Saturday, February 27, 2021

So...You Want to Hold a Video Conference

Earlier this month our contest club (Contest Club Ontario) held a video conference. In the past we held smaller in-person outings with speakers this time of year. It takes more than one because VE3 is big -- 1500 km east-to-west just in the high population corridor -- and winter travel is not always possible or comfortable. 

With the popularity of Zoom and similar technology by various amateur radio clubs and groups we decided to give it a try. There was no other good option for a winter event due to the danger and proscription against gatherings of large groups. They are not the same type of event and planning for them is different. One big difference is that there is no catering; everyone provides their own meals and refreshments.

As the prime initiator and organizer of the event, and not an expert at these things, I gave us lots of time to prepare. I have participated at a few and presented at one. Other than that I have no experience with modern video conferencing services. I did lots of video business meetings years ago using point-to-point technology in purpose-built conference rooms.

Give yourself time

Our first step, way back in September, was to get agreement from the club executive with the rough outline of the event content and format. With that (and a Zoom Pro license) in hand we proceeded with the planning. I had concerns of my own to overcome along the way, and until those could be addressed the event was not formally announced.

Leaving the technology planning to others, I focussed on canvassing potential speakers. Asking for talk proposals turned up little. Most people are not comfortable with public speaking and although they have interesting things to say they will be reluctant. Don't push people. Give yourself time to solicit talks from knowledgable hams on topics that will be of interest to the audience.

Since we're a contest club that is what I focussed on. However it is generally true that enthusiastic contesters are also enthusiastic about DXing, exotic locales (hence multipliers) and big antennas. It was a good bet that what interested me would interest others. However, I was careful to reach out to others about topics that are of less interest to me personally. It is important to address your audience's interest where they differ from your own.

I am glad I gave us lots of time. Running up against reluctance to step forward I had to take the time to reach out to individuals and ask or persuade them to speak at the event. They then need the time to put a talk together. It may be a challenge if they've never done it before, or at least never in this format or to their friends and acquaintances rather than for their jobs.

Much to my chagrin, most of the talks ended up being about 160 meters. I didn't plan it that way, but when that's what I had I rolled along with it. It actually worked out well since 160 meters is a challenging band for most, winter is top band season and everyone lusts for the multipliers to boost their contest scores.

A critique

There are video conferences open to the public that attract thousands of hams to hear renowned speakers on a variety of topics. Of particular interest (to me) is Contest University. Their in-person conferences are recorded and available for viewing. Indeed, this has been going on for years before the pandemic fell upon us.

Despite the efforts of the organizers and speakers at those events, I have a few criticisms. As the audience broadens so does the content. There are too many canned presentations or ones that cater to the lowest common denominator. In other cases, the same speakers giving essentially the same talk are invited back time after time after time.

Most talks can be given once, and they should be left at that. For the good talks, record them and they can be watched forever by anyone. Repeating a live talk is pointless. Leave that for new material and new perspectives. Sticking the usual is laziness. Or perhaps they know their audience, because they do fill the seats.

Video conferences allow us to go far and wide for new content rather than leaning on the old reliable people. Leverage that and every video conference, local or global, can be better. This was my challenge for the CCO event: new and interesting content from speakers who may have never done it before.

Keep it local

When organizing an event for a local club, even one as geographically dispersed as the CCO, widely known and respected speakers from the larger events draw the eye. Avoid the temptation. 

Consider your local event to as a venue for your local heros. They're the ones with a profile that is more limited and yet are expert on topics that are of great interest. Reach out to them instead. Most hams love sharing their knowledge and helping others. Give them this opportunity. Everyone will benefit. For the especially shy, encourage them and help them along.

Going outside the local club is fine, and encouraged, but keep those numbers low. A pinch of exotic spice is nice provided you don't gorge. Don't give the implicit message that only outsiders have interesting things to say. Believe me, it isn't true. It may just be that you don't know them well. Reach out to those with a bigger or different network of local contacts and ask them for suggestions.

Don't stick to what you know or the topics that interest you. Cast a wider net. My contesting is almost solely on HF so I invited someone with extensive experience to speak about VHF/UHF contesting. It's different enough to be novel and with commonalities that make it understandable to the HFers.

Keep it local, but do direct consider external resources. If you know them and you need one more for your program, by all means make the invitation. A talk by a manufacturer can also be a great idea when the products are relevant to the audience.

Gauging interest

Keep the membership informed as the conference planning progresses, just don't write weekly status reports! Report only enough that everyone knows the plan is progressing. Nobody cares about the details that are consuming your time. When the program of speakers is confirmed, that is when you make the big announcement.

I did take a few steps to gauge interest while I was assembling the program. These included a couple of easy one-question surveys to elicit input on potential topics and conference organization. For example, when it appeared that I would have 6 speakers lined up I asked whether to schedule them in series or in two parallel streams. My worry was that doing it in series would make the program too long. I was also worried that parallel streams would be too technically complex for our neophyte team. 

The survey gave a large and resounding vote for talks in series. Unlike typical conferences, attendees can get up and stretch, grab a snack or skip a talk, and do so without being disruptive. Knowing this they opted to have the opportunity to see it all. Even though there is no direct human contact during the conference there is little appetite to watch recordings of talks after the conference.

A survey taken after the conference told me that we got the mix of topics about right and that there would be interest in doing a similar event in future. The message is to keep your membership involved and that will boost your confidence that you are doing the right thing. Feedback can also spur you to correct the plan that's straying from expectations.

Volunteers -- don't fly solo

Don't underestimate the complexity of running a conference like the one we did. Calling for volunteers to help out, especially individually, may make you uncomfortable but do it. You need moderators who can diplomatically manage the clock and feed questions to the speakers. Yes, we're amateurs, however it is important to treat this as if it is a professional conference. Keep it smooth.

One or two technically adept volunteers are needed to keep the conference running well. They are in the background and may not be immediately recognized so do highlight their contribution. Their jobs may include filtering joiners to see if they're on the invited list, forcing microphones to mute, recording the talks, fixing service glitches that may appear, and to interact with speakers off line to deal with any problems or emergencies.

Another constraint to how much I could accomplish was my internet service. It can barely keep up with the downstream audio and video. Upstream video was impossible. Even had I been adept enough to do more it would have been impossible. Don't underestimate the resource demands of Zoom and similar services.

You wouldn't operate a contest as SO3R if you've only ever operated SO1V. It won't go well so don't even try without lots of practice. Ask for assistance and don't try to be a hero. We received some priceless advice from others who've run similar events. Hams are friendly so reach out and ask.

Assembling a program

My first attempts to sign up speakers fell flat. Almost no one would consider volunteering. I was disappointed since I believed they were good choices because they have interesting things to say. As time went on and I got more rejections I also received hints about others that might be receptive. So I had their close contacts reach out to them or I solicited an introduction. This is no different than how I got things done in my professional career.

The result is that the program steered in a different direction than the one I had chosen. I accepted that and adjusted my expectations. Although this may seem disappointing it really wasn't. I had no assurance that my original plan would result in a good program. Sure, I believed it, but I could have been wrong. So I rolled with the changes. We ended up in a different place, and it was one that was quite interesting. As I mentioned above, 160 meters stole the program and yet it worked.

A couple of my intentionally solicited speakers worked out despite being a little out of the typical contester's interests. There were VHF/UHF contests and IOTA expeditions. Most contesters are focussed on HF and, although DX, island expeditions have different objectives. Stretching outside of the most people's comfort zone is okay if it is not overdone.

11:30 - 12:00  Open Mic
12:00 - 12:45  Rick VE3MM: 160/80 meter FCP vertical
12:45 -  1:30  Dana VE3DS: VHF/UHF contesting
 1:30 -  2:15  Steve VE6WZ: High-performance 160 meter remote
 2:15 -  3:00  Chris VO2AC/VE3FU: CQ 160 Expedition to VO2
 3:00 -  3:45  Cezar VE3LYC: TX0T and other IOTA Dxpeditions
 3:45 -  4:30  John VE3EJ: 160 meter 3-element vertical yagi
 4:30 -  5:00  AGM


With so many people involved there are sure to be problems. Those issues are not always delivered politely. Yet it is absolutely necessary to deal with everyone respectfully. More often the messages that seem venomous are not intended that way. People may unintentionally come across badly when they are feel put out, ignored or not given the information or help they need or expect. 

Whether it is a volunteer, a speaker or a member of the audience it is important to put your own attitude aside and deal with each issue calmly and respectfully. Do that and the temperature quickly falls and further trouble is avoided. Questions get answered, remedial action taken if required and both sides exit the situation with at least a better understanding when the desired outcome isn't possible.

Respect goes further that just that. Recognize that the speakers and volunteers are generously giving of the time and talents. When they make a request, or a demand, deal with it promptly to the best of your ability. Don't be afraid to push back or to ask for time to deal with the matter. When you do so be respectful of them and their contribution to the event.

One example I encountered was trepidation about recording the talks and publishing them. Although this unwelcome request came from more than one of the speakers I pledged to honour the request. We recorded the sessions and afterward asked each for permission to publish their talk. Almost all agreed. That initial trepidation was assuaged by the success of the talks. Had the requests stood we would have erased the recordings.

As the organizer you may have your heart set on a particular outcome. In this instance I wanted the recordings as a record of the conference that attendees and others could enjoy and learn from afterward. I also saw it is a gift to the presenters as something they could point to and say, "I did that!" Nevertheless you must respect the wishes of those giving of themselves to make the conference successful. Although you can't always accommodate everyone, you should try.

Stepping back 

This isn't about you. When the time comes you need to step out of the spotlight and cede the stage to the speakers and volunteers you've assembled. You've done your job and everybody knows it. Never impose yourself on others when the audience wants to listen to others. 

Your role is to thank the speakers for putting in the time and effort to entertain and educate the audience members. Give explicit credit to the volunteers working in the background who are keeping the conference running in good order.

During my career I scorned managers who took credit for their employees' work and usurped the spotlight when presenting the work to executives and customers. I put my staff members in the spotlight, even if they were shy or uncertain about themselves.

There were times they were worried that I wouldn't get credit for all my effort to help bring their project to fruition. My response was to tell them not to worry about it because everyone is aware of my role. Putting them up front was good for them, and it was also good for me.

Don't hog the spotlight. If you do you'll loss most of the goodwill you've painstakingly gathered. Know when to step back and let others shine.

Looking back, and forward

Feedback on our conference has been very good. A post-conference survey indicates strong interest in doing it again next year. It will be interesting to see if the interest persists when in-person meetings are again possible. Despite the success of the video conference there is strong preference for meeting face-to-face.

In non-pandemic times we have two gatherings each year: a summer BBQ and winter lunches with club member speakers. These event have multiple objectives, however socializing is the primary driver. We are unlikely to try to squeeze a conference into them. In any case, many of the talks we had are more conveniently done by video. Speakers don't have to travel and we can reach a larger audience.

I have several months to ponder alternatives.

Monday, February 15, 2021

10 Meter Yagi Design: 5-elements on a 24' Boom

10 meter yagis are in my 2021 plan. These will be smaller than the long boom yagis I built for 15 and 20 meters last year. On a 24' boom, 5 elements on 10 meters has the same performance as a 5-element 20 meter yagi on a 48' boom, and that is certainly a huge antenna. Despite the relatively small size the performance is excellent.

Many hams in pursuit of ultimate performance take advantage of the smaller size and increase the boom length by 50% or more than 24'. Diminishing returns come into play so one should consider the trade offs. For example, 6 elements on a 36' boom (50% longer) has about 1 db more gain, a narrower beam width and a slightly broader SWR bandwidth. The wind load is substantially greater so the boom, truss and mast must be stronger, and that has a cost.

For the DXer the additional performance may be worthwhile. As a contester I would rather have a broader beam width, perhaps a little less F/B and acquire additional gain with stacking. The objectives are to increase the number of workable stations, punch hard into high population regions (Europe, Japan, US) and rapid direction switching. A stack of 2 or 3 individually rotatable and moderate size yagis is a good fit for my style of operating.

Don't reinvent the wheel

The time when we played with yagi designs to optimize them has passed. Computers and software optimization has replaced the excesses of uncertainty and experimentation, at least for mono-band rotatable yagis for the high bands. Sure, you can try it yourself but in the end you will almost certainly end up with a design that is little different from the many computer optimized designs that are already published. Wire yagis on the low bands are another matter with their broader range of design parameters, but here we're discussing 10 meter rotatable yagis.

What I do is to pick a published design and perhaps tweak it to get a little more gain or a little more bandwidth, depending on my need and the construction material on hand. When I do so there is often a performance metric that will degrade, if only slightly. Optimum designs really are optimum across all metrics. More often I will scale a yagi from one band to another, do the SDC (stepped diameter correction) for my tube taper schedule and element clamps, choose a matching network for the feed point and then build it.

This 10 meter antenna is right out of the ARRL Antenna Book. There are 5 elements on a 24' boom and it performs well from 28.0 to 28.9 MHz. Getting more bandwidth would require more elements and a longer boom, or giving up gain and F/B. There is no free lunch. As I described earlier, this design very nicely suits my particular objectives. That is, it's optimal in general and optimal for me.

Why would we need more bandwidth than 900 kHz? Having 900 kHz on 10 meters seems plenty yet there are times when more can be useful. Although I don't normally operate above 28.8 MHz, when the solar cycle is at maximum and there is a phone contest the activity extends above 29 MHz! Indeed, my first CQ WW SSB world #1 plaque in 2014 in the QRP category was due to an extraordinary run into Europe at a frequency above 29.1 MHz.

Now that I run higher power and my antennas are bigger there is less need to go quite so high in the band to find a frequency for running. I can compete in the more crowded and popular part of the band. That eventuality is a year away as the new solar cycle waxes.

Choosing tubes and calibrating the model

The tubing schedule for my home brew yagis is not what is typical of commercial antennas, due to cost or availability. As I've related in the past, that although Canada is awash in aluminum and aluminum products at reasonable prices, tubes of the alloy and sizes needed for telescoping yagi elements must often be imported at high prices. So I adapt by choosing alternatives and machine tubes as necessary to make them fit.

First I decide on the tubes and pipes to meet the requirements of survivability, cost and the ability to nest easily or with minimal machining. Next I sit in front of the computer and scale the yagi design for my selected element construction. Element taper has a modest though important effect on the reactance and therefore resonance. 

For this design my initial selection is 1" schedule 40 6061-T6 pipe 3'-4" long for the element centre. That may change when I compare the spot price this spring. The length is chosen to eliminate waste when cutting a 20' standard length pipe. The OD is 0.84" and the ID is 0.622", for a wall thickness of ~0.09". This is about the same strength and weight as nesting a ⅝" × 0.058" tube inside a ¾" × 0.58" tube, as specified in the ARRL Antenna Book. The pipe is easy to acquire locally. Reaming the pipe to nest a ⅝" tube is a quick job in my workshop with the 0.627" reamer in my toolbox. 

The ⅝" tube will be 2' long per half-element. For the usual 3" nesting, the net length is 21". Again, this is to eliminate waste from sectioning the 6' long tubes -- the standard length of aerospace aluminum alloy tubes is 12'. The element tips are ½" × 0.065" tubes. Boom construction will be decided by what material I can acquire surplus at a lower price than new tubes and pipes. Based on other designs I expect that a 2" × ⅛" wall tube or similar size pipe will support the antenna well in extreme weather.

Deviations that do not matter much for a single element antenna like a dipole become quite critical in a high performance yagi. Without taking the taper into consideration the yagi will still work though not nearly as well as it might. A little effort up front ensures that the time and effort you invest will pay dividends once the antenna is on the tower. This is not the place to be lazy or to take shortcuts. Mistakes happen, just as it did with my 15 meter yagis.

One of the easiest ways to calibrate the element with a published design is to model one element and determine its resonant frequency -- where X = 0. Do this in free space and without a boom. This is accurate for a yagi made of tubing and elements clamped to a plate sitting on the boom. The effect of the boom is a small fraction of the boom diameter. A yagi well above ground is effectively in free space, and therefore so are the elements. This is quite different from a one element antenna over real ground which will be affected by the ground.

I modelled the driven element per the ARRL Antenna Book and found a resonant frequency of ~28.85 MHz. Next I rebuilt the element with my selected tube schedule (it may change before it's built). I adjusted the ½" tips so that the resonant frequency was exactly the same. My half-elements are only ⅛" longer. It's chance that they agree so closely.

For such a small difference it is sufficiently accurate to arithmetic scale the half-elements by lengthening them by ⅛". For larger differences it is better to scale the elements geometrically. Do this by calculating the ratio of the original and scaled lengths and multiplying all the half-elements by that ratio. For exceptionally large differences or for elements with unique tapers an SDC must be redone for those elements by following the calibration procedure described above.

Model Performance

This is the boring part. The modelled antenna performs very much like the one in the ARRL Antenna Book. It is nevertheless a useful exercise to confirm that scaling had no deleterious effects and that the model is reliable.

The gain is very flat from 28 to 29 MHz. It rises from 10.1 dbi at the bottom of the band to peak at 10.6 dbi at 28.8 MHz. The slight 0.1 db gain drop at 29.0 MHz is mostly due to ohmic loss in the aluminum elements as the radiation resistance falls to a low value. There is little here to complain about.

The exceptional F/B is deceptive. There are rearward minor lobes that are worse. On balance, the directivity is very good. Perfection in all yagi performance metrics is impossible. 

Overall performance is excellent for a 10 meter yagi of this size. There was nothing found in this exercise that deters me from proceeding with construction of these antennas.

Feed point match

The 10 meter band is quite wide at 1.7 MHz. Put another way, the range is 6%. In comparison, 40 meters is 4% (7.0 to 7.3 MHz). We've seen before that it can be a challenge to match a 40 meter yagi across the entire band, and 10 meters is wider.

A full band match isn't necessary. For CW, SSB and digital modes it is sufficient to cover 28.0 to 29.0 MHz, or a little more than half the band. This is doable without special techniques such as OWA, with its requirement for an extra element as a coupled resonator the driven element. 

The SWR curve for this antenna shown in the ARRL Antenna Book is below 2 in this 1 MHz segment. I can live with that.

I have not decided on a matching network. I could use a gamma match, as I did for my 15 and 20 meter yagis, or I could use a beta (hairpin) match. The latter requires a split element that is isolated from the boom, and that involves additional work. Since the elements are substantially smaller it is less difficult to do this in a robust fashion. I have the fibreglass tubes to support the split elements and the u-bolt interiors for the element clamp can be covered in rubber. The rubber needs UV protection, and that is likely easier to achieve than machining suitable plastic stock.

The SWR bandwidth will be about the same with most conventional matching and feed systems. In the model I used a beta match since it is far easier to implement with NEC2 than a gamma match.

That's pretty good. The SWR remains low for a few hundred kHz below 28.0 and so it is tempting to shift the entire yagi upward. The downside is that the gain and F/B are poor at the lower frequencies. For my purposes it is preferable to maximize gain and directivity in the band segment of interest, and an SWR below 2 at up to 28.9 MHz is acceptable. I expect to rarely venture that high in the band.

Where they're going

My plan is for a stack on 10 meters, just as for 15 and 20 meters. The top yagi will go to the top of the mast on the 150' tower, where the 40 meter dipole is currently mounted. As my plan develops this tower will be primarily devoted to 40 and 10 meters, much the same as the 140' tower is for 20 and 15 meters. This is generally considered a good apportionment for two towers flexibility and minimal interaction for contests.

The lower 10 meter yagi is more difficult. Although it doesn't need to be too far beneath the upper yagi there are guys in the way. Even if its orientation is fixed the proximity of the upper guy set will have unwanted interactions, mostly of the non-resonant variety. Directivity will be impacted by the growth of the minor rear lobes. The degree of the interaction will have to be determined before the antennas are installed.

If it is to be rotatable then it must go lower to clear the guys. This would separate it from the top yagi by 30' to 50' (0.9λ to 1.5λ).

For 30' spacing the stack elevation pattern is good but not great. Although gain is a near perfect 3 db the nulls in either yagi are not entirely filled. It may be better to separate the yagis closer to the maximum of the range mentioned earlier. Alternatively a third yagi at a lower height would be even better, and supply additional gain.

I am undecided on the placement of the lower yagi. There are other antennas planned for the tower, including a 40 meter yagi. Further investigation is required.

Construction plan

I have no firm construction schedule as yet, other than wanting two of them on the tower by early autumn. In the spring I'll hunt for new and surplus material from my usual suppliers. These antennas will be easier to build than their larger cousins, the 15 and 20 meter 5-element yagis. That removes some of my worry about keeping to my plan for the year.

Thursday, February 11, 2021

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: ae = ½[SQRT(A/π) + P/(2π)]

The effective diameter: De = 2ae

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.

Thursday, February 4, 2021

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.


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.