2020 - Looking Ahead and Looking Back

It's that time of year again: the end of one year and the start of the next. It's my cue to take a look back at the year that was and plan for the coming year. This is a ritual I've followed on this blog for several years. In our extreme climate the weather makes its own statement this time of year. Antenna and tower work stops or slows for several months.

Over the winter my radio activities are mostly confined to indoor activities, whether it be operating, equipment work or planning for the future. There is always a lull during the changeover as priorities reset and a human tendency to "hibernate". Soon enough the energy returns as the sun begins its long climb out of the winter solstice. This is an opportune time to look back and consider the path ahead as I do each year since starting this blog 7 years ago. Even so I have been active outdoors, as you'll discover.

This article is of the type that will interest few readers. I do it for myself, to honestly measure my progress and to plan for the future. What readers may get from it is the discipline of making a plan and being accountable, so unlike new year resolutions which are lightly made and soon forgotten. Anyone can check on how I'm doing by comparing my written plan at the start of the year and my year end review. Although I almost always fall short I still prefer to think big.

If this is not the type of article that is of interest to you, stop reading. For everyone else you are welcome to follow along. What's a little different this year is the combining of the 2019 review and 2020 plan in one article.

If you do continue reading keep in mind my primary interests in ham radio determine the projects I take on. These are contests, DXing and playing with antennas. Even if these are not your cup of tea hopefully there are ideas and thoughts that will be of interest.

I called 2019 the year of the yagi for the major activity in my station building plan. It didn't go as fast as planned. The new 140' (40 meter) tower had to be raised and the details of large HF yagi home brew construction ate up the calendar. Even so I can see the light at the end of the tunnel, it was just a little further away than estimated.

As matters stand 2020 will be the final year of the intensive phase of station building that began with my move to this QTH over 3 years ago. In 2021 I'll most likely be tying off loose ends and focussing on matters in the shack and operating. Things inevitably break so maintenance is always there to be done.

15 and 20 meters

The 15 meter and 20 meter stacked yagis are partially complete. The side mounted lower yagis are up and working. As of this writing only the 20 meter yagi is usable since the 15 meter yagi needs another 100' (30 m) of coax on the tower to reach the main run of Heliax to the shack. A future article will cover the side mount yagis, including some of the lifting and mounting details and initial performance insights.

All this work was done this month with the help of VE3DQN and VE3KAE who, like me, know that the best way to survive a Canadian winter is to go outside and do something!

The upper rotatable yagis are partly assembled and will wait for warmer weather to be lifted. You can see them in foreground. The nearly complete 15 meter yagi is on the left and the bare 20 meter yagi boom is on the right. The 20 meter upper yagi will be a monster weighing ~115 lb (52 kg) that requires careful thought to the lifting process. I redesigned the 20 meter boom to be more robust.

The prop pitch motor for the upper 15 and 20 meter yagis is partially disassembled in my workshop. I am performing preventive maintenance so that it is as reliable as possible. The mounting position for the motor will make it inconvenient to pull out for repair. More on this when the rotation system is complete and installed, hopefully this spring.

For the present the TH6 and TH7 on the other tower will remain as they are until I make progress on 40 meter yagis. The TH6 is fixed approximately south up 23 meters as a contest multiplier antenna to Caribbean, Central America and South America, at which it is very effective. It is also used to work the southeast and south-central US. The TH7 up 43 meters is used for long haul DX and the west coast. Eventually the TH7 will come down the tower to be stacked with the TH6.

When the stacks are complete I will have excellent instant compass coverage for DX contests. In everyday use I can pounce quickly on a DXpedition without having to rotate an antenna in the needed direction. Those prop pitch motors are powerful but can take up to 2 minutes to turn 360°.

Until the sunspots return I am content with the two tri-band yagis for 10 meters. I expect to design, build and install a 10 meter stack on the 43 meter tower as early as 2021. Along with the tri-band yagis this will position me well on 10 meters during the productive high sunspot years. That time is closer than you think!

40 meters

This band is a dilemma. My long term goal is to have a full size 3-element yagi on the 43 meter tower. I have been investigating electrical and mechanical designs and I've talked to a few hams with one of these monsters. A friend with a full size 3-element yagi sent me pictures of it under the weight of at least ¼" of ice. It looked awful yet it bounced right back when the ice melted. His antenna weighs substantially more than the one I'm planning.

No reasonably survivable element is less than 50 lb (23 kg). Add two more elements and a boom and the antenna is certainly going to weigh 250 lb (115 kg) or more and have a cylindrical wind surface of about 30 ft². I decided to proceed in steps. At some point I will decide I've gone far enough for my comfort with a smaller design or continue all the way. Later in the year I'll talk more about this subject.

Step one is to make a full size rotatable dipole and put it up 46 meters. I will see how it performs relative to my other 40 meter antennas and, importantly, how it survives at least one cycle of seasons. We get a lot of ice storms and that is the greatest danger. For most hams it is high winds.

Unfortunately I failed to get the dipole up this year. In preparation for it I lowered the XM240 from that 46 meter high perch and put it back on the Trylon tower where it is up 21 meters. I have no other 40 meter antenna. When the XM240 developed a problem during CQ WW CW my score suffered accordingly. That is the danger of getting only halfway through an annual plan.

I will get the dipole up sooner rather than later. Although I scavenged part of it to repair the ice storm damaged 80 meter vertical yagi it is readily replaced with aluminum on hand.

In addition to these two antennas I hope to put up a wire yagi on the same tower this fall. It will be at least 3 elements and pointed at Europe to boost my contest scores. Making it reversible remain a possibility but not a necessity with the XM240 for working the North American and further south.

80 meters

I am pretty well set up on this band so no major changes are on my priority list for 2020. Alternatives to improve the performance of the 80 meter vertical yagi were touched on in previous article and will be dealt with as time (and ticks) permit. Adding yagi operation for SSB is not a priority since my interest in SSB contests is not high. That may change.

The high inverted vee can remain for the present since it is low maintenance and gives me a fallback in case the yagi suffers a catastrophic failure. Other antenna ideas are shelved for reconsideration further into the future.

160 meters

My top priority is to add 160 meters to the 80 meter vertical yagi before haying season gets underway this spring. That will give me year round access to the band. It's a simple addition -- a coil -- since everything else is installed including a switch on the operating desk.

After haying is done and the time comes to reinstall the T-top vertical there will be changes. The first is to reconfigure the element to raise the radiation resistance and thereby improve efficiency. The set of 8 × 30 meter long radials will be at least doubled for added efficiency. Between these two changes I expect from 1 to 2 db of improvement.

Considering how marginal conditions usually are on top band the small improvement will pay dividends in contest scores and DXing. Gain and directionality with two or more elements is left to future years when I have more time to play with various designs.

Receiving antennas

This winter I have lower receive antenna capability on the low bands than last year. I did not reinstall the west Beverage so all I have is the northeast Beverage. It's a great antenna but not nearly enough. Especially now that I'm using the amplifier more often it would help me to work the weaker stations that call me.

I have admittedly given priority to transmit antenna. Since, as they say: you can't work 'em if they can't hear you. Okay, that's not really what they say but you get the idea. I can no longer defer work on receive antennas.

With some imagination I see Beverage antennas

My dilemma is whether to stick with the tried and true Beverages or switch to vertical arrays. The vertical arrays require more work and deliver better RDF (receiving directivity factor). I have ample room on my 48 acres (20 ha) for both although the feed line lengths can extend many hundreds of meters. The antennas, feed lines and remote switching systems would be difficult to access for over 6 months out of the year.

My tentative decision is to proceed with Beverages. Additional RDF is helpful for general DXing but not for contesting; in contests some leakage that will let me hear callers from other directions is a feature not a bug.

I want to install at least one reversible Beverage this winter pointing north/south or east/west. The second will go in next fall after the first killing frost. I also hope to make the northeast Beverage reversible northeast/southwest. That will give me 6 directions on all the low bands.

The switching system can be kept reasonably accessible (out of the thick bush). The cabling and switching requirements are modest. I have trenches to dig this spring and that is my opportunity to lay the infrastructure for the system.

Operating equipment

There will be changes inside the shack as well as outside. The major planned changes are to replace the FT950 with a modern high-end transceiver. That and a 160 to 6 meter amplifier will put me in good stead for SO2R and multi-op contests and provide a degree of redundancy should something fail. I do not want to be in the position again where an amplifier fails during a contest and there is no backup. I delayed replacing the FT950 in 2019 since my SO2R and multi-op progress has lagged.

The operating desk will be replaced. Although I love my hand built desk (made in 1985 with the help of a woodworking friend) it is unsuitable for multi-op contests. I have developed a design to meet my needs and most of the lumber is on hand. It'll be cheap but functional. With a bit of paint it can be made presentable as a piece of furniture.

With the addition of a second prop pitch rotator and just the one power supply and control unit I am planning to home brew a control panel to allow operation of both. Not being able to turn both motors at the same time should be acceptable although I can always build another or larger power supply later. A new position indicator is being designed, possibly with software for at least the display function. I have candidate designs that will lead to implementation later this year.

Station automation and contesting equipment

For a complete two position contest station I need the following:

• Band pass filters for 160 through 10 meters. These will be placed between the rigs and amplifiers. They must be automated so that the filter follows the rig. Outside of contests the filters will be bypassed. These will be commercial products. Additional harmonic filter stubs are not planned this year and will only be added in future as experience dictates.
• Antenna switching: The manual switching system will be automated. I am leaning toward a home brew software-controlled system. It must follow the rigs and support multiple antennas per band, multi-band antennas and non-contest band antennas. I will likely retire the existing 8 × 2 switch, which has insufficient ports and ongoing performance problems, and opt for a home brew system. It is probable this project will be delayed to next winter.
• SO2R control system: I recently purchased and built the SO2R Mini kit. It will replace the WinKeyer and my manual headphone splitter. It has microphone switching for SSB contests which my home brew SO2R starter system doesn't have. It's the box on the right.
• A second networked PC will be needed for multi-op logging software. I use N1MM Logger+ and I plan to stick with it. The SO2R Mini work with Logger+ software.

Future years will likely see more improvements to station automation and possibly remote operation capability.

VHF and other HF bands

I would like to return to more active VHF DXing. At present my only VHF antenna is the Cushcraft A50-6 for 6 meters. This antenna must come down for adjustment because the gamma match slipped when it was lifted two years ago. I want to correct the 1.7 SWR before I buy an amplifier. The rig's ATU is sufficient for the present. My immediate aim is to achieve 6 meter DXCC using FT8. My country count over the previous two sporadic E seasons is 71. It won't be easy!

Last year I replaced the old RG213 transmission line with LMR400. This is better but still not good enough. Now that I know I have enough Heliax to spare the LMR400 will be replaced with LDF5-50A. It will run directly into the shack instead of going through the 8 × 2 antenna switch where it is occupying a valuable port. Over the winter it is disconnected (except during the RAC Winter contest) to make room for new antennas on the antenna switch.

I have a 7-element 2 meter antenna in my junk pile that I may put underneath the 6 meter antenna. With a remote antenna switch to select between them I will have all the VHF antennas I want for now. Of course I will need a 2 meter rig since I sold my VHF and UHF equipment many years ago while I was out of the hobby.

I'll admit I've given little thought to other HF bands. The big gaps are 30 meters and 17 meters. The latter I can do reasonably well using the ATU into the XM240 40 meter yagi. For 30 meters all I have is the 80 meter inverted vee. It performs poorly since on the antenna's third harmonic there are many lobes and nulls in the azimuth pattern. On some stations it works well and on others it is awful.

Anything I do for 30 and 17 meters will be simple. It isn't worth the effort in 2020 considering the many important projects I have planned. The best I'll accomplish is software designs for antennas to be considered in 2021.

Wrap-up

With this annual ritual out of the way the blog with return to antenna and operating topics. I have quite a few projects in progress so there will be lots to write about. There are several draft articles in the pipeline which are begging for more of my time to finish them. Winter antenna work will continue, weather permitting.

You can comment on articles, but realize that because of all the spam I get these are moderated. Direct email is to my call sign at rac.ca. Readership is stable to rising and I often hear from hams on the air that they follow the blog. I hope you are enjoying it. Among the mix of topics there should be something for most everyone.

I am not an expert in any one technical or operating aspect of ham radio and I try to steer readers to reliable external resources where appropriate. I try my best to avoid the myths and guesswork that is all too common among hams.

Onward to a new decade. For my amateur radio pursuits it may be the best one yet. May your decade be the same. 73

Air Core Coax Chokes: Good, Bad and Ugly

Ugly coax choke, but it worked

To give you an idea of how effective a poorly made air core coax common mode choke can perform I'll refer you to one of the oldest articles in this blog. It's wound with spliced together lengths of RG58 I pulled out of a junk box. It's ugly yet it worked beautifully, in that it solved the common mode problem I had with an end-fed antenna.

Common mode chokes on antennas can be very beneficial. All kinds of ills result from RF currents flowing on the exterior of the coax, on both transmit and receive. However it is surprisingly easy not to recognize the problems since they are often blamed on other causes such as proximity to the antenna, a poor receiver and cheap consumer electronics, among others.

It is usually easy to install a common mode choke so there is no reason not to do so even if there are no obvious common mode ills present. The choke presents a high impedance on the coax outer shield surface to prevent conducted current on the coax. The impedance can be a resistance or a tuned circuit, with the former having the most predictable characteristics and being broad band and the latter being narrow band with relatively unpredictable characteristics.

I am not here to tell you how to choose or build a common mode choke. For that I'll refer you to the experts. Probably the best explanation, analysis and recommendations was written by K9YC. There you'll learn that the best chokes use large ferrite toroids, wound with the coax itself or even THHN electrical wire. Instead I'll speak to a commonly used and admittedly inferior solution: the air core coax choke -- in this article I'll often call it a "coax choke" for brevity.

I've used many over the years, sometimes because I was cheap and it's easy to make. It is nothing more complicated that the coax wound into a coil. The coil inductance itself has choking properties, as does any inductor. However most of the choking is courtesy of the distributed capacitance among the turns that in combination with the coil inductance forms a resonant circuit. If the circuit has a high impedance at the frequency of operation (resonant) it can work very well indeed.

Unfortunately it's easy to get it wrong or to have unreasonably founded expectations. Most hams don't have a two port VNA (vector network analyzer) or the expertise to use them properly. I don't have one either. The question is: can we rely on an unmeasured coax choke to be effective?

Before going further we have to review what we mean by effective. What effect? How much? Without a clearly defined problem to solve or an operating objective to be met there is the risk of doing too little or too much. At least with the latter you can be successful though perhaps at a price or time investment that isn't strictly necessary.

To study effectiveness let's briefly list the potential benefits of common mode chokes:

• Antenna impedance: Common mode on the coax will alter the antenna feed point impedance. This may be unnoticed since when we tune the antenna (e.g. beta or gamma match) that component of the impedance is accounted for. However that may be insufficient since the common mode impedance can vary widely with frequency, especially when a reactive choke such as a coax choke is employed.
• EMC (electromagnetic compatibility): RF travelling down the coax will radiate. In our dense neighbourhoods this places the "antenna" closer to us and our devices. There is an increased probability of EMI to those devices and received EMI from those devices. Expect the tower and other cables to join the fun since the common mode current will couple to those parallel conductors.
• Antenna pattern: Even a small amount of radiation from the coax can ruin otherwise good antenna directionality. When the F/B is 20 db or greater it takes very little undisciplined radiation from reducing that to 10 db or worse. Routing the coax perpendicular to the antenna reduces induced RF but does little to suppress conducted common mode RF.

Coax chokes are very attractive since they are cheap, easy to construct and can work well in select situations. Let's consider them with respect to the above metrics.

• Modest choking is sufficient to avoid difficulties with the antenna impedance. Once the choke impedance is above ~500 Ω further improvements have negligible impact.
• EMC is not a large problem in my station since the towers and antennas are far from the house and my neighbours are far away. This isn't typical of most hams. I can get away with a little leakage.
• Very little choking is needed to protect antenna gain. Directionality requires better choking. For an omni-directional antenna this is of low importance. I am more interested in gain than directionality since my primary interest is contesting where it can be beneficial to attract callers from directions other than where the antenna is pointing. 
• For low band receive antennas such as Beverages and vertical arrays the use of high impedance common mode chokes is mandatory. These require ferrite cores to cover both 160 and 80 meters. Besides which a coax choke at 1.8 MHz is quite large and difficult to build, and can actually be more expensive than a ferrite core choke.

A common impedance objective for common mode chokes is at least 5000 Ω, or 100× the nominal antenna feed point impedance. This is difficult to achieve with a coax choke. You can do it on a single band but may need to be optimized with the aid of a two-port VNA. They are narrow band since their resonance (LC tuned circuit) is sensitive to construction technique.

"Scramble wound" coax choke that I made in ~1987 for a TH6: bad!

The scramble wound choke pictured above replaced the original burned out BN86 balun on my TH6 ~30 years ago; the Hy-Gain voltage balun is in any case a poor choice for a common mode choke. Asking a coax choke to be effective across the 2:1 frequency range of a tri-band antenna is inordinately optimistic. I could say the choke "worked" in that I didn't have any obvious common mode problems. It is likely that it had a choking impedance of less than 500 Ω on one or more of the three bands. Depending on circumstances and expectations even that small an impedance can be considered effective.

There are impedance measurements for a variety of coax chokes available. Most hams would prefer to rely on those rather than do their own measurements, in the hope that they deliver the published performance. The important parameters are diameter, coax type (outer conductor OD) and winding style (solenoid, scramble wound, etc.). Scramble wound is the easiest (see picture above) but has unpredictable performance due to the unpredictable L and C values.

One resource I've turned to many times is the measurements of various air core and ferrite core coax chokes by G3TXQ (SK). I've extracted part of the table below since I cannot assume that the web site will be around forever now that he's passed on. This is the data by which I recently made chokes for my new 15 and 20 meter stacked yagis.

These are solenoid wound coax chokes. Always wind air core coax chokes in this manner and never use scramble winding. That's the only way to achieve predictability performance. Notice in the table how difficult it is to make a high impedance coax choke that covers more than one HF band. You can do reasonably well if, like me, your station and operating style can tolerate imperfection.

For the 15 meter yagis I used 5 turns and 6" diameter of LMR400UF. On the above chart you can see that I interpolated between two known designs to get one that has the diameter and turns count that I prefer for the chosen coax. The PVC strips and cable ties hold the turns in a solenoid form. Tape was used while winding the coax to keep the diameter consistent and to discipline the turns. A temporary form can be used if you have one of the desired diameter.

Solenoid wound single-band 15 meter coax choke: good!

Pay close attention to the bending radius specifications of the coax before winding your choke. I prefer to use RG213 or the ultra flex version of LMR400 since they are more flexible. Greater care must be take with foam dielectric coax to prevent the centre conductor from pushing through the foam and shorting to the outer conductor or altering the impedance.

These danger of excess or repeated bending can take months or years to manifest so build carefully and don't rely on a one time measurement. Avoid bending the coax more than once, especially with LMR400 with its solid centre conductor, since the minimum bend radius is far higher for multiple bends. Study the mechanical properties specs and use accordingly.

Here's the same choke installed on a 15 meter yagi. One of the PVC clamps doubles as a boom clamp. Yes, I do antenna and tower work in winter! Shortly after the picture was taken the antenna was trammed to 100' (32 m). The yagi is side mounted and fixed northeast as the lower yagi in the stack.

Speaking of stacking, if you use common mode chokes of any variety in a stack it is important to use the same choke (or current balun) on all yagis in the stack. Otherwise there will be a phase shift. Unless you compensate for the phase shift, gain and lobe formation for the stack will suffer. For these coax chokes I measure the length and type of coax, data which I'll use to ensure the yagis are fed in phase.

As much as I love coax chokes I avoid them for multi-band antennas and receive antennas. Almost all my tri-band yagis and lower frequency antennas have commercial ferrite core chokes that have high impedance across the bands the antennas cover.

My Beverage receiving antennas use binocular ferrite core 1:1 transformers at the feed points. It is also good practice to use them at the switching system ports and at intervals on the transmission line, especially if it parallels a Beverage.

Breaking up the system in this manner keeps common mode currents at bay thus protecting the high directionality of the antennas. You can also wind the coax on a suitable ferrite toroid. It is very difficult to achieve high choking impedance on the low bands with an air core coax choke.

In conclusion, go ahead and use a coax choke if it suits the application. Remember to wind them properly, use reliable specifications or measure them yourself with a two port VNA and try to limit their use to one band rather than two or more. But don't expect more from them than they can deliver.

Call History

For the first time I made use of a call history file in a contest this weekend. It was the North American QSO Party (NAQP) CW contest. To those unfamiliar with this feature of modern contest logger software a call history file contains fixed exchange information cross-referenced with call sign. For example, in NAQP when you enter a call sign and tab to the exchange it will be pre-filled with RON for the name and ON for the state/province/country.

I want to talk about the how and why of call history usage and philosophical objections. The mechanics of call history can be found in the manual for your favourite contest logging software. I will not provide a tutorial.

This screen capture shows what I get when I enter the call of my friend VE3JM -- a dedicated contester with a big antenna farm. After I enter the call sign and call him by pressing enter (ESM, or by manually tabbing to the exchange) the software pulls exchange data from the call history file. The exchange can be left as is, saving typing, or overwritten with what is copied by the operator.

Call history is not the only source for pre-filled exchange data. It is typical that for stations already worked the exchange data can be pre-filled from the current contest log. For these contacts the call history only assists with the first time a station is worked in the contest. Some exchange data requires neither since it can be often be derived from the call sign. Examples include CQ and ITU zones, Canadian provinces, etc.

An extract of the N1MM call history file for NAQP surrounding my own call looks like this:

VE3VFN,VINCENT,ON,
VE3VGI,JOHN,ON,
VE3VN,RON,ON,
VE3VRC,VARC,ON,
VE3VSM,DAVE,ON,
VE3VV,TED,ON,
VE3VY,AL,ON,

You can create a call history file from your own past logs. However it is usually better to use one like the one depicted (compiled by VE2FK) since it is current, cross-checked against logs from many people and will include entries for stations you do not have in your old logs. I used a different publicly available call history file in NAQP. I probably ought to have used Claude's since the one I used had problems, as I'll discuss later.

It should be obvious that call history cannot help you with serial numbers and other unpredictable exchange fields. A wise contester will always verify that the pre-filled exchange data is the same as what you copy. Trust your ears. Override the pre-filled data as necessary. The call history saves typing but should never be relied upon as a primary source.

The exchange in some contests is so predictable that a call history file is unnecessary. A good example is CQ WW in which the zone number can almost always be uniquely derived from the call sign. In cases where it is wrong call history can help as can other data sources used by modern contest logging software.

Why I used call history

I practiced SO2R (single-op, 2 radios) in the RAC winter contest last month at a more intense level. That includes running on two bands at once. The RAC contest exchange does not benefit much from a call history file since the exchange is either unpredictable (serial number) or very predictable (province).

That went well enough that I decided to apply the lessons learned to NAQP CW this month. I used call history as an insurance policy in case I found myself getting confused or out of sync between radios that would cause a lapse of concentration when copying the exchange. It did indeed help by lowering my stress level. SO2R novice mistakes due to the stress of operating two radios simultaneously were reduced.

That said the benefit was not large. Once a station was worked the pre-fill from previously working them on another band took precedence over call history. That's a good thing since call history does not always predict what the other station sends.

What to watch for

Call history is not reliable. Give more credence to what your ears hear that what the call history pre-fill provides. There are several reasons:

• The call history file includes errors. Logging errors from previous contests reappear when those logs are used to build the call history file. This is true whether it is built from your own logs or that of others. Typos and copying errors of name and state/province were not uncommon with the call history file I imported for use in NAQP.
• NAQP brings out the weirdness in some people. Very strange names may be used just on a whim or out of perverse pleasure. This is completely within the rules. Other contests have their own variation of this whimsy. One example is sending 000 as the power by KP4 and KP2 hams in a previous ARRL DX contest to draw attention to the failed power grid due to a hurricane.
• NAQP has become a means of paying tribute to recently passed on contesters and prominent hams. For example, many Florida participants used the name Walt to commemorate the recent passing of W7SE.
• Special multiplier stations in many regional contests send section/county/region other than what is usual, and may even be in a different format. I most recently ran into this one in the Worked All Germany (WAG) contest.

The lesson is to expect the unexpected. Call history is an operating aid not a crutch. Put too much of your weight on it and it will break, resulting is substantial penalties during log checking.

Philosophical perspective

As a matter of operating ethics I remain leery of the call history files, whether those compiled by others or from my own historical contest logs. Pre-fills reduce operator involvement in the QSO by reducing the need to fully copy and enter the exchange. The mental effort of doing these tasks adds stress by increasing operator focus to ensure no mistakes are made with a consequent penalty during log checking by the contest sponsor.

It's a philosophical issue, one with adherents and proponents on both sides of the question. The matter appears to be far less controversial than some others such as excess power and remote receivers yet it does raise interesting questions of just what skill set exemplifies excellence in contesting. Until now I was of the opinion that I ought to copy the full exchange.

Call history is not the only exchange copying aid:

• Current contest log: Fixed exchange data is pre-filled from previous contacts with the same station, usually on another band.
• Country file: Zone and country by prefix or individual call sign are pre-filled. This can be especially helpful when working Americans because their call signs do not correlate with a zone or country. For example, a KH6 in the continental US and vice versa.
• Super check partial: Master data base of call signs appearing in contest logs. It is used to correct call sign copying errors. Not really a pre-fill aid but it does reduce the importance of paying attention. I always confirm a call if I substitute an SCP recommended replacement.

With all these operating aids reducing the need for careful listening and typing is the use of call history a significant factor. Incrementalism can be insidious. Just like adding a fraction of a decibel at a time with station improvements you eventually have a very big signal the use of call history is one more incremental change reducing the required skill to be a top contester.

Does it matter? Until now I believed that it does, which is why I have not used call history. I also felt uncomfortable when I enabled SCP. Yet I've never had a qualm about pre-fills from the current contest log. Operating ethics is a slippery concept. I see no clear answer. Resorting to using the same aids as your competitors is understandable.

I don't expect to use call history in many contests and I may decide to stop using it altogether. Most contesters do not share my misgivings and perhaps they're right. It's an individual choice based on one's personal view. I will not judge others.

L7 Amplifier New Filter/Rectifier Board

During the ARRL 160 meter contest my Drake L7 kilowatt amplifier failed. It happened while I was checking email during an off period. There was an almighty bang and the amp went dark. Out of the corner of my eye I saw a flash of light in the darkness under the operating desk where the power supply is located. I didn't leap too far out of my seat but it was startling.

The problem was easy to diagnose. The amplifier is ~40 years old and has the original filter capacitors in the high voltage power supply. Electrolytic capacitors have a finite lifetime, especially high voltage ones of an earlier generation. I made a note to replace them at some point. Of course I didn't.

A temporary repair to route around the failed capacitor was attempted so that I could run the amplifier at its lower B+ setting. It didn't work properly so I continued the contest without the amplifier.

There are two filter/rectifier boards in the power supply, one for each side of the full wave rectifier. The large cylindrical parts are 220 μF 450 VDC electrolytic capacitors wired in series to give 55 μF at 1800 VDC. They see half the 2800 VDC of the no-load plate voltage (B+).

You should have no difficulty identifying the failed part in the picture above. I cleaned the power supply and surface it was on of the solid mass and liquid electrolyte that escaped from the ruptured capacitor. The material is not dangerous to clean up if you are careful to wash your hands afterward.

Pricing of the individual parts is not high but inconvenient to order and would not easily fit on the original PCBs. For a modest premium I ordered the Harbach Electronics PM400 kit that includes all the parts and one PCB. Modern electrolytic capacitors of the same rating are much smaller so it all fits on one PCB.

The kit is excellent. I had heard good report of Harbach's amplifier kits and I was not disappointed. The parts and PCB look excellent and, perhaps most important, there are detailed instructions for installing the new board in vintage equipment like my L7. The instructions proved accurate, right down to the length and colour of wires in the power supply.

After I assembled the new filter/rectifier board it sat on my work bench for a couple of weeks. It was the holidays and my free time was spent on a variety of other projects. Then the ice storm hit. I was so relieved after repairing the 80 meter array that I dove in that very evening to install the board in the power supply.

Installation was quick and went smoothly. I carried it upstairs to the shack and plugged it in. It worked perfectly. My first QSO using it was ZC4UW on 160 meters, with whom I had been unable to complete a QSO running 200 watts.

Voltage and other operating parameters are the same as before. The power output is limited by the plate transformer not the power supply filter and rectifier so there is no increase in power output.

The pair of 3-500 tubes is capable of more than the L7 delivers with the relatively low anode voltage and current capacity. I have no intention of replacing the transformer.

I am now ready for the CQ WW 160 contest later this month. Eventually I will have a second and more modern amplifier added to my station for high power SO2R and multi-op contesting. It made good sense to start with an inexpensive vintage amplifier. Despite this understandable failure the L7 has not disappointed.

80 Meter Stinger Version 3.0

As I wrote several days ago an ice storm damaged my 80 meter vertical yagi. Weight of ice on the catenaries ropes supporting the parasitic wire elements was too much for the stinger at the top of the tower driven element. Unequal ice weight on the four wire elements was a factor, probably a result of partial tree cover on the southeast element and the variety of rope diameters being used.

This is the second stinger to fail. The first one failed due to expedience: I made a couple of poor material choices because I was in a rush at the time. The second stinger survived winds well over 100 kph last summer and I thought it was strong enough to last a while. However ice is often a greater hazard than wind, and around here ice is more common than high winds. Obviously I did not design the stinger well enough.

The stinger failed where the 1.5" OD tube joins to the 1.9" OD pipe below it. This is a high stress point. After tearing the antenna apart and lowering the broken version 2 stinger I inspected the break.

I thought I had used 0.095" wall tube for this section. Turns out it was no more than 0.065" wall. Thinking back to when I built it I remembered that the 1" PVC pipe above it was slightly too large at 1.315" OD to fit inside the 0.095" wall 1.5" tube so I substituted a thinner wall tube. Amateur forensic analysis of the bent tube leads me to believe that this surplus tube is not 6061-T6 unlike the standard pipe sizes I've accumulated over the past few years.

We just had two days of balmy 5° C weather that was perfect for tower work. I dropped other projects to focus on repairing the 80 meter yagi. As the sun set on the second (and last) mild day the antenna was back in service. I had to work fast and not make the same expedience driven error I made the last time.

The version 3 stinger is exactly the same length as version 2. This is important since now that the antenna is tuned and the matching networks are fixed changes would consume far too much time and be very uncomfortable in our winter weather.

I reused the lower 1.9" OD pipes since they were undamaged. The lower pipe was left on the tower. The broken 1.5" tube required effort to remove since it was distorted by the bend. It was replaced by a 1" schedule 40 6061-T6 pipe and reducer already fabricated for another antenna project.

I slipped it into the 1.9" pipe and drilled the new pipe through the outer pipe's existing splice holes. This was quick and allowed the stainless hardware to be reused. Beware cutting debris on stainless threads since that is guaranteed to seize and destroy the fasteners. I learned this the hard way some time ago. Brush the threads clean before tightening.

The 1" pipe is shorter than the old 1.5" tube. I cut the undamaged top end of the 1.5" tube to reused the PVC top support and make up the missing length. The top segment of catenary ropes could be left in place which saved a lot of time.

With the broken tube as a length guide the tube and pipe were drilled and screwed together. Now all I had to do was install the new stinger. This is the most difficult part of the repair job.

Despite a couple of fumbles the new stinger was installed in a couple of hours. The dangling ropes inevitably tangled and had to be carefully separated and then held apart while I went up and down the tower attaching and suspending the four parasitic elements.

With that done I pushed the stinger to its full height and tightened up the tower clamps. Some lateral adjustment was needed since the force of the ice pushed the clamps out of vertical alignment.

Back on the ground I walked back and forth among the four element anchors carefully pulling them to working tension. It is important to do it in steps so that the stinger is not put under bending stress. It's tedious but necessary.

Finally it was done as the sun set. I cleaned the site, put away my tools and went indoors to check it out. The SWR was perfect in all of its directional and omni-directional modes. Mission accomplished.

Losing this antenna worried me because it keeps me competitive on 80 meters. The high inverted vee performs poorly on paths longer than 2000 km.

Now I have to hope for the best with stinger version 3.0. It is stronger but still a concern since it is quite tall and under stress during adverse weather events. Ideally I would like to increase the tower height and use a short stinger. It's in my plan though perhaps not this year.

All the ice storm damage to my antennas has now been repaired. It could have been worse and for that I'm thankful.

Ice Storm

This is not the article I wanted to finish the year with. On December 30 we had an ice storm that deposited from ¼" to ½" ice on all my towers and antennas. Unfortunately there has been damage. With all the tree limbs and chunks of ice falling it's still too hazardous to do a full inspection, not to mention the treacherous surface ice.

Freezing rain requires a fine balance of atmospheric conditions. There was little of it 100 km north in Ottawa and 200 km to the west. It's very possible that I am the only ham with a large station that has been affected.

The worst was to my new 80 meter vertical yagi. The stinger at the top of the tower folded from the weight of the ice on the parasitic wire element support ropes. Yet the weaker PVC pipe at the very top, to which the catenary ropes are attached, survived.

Shortly before the failure I tried to shake the ice loose because the stinger had a pronounced bend. Ice tumbled off the smooth surface of the insulated wire elements but was hooked deep into the rope fibres. An hour later the upper 1.5" × 0.095" wall tube collapsed at the joint with the larger pipe below.

This is disappointing since I thought it would withstand ice as well as it has 100+ kph winds. In this region ice is a greater menace than wind. The weight of ice on those long ropes is substantial. The towers themselves are fine since the ice is a modest addition to the tower weight and 1000 lb guy tension. Self supporting towers are more at risk should the wind blow hard while ice is present.

Luckily the yagis held up to the abuse. The elements bent quite a lot under the weight of the ice but bounced back afterward. The tips on the Hy-Gain yagis worried me since they're thin and low tensile strength aluminum alloy. They will break off with severe ice loads.

The XM240 elements curled downward quite a lot then bounced back as the ice broke off. Notice the condition of the trees in the photograph below. The boom of the 6 meter yagi above it was also sagging. The foreground guys are twice their normal thickness.

With most of the ice now fallen or melted all antennas other than the 80 meter array test fine. The SWR of the 80 meter vertical is low enough at 1.7 to at least be usable in its omni-directional mode. Wire antennas have stretched from the high load and will have to be tightened. Going by the SWR the stretch is in the ropes and not the soft drawn copper wires.

If repairs to the 80 meter yagi have to wait until spring I can fall back to the high inverted vee. Hopefully there will be enough mild weather to permit repairs to be done. A thorough upgrade will have to be scheduled later in the years. Antenna repairs will inevitably slow the pace of work on new antennas.

It's a somewhat sombre Happy New Year at VE3VN. See you on the bands in 2020.

Tuning Big Yagis

Among the many projects simultaneously underway as 2019 draws to a close is the completion of my 15 meter and 20 meter stacked yagis. Design and construction of these home brew antennas took longer than expected so here I am working away into the coldest time of the year.

Progress was quite literally put on ice for over a month when winter arrived early and fierce. Although it's Christmastime I have been creative with my schedule to take advantage of a period of mild weather. I can even work outside without gloves, which is pretty good for our chilly climate.

Rough tuning of one each of the 20 meter and 15 meter yagis was done in unusually warm October weather with the help of friends. I rigged a temporary tram line and several ropes to manipulate the yagis to get them off the ground and relatively easy to access the feed points. Gamma matches were rough made to allow easy tuning using a variable capacitor.

For these monsters I found it easier to raise the yagis above ground in a horizontal orientation rather than attempt to point them vertically upward. This appears to be the preferred method of the friends I canvassed who have big antenna farms. You'll understand the challenge with these big antennas in the picture below taken in October when the weather was warm and pleasant.

This is my side mount 5-element 20 meter yagi with a 40' (12 meter) boom approximately 20' (6 meters) above ground. It takes four strong arms to haul this heavy antenna up the tram line for tuning. My ever dependable assistant Don VE3DQN (left) and Janek VA3XAR demonstrate how the ropes are used to swing the antenna. The feed point is reachable from the ladder when the boom is pulled downward. A short run of coax and an analyzer are attached.

Surrounded by guys and the tower the antenna must be carefully oriented for accurate impedance measurements. Best results were with the yagi pointed slightly upward and away from the guys, as shown above. Assembling the guys with non-resonant segments in any HF band is not enough to completely prevent deleterious interaction.

In this article I will discuss how high a horizontally oriented yagi needs to be raised for reliable impedance matching, and then how to adjust the physical antenna so that it performs according to the computer design. For this exercise I'll focus on the 5-element 15 meter yagis since this is the one I first ran through the full process to prepare it for use.

The side mount 5-element 20 meter yagi has been successfully rough tuned. It needs a permanent gamma match and further adjustment before being raised. I will gloss over the details of the gamma match designs and tuning process since it is a topic well worth its own article. Had I known what I was getting into I might very well have opted for a different feed system!

How high?

As we saw with pointing a yagi up there is little advantage going higher than the reflector being λ/4 above the ground. This works since field cancellation off the rear is typically high so that all we need is a modest reduction of mutual coupling with the non-resonant ground to achieve an impedance close to that in free space or high up a tower. A horizontal yagi is different since there is substantial radiation downward and therefore interaction with the ground reflection.

There is no general rule since yagis of unequal size and configuration have different elevation patterns. Luckily it turns out that you don't have to go too high for reliable impedance measurements. Performance metrics of gain and pattern need a little more height. The height of the 20 meter yagi shown above is sufficient for impedance matching.

Let's take the 15 meter 5-element yagi and model it at several heights. Comparison of the SWR curves is compelling. You can reference the linked article for further detail about the antenna design. The current model includes the actual tubing schedule. Although a beta match is used in the model there is negligible difference from the gamma network used in the physical antenna.

It is perhaps surprising that you need only go up 15' (4.5 meters) to have an impedance curve similar to that in free space. At 20' (6 meters) the difference is negligible. It is possible to rough tune the impedance even lower and do the fine tuning a little higher up if that is helpful. For the 20 meter antenna simply scale these heights by the wavelength ratio: ~1.5×.

I took measurements at both 15' and 20' with the gamma match adjusted close to its final setting. Pictures of the actual setups for the measurements are included.

There is a 9 meter length of new LMR400 hanging from near the boom centre. The AA54 analyzer is on an empty cable reel. The reels keep the antenna off the ground and protect the fragile gamma match. Ropes at both ends of the boom are used to orient the yagi.

Adjusting the SWR

As a general rule do not adjust a yagi for minimum SWR at the centre of the band or, on the low bands, the centre of the design frequency range. The R and X impedance components rarely change symmetrically on each side of centre: the SWR curve is not the perfect parabola often depicted.

My 15 meter yagi is an example of a wide band high performance design that exhibits two SWR minima. This is not unusual for optimized yagis with 5 or more elements. Adjusting the matching network for minimum SWR at band centre results in an inferior outcome.

Assuming the antenna matches the model (see next section) you should adjust for an SWR of 1 at the frequency where the model shows its lowest minimum. For my 15 meter antenna that frequency is 21.100 MHz. When adjusted that way and with the physical antenna matching the model the SWR curve across the band should match the model. For commercial antennas proceed as the manufacturer recommends.

Once you have the matching network at the sweet spot raise the antenna higher and confirm that the SWR curve across the band remains where it should be. Lower and adjust as necessary, then repeat. Make sure the components of the network cannot move around during and after adjustment. Yagis are finicky beasts and it takes very little motion of the network components and antenna elements to spoil perfection.

That said, getting to an SWR of precisely 1 is not necessary. The way antenna impedance typically varies with frequency you'll notice that although the minimum is a little high there is almost no impact on the SWR where is it normally higher. A few ohms of R or X make little difference where the deviation from 50 + j0 is greater.

More important is that the SWR across the band be below your chosen maximum, or what the design or manufacturer promises. Ideally it should be less than 1.5 everywhere, especially for a contester like me. Then you won't have to worry about tuners for your rigs and amplifiers as you change bands and frequency.

Interactions with guys, towers and other antennas will upset the SWR once you move it into position after it has been tuned. If you've planned well the change will be inconsequential. If the change is large there is no point in readjusting the impedance match since the problem lies elsewhere. Find that interaction and fix it. A deviation of the SWR often indicates that the pattern is being degraded by an interaction.

Confirming the design

For the typical amateur directly measuring and optimizing the pattern of an HF yagi is difficult and almost always avoided. I am no different. I rely on software models and careful construction for my home brew antennas. Even with NEC4 it is nigh impossible to get the physical antenna to exactly mirror the software model. With NEC2 and SDC (stepped diameter correction) the divergence can be worse when good modelling practice is not followed. NEC2 has numerous quirks.

I use EZNEC with the NEC2 engine and the supplied SDC algorithm. These antennas came surprising close to the model which was a great relief. But how do I know since I cannot do a field measurement of the pattern? There are ways to go about it so that one can be confident even without a direct measurement.

Impedance is easy to measure with accuracy using modern antenna analyzers. Fortunately impedance holds the key to an indirect though quite good method of confirming the model. Refer back to the SWR curves earlier in the article for the following discussion.

If the antenna impedance is adjusted as described earlier the SWR curve will closely match the modelled antenna for the antenna reasonably high and in the clear and a software matching network that follows the same procedure. In the EZNEC model I use a beta (hairpin) matching network since unlike a gamma match it can be reliably modelled, it closely mimics similar matching networks such as L-networks and gamma matches and doesn't preclude use of SDC on the driven element.

Although the curves appear to match there is an important difference. In the model the second dip is at 21.410 MHz and is around 21.450 MHz in the physical antenna. Assuming the yagi has been constructed per the design the divergence is most likely due to element self-resonance and not interactions and ground effects. A broader measurement spectrum is useful at this point so I raised the antenna higher and measured the SWR up to 21.600 MHz.

What we have is an impedance inflection point at 21.450 MHz. Above this frequency the radiation resistance drops sharply and the resulting SWR cannot be corrected with the matching network; no simple network can tame that slope while also matching the antenna within its design range. The software model exhibits the same behaviour.

The inflection point is a proxy for the true frequency range of the yagi. You'll find an inflection point like this in almost every yagi, perhaps two or three of them. Their presence at the correct frequency is strong evidence that the yagi is tuned for optimum gain and pattern. If not the antenna elements require adjustment.

Here we have the inflection point 0.15% higher in frequency. Considering all the small construction inaccuracies, reactance "bumps" from all the hardware, elements curving under their own weight the software did a remarkably good job predicting the yagi's real behaviour. In practice this small a difference can be ignored. I didn't ignore it.

Calculation suggests that the antenna elements should be lengthened by a little more than 1 cm (½") to bring it into agreement with the model. All the half elements tips were lengthened by ¼", except for the driven element: the DE length affects the impedance match not the gain and pattern. I adjusted the second untested 15 meter yagi at the same time so that I don't forget to do it later.

The yagi was lifted and measured. The improved match at 21.100 MHz is due to bumping the gamma match whose components at the time were not fully tightened. That was dumb luck.

I call this a tremendous success. Now I have confidence the antenna will perform as designed. Perfection like this isn't necessary but I do enjoy being presented with a measurement that so nicely mirrors the design. It makes me feel good after all the work that went into this project.

Next steps

For this tuning process the tram line was moved higher up the tower so that once the yagi is ready (choke, coax run, truss) no rigging change is needed to haul it up to the waiting side mount bracket. If the weather and my luck hold that should happen before the new year arrives.

There are two LDF5 Heliax run to the new tower ready for use. They are overground until the spring when a trench will be dug for burial, including control lines and rotator power. For now I will directly connect the side mount yagis to the transmission lines and add the stacking switches later.

I hope to have the 20 meter side mount yagi tuned and raised in January in time for late winter contests. The antenna is quite heavy and I'll need a couple of helpers, none of whom are (not surprisingly) unavailable this time of year.

Once all that is done I can tune the upper 15 meter yagi at my leisure and assemble the upper 20 meter yagi. A better and stronger boom for the upper 20 meter yagi is built and ready. As the weather allows the mast will be raised and then the upper yagis lifted. That may have to wait for warmer spring weather.

I will end here and prepare to wrap up the blog for 2019. Expect a year end review article before or shortly after January 1. Merry Christmas, Happy New Year and see you on the bands.

FT8 - The Universal Solvent

FT8 keeps eating away at the bands, one ham at a time. Like the mythical universal solvent it cannot be contained: FT8 dissolves every container traditionalists attempt to put it into. The digital wave inexorably marches onward.

Lately I've succumbed further. Until now I've restricted my use of FT8 to 6 meters. With the long winter nights of a deep solar cycle minimum there are only the low bands available most of the time. I enjoy the low bands yet it can get tedious outside of the excitement and intensity of contests and DXpeditions.

Every night there are same stations working each other on CW. Top band aficionados continue their vigil for propagation and welcome all comers. The regulars exchange signal reports and, this time of year, supplement that with seasons greetings, wishing MX and HNY to all. Activity briefly spikes to include a broader range of stations during sunrise and sunset enhancements.

It's all very cozy. I have good antennas for 80 and 160 so I can hold my own even without enhanced propagation, although I would benefit from more receive antennas (they're coming, eventually). With my amplifier out of service until parts arrive it is a little more difficult to work DX in the everyday challenging conditions.

Then there's FT8. I have taken to monitoring 1840 kHz many evenings just to keep an eye on top band propagation when I am busy doing other things and I'm uninterested in pursuing routine CW QSOs. Of course the inevitable happened: one day I hit the Enable button in WSJT-X. My log has begun filling up with top band FT8 QSOs.

The breadth and depth of activity is startling for anyone daring to venture beyond the traditional modes. In amongst the multitude of call signs never heard on CW there can be found familiar call signs of contesters and DXers. The DX to be found is itself quite surprising. Every night I hear UA0, Africa, South America and in the mornings there's the Pacific and Far East.

Try to find these distant stations on CW and you will be disappointed. It isn't that FT8 is so much better than CW (it isn't). You can only work what's there and what's there is on FT8. The clear implication is that many so-called difficult propagation paths on 160 meters aren't really difficult at all, there's just no one active on CW.

The transition to digital modes is less extreme than on 6 meters, so far. To escape from routine QSOs with the regulars it is necessary to spend some time on FT8. My top band FT8 log is filling up with DX QSOs and DXCC countries I rarely hear on CW outside of contests. In a way it's sad that the hobby is changing yet exciting in that digital modes are spurring activity from newcomers and old hands alike. That's a good thing.

Will CW survive? Perhaps until 2040 when most of the older generation will have passed on. There are not enough young people entering the hobby with an interest in CW although it may survive among a small minority. Obsolete technologies do attract some among the younger generations, whether it be vacuum tube appliances, vinyl records or mechanical clocks. CW will have its adherents as well for many years to come.

I will continue to spend a portion of my top band time operating FT8 although CW will remain my first choice. Two nights ago I heard A50BOC on 160 meters, barely audible and not workable and it was exciting to hear. CW signals from JA and HL are far more attractive to me than FT8 despite the difficulty of making the QSOs. However I will go where the activity is, just as I did on 6 meters.

Okay, that's enough philosophical rambling. During my short time on 160 meter FT8 I've been learning a few things. Operating there is not the same as 6 meters. Openings are longer, the atmospheric and man made QRN dominant, QSB slow and deep and the activity is far greater most of the time. The spectrogram shows a busy 1840 kHz on a weekday evening.

Reciprocity of station capability is less than on higher bands. Decoding a station does not mean they can decode you, and vice versa, when your power and antennas are comparable. This is as true for FT8 as it is for CW and SSB.

• Local QRN can differ by 10 db or more. This varies by time of day, latitude, urban/rural locale and other factors well known to low band operators. Don't be surprised when some stations don't answer you.
• Many top band hams are unintentional alligators since, apart from the above QRN factors, most do not have low noise (directional) receive antennas.
• Too many stations call on the CQing station's transmit frequency, which often means none of them are successfully decoded. I don't know why this seems to happen more on 160 than 6 meters, or perhaps I am suffering from selective memory.
• Clear frequencies don't last long in that 3 kHz FT8 window. It is commonplace to have someone start transmitting on another station's transmit frequency and time slot despite signal levels implying that they must be able to hear the other station. Everyone suffers as a result. 
• You can see a couple of poorly adjust transmitters in the spectrogram above. It is often worse.
• DX stations are regularly covered up by nearer stations that cannot hear them and think the frequency is clear. There is no QRL? equivalent on FT8. If the spectrogram looks clear (or not) away you go.

Some of the problem is poor operating though mostly it's just regular hams doing the best they can with what they have on a band with difficult operating conditions. It's all a part of the game so get used to it. Those with skill and superior antennas have an advantage as they do on any mode, on any band and whatever the prevalent propagation. Experience and practice make a difference.

While it's nice to try something new and work new stations I don't take FT8 operating on 160 meters too seriously. That may change if the migration from CW continues. If it does I may have to concentrate on 160 meter FT8 for real just like I now do on 6 meters. I intend to hold off on other bands for a while longer, hopefully a long while.

Change is good even when it makes us uncomfortable.

Performance of the 80 Meter 3-element Vertical Yagi

The 3-element, 4-direction vertical yagi I recently completed is not a perfect antenna although it does perform very well. It has its pros and cons. I learned a great deal designing and building it, which was one of my main objectives apart from putting out a competitive signal on 80 meters. The antenna is a variation of the K3LR array described in ON4UN's Low Band DX'ing book.

No antenna stands on its own merits; every antenna must be compared to alternatives. For this discussion of the yagi's performance I will use the big gun antenna standard for 80 meters, the 4-square.

This is the sensible baseline since it is important how I do relative to other serious contesters and DXers. It makes little sense to compare the yagi to an inverted vee -- of course it's better but the comparison is of little value.

This article is not a mystery novel so I will put the answer right up front: the 4-square is superior on the majority of metrics. That said the details of the comparison can be subtle and enlightening for those with a passion for antennas. A truthful comparison helps direct my future plan for 80 meter antennas. That will be briefly addressed towards the end of this article.

Let's start with the basics before delving into details.

First up is a fundamental of physics: conservation of energy. For antennas of equal efficiency a corollary is as follows:

Gain = Directionality

To achieve gain in one direction requires taking energy from other directions. Conservation of energy informs us that to achieve gain the antenna must be directive, and vice versa. The two are inextricably linked. The 4-square's better directionality largely explains its gain advantage over the 3-element yagi.

However it is not quite that simple. Dropping a secondary lobe from -10 db to -20 db (assuming for the present argument there is only one lobe other than the main lobe) the main lobe energy increases from 90% to 99% of the energy. This is an almost negligible gain improvement of 0.4 db. Reception improves but not transmission effectiveness.

Further gain improvement requires narrowing the beam width of the main lobe. For a non-rotatable antenna like a 4-square or wire yagi too narrow a beam width can be detrimental since there will compass points where gain is poor.

Although the 4-square is more directive than the yagi the gain improvement is not substantial. The better gain of the 4-square mostly comes from other differences between the two antenna types. Both have sufficiently modest gain/directionality that 4 direction switching covers 360°.

With that fundamental observation made let's look at how the antennas differ. There are several factors:

• Element spacing: On a side the 4-square element spacing is 0.25λ, and the diagonal spacing is 0.35λ. For the yagi the element spacing is 0.125λ. The closer spacing of the yagi increases the mutual coupling. This is required in a yagi but not is a 4-square.
• Element shape: It is typical to use straight elements in a 4-square although that isn't necessary. The yagi has a straight driven element and sloped T-top loaded parasitic wire elements. Again, that is a choice not a requirement. Element shape and diameter effects both antennas and we will have to normalize them to make a fair comparison.
• Forcing: Yagis work by mutual coupling alone. The 4-square uses phasing lines and combiners to engineer phase and amplitude of antenna currents. However mutual coupling exists in a 4-square and is a significant factor in its design and engineering.
• Ground dependency: The antennas behave differently for the same radial system (near field). Distant ground (far field) effects are the same for both.

These are the major electrical factors. There are also other factors, such as cost, that must also be considered.

Notes on modelling

All the software modelling is done with EZNEC. Medium ground (0.005, 13) is used throughout even though the ground conductivity in my rural locale is better than that. A fair comparison depend on a standard environment.

MININEC ground is used rather than "real" ground so that the radial system can be easily modelled as a resistance load at the base of each element. MININEC assumes a perfect ground with respect to the near field. The resistance accurately represents the equivalent series resistance (ESR) of the radial system and ground beneath. But you have to know the ESR of your radial system. The model departs from reality for a small number of radials since they affect the antenna resonance. These effects must be compensated for during antenna construction and testing.

There is loss in more than just the ground. Wire elements have non-negligible loss whereas tower and tubing vertical elements have negligible loss. Coil, capacitors, phasing lines and hybrid combiners each contribute loss. In particular the 4th port of the hybrid combiner used in most 4-square antennas goes to a 50 Ω dump load, which can be as lower gain by as much as -0.5 db at the band edges, though -0.1 to -0.2 db is more typically .

Since this is comparable to the approximate -0.15 to -0.2 db resistance loss in the wire yagis elements I will treat them as equal, and leave them out of the antenna comparison. The 4-square model is adapted from one packaged with EZNEC uses lossless phasing lines and no combiner or dump load.

The azimuth pattern comparison is typical. The difference in practice has many factors, as listed above. For my current radial system the 2 db difference of the inner plot is a fair representation. In other configurations the difference can be better or worse and in the ideal can approach equality. We'll come to that later in the article.

The elevation patterns are similar for both antennas. This is primarily determined by ground quality and topography outside of the antenna's local environs.

Turn a yagi on its side

Verticals arrays -- yagis and 4-squares -- have relatively poor side lobes in comparison to horizontal arrays. Many of you know why that is but let's review it anyway.

A dipole has low radiation off its ends. An array made of dipole elements is the same since adding nothing to nothing equals nothing. Therefore the typical horizontal yagi has deep side nulls. In free space the elevation pattern has quite a lot of radiation directly up and down. For a typical 3-element yagi in free space the blue plot is the elevation pattern and black is the azimuth pattern.

Over ground the way to remove the high angle radiation is to place the yagi at a height that is an odd multiple of λ/2 so that the ground reflection is out of phase with the direct wave resulting in cancellation. At intermediate heights there can be substantial high angle radiation, and that is rarely desirable.

Rotate the boom 90° and the elevation and azimuth patterns are swapped. That is in essence what you have with a vertical array: lots of radiation off the sides and very little at high elevation angles. In a conventional vertical yagi like my 3-element 80 meter antenna radiation to the sides is worse than shown in the adjacent plot.

For a driven array such as the 4-square it is possible to reduce the side lobes. Thus a 4-square can have better directionality than a 3-element yagi. Of course the 4-square has one extra element, which may seem an unfair comparison until you consider that the two antennas are of similar size.

Element spacing

Comparing element spacing of the two antennas can be confusing since although they occupy a similar area the yagi has a fifth element in the centre -- the driven element -- and two of the elements are inactive. Further, because two elements are inactive the 0.35λ spacing between adjacent parasitic elements is irrelevant. The element spacing is 0.125λ for the yagi and 0.25λ for the 4-square, a ratio of 2.

The significance is that the mutual coupling between yagi elements is higher than the 4-square. The elements can be more widely spaced to equalize the antenna footprints. This would increase the boom length to 0.35λ (0.175λ element spacing), a length that is near optimum for a 3-element yagi. That does indeed improve the yagi's performance, as we'll see.

In addition to achievable gain the increased spacing modestly improves F/B. Of perhaps greater importance is that the mutual coupling is reduced which increases radiation resistance, and that lowers antenna currents and I²R ground loss. Driven at 1000 watts the typical 4-square element current is ~2.5 A. Currents in the yagi elements cover a wide range, from as low as 1.5 A to as high as 9 A, with more typical values between 2 A and 7 A.

The gain improvement of 0.175λ yagi element spacing is ~0.6 db (perfect ground), which is marginally significant. Reduction in ground loss results in greater efficiency for the same radial system. Gain improvement is greater with a poor radial system and less with a better one.

Element shape

The sloping T-top wire parasitic elements are convenient since it uses the driven element as the support structure. It comes at a performance cost since the element shape is not optimal. There are two problems:

• Radiation resistance: The acute angle on the lower side of the T causes field cancellation with the monopole part of the element. Field cancellation lowers radiation resistance and this increases loss in the radial system and to a lesser amount in the element wire.
• F/S: There is a horizontal component to the azimuth pattern due to the T which lowers overall directionality by increasing radiation to the sides and rear.

The lower acute angle (close to 45°) requires NEC4 for accurate modelling. With the more commonly used NEC2 there is a significant discrepancy so the wire elements dimensions must be determined in the field. NEC4 isn't perfect but you will get close.

Modelling with EZNEC predicts an approximate 5 Ω reduction of radiation resistance from 31 Ω to 21.5 Ω. compared to a straight wire element. With my analyzer I measured 25 Ω including an estimated ground loss no worse than 5 Ω. For a 5 Ω radial system the loss is 16% versus 14% with straight wire elements. Although that's small the loss multiplies for poorer radial systems and in a yagi where the radiation resistance is lower and the current higher.

A comparison of straight wire elements versus the T-top wire elements was discussed in a previous article. Look there for the relevant charts since I won't reproduce them here. You will see that directionality and gain are better with straight elements, especially directionality . Unfortunately straight elements are not easy to make from wire due to the need for suitable supports. A coil loaded shorter straight element is feasible except that efficiency is far worse. If you go to the trouble of rigid parasitic elements I believe it is more sensible to build a 4-square rather than a yagi.

Forcing

Yagis rely on mutual coupling alone to achieve current amplitude and phase for desired behaviour. Current forcing is a feature of driven arrays. Since there is substantial mutual coupling in a 4-square it is not a purely driven array; the elements would have to be much farther apart for that.

Forcing is simple in its basic concept. The generator always sees a single impedance. By tying all the elements to the feed point the amplitude and phase is uniquely determined. Networks between the feed point and elements set the amplitude and phase to achieve the desired behaviour.

It is quite complicated since you want a 50 Ω load for the generator and accurate power splitting and phase across 4 elements with network that must sustain complex loads (high voltage and current) at high power and with direction switching. Elements must be made as identical as possible. Not many hams design and build their own 4-square control systems!

The EZNEC model used in this article is adapted from one provided by W7EL with the software. It uses fixed phase lossless transmission lines. This is impractical for real antennas due to the direction switching challenges and the frequency sensitivity of the phasing lines. Hybrid combiners are more suitable.

More than you could ever want to know about 4-square design and hybrid combiners can be found in ON4UN's Low Band DX'ing book. For the present discussion I will only mention a couple things. First, the phasing lines experience high SWR and have attendant losses, although those are low with good quality coax at 3.5 MHz.

Second, hybrid combiners are not lossless since frequency dependent imbalances among the 4 elements present at a 50 Ω port where a dummy load dissipates the power due to the imbalance. A failure in one element or icing can cause a large increase in the the dump power. Monitoring or protective circuitry is important.

Modern 4-square controllers usually offer an omni-directional mode in addition to the 4 directions, just like I built with my 3-element yagi.

Ground dependency

Ground ESR in series with the antenna impedance is the most important factor affecting the yagi in comparison to the 4-square. For the same radial system the ground loss for the yagi is higher, and it can be substantially higher. That is due to the low radiation resistance due to the aforementioned factors: element shape and mutual coupling. The better the radial system the closer the yagi's performance to that of a 4-square.

The yagi should have a radial system ESR of less than 5 Ω and lower is highly desirable. In my antenna I have twice the number of radials on the driven element as the parasitic elements since currents are highest in that element. Current in the yagi elements can be more than 3 times higher than in the 4-square. If you are limited in how many radials you can put down go with the 4-square.

Measuring the ESR of a radial system is difficult. My estimate for those in the yagi is based on the trend line of element self-impedance as radials are added. This is a common technique and usually the only practical one. The measurements suggest that the driven element radial system is in the range 2 Ω to 3 Ω, and that of the parasitic elements 4 Ω to 5 Ω. For modelling purposes I use the values at the high end of these ranges.

I will keep it simple and state a few modelled comparisons rather than draw up a bunch of charts. As a baseline with a perfect radial system of 0 Ω the 4-square has approximately 0.5 db more gain than my style of yagi, assuming the previously described internal loss typical of the 4-square and yagi. For a 5 Ω radial system the 4-square gain declines by 0.5 db and the yagi gain declines by 2 db. Therefore with a large but not extreme radial system the 4-square gain is better by 2 db. There is frequency sensitivity in these figures for the yagi so I took the average.

That's a substantial difference. With a smaller radial system the difference will be larger. You need a lot of radials to make the yagi perform well. As I said in an earlier article that although the directionality of the yagi is lacking it is of little consequence in contests since I can work stations off the back and sides with good success and that puts more QSOs in the log. Receive performance is compromised so it is occasionally helpful to use a high directionality receive antenna.

Pros and cons vs. the 4-square

This list is a set of subjective and objective observations of the yagi versus the 4-square. You may disagree with some points or weigh their importance differently.

Pros:

• Low cost
• 20% less land use
• Flexibility of direction choice, more than 4 directions, and ability to add more directors
• No dump load or phasing harnesses: all the power is radiated or lost in the ground

Cons:

• Lower efficiency for the same radial system
• Must home brew: there are no commercial control systems
• Directionality and gain

I believe most hams would, and should choose the 4-square. It is possible to build it with wires to reduce the cost with external supports or with elements similar to that used in my yagi.

The decision is not quite so straight-forward since my yagi design is not the only one. The yagi can be improved in various ways.

Alternatives

The yagi will remain as it is for some time. There are too many antenna projects for the next year to worry too much about 1 or 2 db. What I can do, now that I am indoors more often due to the weather, is to explore alternatives. Alternatives range from the highly disruptive to modest.

Taller centre support to allow straight (unloaded) elements

Straight wire elements increase gain by ~0.5 db. Side lobe radiation is reduced almost to that of the 4-square. Directivity is improved so that that it comes close to that of a 4-square though frequency dependent. The taller central tower can serve as an efficient 160 meter antenna with suitable switching to retain its performance as an 80 meter omni-directional vertical and yagi driven element.

Increase boom length so that it covers the same area as the 4-square

Element spacing increases from 0.125λ to 0.175λ, for a boom length of 0.35λ. Gain increases ~0.6 db and directionality is improved. Of course the radials for the parasitic elements must be relocated, and that job takes several days. The increased spacing permits converting the array into a 4-square. The central tower can be used as a simple support, or continue as an omni-directional vertical (if the commercial 4-square controller doesn't have this feature) or as a 160 meter vertical. For the latter case modelling confirms that a central 160 meter vertical does not affect 4-square performance on 80 meters.

Bent elements

Removing the lower half of the sloped T-top loading section on the parasitic elements has several advantages. Parasitic element efficiency because the radiation resistance rises from 21.5 Ω to 31 Ω. Gain increases 0.6 db with the existing radial system. Directionality is within a few decibels of a 4-square. There are no mechanical changes. Parasitic elements must be tuned for different self-resonant frequencies and the L-network adjusted to compensate for the higher feed point impedance.

More radials

This is perhaps the simplest alternative. By doubling the radial count the ground loss is reduced. In addition to a gain increase of 0.6 db the directionality is modestly improved. Apart from laying the wire the L-networks must be adjusted for the lower feed point impedance and the parasitic elements retuned to the desired self resonant frequencies. Wire isn't always cheap and doubling the radials will require 1600 meters of wire and many days to install them.

Paths forward

The described alternatives can be combined for further performance improvement. For example, by doubling the radials, using bent elements and a 0.35λ boom length the gain comes within 0.5 db of a 4-square and directionality is similarly close.

One or more of the alternatives will be explored in depth in future articles. This one is already long enough and I don't have the time right now. Although I may eventually go for a 4-square I am not done exploring yagi designs. Modifying the existing yagi is far easier than rebuilding.

A little more gain and directionality would be beneficial, especially on receive. It would be advantageous during contests to keep receive antennas primarily for 160 meters to reduce contention between operating positions. In contests I often use the northeast Beverage while working Europe to improve copy of the weakest callers.

In conclusion there are many ways in which the yagi can be improved and experimented with. In that light this is an ideal antenna for me and my interest in antenna design. A 4-square with a commercial switching system is not so interesting to me. Others may have different objectives.