Case of the Missing HF Spice

One consequence of the pandemic has been a dearth of DXpeditions. You might therefore think that the DXpeditions or other moderately rare DX stations would receive more attention than usual. This is what economists call supply and demand: there is less supply so the demand should be high because we are spending far more time at home. That is, we should be willing to pay a high "price" for the rare DX.

That hasn't happened. When these stations did appear the pile ups were not deep. For many of them I found it took just one call to get through. As regular readers know I do have a few big antennas, and that does make it easier. Yet there is more to the story because there is less competition in the pile ups. Most of the time I was successfully working the pile ups without turning on the amplifier. I always try that first since it's a bother to turn on and warm up the tubes and the power boost hasn't been necessary except on 160 meters.

Which brings us to the second consequence of the epidemic: apathy. It has been widely reported that despite the additional time we are spending at home many of us are not taking advantage. For hams that means spending less time on the air or on radio projects. There are notable exceptions, like the increased activity in contests. That is good for me since I'm a contester. But these are exceptions and not the rule.

All communications services are subject to the network effect: service usage strongly outpaces the growth of service users. As deployment proceeds, usage growth is geometric. Think of the telephone in its early years. Imagine you're the only person with a phone in town. You have no one to call so you don't use it very much. As more phones are deployed you have more people to call, so you do, and so does everybody else. 

Amateur radio is the same. When many hams exit their shacks, many more follow. The bands sound dead and we lose interest. Bland food isn't tasty; apathy is contagious. The network effect also works in reverse.

The network effect applies to other aspects of the hobby. You don't like digital? What do you do when you have few left to work on other modes? This happened to me on 6 meters with FT8. The network effect is in play with digital, no matter your feelings or mine. I'm even beginning to like it.

No one to talk to with the same interests you have? You move to where the activity is or you lose interest. You might even leave the hobby. As activity for your favourite mode declines the overall decline accelerates so that total silence seems to happen overnight. The transition to FT8 on 6 meters was measure in months, not years. You can call CQ using AM but do not expect a reply except on select frequencies where the remaining aficionados congregate.

Another reason activity declines is due to the same old, same old syndrome. For many, interest is spurred by novelty. DXpeditions spur our interest. The novelty of digital modes is the same. It's akin to spicing our bland foods.

Non-DXers may grow curious and increase their activity when they hear the excitement on the bands over a rare one. Some will jump into the pile ups despite their indifference. The same happens in contests, with non-contesters coming on the band, hearing the activity and jumping in to make a few contacts. Do you hear some peculiar warbles on the band? You download the software and have a look to see what the excitement it's all about.

Excitement breeds excitement. Imagine going for a walk in the quiet of night. You unexpectedly run into a street party with music and dancing and happy people. You stop to watch. Someone grabs your hand and you think, why not, and soon you're dancing, too.

Getting back to DX, maybe it's just my imagination that I am beginning to see more excitement on the bands. The DXpeditions that make an appearance are garnering bigger and more enthusiastic pile ups than they have for many months. 

Perhaps it the rollout of the vaccines that promise an end to the pandemic. People are perking up everywhere, and not only on the ham bands, so it may be more than my overactive imagination. I've seen the renewed excitement with the A25RU operation and others.

Sunspots, vaccines, contests, DXpeditions and more. HF is once again tasting spicy.

Reflections: The Downside of Height

As my antennas get higher I run into novel difficulties. In one sense it's a nice problem to have considering that few hams have antennas that are large or high. Nevertheless it is a problem. In this article I'll review the affect of height on horizontally polarized antennas (primarily yagis) before discussing my own particular challenges and mitigation strategies.

Even for those without this problem the discussion may be of interest and educational. Some of the material is elementary. Antenna height has been covered numerous times in this blog (and countless times elsewhere) and I will reference earlier articles for details that are only touched on lightly in this one.

The antenna does not determine the path

Higher antennas are not always better. More precisely, for an antenna that is already reasonably high, higher is not always better. This is not due to diminishing returns so much as the potential mismatch between the antenna's pattern and what the ionosphere requires for communication.

Put another way, an effective antenna is one in which its most effective direction is the one that nature demands for the intended communication. Nature chooses the direction. Your job is to design and install an antenna that is effective for that direction. The antenna does not determine the path.

Direction is 3-dimensional so we must consider both azimuth and elevation. Good presentations of antenna patterns show both. Let's dispense with azimuth quickly by noting that the correct azimuth is the great circle route (short or long path); that is, except when it isn't! Skew path is not at all rare on the lowest HF bands and on the band closest to the MUF. Smart operators turn their antennas to find the optimum azimuth during difficult conditions.

With that out of the way let's turn to elevation angle. Good DX paths are more common at low elevation angles. There are exceptions; there are always exceptions. An effective vertically polarized antenna with its far field reflections from a high conductivity ground (e.g. seawater) can have an impressively low elevation angle for its main lobe. Most vertical antennas don't do nearly so well. 

Horizontal antennas usually do better over typical ground (medium to poor) when they are high enough. In context, high is with respect to wavelength. On 40 meters and down the height to put the maximum radiation at the required low elevation angle for most DX paths is difficult to impossible for most hams. Hence the prevalence of verticals on 80 and 160 meters. For DXing on these low bands, a moderately efficient vertical typically outperforms a horizontally polarized antenna with the same apex height.

When great height is possible there are dangers lurking. Higher isn't necessarily better. This is a lesson I am learning every day with my complement of low, high and higher antennas.

Modelling height

Software makes it easy to inspect the elevation patterns of antennas at various heights. Consider the following set of patterns for a 5-element yagi at heights from ½λ to 4λ over medium EZNEC ground. Although I am illustrating the effect of height with a 20 meter yagi the pattern is scalable to other bands. 

The elevation pattern scales with wavelength. If you get dizzy thinking about an 84 meter height for a 4λ on 20 meters, you can instead imagine a 2 meter yagi that is merely 8 meters high.

This is a busy plot that may be difficult to read. To help out I'll list a few key points:

• Starting at 1λ there is more than one forward lobe. Their quantity increases as height increases.
• There are deep nulls between those lobes, and that will cause difficulties on the air.
• Maximum gain increases with height due to the concentration of energy at lower angles.
• Low angle radiation increases quite a lot at greater heights. For example, at 5° the gain for the yagi up 2λ is ~6 db better than one up ½λ. Diminishing returns are rapid at greater height.
• By choosing heights that are an integral multiple of ½λ the radiation directly upward is cancelled. I did this deliberately for the plot and it is worth keeping in mind when planning your next tower.

As a general rule, the higher you go the greater the number of elevation lobes and nulls. These can be aggravating since when the signal comes in at an angle where there is a null the antenna will not serve you well. Unfortunately there will always be signals that strike those nulls. It is worth addressing for the contest enthusiast, but also for daily operating enjoyment and DXing.

Many VHF operators may be unaware of the problem since DX paths tend to be at low elevation angles. That is often not the case for sporadic E propagation, as one example. An elevation rotator for satellites and EME can deal with the problem at high elevation angles, where "high" means an elevation angle greater than the half-beam width of the main lobe in free space (see below). 

How those lobes and nulls form

The pattern of any antenna doesn't start at the horizon. All radiate downward. A free space elevation plot makes this evident. At right is one for the yagi discussed above.

The elevation patterns above and below the horizontal axis (0° elevation) are mirror images. When placed over ground the downward radiation is absorbed (dissipated) or reflected upward. 

The half of the radiation that reflects from the ground adds to the direct (skyward) radiation to form an interference pattern by superposition. That interference pattern is the series of lobes (reinforcement) and nulls (cancellation). 

Perfect addition and subtraction requires the amplitude of the ground reflection to be equal to the direct radiation. This is approximately true for horizontal polarization even for poor ground quality. 

When the fields add the radiation in the lobe is boosted by 6 db. Where the phase difference is 180° the null is exactly zero. Of course it's never exactly zero, and over real ground will rarely be deeper than -20 db below the peaks of the adjacent lobes.

At right is the broadside elevation pattern of a simple dipole 4λ above ground. Perfect and poor ground are compared. The effects of ground are easier to see with a dipole than with a yagi.

The first thing to notice is that over poor ground the nulls are not so deep and the lobes not so large. Poor ground absorbs more at high incidence angles so the reflections are weaker. In addition to that, the phase shift will not be 180°. Perfect ground does not have these deficits. The effect of poor ground is modest with respect to filling the nulls, and is negligible at low angles that are of interest to DXers. At low angles even poor ground reflects well.

The second is that the angle between adjacent lobes and nulls is smaller at low angles than at high angles. This is due to the more rapid change in the path length of reflections as the elevation angle decreases. This puts more of those deep nulls at low elevation angles where we don't want them. The higher the antenna the worse the problem.

This review should have been elementary to most hams. It is nevertheless worth recapping the basics before going further.

Terrain

The previous discussion assumes flat terrain, and that is not the case for many. Terrain plays an important role in determining the elevation angles of lobes and nulls, and can be the dominant factor where there are major slopes, hills and other large geographic features.

To solve the terrain problem the usual antenna modelling systems are not helpful. Modelling terrain requires real topographic data and a ray tracing tool like HFTA. I have never used HFTA for my station since the land here is quite flat, with gentle slopes and undulations for many kilometers in all directions. Urban hams also have little to gain from HFTA since although the land may be flat all those buildings and metal infrastructure are near impossible to model.

For those with topography that is not flat and open it is advisable to use HFTA to investigate candidate antenna heights and to calculate the elevation angles of the lobes and nulls. In some cases a low tower will be sufficient to achieve both a low elevation angle and few nulls. For others no tower is high enough. 

One recent correspondent who is working on a 40 meter wire yagi put up the first inverted vee element. It is outperforming his vertical on his most important DX path. The reason is that the land slopes downward in that direction. His experience is typical. It is possible to get an idea of how an antenna in his location will perform in NEC2 by tilting the antenna upward by the same angle as the downward slope (or vice versa for an upward slope) and subtracting that angle from the elevation plot.

Beyond this rudimentary advice I have little to say to those with complex terrain. Use HFTA to find what will work best in your unique circumstance.

Mitigation

You cannot fill an elevation pattern null by aiming above the horizon on any HF band. The ground reflection remains and dominates the far field pattern. For high gain stacked arrays for 2 meters and above tilting can work very well. For these antennas the elevation beam width is narrow and the ground-directed radiation falls off rapidly when the antenna is tilted up. In essence, the ground disappears and the antenna performs as if in free space.

An elevation rotator is routinely used for satellite and EME communication. For low elevation angle terrestrial paths or for low elevation EME and satellite work the ground is as much a factor as it is at HF. At the lowest elevation angles the ground reflections will dominate and cause elevation pattern nulls. Too often those nulls are at inconvenient angles. The only good options are to switch to vertical or circular polarization or to wait a minute or two for the moon or satellite to move.

To fill elevation pattern nulls there are a few common strategies:

• More than one antenna: Having one horizontal and one vertical antenna is perhaps the easiest way to deal with nulls. Switch between antennas and see which is better. The comparison must be longer than a few seconds because of signal fading and Faraday rotation that continuously changes signal polarization.
  
• Stacking: Yagis at different heights are fed in phase, out of phase (BOP) or separately to select the one that works best.
  

Did you notice that the two bullets are related? A stack has more than one antenna, and it is important that they can be individually selected. This is typical for HF stacks since it is so useful for optimizing elevation angle to the path and for avoiding nulls. Yagis in a stack for 2 meters and up are rarely configured to allow selection of one or a subset of them since it isn't as beneficial as at HF.

By feeding the yagis out of phase the nulls and lobes largely reverse. The elevation plot compares BIP and BOP for my stack of 5-element 20 meter yagis. The reversal isn't perfect but it is close. Gain in the BOP lobes provided little if any advantage over selecting the lower yagi alone. BOP was enough additional work for my home brew stack switches that I decided it wasn't worth the bother. Many commercial stack switches have the BOP feature, at a price.

For maximum versatility of elevation angle it is necessary to have at least two antennas, either in a stack or at different heights. One antenna, be it high or low, is a competitive disadvantage for contests and for DXing. I am sure that readers struggling to raise just one antenna per band, or even just one multi-band antenna, are feeling less than sympathetic about my plight! Nevertheless this is what I must deal with to achieve my operating objectives.

By the end of this year I'll have stacks or multiple antennas for 40, 20, 15 and 10 meters. For 80 meters I may reinstall my trusty inverted vee to have a high angle antenna to complement the vertical yagi. It would be useful on some paths, especially when I'm not running low power or QRP. With a kilowatt I can almost always work the nearby stations with the less effective low elevation angle of the vertical array.

On 6 meters I have a problem with just the one yagi. It is up 4λ and has the elevation pattern shown in the plot at the top of this article. Sporadic E and aurora often have optimum paths well above the horizon. That said, the antenna works well for the longest DX paths with that very low main lobe. There are times when friends nearby with lower yagis do better, which is strong evidence that the elevation pattern nulls are putting me at a disadvantage some of the time.

I would like to have at least 2 yagis in a stack for 6 meters. Unfortunately that's not a project for this year. It isn't even obvious where I could put it; the towers are rapidly filling with HF yagis. I need the gain and I need to fill those nulls to aggressively increase my country count on the magic band. I'll come up with a plan next winter in the hope of building a stack in 2022.

Now let's talk about verticals. These include vertical dipoles, monopoles with a radial system and vertically fed loops. When ground mounted or close to ground they have no nulls between 0° and at least 45°. Like horizontal antennas, the main lobe will split and form a null at greater heights. Although there is no critically located null for most verticals there are other difficulties.

First, verticals for the high HF bands are short, and in almost all locations will have to radiate through buildings, utilities, foliage and other common obstructions. This impairs both efficiency and effectiveness. Even with a good radial system a hex beam mounted on the roof of a house will outperform a vertical monopole or dipole, though usually not a full wave loop in its favoured directions. Ground reflections are not as reliably strong as they are for horizontal polarization, and that can cost a few decibels.

The elevation plot at right compares a ¼λ vertical with 8 full-size radials over medium ground versus a hex beam up ½λ. This is an estimate of what to expect from a ¼λ vertical in many urban and suburban situations. I believe it is fair to compare the vertical to a small yagi with gain (directivity) since the installation difficulties are of similar order. Only half the forward lobe difference is due to the yagi's gain. The rest is due to near field and far field ground loss.

On the low bands it is rare for a horizontal antenna to be very high, and that is why verticals are popular for 40, 80 and 160 meters. Unfortunately the vertical is not a good way to fill nulls on those bands since the horizontal antennas are so low they typically have none. Go back and look at the first plot in this article for yagis up ½λ and 1λ. Verticals are used on the low bands since, as inefficient as they often are, they are superior for low elevation angles over horizontal antenna at practical heights.

No magic

If you were expecting me to propose one highly effective antenna with the magical property of having few or no elevation nulls, I am sorry to disappoint. There are no easy solutions. It is no surprise that big gun stations have lots of antennas on each band, since that is the only reliable way to deal with the vagaries of propagation.

The smart operator at a large station will periodically try different antennas and stack combinations. Propagation changes throughout the day and night, and what worked best an hour ago may not be what works best now.

A Contest of My Own

This past weekend was the annual running of the ARRL DX SSB contest. As contests go this is no longer one of my favourites. Also, I don't really enjoy phone contests as much as I once did. It is a DX contest, which I find attractive, but the experience is different for most outside of the US and Canada. For them it's more of a QSO party in which everyone within a limited area work those outside and vice versa. For example, if you're in far away Australia or south Asia the possibilities in this contest are terribly limited. Few bother, and I don't blame them. I would do the same in their position.

I had concerns aside from being busy and wanting to limit my operating time, while still make a good showing. Two of my headsets failed immediately before the contest. That was a difficulty I overcame with an uncomfortable workaround. Another problem was that I wanted to enter a category that the contest sponsor does not support. 

For those reasons and since I had no illusions about winning anything I decided to do it my way. The alternatives -- conforming my operating to categories set by the sponsor, or to sit it out entirely -- were not to my liking. I invented a category that is common in many contests, but not this one. I would not be competitive in the formal categories, and that was okay. 

Contest within a contest

You have an amateur radio license. Provided you operate in accordance with that license your on air activity is yours to determine. When there is a contest underway you choose whether to participate and how to participate and who you work. You are under no obligation to participate in a manner that complies with the requirements of the sponsor's entry categories.

There are interesting examples that are more common than you might realize. For example, to only make contacts with unique multipliers. At the end of a contest your QSO and multiplier totals are equal. There are DXers who enjoy doing this since in global contests like CQ WW there are many contest DXpeditions and widespread interest that brings a lot of DX onto the bands. They have fun and don't care about their score in the actual contest.

Similarly, you might want to work as many stations as possible in just one country, or with call signs that end in the letter "D". Why? Why not! You can do whatever you like. Some clubs or groups of friends agree to a common set of rules and only compete against each other. They have fun and other contest participants benefit from the increased activity. The contest sponsor is uninvolved. It's perfectly legitimate fun.

I chose to enter the 20 meter single band, high power unlimited category -- SO20HP (A) -- in the ARRL DX SSB contest. However, the single band categories are all unassisted. Assistance forces you into the all band category. My reasons for doing it this way included:

• Time: By restricting myself to almost entirely daylight hours I could sleep normally and have time for other activities. At this point in the solar cycle, 20 meters opens around sunrise and closes about 2 hours after sunset. It worked for me since I find that SSB contests are less interesting than CW contests. SSB contests have unique challenges , some of which are listed below.
  
• Limited prospects on 10 and 15 meters: Again, for reasons of propagation, few DX contacts are possible on these bands. After chasing the available multipliers, at a painfully slow rate, there is little left to work.
• 40 meters is a morass: Almost all US activity is squeezed into 75 kHz from 7.125 to 7.200 MHz. There are a few ITU Region 2 stations operating above 7.2 MHz, but nothing in Region 1 or 2. Although Canadians can operate below 7.125 MHz most DX stations focus on that narrow 75 kHz window with the bulk potential contacts. The QRM is overwhelming and QSO potential is low. Some DX stations operate split to compensate. 
• Noise on 80 and 160 meters: SSB modulation has a wide bandwidth and thus a poor SNR. Except under exceptional propagation the rate of DX contacts is slow compared to CW. Staying up all night on the low bands hardly seemed worthwhile when I had no interest in being competitive.
• Station exercise: My best band at the moment is 20 meters. With all the challenges on the other bands I preferred to see what my antennas can do on 20. Despite a few problems with my antennas and antenna flexibility and a vintage amplifier that is not competitive, I believed I could do well. This was an opportunity to find out for sure.
  
• Practice being assisted: My preference is to operate unassisted in most contests. I need more practice being agile when new multipliers are spotted. For example, when during a high rate run of Europeans a needed multiplier in South America or Africa appears it is necessary to move quickly to avoid the inevitable pile up while not compromising the run or losing the run frequency by being absent too long. Just 20 to 30 seconds can be too long.

Those are my reasons and you will have your own to consider before a contest. The point is you can do what you want without feeling constrained by the categories offered by the contest sponsor. Of course if you do intend to be competitive you must fit yourself into a category and maximize your score for that chosen category. The decision is yours and yours alone.

How it went

To be competitive in my invented category I have to compare myself to the single band unassisted participants and to the 20 meter results on the all bands assisted participants. In those comparisons I am still a loser though not by a lot. I'm pretty happy with how I did. There is certainly room for improvement in my skills and the station. 

Propagation was one important factor. I am too far east and north in North America to place highly. A distance of a few hundred kilometers is enough to escape attenuation through the auroral zone. Stations in W2 and W3 had more success working Europe and further afield to Asia and the Pacific. VE1 and W1 have more daylight in common with Europe so that the opening lasts up to 1 hour longer. 

South is also a challenge. W2 and even those further southwest in VE3 often had a better shot to multipliers in the Caribbean and South America. I would get through, eventually, after those with more favourable propagation. I usually do better to the south on 15 meters under poor conditions since closer to the MUF the longer path to my latitude is favoured over those to the south. That isn't the case on 20.

Power is a problem. My vintage amplifier is well below our legal limit, which on SSB is 2250 watts PEP, or triple the 750 watt limit for constant carrier modes like CW. That puts me at a disadvantage that I keenly felt in the fiercer pile ups. I have a new amplifier on order that will fill that deficit.

The TH6 and TH7 tri-band yagis I rely on for most directions on 20 meters do not have the gain of long boom mono-band yagis. The 150' height of the TH7 is wonderful except when competing against those with bigger antenna farms. Due to in-shack control problems I am not able to easily rotate the upper 5-element 15 and 20 meter yagis of my stacks. Until that is properly dealt with they are usually left pointing at Europe.

There are always a maximum number of multipliers available on any band in a contest. Being assisted makes it possible to work all but a few of them. I worked 110 DXCC countries and the biggest guns did perhaps 10% better. In most cases I could not get through the pile ups due to the aforementioned reasons, or I was shy a few decibels to rise above the DX stations local noise.

Working multipliers is not always a hunt. By running on a clear frequency with a big signal most multipliers will find you. You will never work those stations by S & P (search and pounce). At times I was astonished by who called me. One rare multiplier in Africa called me on Sunday after I fruitlessly sat in their pile up the previous day. 

Another time I was startled when I starting being called by stations in southeast Asia with quite strong signals. In the midst of a European run I'd forgotten the band often opens briefly in that direction mid-morning. They weren't running so there was nothing seen on the spotting networks. It was delightful for a DXer like me to have that happen.

Other observations

After the CW version of the ARRL DX contest I used a text editor to extract all the contacts with QRP stations. This can be done easily because power is part of the exchange for non-W/VE. Accuracy is not high because some non-contesters instead send a serial number, their zone or whatever comes to mind. I filtered out those I could and came up with 2.3% of my 2400 contacts were with QRP stations. There were many more using 10 or 20 watts.

This interests me since I am a QRP enthusiast. That's how I returned to the hobby in 2013 and it has remained a passion. That I typically run much higher power nowadays does not diminish my interest in QRP. As a consequence I really enjoy being called by QRP stations in contests. With a big signal I know that I attract those with small antennas, low power or both.

You might expect that QRP would be less common in SSB contests due to the poorer SNR. This seems not to be the case. Although I didn't fully analyze my log the QRP percentage appears to be comparable. My furthest QRP contact was with Japan. That is not easy on 20 meters! I know because I've done only a few times myself when calling Japanese stations with just 5 watts.

Spotting networks are critical to success. Starting a run is slow because many stations click spots and don't tune with the VFO dial. I could monitor this in real time on the Telnet window. Within 30 seconds of seeing my call and frequency spotted the European pile up resumed. I once humourously referred to spots, human or CW skimmer, the QSO faerie.

The downside is that sometimes the spotted call is wrong. When I was spotted as VE2VN on Sunday, when everyone's rate had slowed considerably, I was deluged with dupe callers. For several minutes it was helpful to enunciate my call as Victor Echo 1-2-3 Victor Norway. Until spots aged out on most operators' software the dupe rates remained at 10% or so.

I used the contest to experiment with phonetics in my pre-recorded messages. While running I tried a shorter exchange: "five nine, oh en". This worked very well at first since regular contesters know that VE3 is Ontario (ON). Contest software will helpfully prefill the exchange accordingly. As the rate slowed and there were more casual contesters answering my CQ it caused problems. On Sunday I went back to using "five nine, oscar norway". Problem solved. 

My closing message was "thanks! victor echo three victor norway" and not the shorter "thanks! vee ee three victor norway". When I tried the latter in CQ WW SSB last fall it caused a surprising amount of confusion. This attempt to increase run rates didn't work out. I have always use full phonetics in the S & P message set.

Afterwards

My total operating time was under 17 hours. Had I operated long my score would have been higher. There was no point since my non-categorized entry would win nothing. I don't enjoy endlessly calling CQ or spinning the dial to hear nothing new. When that happens I take a break and find something else to do. I went so far as to take short breaks during the morning openings to Europe. To win it is necessary to practice BIC (butt in chair) and to keep the CQ machine going, no matter the propagation or the rate. Every QSO makes a difference.

There is a rumour that ARRL will expand the categories next year. That may not affect my behaviour since my focus on 20 meters this year might never be repeated. It's more likely that I'll do something completely different. Regardless, it'll be interesting to see what transpires.

I had fun in my own little contest, and that is what matters to me. I'd rather do these long contests as part of a multi-op, and I hope to be ready to do that later this year. It's not just the pandemic causing the delay since I have work to do to prepare the station for it. The work is ongoing. Indeed, that's why there's a long gap between the previous article and this one. I'm keeping busy and the whiff of spring antenna season is in the air.