shaft that turns. The wires must turn with the shaft. Alignment of the shaft is critical to avoid bending force that can bind the pot during rotation. As for the first version, the pot is mounted on thin aluminum flashing that flexes to protect against a minor misalignment.

I tied down the wires to prevent tugging on the pot terminals. The 3 wires are coiled around the coupling. The wires are AWG 24 scavenged from stranded Cat5 cable. The plastic insulation is very pliable but it is stiffer than the wire when used in this application. Disciplining the wire coil is therefore not easy. It looks ugly but it works. Now that winter has arrived we'll see how it does when coated with snow and ice. A snow shield might be necessary.

On the other prop pitch motor turning the 15 and 20 meter yagis I encountered a different problem with the direction pot. A few months ago I replaced the temporary rope belt with higher quality ⅛" nylon weave rope. Since little friction with the mast and pulley is needed to drive the pot I kept the tension low. The rope loosened only slightly but that was enough for it to slip. Worse, it preferentially slipped in one direction. 

At first this could be dealt with by adjusting the zeroing pot on the op-amp direction indicator. With the continual back and forth rocking of the mast the pot soon hit the end of its 10-turn rotation and could no longer be adjusted. I climbed the tower and confirmed the nature of the problem. I centred the pot and pulled out the adjustment bolt to increase tension on the rope.

With the higher tension the mechanism has been working well for the past few weeks. I hope that it survives the winter. Another design may be necessary. One example I've considered is a chain drive. It would provide positive engagement without fine adjustment of chain tension.

I have discarded bicycle chains and cogs (½" pitch) to work with. The challenge is that there is no way to slip a cog over the mast. The cog would have to be cut in half and machined and attached to a collar that wraps around and is affixed to the mast. The pulley on the pot shaft would be replaced by a small chain cog. A master link solves the chain wrap problem. It's straight-forward work that I hope to avoid. Time will tell.

The direction indicator circuit described in an earlier article works perfectly well but it is more complex than currently needed. The goal was a circuit to drive either a physical meter or an analogue Arduino GPIO. The needs are different because a meter responds to current and the GPIO ADC responds to voltage. A second gain stage provides the required voltage range without risking the linearity of the differential amplifier.

Since my immediate plan is to use physical meters the second stage has been eliminated in the schematic shown above. I used the freed space on the breadboard to build two of the circuits. A few days before CQ WW CW I discovered that the meter movement of the old direction indicator (for the 40 and 10 meter yagis) had malfunctioned. The single op-amp circuit is a temporary fix since I needed it for the contest. As these things go, I expect it'll be in service for a while yet.

The circuit provides a minimum 10 kΩ load for the op-amp to keep it stable. The pot is tapped with a current limiting resistor to protect the meter movement. The resistance range was selected to support a large range of current requirements and drive ratio at the direction pot. The circuit is simple and works well. Calibration is performed in the same way as for the original circuit. Substitution of the current limiting resistor may be needed for meters other than the ones I have tried.

Because there's just one meter, one of the meter wires must be moved between circuits to monitor the direction of each prop pitch rotator. An SPDT switch would make this job easier. The arrangement is far from ideal but acceptable in the short term while I decide on a final design. 

I may do what some others have done, by repurposing an orphaned Hy-Gain rotator controller. The meter indicates direction and the levers operate the motor. Unused circuitry in the controller can be removed or left in place in case it is later returned to service as a Hy-Gain rotator controller. It also looks good on the operating desk. A home brew professional looking controller is a lot of work.

There is RFI, which shouldn't be a surprise considering the layout. You can see one RF choke at left on one of the pot wiper lines. This was proof of concept to see how it would help. It suppressed most of the RFI but not all. When properly built the lines will be choked and bypassed to suppress RF getting into the circuitry. Lightning protection must also be included, but probably at a connection point far from the shack for maximum safety.

My next step is to find a used orphan rotator controller and build permanent direction indicator circuits. The ±12 VDC for the op amps is not easily built with the stock transformers in Hy-Gain rotators so I may use the existing power supplies and wire them up to the controllers. The motor controls can be implemented at the same time or later.

Wednesday, November 30, 2022


Of the many types of articles on this blog, the statistics tell me that contest reports are among the least popular. Well, too bad, because this is another one. I decide on articles based on my personal interests in the hobby and while it's great when the reader's interests coincide with mine that is not why I choose a topic. 

Many will skip this article and that's okay. I write them to reflect on these events in written form because it helps me to understand what happened and what I might or might not do differently in the future. If you're still with me, let's dive in.

Picking a category

After my burnout in last year's contest I was not enthusiastic about doing an intense all band 48 hour contest. It's hard on the body and mind. The impact increases with bigger stations (and rare call signs) because the pile ups are intense and they go on for hours. To be truly competitive you must use SO2R and 2BSIQ. As they say, it isn't my cup of tea. These and more lessons are in the article I linked to immediately above.

The alternatives are the Classic 24-hour no frills category or a single band. I wanted to be active throughout the contest period so a single band entry made sense to me. But what band?

I did 15 meters for the SSB contest and the low solar flux did not bode well for 10 meters. Reports by friends that entered as single band 10 meters suggest that I made the right choice.

20 meters is really tough due to the sustained high density of stations and the long openings. There are enough 160 DX contests to scratch that itch and 80 meters can be a painful noise filled slog. I am reasonably competitive on 80 with my vertical yagi but it is inferior to many of the big guns.

Which brings us to 40 meters. Propagation on 40 is quite fascinating since it is open day and night -- though far better at night -- and globe circling short and long path openings are surprisingly common. A middling solar flux is ideal on 40 because the high traffic paths, especially the one to Europe, can last all night long. Peculiar and surprising propagation entices me in much the same way as 6 meters. But outside of contests those openings are not well exploited and the band can seem dead most nights.

It was also my first opportunity to try the new 3-element yagi in CQ WW since it went up last December, a few weeks after the contest. The antenna is very competitive and I thought it would be a lot of fun to see what it could do for me in this premier event. Combined with the XM240 at half the height the antennas offer good performance and operational flexibility. 

So that's what I chose: 40 meters. I opted to make use of spots to maximize the potential for multipliers and reduce the tedium of constant tuning and finding mostly dupes. That's expected for a single band contest or single band entry in multi-band contests.

Sticking with SO1R

SO2R is very difficult to do in a single band entry. Getting antennas far enough apart to prevent receiver damage is rarely practical. The alternative of wiring the transmit antenna through a receive port to the second station limits listening to when the primary station is also receiving. Hunting on the second receiver is constantly interrupted and the operator can't escape having to listen to both receivers while hunting.

I still wanted to try it. One stumbling block is N1MM Logger's lack of support for two keyboards in SO2V operation. In this style of operating the sub-receiver (or SDR slice) in rigs like my FTdx5000 has its own entry window. With one keyboard the operator uses keyboard shortcuts to manage use of the two VFOs. That can be difficult and is why I do SO2R with two keyboard. When the challenges already mentioned are included, SO2V was a step too far.

I stuck with SO1R and manually tuned and switched the VFOs. I've done this before with a K3S and it works well if you are careful. Being assisted helps because you really only have to click on spots. The trick is in timing the VFO switching so that you hold the run frequency and send your call and exchange in sync with both the running VFO and the hunted station's transmissions. 

It did it numerous times when the run rate was low. Doing it when the rate is high is well beyond my ability. A second operator to hunt is better but you still can't listen full time unless you design some way for the sub-receiver to withstand the kilowatt transmitter only a few kilohertz away.

Propagation and antennas

Despite less than quiet geomagnetic conditions the band was very good. There was no noticable attenuation on paths that skirt or cross the auroral zone. That's often a problem for those of us located at a high geomagnetic latitude. In fact, signal levels were very strong at times. 

Many QRP stations made it into my log, including JA6GCE. It is no surprise that a big signal attracts the smaller stations. I did the same when I regularly contested with 5 watts and low wires. I am happy to swap roles to put more contacts in their contest logs.

Relative performance of the high and low yagis made apparent the daily cycle of propagation on 40 meters. You can work the European big guns during full daylight but not the smaller stations due to D-lay absorption. That isn't necessary since they'll still be there when sunset approaches. Getting a few hours of sleep is more important. 

We can easily work Americans throughout the day, if only they were active. Daytime contest activity is high within Europe but not here. There's little point for the Americans in CQ WW when they only have a handful of Canadians to work. They do far better to stick with the high bands. The situation is very different for domestic contests like Sweepstakes and NAQP with high 40 meter daylight activity.

About 2 hours before sunset it becomes possible to run all European stations. At that time the best antenna is the low yagi. It outperforms the high yagi by 1 to 4 S-units. During daylight the ionosphere's D-layer preferentially attenuates low elevation angle radiation since the traversal path is longer than at high angles. A similar effect dims and reddens the sun when it is low to the horizon.

Around 30 minutes before sunset the relative performance of the yagis undergoes a rapid transition. The two antennas become equally effective and then the high antenna easily does the best. That continues until sunrise. The EZNEC elevation plot is of a typical 3-element yagi at heights of ½λ and 1λ. Notice the null in the pattern of the high yagi. It doesn't do well at elevation angles around 30°. 

Of course this is why many contesters stack yagis. You can choose the antenna that does best and combining them for extra gain. My yagis are not stacked so I pick the one that performs best at any given time. When I turned an antenna to work a multiplier I could keep running on the other, even if it was not the best. A kilowatt can overcome much of the deficit. Indeed, many times it hardly mattered where the antennas were pointed: everyone called me and I could work anyone I called.

Activity level and patterns

In single band contests, and Sweepstakes, you can run out of stations to work. Although CQ WW is a 6-band contest the concern still applies to single band entries like mine. Conditions and contest popularity are critical to sustain rate for the duration of the contest.

I am happy to say that I never really ran out of stations to work. However, there is a rhythm to any contest that relates to time zones and personalities. Understanding these factors can improve your score.

Committed contesters are active for most or all of the contest. Most are active on all bands, but they show up on 40 meters often and they are easy to work. If the opening is brief you hope they are aiming for eastern NA at the best times. This is especially true for those in distant zones and rare countries.

Casual operators are the majority and they tend to be active according to their personal schedules and not the propagation or necessarily in a fashion to maximize their scores. Hams, like all people, can be broadly classed as morning people and nighthawks. I am among the latter. That doesn't matter in a contest since I put in the time regardless of my preferences. To contact the casual operators I take account of their operating patterns.

Let's take Europe as an example since it's a rich vein of contacts and multipliers and relatively easy to reach on 40 meters. Most hams are free in the evening to operate and so they do. That's late afternoon for us, which is perfect for the early sunsets this time of year. The rates are high. As midnight comes and goes in Europe only the nighthawks remain among the casual operators. Conditions may remain good but the rate declines.

Sunrise sweeps across Europe starting at about 2 AM in eastern NA. That's when the morning people in Europe appear. The rate picks up and holds until the high bands draw them away or the day is too far advanced and conditions deteriorate.

The lesson for score conscious contesters is that you must be there at the appropriate times to work both groups of casual operators. Their preferences should guide your activity more than your own.


I used the Acom A1500 exclusively in the contest. It is a manually tuned tube amp. Settings for the Load and Tune controls is determined by the output impedance and frequency. The impedance is never the same for two antennas unless the SWR is exactly 1. The CW spectrum commonly used in a busy contest like CQ WW is from 7000 to 7080 kHz. Amplifier adjustments are typically needed for a QSY of about 30 kHZ for optimum performance.

Optimum performance is desirable but not strictly necessary. If you don't adjust the amp, the most common outcomes include reduced power, lower efficiency (higher heat dissipation) and excess screen and control grid current. For my 40 meter antennas and the frequency range it was not absolutely necessary to adjust the tuning after every change. A drop of 200 watts is not that much and it rarely affects my ability to snag a multiplier or work a station in a different direction.

I regularly monitored the screen current and temperature and I never had a problem. I grew comfortable only adjusting the tuning when I changed my antenna preference to target or QSY'd more than about 30 kHz. Exhaust air temperature was never uncomfortably high under worst case conditions, which was CQ'ing for several minutes without a reply.

Perfection has expensive taste. Don't let it seduce you. Good enough is good enough.

Running vs chasing multipliers

A multi-band SO2R operator can very effectively run on one band and hunt multipliers on another. All you must do is time your transmissions to smoothly interlace the QSOs. It is far more difficult for the single band operator since you will have great difficulty receiving on one frequency when transmitting on another. Unless you're an extreme case you cannot receive while transmitting. 

That makes multiplier hunting far more difficult. It is more difficult for unassisted operators. That is why, although I prefer unassisted operation, that I have only one band to work with.

Using the SO2V feature of N1MM can help. The second receiver or slice has its own window. Since the feature doesn't support two keyboards you have to use keyboard commands to switch windows/VFOs for entering data and sending messages, while paying close attention to coloured dots that tell you which VFO is doing what. That's a problem for me and is why I use two keyboards for SO2R.

I did it manually by manually activating the sub-receiver of my FTdx5000 and used the 'A⇨B' and 'A⟺B' buttons to sync and swap the VFOs, respectively, so that I always transmit with the main VFO. There are AF Gain knobs for each receiver. I set the level of the sub-receiver lower to avoid copy errors on the run frequency, which is more important to me. It's awkward and I made many mistakes, such as punching the wrong button or losing the run frequency. Perhaps practice will improve my success, but I don't know how much importance to attach to this skill.

Most logging software will helpfully tell you the marginal value of a multiplier. For example, if you have 100 QSOs in the log at 2 points each the total QSO points is 200. If you also have 30 multipliers the calculated score is 6000. A new multiplier is worth 200 points in addition to the 2 points for the QSO. The marginal value of an ordinary QSO worth 2 points is 60 (30 × 2). Therefore the marginal value of a multiplier is approximately 3.3 QSOs.

If your run rate is 1.5 per minute the implication is that you should not dally with the multiplier if it costs you more than 2 or 3 QSOs on the run frequency. The chase tends to cost more on a single band than with SO2R on two bands due to the challenges described earlier. You have to decide what to do based on your abilities and the trade off of cost and benefit.

However that is not the whole story. The marginal value of the multiplier is not the value of the multiplier for the full contest. The multiplier continues to apply to all future contacts. A multiplier's marginal of value of 200 when you have 100 QSOs in the logs grows to a value of 1000 if you expect to make 500 contacts in the contest. In that light the multiplier is really worth 16 QSOs, not 3.3. If you pay attention to this statistic you'll notice that it increases as the contest progresses.

On the other hand if it is indeed early in the contest you can hope to work the multiplier later and focus on running at present. Of course that is a risk. I often took the risk because of the difficulty of single band hunting while the runs were good. Sometimes it worked out and sometimes it didn't. Those desired multipliers don't always reappear.

There were many times that I had to abandon chasing a multiplier to return to rate production. One example is 4U1UN. They are close enough to me that at night all I had for propagation was watery back scatter. I could not get through the massive pile up, and I could not afford more time since it was prime time for Europe.

For a final observation, be aware that CW spots have two sources: human and skimmer. I notice a dearth of human spots from outside of Canada and the US, inside and outside of contests. Most operators now appear to rely on skimmers and no longer bother posting spots. SSB is different but this is a CW contest. The pile up starts seconds after I see the skimmers broadcast my CQs. That typically takes 15 seconds or 2 to 3 CQ's. 

I have mostly relied on human spots and I disable most data coming from the RBN (reverse beacon network). That is a mistake. I plan to change my cluster settings to pull in more skimmer data.

Trouble with dits

Over the years I've become far more proficient distinguishing 'S' and 'H' and other characters with strings of dits at high speeds. Others are less proficient. It is also a frequent problem with skimmer decoding. Few have difficulty understanding 'VE3' since it's common and expected. The 'V' in my suffix is a source of trouble when I send CW at high speed in a contest.

A bad skimmer spot or human spot can cause grief. My call is regularly miscopied as VE3UN. It is so frequent that the call appears in the master database that most contesters use for the SCP feature (super-check partial). Worse, it appears in the list above my true call. So when mistakes occur that's what they pick.

The bad spot draws assisted operators by the droves late in the contest when there are few stations left to work. Working dupes during my run improves no one's score, and it drives away good contacts that, understandably, won't wait in the queue. Telling everyone 'B4' wastes even more time. I have a function key that sends my call with 'VN' at reduced speed, but even with that many operators pay no attention and keep calling. I could try changing my call by battling the federal bureaucracy but I like what I have.

Experienced contesters know that it is better to accept the inevitable and QSY. Don't become stubbornly attached to a run frequency. The minute or two it takes to find another is well worth the effort.

Fatigue and time management

They award no prizes for good time management in CQ WW. Whether I operate 48 hours or 15 hours, all that matters is the final score. There is a Classic category where the time limit is 24 hours, which did not interest me. Only then do you need to pay close attention to off time rules and schedule your time accordingly.

I don't know my official participation time since I didn't look and I don't care. When I needed a break and the time was opportune I stepped out of the shack. The 30 minute rule was irrelevant. Fighting fatigue by taking care of my body and mind took priority. 

I operated right through both nights of the contest because the band was open and productive. That takes a toll. The few hours of sleep I got was at midday. I had to fight the decline of my faculties as the contest wore on. In the final hours I was making mistakes that I rarely when I'm alert. 

One example is short term memory. When I'm distracted my mind records the CW I hear and I then play it back to copy the call sign. When fatigue set in the recording was blank and I had to request a repeat. A second example is that I once hot switched the antennas. The amplifier instantly faulted and went offline, protecting against damage. Hot switching is prevented with my station automation system but it is not yet installed.

As I type these words I am mostly recovered from the contest and my sleep cycle is back to normal. I am taking it easy today and writing this article because following the contest I got a COVID booster shot. That result in one day of minor aches and lethargy. The rain is pouring down so I don't care. I purposely delayed the appointment until after the contest. There was no point going into the contest with an avoidable handicap.

Bottom line

I exceeded my informal QSO goal of 2000 by over 10% (2231, not including dupes). Despite surpassing DXCC before sunrise on Saturday morning my country total hit a wall. The same with CQ zones. There were many multipliers that were almost worked or that were unworkable. 

40 meters is perhaps the easiest band to sweep all 40 zones in CQ WW from this part of the world. I did pretty well by logging 37 of them but the other 3, all in Africa, somehow eluded me. On the other hand, sweeping all the Asian zones is remarkable. The openings over the north pole were extraordinarily good this weekend.

A couple of club members informed me that my raw score is a new Canadian 40 meter record in this contest. That would be wonderful despite my total ignorance of the record and having set no explicit goal. My objectives were to do well and to have fun. Those objectives were achieved. 

My final score and the status of the record will have to wait for log checking and the publication of the results next year. Mistakes are inevitable and my final score will be lower. I don't anticipate a large score reduction.

Lessons learned and station plans

No matter how big your antennas or the skill of the operator there is always a station better equipped. A full-size 3-element 40 meter yagi up in the lower stratosphere is a great antenna, but it pales in comparison to the even bigger antennas and stacks at the largest contest stations. 

I was outgunned more often than you might imagine. Even where my station was superior I could be beat by a more skilled operator or by the unavoidable vagaries of geography and propagation. Life isn't fair, and I'm okay with that.

Can I do better? Of course. Should I do better? Aye, there's the rub.

My preference is to organize multi-ops in the major contests. That way the station is maximally utilized and we can compete at a high level. Repeated high intensity single op entries is not what I want. I will continue doing it for a while longer. 

Although it has been interesting to learn the necessary skills to be a more competitive single op, and thus improve my skill level and results, it is not what I want to do all the time and, frankly, I will never do it particularly well. I am a good contest operator but I will never be a great contest operator. The unplanned long length of this article contains various lessons I hope to learn from.

In regard to the station, I absolutely will not stack a similar 3-element yagi on the tower. I'd need a ring rotator at the least and I'd have an ongoing worry about the tower's ultimate capacity. 30 ft² per antenna is a lot! The incremental load on station maintenance is an additional burden. The stack would have less than optimum performance since the antennas would not be high enough and the ½λ spacing not wide enough. For the predicted improvement it isn't worth the investment and maintenance. Others choose differently. 

What I will consider is a fixed wire yagi or lightweight rotatable yagi. That would give me stacking gain and additional flexibility on this important contest band. Over the winter I'll model alternatives and develop a tentative plan. There are unique requirements for equalizing phase in a stack built with dissimilar yagis.

It seems fitting I am closing what many consider an uninteresting article with a reference to the most read article on this blog. I'll return to technical subjects in the next articles.

Monday, November 21, 2022

Rebuild of the Beverage Antenna Head Ends

Lightning destroyed 2 out of 3 of the Beverage antenna head ends. These home brew devices select the normal and reverse direction. They also terminate the unused direction in a dummy load (resistor) to prevent reflections that would cause a bidirectional pattern. They contain transformers, relays, resistor and a bias-T to separate RF and the DC reversing voltage that share the feed line. 

There are articles for each of these devices and their matching reflection transformers. Rather than sprinkle the text with links to the articles I'll list them here. Refer to them for technical details since I will not repeat that information here. In this article the focus on the rebuild and design differences.

The north-south Beverage head end was taken indoors before the lightning strike so it didn't suffer the same fate. That was because it, too, was malfunctioning. After completing a variety of other higher priority jobs the time had come to deal with the broken units. The top band season is well underway and I need the Beverages to hear stations that my big transmit antenna attracts.

Many of the components in the affected devices were destroyed, even the PCB copper traces. Since there was little to salvage I opted for a complete rebuild of the electronics. The plastic (ABS) enclosures and hardware were okay so I cleaned and reused them. Connectors and their wires were removed from the old boards and reused.

Hoping for good news, I removed the transformers and tested them. Several were okay but the rest had melted or shorted windings. Winding miniature binocular ferrite cores is unpleasant work and I wanted to avoid as much of it if as possible. The Fair-Rite cores are ½" on a side and the holes are ⅛" wide. I did not reuse the cores for the discarded transformers although they are probably okay. Time is of the essence and they're inexpensive.

I started with the north-south RG6 Beverage since it had no lightning damage. I removed and tested the transformers and they were both good. That was fortunate. The fault appears to have been one of the SPDT reed relays. It had a lot of material between it and the PCB from an insect infestation. A thorough cleaning did not resolve the problem. By holding my ear close to it while applying voltage (they switch very quietly) I could tell it wasn't healthy. They're sealed so I'll never know. The coil resistance tests normal.

I selected new parts and ordered them. The proto boards come from my stock. On a cold and miserable day I got down to work.

The new proto board happens to be designed to fit the Hammond 1590 enclosure. It's quite a common enclosure and it is available as plastic or cast aluminum. Plastic is easier to work with and unlike many other RF devices there is negligible benefit from an RF tight enclosure. Please note that the relay has a wiring error in this picture that I discovered during testing. Don't use it as a template! I was lazy and didn't bother to take another picture after correcting the error. You might find it educational to refer to the schematic (earlier linked article) and try to find my mistake.

Unlike many proto boards, the copper traces only connect two adjacent holes. To simplify the wiring there are several soldered joints above the board. Where I could stuff two wires into one hole I did. I am using the same type of RF choke and low voltage bypass capacitor in the bias-T. The new DC blocking ceramic capacitors are rated for 630 volts. They replace the 40 volt devices that lightning destroyed. Of course lightning induces a far higher voltage but these will have a fighting chance if the pulses are short enough. The difference in price is small and worth the experiment.

Reed relays are small and very good for small signal switching. But they're relatively expensive and two are needed since DPDT reed relays are rare or nonexistent. I decided to go with the larger and cheaper Omron G5V DPDT relay. It's small and sealed, and it is found in many commercial receive antenna products. That's good enough for me.

There is no flyback diode on the relay coil. I was in a rush and it can be easily added later. Alternatively, the diode can be placed in the shack controller, either on each control line or the positive line from the power supply.

Wiring and layout isn't critical for receive application below 2 MHz. The proto board is larger than what I used for the first Beverage head ends, which leaves lots of room. The wider separation of components eases construction.

When fully wired the head end is tested. I constructed a test jig on a small "push in" proto board, The analyzer or VNA is connected on one side and the head end on the other. A blocking capacitor protects the analyzer from the applied +12 VDC. The alligator clips connect to the power supply. 

To reduce stray inductance use shorter wires to the power supply or, better, insert RF chokes. For rough testing this setup worked well enough, but don't expect accurate reactance measurements. Resistors are placed across the antenna terminals to simulate the common (normal) and differential (reverse) modes of the Beverage. 

This isn't a perfect test since there is no true antenna, with a long wire (transmission line) and reversing transformer. The 75 Ω load resistor should see a matching resistance at its port via its transformer to minimize inaccuracy on measured mode. Again, for a rough bench test it isn't strictly necessary, but it may be helpful when interpretting measurements that differ from perfection. We'll see shortly that it did lead me astray in one instance.

The rebuilt RG6 reversible Beverage head end was reinstalled. The wiring error was discovered that evening. It was retrieved and repaired the next day. The next evening it worked as it should. That was one head end down and two to go.

If you refer to the article where I twinned the northeast Beverage to make it reversible you'll notice in the schematic that there is only one of the transformers connects to the Beverage wires. The other takes the common mode (normal direction) from the first transformer's centre tap. 

It was no surprise that when the transformers were removed from the lightning damaged head end that the first transformer was dead. The windings were burnt and shorted. The other transformer tested good and was reused.

Unfortunately the 4:12 transformer is more difficult to wind that the others. This is due to the large number of turns (16 in total) and care in construction to achieve best balance in the centre-tapped primary winding. I used a new binocular core and teflon sheeting. Teflon liners prevent wire abrasion by the hard ferrite (it's a ceramic). 

I purchased a small roll of 28 AWG magnet wire rather than the scavenged enamel wire I used previously. The enamel coating may have been abraded when it was removed from an old transformer and a few transformer failed due to shorted turns.

In retrospect it would have been better to use 24 AWG magnetic wire because the thinner wire is difficult to handle. It is also easy to damage the wire when stripping the enamel off the wire ends. For the number of winding turns needed for Beverage transformers there is no need for very thin wire. I often use insulated wire from discarded Cat5 cable for windings with only a few turns. When I do that I can often make do without the teflon liners.

I must be getting good at winding these tiny transformers because I got it right the first time. The impedance transformation of 9:1 (the turns ratio of 3:1 is squared) took the 330 Ω resistor to 37 Ω, which shows as a flat SWR of about 1.4 on the analyzer.

The new transformer was mounted on the PCB. The old transformer is also in the picture. After a bench test the head end for the northeast-southwest Beverage was reassembled and installed. It was tested that evening and although it worked there was a problem with the antenna itself that made it bidirectional. Nevertheless it was nice to have it back.

Suspecting lightning damage to the reflection transformer I trudged through the newly fallen snow to retrieve the transformer. It tested okay so I soldered it back in place and trudge back to reinstall it. I took the opportunity to replace the hastily repaired ground wire that an animal had torn off sometime over the summer months.

The next step was to retrieve and test the head end. After removing the cover it took less than 15 seconds to spot the problem. Instead of a wiring error it was a wiring omission. The picture above was taken before the repair so, again, you have an opportunity to troubleshoot it yourself. If you decide to take the challenge, stop reading now because I'm about to tell you what it was.

One of the two Beverage wire wasn't connected to the transformer. I had cavalierly dismissed a puzzling R component of the impedance measured while bench testing the reverse direction (differential mode). I was sloppy and I paid for it. 

The wire was installed and, without further testing, installed. An SWR sweep looked good and that evening it performed perfectly. That was a relief since CQ WW CW is this weekend.

I have yet to rebuild the east-west Beverage head end because I depleted my stock of proto boards. More will be ordered. With my temporary head end I now have 5 out of 6 directions working. It is east that is missing, and I can live with that for now since there are not many stations in that direction.

I plugged the weep holes I had drilled in the old plastic enclosures. The enclosures seal well on their own and the weep holes only encourage insects to make their homes inside. The moisture and detritus the critters introduce cause corrosion. We'll see how well this works. In any case, next summer I will likely remove the electronics. I want to be prepared for a third(!) lightning strike.