Measure Twice...

We all make mistakes, and with so many projects on the go I probably make more than most. Although it is easy enough to sweep them under the rug and move on that wouldn't be right. This blog isn't just about my successes. Mistakes are educational. I will share two that I recently discovered. 

Consider this an opportunity to learn, and perhaps you will be better prepared to avoid doing the same. With a small dollop of humility let's dive into these latest screw-ups.

Blazing the wrong trail

I mentioned in an article last month that I started clearing a path through the bush for the new east-west reversible Beverage. The west termination is a large tree within the tree line that separates the bush from a hay field. The tree line is also the home for the north-south reversible Beverage. From that tree there is another tree 140 meters due east that was my guide. The full length of the Beverage will be 160 meters.

I selected and surveyed the route with the help of a friend. Guided by a compass we spent a couple of hours picking the best route. Working on my own a few days later, I placed markers every 30 meters along the selected route. I spent several hours work spread over the next couple of weeks, again on my own, cutting down or trimming the bushes and trees that were directly under or too close to the route.

As I mentioned in that article, the path was not perfectly straight. I headed back into the bush to straighten the route. Armed with my compass I carefully sighted to the eastern tree. It wasn't due east. I played with the compass because it was very cold and I suspected that it was sticking. The tree remained stubbornly north of east. Slowly the truth of the matter seeped into my consciousness.

Not too far to the north there is a similar looking tree. I trudged through the snow and bushes and checked again. The tall tree in the distance was now exactly east of my position. I should have marked the tree rather than rely on memory. They all look alike to me. I emailed my friend to blame him for not coming over to check my work. He was not sympathetic.

Most of the desired path is either clear of big trees and, at the eastern end, there is cleared area I can still use. It is no disaster and the bush I cut has no value. It is new growth that naturally sprouted in what had been a tended field decades ago. 

I have more hours of work ahead before I can string the Beverage wire. That work is being delayed by higher priority projects, the pandemic and unseasonably cold weather.

Equivalent diameter of clamps

This one is an old mistake. I discovered it while designing the 10 meter yagis that are on my 2021 project plan. Discovering the mistake was a relief in a way because it explains an anomaly that I discussed on the blog over a year ago. At the time I put it down to a discrepancy between the software model and the physical antenna.

After adjusting the gamma match of the first 5-element 15 meter yagi the SWR curve was very good but not quite in accord with the model. The yagi was set 50 kHz higher than than the design. This was determined by the knee in the impedance curve at the top end of band. This is a good tell in most big yagis for where the antenna is centred because the impedance drops sharply as the frequency of maximum gain is approached.

A quick calculation led me to lengthen every half element by ¼". This small adjustment brought the measured SWR curve into agreement with the model. I thought no more of it at the time since the discrepancy was tiny and no software model perfect mirrors reality.

Recently I built a model for the 10 meter yagis that I plan to build and install later this year. The model deviated from the design in the ARRL Antenna Book. The error was small and at first I was prepared to adjust the element lengths and continue. A closer look revealed a puzzle.

I first modelled a single element using the published dimensions for the element and element-to-boom clamp. While copying the dimensions onto a model of a 15 meter yagi element (to save data entry) I noticed that the effective diameter I used from the 15 meter yagi was different from that in book. That was odd since the clamp design is the same except for the diameter of the centre tube. The 10 meter centre tube diameter in the ARRL Antenna Book is ¾" versus 1" for my 15 meter, yet the effective diameter shown in the book is larger. That isn't possible.

To be exact, my calculation for the 1" tube sitting directly on a 4" × ¼" plate was 1.637". The value in the book is 2.405". I was pretty sure the equations used were the same ones, coming from W6NL's derivation in his Physical Design of Yagi Antennas book (out of print). I wanted to check my calculation but I could find no record of it. It was time to open the book and start from scratch.

The diagram comes from Figure 9-2 in W6NL's book. There are several pages of diagrams and equations about many styles of element-to-boom clamp and the derivation of their respective diameters. Decades ago I used the equations produced by W2PV in his book Yagi Antenna Design (also long out of print). W6NL discusses those results and his, noting that although in most cases the difference is small it can be significant. It was time to sit down to work through the mathematics (again).

For the depicted clamp design the equations are straight-forward, though first appearances may be deceiving if, like many, you have a mathematics allergy. Look at each term in isolation and if you know any geometry at all you'll be able to figure out what's going on.

The area: A = πD²/4 + tW

The perimeter: P = πD + 2(W + t)

The effective radius: a_e = ½[SQRT(A/π) + P/(2π)]

The effective diameter: D_e = 2a_e

If you haven't yet figured it out, here's a hint. The area of the cross-section shown above is the sum of areas of a circle and a rectangle. The same is true of the perimeters. The effective radius is...mmm...sort of half the geometric mean or average of the two. The effective diameter comes from removing the halving operation. Clear as mud? Don't worry about it. It's an approximation that works well in practice, as Dave W6NL assures us.

Riffling through my files I found a spreadsheet with the W2PV equations. I had none for the revised W6NL equations so I added them to the spreadsheet. Having both the old and new equations serves as a sanity check. 

Note that the W2PV equations include saddles on the clamps that raise the tube above the plate. I don't have the equivalent for the W6NL equations. I don't need them, and most don't because it is typical to use heavy wall tube at the centre of the element. A u-bolt is sufficient to hold the tube without risk of crimping it and there is little danger of element slippage.

The value of 1.637" I previously calculated was far too low! I vaguely recall thinking that since the value is intermediate between the tube diameter and plate width it was probably correct. I did not confirm the calculation, not even checking against the W2PV equations spreadsheet.

The error affects the antenna in proportion to the length of the clamp and in inverse proportion to the wavelength. To confirm that my spreadsheet is generating correct results I entered the dimensions for those in the ARRL Antenna Book and I got almost exact agreement with the W6NL equations. 

The funny thing is that Dave Leeson himself pointed me to where I could find a spreadsheet with the equations. I did download it but since it was for an ancient bit of software and had to be converted I decided not to bother and did the calculation myself. I may have done with nothing fancier than a calculator. That was very foolish of me, and especially for not comparing my calculations with the correctly implemented W2PV equations.

With the error identified and corrected I returned to the model of the 5-element 15 meter yagi. Here is the SWR plot of the original design with the 1.637" erroneous equivalent diameter.

Keeping the element tips at their original length I modified the diameter of the 6" long clamps to the new 2.6" value. The SWR was again plotted across the band.

That is just about what I measured in the field and had to correct by lengthening the elements. Next I lengthened the element halves in the model by ¼", just as I did to tune the built antenna.

Lovely. There is no discrepancy between the model and the built antenna; the problem was human (ham) error. The software did exceptionally well to achieve accuracy far better than the misleading ¼" correction. I should learn to trust my software and the experts more than unverified calculations done by hand.

The enduring lesson: measure twice and adjust (or cut) once. As antennas grow larger these avoidable mistakes become more difficult to correct.

Eking Out the Decibels on 160 Meters

160 meters has a lot in common with VHF and UHF. Propagation effects are subtle and often there is no skip zone. This means that the farther the station, the weaker the received signal.

From day to day the signal strength of the same station varies a modest amount, and not to extremes we see with HF ionospheric propagation. If you can't work a station today there's a very good chance you can't work them tomorrow, or if you do it'll be marginal. Every decibel counts, even if you are patient and willing to wait for enhanced propagation. 

On HF,  due to the wide hourly, daily and monthly signal strength variation, you need only wait a little while for propagation to come your way. When it's good, QRP can work the world. When it's bad, a kilowatt and stacked yagis are not enough. Power and antenna gain certainly matter on HF for more reliable communication (and contest scores!), but for the casual operator it is usually acceptable to work what they can with the station they have.

Which brings me to the frustration of the CQ 160 contest last weekend. Overall the conditions were atrocious. It is in these conditions that every decibel counts when it comes to being heard. The small differences among stations -- antenna, power level -- made a large difference in the outcome.

When signals are close to the noise level even 1 decibel can make a large difference in whether a QSO can take place. When conditions are good that slight edge is nearly irrelevant: S7 and S7 + 1 db are indistinguishable.

Under the poor conditions prevailing during the contest only the very best stations and the most persistent operators did well when it came to working stations far away, whether it was across the ocean or across the continent. Success also requires good ears and high RDF receive antennas, however in this article I want to focus on the strength of the transmitted signal; that is, being heard far away.

Barring a change of QTH, there are several strategies available on 160 meters to improve transmit signal strength:

• Improve antenna effectiveness
• Improve antenna efficiency
• Increase antenna gain
• Increase power
• Wait for the other station's reception to improve

Antenna effectiveness

An effective antenna on 160 meters is difficult for the majority of hams. My first effective antenna went up in 2017 and I've been a ham for almost half a century. Many never have the opportunity. The wavelength is so long that it is difficult to have an antenna that is big enough or high enough.

An effective antenna is one that is compatible with the propagation mode and direction. With limited exceptions the most effective antenna on top band is a vertical. A horizontally polarized antenna, such as an inverted vee, is so low to the ground with respect to wavelength that it is very poor at low elevation angles, and like a vertical it is vulnerable to ground loss.

The 160 meter antennas of most hams are only moderately effective. For casual DXing it may be acceptable to wait, but in a contest waiting isn't an option. Unable to wait or raise a more effective antenna, the contester must focus on other strategies.

Antenna efficiency

An efficient antenna is one that radiates most of the applied power rather than dissipating it in the antenna or the local environment. Short antennas require loading or matching networks that can turn a large portion of the power into heat. Low horizontal antennas and vertical antennas lose a lot of power in the environment surrounding the antenna, most notably the ground. The wavelength is long so the antenna near field is large, with ample opportunity for loss.

A half size antenna (e.g. 20 meter high vertical) has a radiation resistance of several ohms. As a consequence, the ESR (equivalent series resistance) loss in loads, matching networks and ground can easily surpass 50%  (3 db) of the applied power. It is often far worse. For example, in my on-air tests of my short vertical (base matching of an 80 meter vertical) it is at least -6 db compared to my full size vertical.

For greatest efficiency the loading elements (coils, capacitance hats) should be far from the feed point and have the maximum Q (minimum ESR) we can attain. Inverted L and T antennas are examples of short verticals with large capacitance hats.

Verticals need a ground with the lowest possible ESR. This requires many on-ground radials or a smaller number of elevated radials. The elevation of the latter should be at least 10 meters or you'll still need lots of radials. As the vertical gets shorter, and the radiation resistance drops, the radial system becomes ever more critical. Unfortunately, an extensive radial system for a short vertical is often impractical, usually for the same reasons the vertical is short: not enough land.

For the same radial system, an antenna with gain will be less efficient because the gain is almost always accompanied by a lower radiation resistance. Efficiency on top band is never easy.

Antenna gain

Gain requires more than one antenna element. For those struggling to raise one antenna that is both effective and efficient, imagine how much more difficult it is to raise 2, 3 or 4 elements. It may be more than 2, 3 or 4 times more difficult. There is the increased land area, increased material quantity, pattern-destroying interactions with towers and buildings, and a switchable and complex network to phase, steer and match the array. 

The radial system for each element must be more extensive than for a one element antenna due to the lower radiation resistance. Otherwise the realizable gain will be reduced, calling into question the additional investment.

Should you decide to proceed, be prepared to achieve a maximum of 4 to 5 db. Getting beyond that will require an effort that only a handful have done. For example, a full size 4-square with 10,000 meters of radial wire. The simplest 2-element vertical array will net you no better than 3 db gain.

On top band, antenna gain does not come easily. It requires passion, time, money and land. Acres of land. The poorer the soil the more that must be invested in the radial system.

Power

Changes in the shack are always easier than changes outside. Wire an outlet, plug together a few more cables then browse the web site of your favourite ham retailer and click "Buy". A few days later you will see a 10 db boost to your transmit signal, on 160 meters and all the HF bands. 

This may not the cheapest path to a big signal but it is a dependable one. Many hams are old enough to have a little money saved up, so the purchase is within reach of most. You can't buy a 160 meter antenna that will get you anywhere close to the same improvement. Antennas must be built, while power can be bought.

You are not necessarily limited to 10 db. Starting with 100 watts that will take you to 1000 watts, and in many countries you can legally go beyond this by 2 db or so. I am sure you know hams who have not stopped there. I have been in shacks where a 4CX2500 is humming, and sometimes two of them. 

Many years ago I had an amp with a 4CX1500B and a stiff power supply that easily exceeded our legal limit. I rarely used it that way since that was back when home electronics were more susceptible to EMI. I chose to minimize friction with the neighbours. In any case, I didn't have an effective 160 meter antenna. I rarely operated on top band.

Unlike antenna improvements, boosting power is not reciprocal. Unless you invest in high RDF (directive) receive antennas the improvement may be wasted. We have all experienced the alligators with big signals and no ears. They're solid copy but respond to few. CQ machines only benefit the local electrical utility. But they do keep the shack warm through those long winter nights.

Other station's reception

Waiting for better propagation is always an option. Unfortunately, like Godot, it may never arrive. Hope is not a strategy. We need a more predictable outcome, whether it is during the heat of a contest or for chasing rare DX.

One semi-reliable method is to watch the sunrise terminator as it sweeps across the target. For a brief time, from a few minutes to half an hour, their noise level drops and the path remains open. The key on our end is the former: their receive SNR increases at their sunrise as atmospheric noise from the other direction, towards daylight, is attenuated by the re-ionization of the D layer.

I did not stay up until European sunrise either day of the contest. Those who did were able to work stations they could not work earlier. Of course I knew this might happen but I didn't think it worthwhile to stay up into the wee hours to win multipliers in a contest I was not competing in. 

A few decibels on the other end of the path can do wonders for your contest score or to put a new country into your top band log. Those decibels are a gift because you cannot buy them. When it happens you need to be there to receive the gift.

Summing up

The quickest route to being heard is more power. Going from 100 watts to 1000 watts is 10 db, and it is impractical for the majority to get anywhere near this from antenna improvements on 160 meters. If you're already using a small 800 watt amplifier, going to 1000 watts is 1 db, and even that small increase can be difficult to get from antenna work.

During the CQ 160 contest, with my Beverage receive antennas I heard far more DX stations than heard me. My enthusiasm to continue operating quickly waned since my top objective was to use the contest to work DX. A full size vertical with 8 radials didn't give me the edge I needed. 

With lots of effort I can squeeze a few more decibels from my 160 meter antenna. Some of that work I will certainly do, however I won't go to an extreme effort. I can already put plenty of contacts and multipliers in my contest log, and I am competitive in the pile ups. A better amplifier will suit me better.

Although I love antennas and antenna work this is one of those places where power rules. I am not saying that antenna work is pointless, just that the fastest, biggest and often the cheapest solution is more power. To be a top band big gun you must do both. There are no shortcuts.

In the end, you invest the time and money you want. After that, for most of us, you learn to appreciate what you have.

Beverage Selector: Initial Prototype

After building and installing my two reversible Beverage receive antennas and the remote switch to select the 4 directions (and expandable to 8) I wired up a simple switch arrangement at the operating desk to control the system. Temporary solutions do have a tendency to linger and I have been living with it and its limitations ever since. 

I have now made definitive steps towards a permanent control system for the operating desk. I modelled the home brew system based on the ergonomics of the control systems I've admired in the shacks of other low band aficionados. The prototype software is complete and the design of the enclosure and controls is almost done. Soon I'll be punching holes and putting it all together. 

Completion is still weeks away because there are several equally important projects filling my time. Rather than wait I thought it would be interesting to describe the design and the prototype so that you can see the project midstream. Too often when showing the final product many important steps and decision points are omitted, yet they are quite interesting to other prospective builders.

Design objectives

The design is focussed on ergonomics. It needs to fit comfortably on the operating desk among all the other paraphernalia needed for two keyboard SO2R. Room on the desktop is at a premium. I expanded the original plan to make use of the additional space on the sloped project box a friend (VE3WMB) gave me to include the 80 meter vertical yagi and control of high and low antenna combinations on all bands. 

It is not and will not become an antenna switch. This direction and high-low antenna selector works in concert with my existing controller for the 2 × 8 antenna switch. Automation will be added in due time.

The design objectives, as I originally conceived the selector:

• Fit comfortably on the operating desk, within easy reach and not crowded out other equipment
• Visual indication of where each antenna is pointed, and whether high or low antenna selected
• Sloped panel for maximum visibility when seated at the desk
• Big, fat buttons that are easy to see and hit when contest fatigue sets in 
• Visual indication of all selection modes so that mistakes are minimized
• Intuitive operation that does not require a manual
• Easy to switch between off/on and omni-directional/directional
• Compatible with future touch screen control
  

Enclosure design

The enclosure I was given constrains the design of the controls and construction. That isn't a bad thing! Ask any poet and they'll tell you that meter and rhyme help rather than hinder their creativity. I stared at the enclosure periodically over a few months until I could envision the complete design. Though not perfect (what is?) it is adequate to my objectives.

As you can see it's small but not tiny. If it is to be central the display will need to be 2" higher so that it fits beneath. Putting it on a transceiver, like the current manual antenna select, would reduce visibility of the sloping panel. I may move the rotary antenna switches on the vertical front face to keep all the controls in one place and eliminate one box. Until I have full automation that seems to be a reasonable compromise.

I used OpenOffice drawing software to experiment with the layout -- there are many other choices. It is critical that software dimension controls match what is printed. The rulers and dimension parameters for each object are very helpful to ensure proper alignment. All the sizes you see are exact for the parts to be used. I use squares to accurately and easily place button around their circles. The big buttons have LEDs built in; I purchased a selection of colours.

Each big circle is for a world map projection centred on my QTH with true bearings. Many sites around the internet will produce these for free, a donation or a small charge. I like the ones produced at the NS6T site. They are free (donation requested), visually appealing and the size is customizable.

There are several ways to plasticize the printed map and I am exploring those. I'll use paper until I settle on a durable format.

To control the high band stacks I will initially use 3-way switches (on-off-on) to select lower, upper or both. The LED colours are blue for upper (sky) and green for lower (ground), which I find intuitive and understandable with a quick glance.

Both upper and lower LEDs ought to be lit for both but for manual 12 VDC switching it is easier not to do so even though the logic is easy enough: !U for the lower LED and !L for the upper LED. Later I can wire these into the software to avoid extra logic and for remote control. I follow the same logic for 80 and 40 meter antennas even though they are not stacked. 

Switches for the 80 meter array select SSB and CW band segments and the antenna's 160 meter mode. These switches are software managed. Because the antenna is omni-directional on SSB the direction selection is disabled when SSB is selected. When SSB is added to the antenna the software is easily updated.

Another option is to substitute push buttons for the various switches. Pressing the button cycles through the available choices. For example, the stacks have 3 combinations. Hole size is approximately the same for buttons and switches so they can be changed later. Buttons all around can make operation simpler even when a button must be pressed twice. Software makes this flexibility easy to implement.

By printing the layout and taping it to the box various designs can be tested. Moving the drawing from the screen to the fingers is a useful means to verify that it works for you. Finally, the drawings are taped to the box as a drilling template.

Processor and software

I chose Arduino for this project. It's simple to use and program with the free IDE. Even the small Arduino Nano has more than adequate capacity for the Beverage controller. The greater though still modest complexity of Raspberry Pi isn't needed. The constraint isn't speed or memory: it's GPIO pins. 

The Beverage selector fits nicely on a Nano but to add the others requires the large GPIO count of an Arduino Mega. Alternatively, more than one Nano can be used: one for the 80 meter array and another for upper deck controllers. Multiple processors simplify the software and wiring at the cost of managing multiple Arduino sketches and downloading them. I have a Mega board so I will try it out.

For normal use no USB connection is needed. It is powered from a 12 (13.8) VDC for the remote antenna relays and, via a 5 VDC voltage regulator, the Arduino(s).

The main difficulty building the breadboard prototype for the Beverage selector is the quantity of LEDs and controls. There are 8 direction LEDs (top left), 5 relays (bottom right LEDs) and 8 push buttons. There are so many wires and LEDs I needed two breadboards. The sum (21) is more than the GPIO complement of the Arduino Nano.

To conserve GPIO pins the direction selector buttons connect to a single analogue GPIO pin. A resistors in a ring among the buttons comprise a voltage divider. When a button is pressed it puts a voltage in the range of 0 to 5 VDC on the analogue pin and converted to a digital value by the ADC.

The resistors are equal (220 Ω in the prototype) to ensure the voltage steps are near equal. The blue wire from A0 and resting at top centre is the "button". It is touched to a junction of the resistor ring to simulate a button push.

The picture shows the north direction has been selected. The LED at the top is for the button lamp. It's dim because I ran out of 220 Ω resistors and the GPIO high level is less than 5 VDC and is pulled down by LED current. The relay for the north-south Beverage is on (blue) and because south is the normal direction the reversing relay (red) is on.

A high value resistor (bottom left) from the pin to 5 VDC acts as a pull-up resistor that puts 5 VDC on the pin when no button is pressed. Although there are software selected pull-up resistors for the GPIO pins these are of uncertain value and we need one whose value is much greater than the sum of the resistor network. It is 33 kΩ only because that was the first suitable one I pulled from my resistor bin.

The Arduino code to interpret the analogue input is simple and reliable. ADC_MAX is 1023, the maximum value for a 10-bit ADC referenced to 5 VDC.

int buttonValue (int adcValue, int buttons) {
  if (adcValue < 0 || adcValue > ADC_MAX || buttons < 1) return -1;
  int difference = 1000;
  int button = -1;
  for (int i = 0; i <= buttons; i++) {
    int newDiff = abs(adcValue - i * (ADC_MAX / buttons));
    if (newDiff < difference) {
      difference = newDiff;
      button = i;
    }
  }
  if (button >= buttons) button = -1;
  return button;
}

Button presses are detected by periodic polling. Event driven (interrupts) are preferred but this is not practical on the Arduino, and not available on the Nano. There is a trade off among fast polling, processing cycles and human perception. As polling frequency increases the behaviour is closer to that of interrupts, which is good. Since the Arduino is doing nothing else this is not a problem, and the power dissipation penalty of the additional processing cycles is negligible. The prototype uses slow 100 ms polling (BUTTON_FSM_STEP) to aid debugging. That is slow enough for the polling rate to be noticed.

void loop() {
  int bevButtonSense = analogRead(BUTTONS_BEV_ADC);
  int bevButton = buttonValue (bevButtonSense, BUTTONS_BEV);
  bevButtonFsm (bevButton);
  delay(BUTTON_FSM_STEP);
}

A finite state machine (FSM) is used to interpret and act events. This is a common algorithmic technique that may be unfamiliar to many hobbyists. I'll omit the details in this discussion. The FSM debounces the buttons, differentiates short and long presses and controls the states of indicator LEDs and antenna relays. One FSM is needed for every selector: Beverages, 80 meter direction, 80 meter mode, stacks, etc. There's just the one for the Beverages in the prototype.

A short press is one that passes the debounce check and the button press is longer than 200 ms. A short press selects the direction and updates the state of the indicator LEDs and relays. A long press of 2000 ms on the currently selected direction turns off all the relays and LEDs. It is equivalent to an off switch. I like to have the relays off when I'm away from the shack. I will decrease the timers after the controller is complete. Others may prefer more relaxed time limits.

The prototype does not account for the processing between polling steps since it is brief. For more precise timing the software can use the Arduino clock to adjust the step time to compensate for processing time. A fast poll rate avoids this perception problem for short press and button hold times to improve system response for hasty operators such as myself.

const int BUTTONS_BEV_ADC = A0;
const int RELAY_BEV_NE = A1;
const int RELAY_BEV_S = A2;
const int RELAY_BEV_E = A3;
const int RELAY_BEV_SE = A4;
const int RELAY_BEV_REVERSE = A5;
int RELAY_BEV_PINS [RELAYS_BEV] = {RELAY_BEV_NE, RELAY_BEV_S,
  RELAY_BEV_E, RELAY_BEV_SE, RELAY_BEV_REVERSE};
int BUTTON_BEV_LEDS [BUTTONS_BEV] = {3, 4, 5, 6, 7, 8, 9, 10};
int BEV_RELAYS [BUTTONS_BEV] = {RELAY_BEV_S, RELAY_BEV_NE, RELAY_BEV_E,
  RELAY_BEV_SE, RELAY_BEV_S, RELAY_BEV_NE, RELAY_BEV_E, RELAY_BEV_SE};
int BEV_REVERSE [BUTTONS_BEV] = {true, false, false, false,
  false, true, true, true};

The GPIO pins and options are put into arrays and constants. This makes it easy to reassign pins without finding and editting each instance throughout the code. Clearing a set of LEDs and relays can be done with a single subroutine that is passed the array. 

Since not all 8 directions are currently installed I can substitute Beverages in the arrays for ones that are closest. For example, to choose northwest the north Beverage can be selected until the southeast-northwest Beverage is actually built. The northwest or north indicator LED can be lit per your preference. I haven't decided which.

I am using several of the analogue pins as digital outputs, which the Arduino allows and is needed because there are insufficient digital pins on the Nano. The 'An' values are numeric constants above those of the digital GPIO pins. The values are different on different Arduino processors so the constant names should always be used in preference to their integer values.

Solid state switching

I don't like the sound of clacking relays in the shack. For the Beverage controller there will be a lot of that as I cycle through the directions on every CQ to pull weak signals out of the noise. The GPIO pins cannot directly drive the 12 VDC relays in the remote switches so local switching peripherals are needed.

Opto-isolated relays are commonly used since they're inexpensive and widely available. They're also noisy, bulky and overkill for switching currents of well below 1 A. I've operated at stations where a band change is startling because of the all the clacking relays that switch antennas, amplifiers and filters. I want a quiet, compact solid state solution.

One giant hole in my education is solid state theory and circuit design. I have always relied on circuits designed by others or made do with the simplest of circuits for my needs. Often I can troubleshoot solid state equipment since you don't need a lot of the theory. The lack is a problem because the commercial products for solid state switching are unsuitable and designing switches from discrete components is a challenging exercise for me.

My home brew switches are high side, where the relays are grounded and they are powered by placing 12 VDC on the control lines. Solid state high side switches are more difficult to design than low side switches, which should be low loss and must prevent the high relay voltage appearing on the GPIO pins and thereby destroy the microprocessor.

I educated myself from what I could find on the internet. Finding simple yet sensible design advice was not easy. Most is vague or far too technical. 

Once I settled on an approach I purchased parts to experiment with. Candidate circuits were built and adjusted on a breadboard until I got the performance I wanted. The circuit at right is successfully emulating a relay switch for the reversing relay GPIO pin. It is shown operating at 5 VDC and it has been successfully tested at 12 VDC. I have yet to test it with the full range of load currents it will have to deal with in my station.

High side solid state switching for GPIO pins is an interesting topic that deserves an article of its own. Look for it within the next month.

Construction

Other than a long list of projects to do the prototype is done and construction of the final product can proceed. It's difficult to predict when it'll be done, other than I am determined to have it in use before the end of the winter 160 meter season. 

When it's complete and in use for a while another article will follow to describe the controller in its entirety. I may make the final Arduino sketch available if there's interest.

2021: The Final Stretch

For most hams 2021 promises sunspots from solar cycle 25. For me 2021 brings the final push to complete my station. This project began in late 2016, with planning beginning almost two years earlier. By fall of this year my station should be active on 160 through 6 meters with high performance antennas and operating positions. There's a lot of work ahead to get there.

As I do every new year I recap the year that was and my plans for the year that is. It's my way of keeping myself honest and to track how well I'm keeping to plan. I have yet to execute or complete all the projects planned for the year. However, I usually come close. That's pretty good. You can check on how I'm really doing by reading those past articles. For example, here's the one from last year.

To recap my own history for new readers, I have been a ham since 1972. As life goes, I was inactive about half of those 49 years. After several changes in my life I reentered the hobby 8 years ago. I started with QRP and an improvised antenna from my home in Ottawa. I started the blog soon after, partly as a diary and partly as an experiment in writing and communication.

The small station didn't last; I just don't roll that way. Soon small towers appeared and the antennas grew bigger. The countries piled up, as did my reinvigorated enthusiasm for contests. 

From the very beginning I have been an avid CW DXer and contester. It is no surprise that the urge to go big returned. Unlike most hams I am comfortable building and working on large towers, so I had that going for me. For many that is an impediment unless they have very good friends or money to burn. 

Coming from humble roots I like to do things on the cheap by building as much as possible myself and scrounging for deals. Learning how to do it is an objective not an obstacle. I approached the project with the same philosophy. The previous big tower jobs I did for friends taught me a great deal and prepared me for the challenge. I reached out and received excellent advice from other hams and from professionals.

The following is a summary of the station as it is today. All except the Beverages are visible in the above south-facing panorama. The 21 meter tower is difficult to see behind the big to the left of the 80 meter yagi central tower, but it is there. Instead of putting in links to articles about these antennas and towers you can use the blog's search feature.

• 21 meter (70') self-support tower: T2X rotator and 3.5 meter mast
  
• 43 meter (140') guyed tower: prop pitch rotator and 3.2 meter mast
  
• 40 meter (130') guyed tower: prop pitch rotator and 3.8 meter mast
  
• 160: shunt fed 40 meter tower with several long boom yagis and a mast
• 80: 3-element, 4-direction vertical yagi, with a short vertical mode for 160 meters
  
• 40: XM240 at 21 meters and rotatable dipole at 46 meters
• 20: 5-element stacked yagis at 40 meters (rotatable) and 22 meters (northeast)
  
• 15: 5-element stacked yagis at 43.5 meters (rotatable) and 31 meters (northeast)
  
• 10-15-20: TH7 at 43 meters and TH6 at 23 meters (south)
• 6: A50-6 at 24 meters
• Receive: reversible Beverages NE-SW (175 m) and S-N (150 m)

If all goes very well this year the following additions and changes will take place. Antennas not mentioned will remain as they are.

• 160 meters: same but with more radials
• 80 meters: yagi efficiency improvements, and perhaps the return of an inverted vee
• 40: 3-element yagi at 43 meters, and XM240 at 23 meters
• 10-15-20: TH7 at 22 meters (rotatable)
  
• 10: 5-element stacked yagis at 43 meters (rotatable) and 33 meters (northeast)
• 6: longer boom yagi
• 2: something for contests and DXing
  
• WARC:something, maybe
  
• Receive: reversible Beverage E-W (160 m) and possible SE-NW (150 m)

Trap tri-band yagis are lauded by some and derided by others. Traps do dissipate significant power, though how much is difficult to measure other than by precise field measurements. I like the TH6 and TH7 for their utility: reasonably long booms and decent performance. In comparison to the competition Hy-Gain traps are pretty good.

Now that I have these antennas in direct A-B comparisons with the mono-band 20 and 15 meter yagis at similar heights I admit to some disappointment. The difference is only partly due to the shorter boom lengths and the number of active elements per band. Performance lags, probably due to a combination of trap loss and compromise element tuning and spacing. 

Although they will remain in use this year I will investigate alternatives. Having tri-band yagis at a lower height in fixed directions or rotatable is beneficial in contests to snag multipliers or to rapidly alternate between working DX and North America. I will think upon the matter while keeping in mind that their replacement will be low priority for some time.

I've begun clearing the bush for the new east-west reversible Beverage. Pictured is the view from the west terminal, at the middle of the north-south Beverage. The east termination is 20 meters past the tall tree you see 140 meters away just left of centre. The path is a little askew since it was difficult to cut the path straight east until most of the bush was out of the way.

In the shack the following changes are planned for 2021:

• New transceiver to replace the ancient FT950
• 160-6 meter kilowatt amplifier: I've picked one and I just need to order it
  
• Band pass filters: the kits and parts packages arrived this week
  
• Automated antenna control and switching: this one is a stretch objective
  
• New operating desk for (post-pandemic) multi-op contests: 80% built then put aside
  
• Improved prop pitch rotator control

Some items have been on my list for a long while. Other projects took priority and then the pandemic put preparation for multi-op contests on hold. The deferral is no longer tolerable or necessary and I believe my schedule this year allows for getting them done. I see the possibility for multi-ops this fall.

There will be no new towers this year. It is quite likely there will be no more towers ever. I am not getting any younger so I must limit my ambitions to avoid overbuilding and creating a maintenance nightmare. At some undetermined future date my climbing days will be over, and I hope that will occur many years in the future. Paying professionals for tower and antenna maintenance is expensive and my funds are not unlimited.

Beyond 2021 no major antenna projects are planned. There will continue to be refinements and improvements, and I will likely dabble with experimental antennas and related projects. I still lack effective antennas for the non-contest HF bands -- 30, 17 and 12 meters -- and for 2 meters. There will be no shortage of blogging material for years to come!

This year's summary and plan article is more bullets, less prose and therefore less tedious detail. This format will help me to review my progress at year end. I am trying to write more concisely. We'll see how that goes!

Administrivia

One of the disadvantages of the blog format is that articles vanish down the memory hole, hidden in the chronological archive. That's why I added a search function. Try it with terms describing projects of interest to you and the results can be surprising. I've written hundreds of articles and the laws of physics haven't changed.

Another problem is that I do not have a static page containing details of my interests, the purpose of the blog, my current activities, etc. I'll take this opportunity to speak to that lack.

• The blog is about my journey in amateur radio. It is not a reference work. New articles may supersede older ones, and might not reference the older articles. Search is your friend. I only correct articles for egregious technical errors, and only for recent articles. There are sites that index or reference my articles, and I have no control over that. I will take steps for unattributed republication.
• I try to get the technical matter as accurate and reliable as possible. I also vet the reliability of external sources that I reference as well as I can. I am repeatedly appalled by widely circulated or published material that is simply wrong. Keep me honest by telling me when I'm wrong.
• I make many typos and grammar errors. Proof reading is time consuming and I have better things to do. Be patient and deal with it.
  
• The blog is not a vanity project. One way I keep it that way is by excluding pictures of myself other than long shots of me on a tower taken by friends, or perhaps a pic taken by me that incidentally includes a boot or glove. In reality I am not particularly ugly!
• All comments are moderated so there will be a delay before they appear. The reason is spam. Critical comments are welcome if you keep the language clean. I don't get a lot of comments anyway despite having many readers. To communicate directly email is a better choice: my call sign at rac period ca. I almost always reply to direct email, and far less to blog comments. Despite that I do appreciate receiving comments.
  
• I do not keep an online repository of antenna model files, pictures or software. I am happy to oblige in response to direct email requests.
• I sometimes will design or model an antenna on request. You should never expect it. It depends on my schedule, my mood and whether the project is of interest to me. If I do it, it's free and you get what you pay for. 
• Do not assume that I've built every antenna I've modelled and discussed on the blog. If I have done so or plan to I will state it explicitly. I explore many good and bad ideas that go nowhere.
  
• I aim for one article per week, a rate I've maintained for 8 years. Some articles are technical, some are not and a few are opinion pieces. Occasionally there are long gaps between articles while others appear in quick succession. Don't fret over extended silences unless and until my call sign is listed as a silent key.
  

With that out of the way all I can say is: welcome to 2021! A return to normalcy is on the horizon, along with the promise of improved high band conditions. It's going to be a lot of fun so get yourselves ready to take advantage of it. Now is the time to plan and build the antenna you've dreamed about. 

Amateur radio makes being locked up at home more tolerable. When you hear me on the air be sure to say hello.

SO2R Benefits Everyone

Don't you hate it when you try to work a station in a contest who is doing SO2R? To synchronize their transmissions and QSO flow their response to you may be delayed a second or two, or three. Or they vanish entirely or ask for repeats that seem perplexing with loud signals and a clear channel. Transmissions, especially CQs, are often interrupted. There are more of these peculiar behaviours of SO2R stations.

Working those stations can be irritating in a contest when every second counts. Indeed, many do complain, and loudly. Why does it happen and how should we deal with it? Some is due to inexpert or novice practitioners of the SO2R art -- I plead guilty. Other times it's due to the unpredictability of the stations they're working.

Some operators send slow, repeat their call or exchange without being asked, or add other non-essential tidbits -- "73 and good luck in the contest!" This upsets the SO2R operator's timing on the other radio. QRM, QRN and multiple callers can cause the SO2R operator to ask for repeats or delay their reply to you. These are common problems for everyone but more so for SO2R. 

Because we don't hear what the SO2R operator is dealing with on the other radio their behaviour can seem inexplicable -- in a sense we're only hearing one half of the "conversation". We may become irritated or frustrated, and perhaps QSY without completing the QSO. Both contesters lose in that case.

Improvement is within reach with practice. Perfection remains elusive. No matter the skill level there will always be factors out of the operator's control: propagation, QRM and other challenges. Dealing with the real world of radio is part of the contest experience. Those who prefer a more predictable competitive environment should consider e-sports. Radio can never be like that, and that's what makes it so wonderful.

All that said, is SO2R worth it? My unqualified answer: yes!

Consider the SO2R operator who annoys you on 20 meters with a delay or a request for a repeat. Had they not been SO2R you would not have been annoyed. You also would not have made a 20 meter QSO with them because they wouldn't have been there! Sure, the QSO may have taken a few seconds longer but it is still one more QSO for your contest log. 

It is easy to overlook SO2R benefits for other than the SO2R operator. Everyone they work benefits. There will be glitches, but when the alternative is no QSO at all I am happy to accept a little inconvenience.

Radio contesting is a peculiar type of competition. You and your competitors must cooperate to work each other. You put a QSO in your log, they put a QSO in their log. It's win-win. SO2R boosts everyone's scores.

If you hate dealing with SO2R operators and wish that the practice were banned, be very careful what you wish for. Your score and the joy of finding the bands full of signals would both be lessened. Consider last weekend's NAQP CW contest. What an intense 10 hours that was! 

A novice SO2R operator like me achieved an average rate of 2 QSOs per minute over that 10 hours. Yet my score was so far down the standings that I am invisible. But I had fun, and I boosted my score by at least 50%. My NAQP teammates also benefitted. You worked me more times than was otherwise possible because of it. Often I was running on two bands concurrently.

Give SO2R a shot. It's intense, maddening and a lot of fun. It takes very little to get started. Start easy, practice and as your proficiency increases your contest scores will take off. So will the scores of those you work and, in a contest like NAQP, so will that of your team or club. You can add additional equipment later if you decide to up your game. 

I use N1MM Logger+, 2 keyboards, 2 radio antenna switching, and an SO2R Mini. I don't have band pass filters and I can do it at 100 watts quite comfortably except for a few band and antenna combinations. Band pass filters are on my winter project list and I'll have more to say about it when it's further along.

Now I need practice to improve my scores and, eventually, annoy fewer of the stations who call me.

Beverage Feed Line Interactions

At the back of my mind there lingered a concern about the planned path of my newest east-west reversible Beverage receive antenna. Due to its location the feed line would have to lie beneath or beside the south-north Beverage. Placing a long conductor alongside or below a Beverage will affect its performance. After a futile attempt to find a better location I am stuck. 

The alternatives are shown in the diagram. The original plan 'a' was for a coax reversible Beverage running along the treed wooden fence line between the fields, out to the edge of the eastern swamp. The density of the trees along the route are difficult to navigate, with many large trees and tree limbs at the required 2.5 meter height and the risk of deadwood damage is high.

Although route 'b' is better there are still lots of large trees and bush along the way. The required shift eastward of the west end and the minimum 150 meter length I require pushes the east end into the swamp. Maintenance will be difficult and repairs near impossible except when the swamp is dry (high summer) or frozen (late winter).

Route 'c' avoids most of the these difficulties. Half the route is free of dense foliage and I can extend the Beverage to 160 meters without delving more than a few meters into the swamp. There are large trees at both ends for support anchors. Since there are few trees on most of the route I will build a two wire reversible Beverage rather than one made from RG6 coax. The higher tension possible with wire allows for greater separation between supports. Those must be constructed. 

The problem with 'c' is the routing of the coax feed line to the Beverage remote switch. It must run parallel to the north-south reversible Beverage and interaction is certain without remedial measures. There is little point in going to the trouble of building a great antenna and have interactions ruin its performance.

For background I will note that it is safe for Beverage antennas to cross, provided the wires don't get too close, couple energy and thus affect each others' patterns. Even 30 cm (12") is more than enough in most cases. A common support at the intersection takes cares of this requirement. The other requirement is for feed points and terminations to be at least 5 to 10 meters apart so that the proximity of ground rods or radials doesn't promote common mode transference between antennas, which will degrade the directivity.

Having selected route 'c' I sat down in front on the computer to model alternative coax routes and configurations to get a handle on how to best proceed.

Model

A Beverage requires real ground to be modelled in NEC2. Without a ground connection, doable with a MININEC ground, radials are affixed at the antenna ends to simulate ground. Just two 20 meters radials orthogonal to the antenna orientation and slightly raised are sufficient to couple to the ground for an accurate pattern calculation. These are 0.2 meters high. For this exercise the Beverage is in all cases 2.5 meters above EZNEC average ground.

The wire representing the coax is 0.1 meters high so that it passes beneath the radials without creating anomalous results. This, too, has radials at the far end where it (roughly) connects to the Beverage remote switch and its ground. The feed point to the other Beverage is 70 meters along the Beverage. There it simply terminates because the other Beverage is fed via a transformer (two actually in the reversible Beverage) that block common mode, and the other Beverage itself couples very little since it is roughly orthogonal to the one modelled and the termination grounds are very far apart.

The far end of the coax is 15 meters behind the Beverage and is therefore 85 meters long. It is broken by 1:1 common mode chokes that interrupt the common mode and divide the coax into 3 equal lengths of about 30 meters. The loads represent the capacitance between windings of the binocular core transformers. The value is adjusted per the transformer design. Transformers cannot completely block the common mode so modelling the capacitance matters.

Notice that despite the choke action of the transformer current is induced on their sections. These couple to the antenna above and can distort the pattern. That is what we are investigating with the model. The inter-winding capacitance is 10 pf in the above current plot. That is approximately what was measured by ON4UN for a 2:2 turns transformer on a Fair-Rite BN73-202 binocular core. The frequency is 3.5 MHz since at 1.8 MHz the effect of the coax is less visible.

The Beverage azimuth pattern is compared with and without the presence of the coax, and coax with and without common mode chokes. These effects are not large but would certainly be noticable. 

The main lobe is broadened while the minor lobes are smaller. The RDF is reduced by about 0.4 db which, though negligible, the minor lobe degradation can be a problem. The impact is less on 160 meters since the interaction is (roughly) inversely proportional to wavelength.

In case you're wondering (and you should!) whether the current on the coax is from the primary signal or coupled from the Beverage above I shoved the coax 30 meters to the left. The current plot provides a clear answer. Compare it to the otherwise identical one above.

On a general note, the model calculations should be treated with care. Although NEC2 is fully capable of accurately modelling Beverage antennas there will be inaccuracies. Wires close to real ground are one. Another is the break between coax segments. A capacitance load to represent the coupling between transformer windings should be verified with measurements. There are other environment effects that may be of greater magnitude than the effect of the coax under the antenna. Perfect models are impossible.

Despite the limitations of the model we can learn a great deal about Beverage performance degradation due to the coax lying on the ground. Interaction in the model, while not exact, is a warning sign. With that said, let's continue.

Parameter space

No two installations are alike. Indeed, each of my Beverages is unique with respect to construction, length and routing of the coax feed line. Exploring the vast parameter space of all possible configurations is time consuming, and likely unnecessary. For example, when we talk about a few decibels difference for a minor side lobe, in most cases the effect of the feed line placement is less than that of construction variability, ground variability and other environmental factors.

I limited my model exploration to factors that appear to be the most significant and universal to all installations. For those who want an exceptionally reliable and good pattern it is better to use a vertical array where current forcing ensures greater immunity to environmental factors. Beverages are more affected by interactions with the environment, and those are never fully under our control.

These are the model parameters I investigated:

• Design and placement of 1:1 transformers along the coax feed line
  
• Lateral offset from the Beverage of the on-ground coax feed line
• Beverage length and operating frequency: these two are closely related
• Effect on both directions of a reversible Beverage

I'm sure you can think of other factors; I know I did! But these are the ones that are most relevant in general and to my particular choice of route for the east-west Beverage. The model can be extended or adjusted by others to account for different situations.

The performance metrics that most interest me and most low band operators include the following. The importance of these and other metrics is up to you. The design of your antenna should meet your needs, not mine.

• Gain: signal level in the favoured direction
• RDF: figure of merit for directivity
• Beam width of the main lobe
• Side lobe and F/B magnitudes
  

You can see all of these, except the RDF, in the triple azimuth plot above. The RDF is calculated by subtracting the peak gain from the average gain. For EZNEC users the latter can be found at the bottom of the main panel after calculating a 3D pattern plot.  For a Beverage of 150 meters length the RDF is typically 9 to 10 db on 160 meters and 11 to 12 db on 80 meters.

Chokes

Let's begin with common mode chokes on the coax feed line. The rule of thumb for a 160 meter receive antenna is that common mode chokes on the coax should be no more than 30 meters apart. Otherwise the outer conductor becomes a Beverage itself and the antenna current can seep into the signal path if one is less than careful with termination circuitry and grounds. The separation should be less to protect performance on higher bands.

Transformers wound on the Fair-Rite (BN73-202 equivalent) binocular cores were measured for loss and capacitive coupling and reported in ON4UN's Low Band DXing book. They measured about the same for 160, 80 and 40 meters.

• Loss: -0.75 db for 2:2 turns; half that for 3:3; and, half that again for 4:4
• Coupling: 8 pf for 2:2 turns; double that for 3:3; and, presumably double again for 4:4

Loss can be halved by using two cores at the price of greater coupling. I don't have the capacitance figures for those, however since I won't risk the higher coupling I am happy to stick with a single core. Although the capacitive coupling is frequency independent the reactance is not. Coupling increases with frequency because capacitive reactance is inversely proportional to frequency. 

There are obvious trade offs to be considered. Using 2:2 transformers minimizes the coupling but maximizes the loss: for two of these transformers the total loss is about -1.6 db. That is noticable. Receiver pre-amps have enough gain to deal with the additional loss but it can be a nuisance. 

In the adjacent plot I divided the coax into 5 sections with 4 × 2:2 transformers, represented by 10 pf series loads. The coax is directly below the Beverage, where interaction is worst case. Even on 80 meters the effect of the coax is almost completely neutralized. It is even better on 160 meters. The price is -3.2 db or more of loss and 4 transformers to build, maintain and weatherproof.

Alternatively the coax can be wound on a ferrite core to eliminate the loss. The price is a more expensive ferrite core and a larger weatherproof enclosure. Because of the foam dielectric most RG6 varieties have too large a bend radius for tight turns on a ferrite core. RG59 or similar 70 Ω coax should be used instead.

Should you choose this method be aware that achieving the equivalent choking action (isolation) of a 1:1 transformer on 160 meters is quite a challenge. It is more easily achieved on 80 and 40 meters. Again, ON4UN's book provides details.

I assume transformers in this analysis. These are represented by a series capacitor on the fat insulated wire model of the RG6. The capacitor value is adjusted per the transformer design. I ignore the additional feed line loss although that can be included in the model as a resistance at the feed point. For a coax choke on a ferrite core it is sufficient to model it as a series resistance.

Lateral offset

The farther the coax is from the Beverage the less its effect. Burial is even better. Even 2 meters away the coupling is noticably reduced and gain improved. From my modelling 5 meters is a desirable minimum distance to adequately minimize pattern degradation with respect to gain, F/B and RDF. I have room to do this in the bush to the east of the tree line.

There are diminishing returns. This should be clear from the earlier current plot for a 30 meter separation. Of course the coax has to be extended to that offset distance, if that is possible. In my case I can do it but there is a problem with laying a coax on the ground in the denser bush. Perhaps 5 to 10 meters but no more.

To determine the pattern degradation I modelled the coax laterally offset by 5, 10 and 15 meters. I deleted the chokes and ran the model on 80 meters as the "worst" case. With chokes and on 160 meters the degradation will be less.

As you can see the degradation is not so bad with a 5 meter offset. At 15 meters it is really no worse than the 30 meter case briefly described earlier. 

At a 2 meter offset (not shown) degradation is significant. It is fair to conclude that 5 meters is the minimum desirable offset. As we saw earlier, with chokes it is possible to run the coax directly underneath and achieve a good result. With a combination of chokes and lateral offset, negligible degradation can be attained. The options you choose are a matter of preference and circumstances.

Reversal

My Beverages are reversible. The north-south Beverage that the coax for the east-west would lie beneath is made from RG6. The difference between coax and two-wire Beverages is slight with respect to its common mode use as an antenna. However the feed line beneath is in one case at the rear of the Beverage and near the front when reversed. It is worth a moment to see if there's a difference.

This is easiest done in EZNEC by exchanging the locations of the source and termination resistor since the antenna is otherwise symmetrical in the model. I only tested the worst case, with the coax beneath the Beverage and without common mode chokes.

The interaction is very similar for both directions, with the pattern degradation in the reverse direction slightly less. This is enough assurance that remedial measures will protect the Beverage pattern in both directions. It was worth taking the trouble to check rather than assume that would be the case.

On to construction

This has been a useful analysis. The models are simple to build and the potential consequences are large. This approach is better than relying on vague rules of thumb and unsubstantiated opinions of how to deal with the situation. I have a few options to consider.

In some respects the results of the analysis are obvious, at least qualitatively. Obviously locating the coax further away is better! The benefit of the analysis is to quantify those qualitative factors to reduce uncertainty. Building high performance antennas is a lot of work so don't ruin it by relying on guesswork and opinions.

My next step is to build the east-west Beverage. Until that's done the routing of the coax is moot, so I have time to make a decision. Should the interaction be greater than the models predict it is not difficult to alter the coax route and the chokes. For the latter it is more about transformer design and quantity since that is more convenient to me than coax wound chokes on a large ferrite core. The small transformers are easy to wind with insulated wire salvaged from scrap Cat5 cable.

In parallel I am prototyping an ergonomic Beverage direction controller for the shack desk. I'll have more to say about that in an article later this month.

Seasonal Antenna Effects

Weather in our climate goes from one extreme to another on an annual cycle. The average daily temperature differs by more than 30° C between January and July, and the maximum range is 75° C. In my original home in VE4 these figures were 40° C and 85° C, respectively. When my parents immigrated to Canada and moved to Winnipeg they often laughingly quipped that they'd been exiled to Sibir (Siberia). Siberia (UA0) has an even greater temperature range than north central North America.

The temperature changes and freeze-thaw cycles are hard on people, machines and modern infrastructure. Our antennas are also affected. Beyond the mechanical effects there are the electrical changes that are evident when we turn on our radios. With my many towers and antennas I get to witness these changes firsthand. They are most evident in late fall and early spring when the seasonal shift accelerates.

In this first article of the new year I'll talk about some of these as a light-heartened start to blogging in 2021.

Verticals

The effect of radials on vertical behaviour is strongly dependent on the velocity factor of the ground beneath. This is most true of surface and buried radials, and elevated radials to a lesser degree. When there are too few radials to be an effective non-resonant ground plane the seasons will change the vertical's resonance. 

For a multi-element arrays, and especially for a yagi such as mine, those effects are very noticable. Single verticals are less affected, usually not beyond a small shift in resonance frequency and impedance. It is measurable.

Dry ground, wet ground and frozen ground have different velocity factors. The variability depends on wavelength, soil type and frost depth. My 160 meter shunt fed tower showed such a change recently. I set it to resonance at 1840 kHz when the ground was dry and not frozen. Then the cold came and the ground froze to several inches depth. The resonant frequency rose to 1855 kHz.

A week later the weather warmed and we had 50 mm of rain in one day. The ground saturated and thawed unevenly. The resonant frequency returned to 1840 kHz. The cold returned and the antenna resonance again rose to over 1850 kHz. I'll have to adjust that since the antenna bandwidth is only 75 kHz and that makes the SWR at the low end of the band higher than I'd like.

The 80 meter vertical yagi is also affected. There are 2× and 4× times the radials on the parasitic and driven elements, respectively, compared to the 160 meter antenna. The antenna is broadband enough that it is only slightly effected by the freeze-thaw cycle. However the shift in parasitic resonance moves the frequencies for optimum F/B. The bandwidth for F/B is narrower than that for gain and impedance match. Although not a serious problem it is noticable. In contrast, the pattern of a 4-square is less affected by these changes due to wider element spacing and current forcing.

Although Beverage antennas rely on the velocity factor of the ground beneath I have not noticed any changes with the seasons. I suspect there are a couple of reasons for this. First, low frequencies penetrate further into the ground and so are less sensitive to soil changes close to the surface. Second, the antenna is non-resonant. Any pattern shift will be small and the impedance shift barely noticed. I'm tempted to experiment with time spaced measurements to see how visible the change might be.

Rope

Tension of antenna support ropes does not appreciably change with temperature. The tension will change when ropes become water saturated, and the amount depends on the material and weave. Most of the dacron rope I've used is little affected. Nylon weave is affected more. From reports I've heard, natural fibres are affected a lot more.

When antenna wires sag due to these weather effects their performance is affected. For example, the impedance of inverted vees falls and the resonant frequency increases. For a typical single element antenna the change is rarely a concern. It is a problem for my 80 meter vertical yagi.

As the parastic element support ropes become dry or saturated I find it beneficial to spend a few minutes to adjust the tension of the ropes. When I have an otherwise unexplained degradation of F/B the rope tension is often to blame. Snugging the ropes restores the pattern. A yagi is very sensitive to the resonant frequency (reactance) of the parasitic elements. You should expect the same from horizontal wire yagis.

Last year I purchased a quantity of dacron rope. When I upgrade the 80 meter yagi, probably this year, I will replace the remaining sections of nylon rope. Hopefully that will reduce the periodical need to adjust rope tension. Another solution, where convenient, is to use a weight and pulley to automatically adjust rope tension as the rope reacts to the weather.

Rain, snow and ice

Any dielectric coating on a conductor alters its velocity factor and therefore its resonant frequency. Wire antennas are typically affected more by precipitation induced changes than antennas with tubular elements. However, I have noticed larger changes on tubular elements when water gets into, for example, gamma matches. Although there is little risk of damage to the gamma capacitor, keeping the water out with a weather seal is beneficial.

Heavy ice cover on antennas has a larger effect. That is rarely a preeminent worry while we're worrying whether the antenna will survive! Just be aware of the various precipitation effects and you'll be less surprised and, hopefully, worry less.

Transmission lines

Open wire line is as susceptible to dielectric effects as wire antennas. A coating of precipitation will alter the line's impedance and therefore the match. Ice on open wire line can be destructive because most of the span is susceptible to wind and ice. Coax is typically bonded to a structure or lying on a surface and therefore the risk is lower.

With one reversible Beverage antenna made from open wire line I am on the watch for these problems. My main concern is with the latter: destructive ice loading. Change in velocity factor appears to a largely negligible effect.

Those who use open wire transmission lines need to be aware of these effects. Tuners may need to be tweaked when it rains. Line supports and wire tensile strength must be sufficient to withstand ice loads. Coax cable is affected by ice loading but its velocity factor is unaffected by weather.

One exception is that the nominal impedance of coax does change with temperature. At a lower temperature the distance between the inner and outer conductors increases a small amount. The nominal impedance increases. The effect is rarely if ever measurable, especially in light of the greater weather effects on antenna impedance. But it is there.

Direct buried coaxial cable should be placed below the frost line (depth to which the ground freezes). Water expands when it freezes and increases the pressure on the encased cable. Hardline can withstand the pressure in most cases and I, like many others, have had no problems with buried Heliax. However, if there is a cut in the cable the soil pressure can push melt water into the break. The result is more rapid corrosion of the outer conductor. 

If the outer conductor is breached water will be driven inside the cable and that can cause serious damage. Heliax and other cables with closed cell foam dielectric will resist contamination longer than others. It's a better choice for direct burial to protect against freeze-thaw cycles.

Tower guys

The tension of guys is certainly affected by the wind. It decreases on the lee side and increases on the windward side. Temperature also has an effect. For example, let's say that in mid-summer you adjust the pre-load tension of guys to 1000 lb (450 kg) -- typical for 5/16" EHS. The tension will not be the same in depths of a cold winter.

Materials expand when they are warmed and contract when they are cooled. For a guy this is most evident along their length. Guys are shorter in cold weather than in warm weather. The tension therefore increases. Had the guys been adjusted in winter the pre-load tension would be lower in summer.

For optimum safety and performance the pre-load tension should be 10% of breaking strength. Add a little tension when you adjust the guys in cold weather and it will remain high enough when the weather warms and the tension falls. That said, as long as you're close it isn't critical to strive for perfection. Most tensiometers used by hams are not very accurate anyway.

Animals

Animals change their behaviour in concert with the seasons. Food becomes scarce for herbivores in winter when nothing grows. The abundant deer scour the bushes for edible tidbits such as shrivelled and frozen berries. They paw the ground for edible plants and fallen apples. People in this rural area call these wild fruits deer apples.

The problem is that they are likely to taste everything in reach when they are hungry. There is little that they pass over. While I was taking the pictures for this article I checked on the 80 meter vertical yagi since it showed a deterioration of its directivity in the northeast and southwest directions. To my great alarm the deer had done their worst.

There was no question of the culprit's identity. The deer tracks in the snow were clear, as was their wandering path to the damaged areas. This has happened once before, but in fall when there were no tracks to be seen, which left me wondering whether I did it while mowing with the lawn tractor.

The deer chewed right through a nylon support rope for one of the parasitic wire elements. I retied the rope using its extra length to connect the severed ends. The repair is seen in the picture above. Luckily the improved driven element stinger withstood the tension imbalance.

For the second time the deer chewed and severed the Cat5 cable to the northeast element. The lack of control voltage kept that element offline and explained (along with the wire's collapse!) the directivity problem. The severed ends had to be spliced. An otherwise easy job is unpleasant in an open field with the cold north wind blowing. The repair had to be done before the NAQP this weekend.

The burial rated Cat5 cable is flooded with gel which, supposedly, deters curious critters in addition to keeping water out. So much for that theory! Curiously none of my on-ground cables have ever been molested by animals, not even sharp toothed rodents.

Now that the antenna is repaired I have to consider protection around vulnerable antenna sites. I made the rounds of other antennas and towers to look for more tracks and tooth marks. It's bound to happen again.

2021 begins

I have been busy since the start of the new year. There are a number of projects that will eventually make their way into the blog. With everything I have going on it will be a challenge to write articles for the next several week. But I may surprise myself.

Happy New Year.