Sunday, February 28, 2016

Propagation, Noise and QRP

It is a common saying that when propagation is good you can go around the world with hardly any power at all. What is said less often is how unusual those occurrences can be when using QRP. You can spend a long, long time between those times and frequencies when the magic happens. For everyone else there's QRO.

For QRP contesting it comes down to a throw of the dice. Roll snake eyes and you should prepare yourself for 48 hours of drudgery. Last weekend's ARRL DX CW wasn't that bad, but it sure wasn't good for the run-of-the-mill 5-watter. My QRP era is gradually coming to a close so this was one more chance to see what I could do. Conditions did not cooperate.

A week of geomagnetic disturbances and a regular series of low-level X flares combined to render conditions sub-par, even for the already low solar flux. The result is attenuation (ionospheric absorption) over many paths, especially those north of the east-west line. The effect was more pronounced on the low bands where I am already seriously challenged by my inadequate antennas. Last fall's improvements to my 40 and 80 antennas added several decibels, which was promptly consumed by the ionosphere, and then some.

In this post I'll elaborate and add to the brief notes I appended to my 3830 contest summary. Perhaps I should have titled this article 'the limits to QRP', since that's really what this is about.

SNR (signal-to-noise ratio) is the name of the game

The difference between 5 watts and 1,000 watts is 23 db. When the SNR is 50 db you can drop down to QRP, or even QRPp, and still do very well. When conditions are less than ideal you can easily drop from solid copy to no copy at all. Power, antennas and propagation set the absolute signal level at the far end of the path. QRN and QRM dictate whether it's enough to be heard.

How the SNR is set does not matter. It can be noise, other stations or propagation. The diagram shows that the QRN level determines whether QRP will get through. At the A line it's marginal but doable. At the B line it's impossible (except perhaps with JT65).

The diagram can also serve to illustrate ionospheric absorption. Imagine that the noise level is constant and that the B line represents the impact of -8 db of absorption. For QRP the result is the same. That is, we're out of luck.

Notice that we're talking about the SNR at the other station. There is no reliable correlation between how well you hear them and how well they hear you. You can use your experience to guess whether you'll get through. Better yet, call them and see what happens.

Although we cannot control how well others hear us (aside from switching in the amp!) the situation can often be managed to our advantage. The ways of doing this can be used by anyone, QRP or QRO. But with QRP you have to think your way through the challenges far more often that do others. Let's look at a few.

Ride the QSB

You know you're near the other station's receive threshold (SNR = a very small number) when you notice a hesitation or they respond with a partial call that matches yours. You can persist, if they're patient, and hope they turn on enough filters or a better receive antenna. You are dependent on what they decide to do. Again, this is largely out of your control. When they give up, so must you. Usually.

Propagation is variable. All hams know that signals wax and wane. The changes can be secular (propagation is changing) or cyclical (Faraday rotation, etc.). We tend to lump them all into one basket called QSB. If the QSB is cyclical there is a way to use it to our advantage in contest and DX exchanges, which are very brief.

Cyclical QSB has a cycle time that is often frequency dependent. It is often slower on the lower bands. We can use that to our advantage.

Imagine that you've called a new multiplier on 80 a few times and failed. Listen closely. Try to estimate the cycle time and amplitude of the QSB. If the amplitude range is shallow you may be out of luck. If it's deeper you have a chance. When you hear the signal rising, before it peaks, this is your moment to call. Don't be timid: turn up the keyer to 30 wpm. You want to complete the QSO before the signal ebbs or they may abandon the attempt.

Should you fail, there is always the next peak. Or the one after that. It depends on how badly you want the QSO.

Waiting for propagation to peak

Secular QSB is less easy to play. There are two predictable situations. On the high bands, especially on 10 and 15 meters, signals will usually rise when the sun sets, either on your end or theirs. This is due to the drop in MUF (maximum usable frequency) as ionization dissipates in the F-layer. Attenuation falls as below and near the MUF. Some logging programs will show the sunset time at the other end when you type in a call. Keep an eye on that time.

If it's near sunset, here or there, drop the frequency into a memory or VFO and go work other stations. Check back every 5 or 10 minutes. When (if) the enhancement occurs you'll hear it. This is your time to call.

On the low bands there is a similar situation at sunrise, whether at your end or theirs. Ionization increases, briefly boosting signal strength. I've used this successfully to work European multipliers on 80 as sunrise sweeps across the continent during the hours after midnight here. When the sunrise is yours be aware that the enhancement is short lived. You may have only 10 minutes to work every multiplier to the west before D-layer absorption drives you off the band.

Another type of propagation peak has worked to my advantage on paths north and south. Towards the north there is occasionally an advantage to being north of the US since you are closer to the DX. Even with QRP you can crack a few pile-ups. It took only a few calls to get through the pile-up to work OX on 15 meters in the ARRL DX contest.

To the south the skip distance increases towards sunset on 10 and 15 meters. This is to my advantage in pile-ups to multipliers in the Caribbean, Central America and the north coast of South America. Since I am further from the DX than all of the United States I am often the last to see southerly signals disappear. In late afternoon I have a good shot to work some needed multipliers by putting my QRP against the pile-ups.

This works equally well outside of contests. Late one afternoon this week 4W/N1YC was too weak for me to work on 15 meters. So I waited. Soon the propagation enhanced as the sun dropped toward the horizon and the MUF rapidly declined. His signal increased from S0 to S5 and I easily got through. Minutes later signal strength dropped like a rock. Patience and good timing is required.

Waiting for QRM to diminish

Sometimes we are not heard even though the station we're calling is quite loud. This is often due to QRM or QRN on their end that we do not hear. This, too, can be dealt with.

Let's guess that it's QRM. The running station in a contest (or DXpedition) will strive to hold the frequency in the face of QRM or DQRM (deliberate QRM), hoping to outlast the difficulty. All we know is that they're working few or none of the callers, and just keep CQing. Put the frequency in a memory or VFO, or self-spot on the logging software's band map. Go work other stations for a few minutes later, then try again. This may be all it takes.

When the problem on their end is more persistent, as it often is in contests, a different approach should be tried. For example, on the high bands it can be difficult to work Europe with QRP in my early morning and midday. What we don't hear is how much continental QRM they must contend with. It can be fierce!

As their late afternoon arrives (or evening on 20 meters) their skip length stretches out and eliminates most of their QRM. Yet the band still sounds the same on this end. By knowing how propagation works you pick this time to call the stations you've missed. This is also the time to run. Yes, you can run with QRP on 20 meters in this situation.

One-way propagation

Propagation is a reciprocal phenomenon. For two stations running the same power the absolute received signal strength is near equal. What isn't equal is the QRM and QRN. This is sometimes called one-way propagation. Let's look at a few examples.

The propagation from North America to Europe and parts of Asia and Africa can open on 40 meters well before sunset. Signals are perfectly copied and push the S-meter around. Yet you are not heard by them. The SNR on your end is good. Their SNR is worse, even much worse.

In Europe it is early evening. Skip is short and so the QRM within Europe is fierce. That alone raises their noise floor quite high. Your signal cannot overcome that. They are also receiving atmospheric noise from storms and other weather from a very large area of the globe. That, too, increases the noise level. Unless you run a kilowatt and a large antenna you are unlikely to have much luck. Give it up until sunset when D-layer absorption drops and absolute signal levels rise.

A second example is working stations in the tropics on the low bands. Their atmospheric noise can be quite high while those of us in a colder climate have less of it. We hear them but they don't hear us.

A more local example is where instead of the ionosphere it is your antenna that is at fault. On 80 meters it is challenging to put out a good strong signal for DX work. Most hams cannot get a horizontally-polarizated up high (relative to wavelength) or a vertical with low ground loss. We hear the other stations quite well since both noise and signal are reduced by our poor antennas, thus sustaining a good SNR. This is acceptable for a purpose-built directional receive antenna but not for a transmit antenna.

This is my situation on 80. When my local QRN is absent I can hear reasonably well, while few hear my 5 watts. Notice how this resembles the one-way propagation example above. Unfortunately the only cure is a higher or better antenna. Or turn on the amplifier. Many choose the latter since you can only do so much with low band antennas on a city lot.

Tallying the results

In my estimation I did not do terribly well in the ARRL DX CW contest this year. It was not that I made many mistakes but that propagation did not favour QRP. My ability to run on the high bands was limited and I missed numerous multipliers on 10 and 80 that the New England stations seemed able to catch. Some of it is antennas and, I suspect, being further north a few hundred kilometers was also a factor. I was not able to repeat my low band successes in CQ WW last year.

It is entirely possible that had I stayed up for another hour or two Friday and Saturday nights I could have worked several west European stations. That would have boosted my multiplier count. Instead I went to bed when I saw little or no enhancement on east European stations at their sunrise. On 10 meters I worked little in Europe even though I frequently QSYed to catch any brief opening. I was loathe to repeat the same error I made in CQ WW CW last year. It is possible that the attenuation through the disturbed ionosphere was sufficiently higher here than just to the south to explain what happened. However there is no proof. I may have simply missed it.

When I ran out of stations to work on 20, 40 and 80 Saturday evening I took a break. I was not interested in sticking around for a painfully low rate. Even many European big guns couldn't hear me. I even tried 160 in desperation, but my lack of an effective antenna was like trying to become rich by buying lottery tickets. At least in CQ WW there are Americans to work and keep things interesting when there is no DX within reach of QRP. On the other hand the ARRL DX contests are a fairer comparison of how my abilities and station measure up within the wider geographic region.

Could I have done better? Maybe. Better antennas would help QRP to get through, but what I have is it for this QTH. Despite the difficulties I enjoyed the contest. It was fun and I did quite well, and I did it while eating regular meals and getting plenty of sleep. That's an accomplishment! Should I operate the SSB version of the contest next weekend it will not be with QRP.

Back to antennas, soon

Ostensibly this blog is primarily about antennas and related topics. I'll be getting back to that in the next article. Those articles take more time and effort and I've been increasingly busy lately. The "fill" I've recently written keeps the blog active while I'm otherwise occupied. I trust these have not been unwelcome by readers.

Thursday, February 18, 2016

Calling in the Hole

One of the recent DXpeditions was more challenging to work than expected. That was 5V7TH in Togo. Why that is so and what I did to get them in the log on 30 and 40 meters is the subject of this article. The technique I will describe is known to many DXers, but not all. If it's new to you perhaps you can benefit.

My station is not big. I run 100 watts, a tri-bander up 15 meters and simple antennas for 30, 40 and 80. In some pile-ups I feel as if I were still running QRP. No matter what I do, it seems, sometimes nothing seems to work. That's a sign telling me to change strategy. I wanted 5V7 on the low bands and the usual technique of finding the station working the DX and shifting the XIT/VFO-B up or down a bit didn't work. I kept getting outgunned or passed over.

A big part of the problem was the pattern used by the DX operator. He often avoided the clustering of callers within 1 kHz of the last station worked. So unless you had a big signal staying close didn't work very well. He tended to QSY quite a lot, shifting 2 or more kHz or jumping around in what seemed to be random fashion.

Whatever the reason for this behaviour, it's his choice. It's our job to solve the puzzle if we are to get into the log. The tactic that worked for me was to find the "hole".

It stands to reason that if most stations calling at or near the frequency of the last QSO there are fewer stations calling further away. In the present case the DX used a fairly large window within which he listened for callers. That left a few holes where callers were few or absent. So rather than track the last successful caller I would instead set up near the middle of his listening window (~5 kHz up) and QSY only to avoid other callers. That is, a hole that is empty of other callers.

When he finished a QSO I would listen on my transmit frequency for a moment. If there was no one near my chosen frequency I would go ahead and call. Otherwise I would move up or down a small amount until the frequency sounded reasonably quiet and call there. On the higher HF bands this is unreliable due to the large skip distance. There will be stations within about 500 km or more that you cannot hear except for a few on back scatter. On the low bands it works better since you can hear most of the nearer stations.

At first it may seem odd to call on a frequency devoid of other signals. Yet it can work. On both 30 and 40 meters, within 5 to 10 minutes of using this tactic I had worked 5V7TH. I had spent much longer before this calling in the more conventional manner.

Calling in the hole can work. However you should only use it when the DX operator shies away from the pile-up or you've heard him call others in the hole. Some DX operators may not be comfortable pulling calls out of the QRM, instead preferring an isolated signal that easy to copy.

Whatever the reason, if you didn't know before how to play the described situation, now you do.

Tuesday, February 16, 2016

Trying New Things

One of the old saws regarding amateur radio is that should you become bored with it there is always something new to learn or do to rekindle your interest. This is often very true. However this advice is frequently ignored by many. It's easy to do as we grow older and we get a little too comfortable or set in our ways.

When I returned to the hobby in early 2013 I immediately tried something new. That was QRP, something I've never done before. Oddly enough the challenge of making contacts with only a few watts and a minimalist antenna only spurred me onward. It eventually led to over 200 DXCC countries with 10 watts or less and some excellent placing in international contests. Another effect was to renew my interest in high-performance antennas and improve my operating skills.

With that in mind I have been trying a few new things recently, and I have plans for more. I'll briefly relate these today. My hope is not that you'll want to do the same, but that you'll be spurred to try one new thing, of your choice, in the next month. It can be as simple as turning on your radio and pressing a button you've never before pressed.

12 meters

I've never cared for 12 meters. I don't know why. It's not because it's a WARC (1979) band since I am very active on 30 and 17 meters. I am also very active on the adjacent bands, 10 and 15 meters. It isn't even because I have no antenna for 12, since that has never stopped me on any other band, including 160 meters. My attitude is completely irrational. I suspect the same is true of many of our likes and dislikes, be it in amateur radio or in other matters.

My rig has an internal tuner so one day in January I forced myself to make a QSO on 12. I loaded up the Explorer 14 with the tuner, turned it broadside to Europe (it's really just a non-resonant dipole on this band) and called the first station I heard. A minute later I had my first 12 meter country in the log: DL. That seemed appropriate since a DL was my very first QSO when I got on the air in 1972.

I did nothing more on 12 meters until February. Then, on a bit of a lark, I called VP8SGI on South Georgia. One call and the DXCC #9 wanted country was in my log for country number two. Signals were weak, my tuner losses were high, but there seemed to be no other callers. Sometimes that's all it takes.

I have since gone on to make a few more contacts on 12 meters. I still don't love it. I have more countries on 160 and 6 meters than on 12. Maybe that'll change. The important thing is that I did it.

Assisted contesting

At the time I went QRT in 1992 there was no such thing as assisted contesting. Well, except for a few "mavericks" who seriously bent the rules. With global DX clusters and RBN, and supportive contest software, it is today very easy to operated in the new assisted categories. But old habits die hard. I am of the generation that grew up believing the single-op contesting maxim: a boy (or girl) and a radio, and nothing else.

I have nothing against assistance. Indeed, I use the spotting networks daily for DXing and I don't feel diminished for doing so. In the past I was primarily a multi-op contester, and I was not disturbed by the assistance of my team-mates, whether for logging, copying weak signals or gathering multipliers. Like many I continue to associate non-assisted operation as the measure of operating ability and station-building prowess. That is a prejudice, not a valid conclusion. Assisted operation involves unique skills and has a place in radio contesting.

The multi-op I joined for CQ160 CW was assisted. It was a bit like being thrown into the deep end of the pool when you can't swim: you learn or drown. That's an exaggeration since our operation was a very laid back affair. Every operator made use of the RBN feed as conditions, ability and interest dictated. In theory, nothing on the band is missed and call sign typos are avoided by the use of machine code readers at the skimmer sites. Most often I've been on the other side of the equation whereby assisted operators are drawn to my feeble QRP contest signal.

Our spot feeds were restricted to skimmers in the same broad geographical area: eastern Canada and the northeast US. That way we avoided spots for stations not workable from here -- we did not have the equipment needed to run our own skimmer. N1MM software helpfully plots the spots on a band map, colouring them according to whether or not they are needed multipliers. Stations already logged were not shown.

When I first sat down to operate for a one hour shift the spots were little more than a distraction. It was early in the contest and we were focussed on running. This is the time of the contest feeding frenzy. Leave your run frequency for more than 10 seconds to pursue a spotted station and you'll lose the run frequency. At that point in the contest that loss more than offsets the gain of pursuing a spot. You learn that very quickly.

Later, and especially the second night, the situation is very different. You can switch to S & P (search and pounce) and maintain a high rate purely by pursuing spots. You see the blue coloured call sign in the band map, click on it and wait a few seconds for the right time to call. It's very fast: point, click, enter. That's the easy part.

When you are running you can still pursue spots, once the rate for everyone drops enough that you can hold a run frequency more easily. This is where the skill comes in. It took a bit of practice to become efficient and effective at simultaneously running and pursuing spots. The process is simple enough:
  1. Call CQ.
  2. Answer? Work them. No answer? Click on a spot.
  3. Call the spotted station. Answer? Work them. No answer? Click on the CQ Frequency.
  4. Back to step 1.
I soon learned to keep a mental note of which unworked spots I most wanted or I felt were most workable. Step 2 was thus executed very fast. You don't want to waste time perusing the spots anew each time. Not once did I lose the run frequency. However there were a few times when I did need to assert myself in marginal cases.

The process grew easier at the contest progressed. Few spots showed up since we'd already worked everyone available. More time could be spent chasing multipliers and "fresh meat". The latter are contesters  or casual operators who show up only briefly to play around for a short time. They are very popular, drawing instant pile ups of assisted stations. That was also the time that busted calls were prominent in the spots. This happens because busted (poorly copied) call signs are not in the log. It pays to rely on your ears, not the spots, before calling or logging these stations.

I enjoyed the experience of operating assisted. At some point I expect to try it again. Although not entirely to my taste it is a new skill worth honing, if only as preparation for future multi-op opportunities. It's a little like a video game or (if you're my age) pinball. If nothing else it keeps you productively occupied while the machine sends one CQ after another. It is less stressful than SO2R (single-op two-radio), but with transferable skills.


Yagis need to be rotated, and rotation means bearings. Bearings allow rotation of machinery while supporting loads. Depending on the application in an antenna system the bearings may need to support radial loads, usually due to wind, and axial loads, due to weight of mast and antennas. Often they need to do both.

Most ham rotators are integrated with bearings that will support a quarter-tonne or more of axial load and somewhat less radial load. These bearings are supplemented by mast bearings that help to protect the rotator from radial and loads and bending stress thus permitting tall rotating masts supporting large yagis and their wind loads.

Unfortunately ham market bearings are not always the best. For the typical small tri-bander they may be adequate, and it may be acceptable to service or replace them every 10 or 20 years. For the larger arrays I am planning industrial bearings are needed for the rigours of high loads and extreme environments. The prop pitch motors I acquired last year include a chain drive, bearings and plates for the LR20 tower I hope to put up later in 2016.

Two identical 90 mm bearings support the top and bottom of the chain-driven 3.5" O.D. drive shaft. The antenna mast fits inside the top, secured with bolts. The bottom bearing mostly acts as a thrust bearing, with a collar to apply axial load to the lip of the inner bearing surface. The top one is for lateral wind load, which requires no collar. I plan a third bearing for lateral load on a third plate on the 3" mast (to be acquired). However I had little knowledge of industrial bearings going into this. It was time to learn.

Screen capture taken from the NSK rolling bearing catalogue; the specs tell the story
The bearings I have are NSK 6218 DU. An internet search quickly uncovered this bearing's specifications. NSK is a the manufacturer, 6218 is the model and DU is the type. The 6218 is a 90 mm bore deep-groove ball bearing with a rubber seal to protect against dust and water ingress. With a suitable oil or grease (grease is what is typically supplied) this bearing works over the wide temperature range we experience in this climate. They do not appear to have had external weather hoods in their previous use, and they had been outdoors for many years, both in service and storage. Both were seized. The previous owner and another prominent big-station owner encouraged me to try and save them. Replacement cost is in the range of $175 to $200 apiece.

My first act therefore was to learn about rescuing seized, sealed industrial bearings. I have some experience servicing small bearings, including sealed bearings. Combining that experience with the advice I received I proceeded to submerge the bearings in a bath comprised of equal parts solvent and light oil for a few weeks. I suspected caked debris and grease/oil were fouling the bearing rather than deterioration due to rust, pitting or flaking. After bathing them I faced a problem. There is no easy way to grip the housing and apply torque to the inner surface.
Deep-groove sealed bearing custom fitted to a LR20 tower plate

Looking around my workshop I found an answer: a short length of 2x4 lumber can be hammered into the ~3.5" opening. Each bearing was remounted on a tower plate, to hold it, and a wrench was applied to the lumber. Some motion resulted, but not enough. So back in the bath they went. A week later I was able to force them both into full rotation. I then built a simple jig by which I could turn the bearings at moderate speed with a drill. The result was two functional bearings. I now know something about servicing industrial sealed ball bearings.

With the NSK rolling bearing catalogue in hand, a guide to their application and a list of local bearing suppliers I am now in good stead to fulfill my future bearing needs. This includes side mounted yagis as I discussed in a previous article. I will also explore weather covers for the bearings rather than solely relying on their rubber seals. Since there are no adjusting screws it is necessary order the exact or next larger bore size. A shim, if required, can be made from sheet metal.

Now my only question is: how did they get the balls into the bearing?

New new things

I will have many learning opportunities when I build my next station, which will include larger and more towers and antennas that I've every had before. I have worked on the large stations of others but not for myself. So I know some things but not everything I will need to know. A few examples:
  • Reinforced concrete forms and structures
  • Yagi fabrication
  • Tall, rotating (and climable) masts
  • Phased vertical arrays
Inside the shack I have other needs to support SO2R and multi-op contesting. That, too, involves many new things to learn.
  • Antenna switching matrices
  • Station automation (software control and integration)
  • High-power band pass and reject filters
That's my immediate list. More will be added later. Are you learning new things? Are you planning to do so? If not it may be time to push yourself out of your comfort zone and try something new. I know from private correspondence with readers of this blog that many others get a thrill from learning and trying new things. We can all learn, and help each other along the way.

Amateur radio has a lot to offer. As I approach retirement I get fewer learning opportunities from business and other fields that have kept me occupied for decades. This hobby more than makes up for that learning deficit.

Saturday, February 13, 2016

Side Mounting Yagis

My recent design of a side mounted yagi for 15 meters raises the question of how to do it. There are numerous techniques for accomplishes the feat, each with its pros and cons. My objective is to have the yagis stacked and rotatable. Mounting fixed yagis is relatively straight-forward, and not too interesting a subject for discussion. If I were to choose a fixed direction it would be towards Europe, which is the high-productivity path for contests from this part of the world.

In this article I present my preliminary survey into what's available, advantages and disadvantages, and setting of criteria to make a final decision. I have little experience with side mounting so there is the possibility of an error or two creeping in. Hopefully my calculations and research kept that from happening.

The esoteric: Ring rotators and rotatable towers

Neither of these options is in my plans due to expense and disadvantages with respect to my situation. I may have only one tall tower -- though I aim for two, eventually -- which has implications for contest operation.

A rotatable tower is especially expensive and would require substantial custom mechanical work to adapt my tower-in-waiting (LR20) to commercial products. But with one ground-mounted rotator (e.g. large prop pitch motor) you can turn all yagis on the tower. For daily operation this can be a perfect solution, but not in contests.

In a contest you want antenna diversity, whereby antennas can be simultaneously pointed in two or more directions. You can do this in contests if you have multiple towers, but I will be more limited. I plan to build a small contest station, not a super-station.

Ring rotators, such as those by Prosistel and AlfaSpid, allow full, independent rotation of each side-mounted yagi. But, again, they are expensive and require custom fitting to LR20. They have the advantages of full rotation (360° or more) and support large arrays. In most situations one ring rotator is required for each rotatable side-mounted yagi.

Another, less obvious problem is working on a tower with ring rotators. Safely climbing past one of these obstructions can be awkward, and unsafe if not done properly.

Simple side-mount

In the simplest arrangement two brackets are extended out from a tower vertex as platforms for a rotator and mast bearing. The yagi is mounted to the mast. For a trussed boom or stacked yagis the mast can extend further, with additional bearings as required. The rotator and its bracket typically take the full weight of the mast and antenna. The green circle represents an end view of the yagi boom and its mounting position on the mast.

Although bending moment on the rotator is not large you should consider a bearing directly above the rotator. It depends on the loads due to ice and wind falling within the bending load capacity of the rotator. The plates and tower brackets must withstand the dead and live loads. Here is a commercial example of brackets from IIX Equipment. They can also be home brewed by any ham with suitable metalworking tools.

Some choose a thrust bearing for the bottom plate and place the rotator inside the tower. The rotator turns the mast with a chain drive. Whether this is truly necessary is debatable since the rotator still requires above and below the chain to eliminate lateral loading of the rotator.

So we are done. Or are we? Have we truly achieved our objective so easily? Unfortunately, no.

This simple side mount is too simple. As designed it is not able to achieve 300° of rotation (360° - 60° for the projected angle of a triangular tower). In fact, it doesn't come close. Have a look at the top-down view to see what is going on.

The points where the yagi's boom strikes the tower (red lines) mark the limits of the rotation. This angle is approximately 120°, which is only ⅓ of the compass. Grey marks the azimuth angles the yagi cannot point.

Further, the direction a tower vertex points (there are 3 choices) must be the centre of rotation. The yagi can rotate 60° to either side. If the tower is already standing it may be impossible to select the best 120° range for your specific interests. In my case I want Europe (40° to 60°) within the range. I would then choose either to cover up to East Asia (330°) or Caribbean and South America (150° to 180°). I can't have both. A tower vertex must point approximately 30° or 100°, respectively.

So you would think this method of side mounting is a poor one. Yes and no. For some it may suffice. For others, like me, it is a useful first step. The reason is that it can be supplemented with a swing arm that will give 300° rotation. That's the next subject.

Swing arm

The typical swing arm is a rectangular or triangular attachment to the rotating mast. The yagi attaches to the pipe or plate at the outside edge. The length of the swing arm should just exceed the distance from the mast to the far edge of the tower. LR20, which has 20" faces, requires a swing arm of about 30", assuming a tower vertex to mast distance of 6" to 8".

By swinging the yagi around the tower in this fashion allows the desired 300° of rotation, as shown in the lower diagram.

Most hams build their own swing arms to their own specifications. There are commercial products available, such as that seen at the IIX Engineering link provided earlier. The swing arm must be very rigid and strong in the vertical and horizontal planes to survive high wind and ice loads, and protect the antenna, rotator and tower. The longer the swing arm and the larger the antenna the greater the engineering challenge.

With a swing arm there is some flexibility in choosing the yagi's centre position, something which isn't possible in the previous case. This is helpful if the tower is already built and a vertex is not pointing in a suitable direction. You can see this if you imagine the swing arm at the end of its rotation, up against a tower face. The yagi's boom has up to 60° of additional arc in which it can be oriented. Since this works on both ends of rotation the latitude of boom to swing arm orientation is ±60°. There are no unreachable compass points.

The approach is to first select the vertex that points away from the 60° area that is of lowest utility. In my case that area is between about 90° and 150°, which is mostly the south Atlantic Ocean and long path to the north Pacific Ocean. I therefore want a tower vertex pointing approximately 300°. Second, we must orient the yagi to adjust for the actual orientation of the tower. If the vertex points, say, 275°, the yagi should be turned 25° clockwise on the swing arm mast. That's it.

To close off, I'll point you to a couple of photo galleries of swing arms. First up is K5YA. Notice the rotation offset of the yagis on the swing arms, stacking and eschewing of a bearing to protect the rotator. Many rotators can handle the load, or may require more frequent service. Next up is K7EM. Here we see mast extensions for boom trusses and cohabitation with a yagi on a ring rotator. If you look around on the internet you can find many more examples. You may find a novel approach that strikes your fancy.

Rotator control

Standard controller for rotators typically do not support custom stops. That's a problem with side-mounted yagis. We want the controller to limit rotation before the boom or swing arm strikes the tower. It is preferable to use a controller that permits software-defined stops. Failing this I recommend using a low torque rotator such as a Ham IV (800 inch-pounds) and a spring or similar soft stop on the tower where the boom would otherwise strike.

Also take into consideration the mechanical stops of the selected rotator. Those stops ought to fall within the gray zones shown above, otherwise the rotator will prevent selection of all available direction.

Overall, I consider it almost mandatory to use a software-controlled rotator that can be calibrated to the specific needs of side-mounted yagis, including stops. Mechanical soft stops on the tower can also be used as a form of insurance in case of programming error or the yagi twisting on the mast in a wind storm at night. You can't always be looking out the window to see what's happening.

Electrical considerations

Symmetry is our friend when it comes to managing interactions. When we disturb symmetry we must carefully analyze the situation to assure no interactions disturb the performance of our antenna. Side mounted yagis, with or without a swing arm, are not symmetric with respect to the tower. Hence the concern.

To begin, in EZNEC I added a long wire running through the 5-element 15 meters yagi I propose to side mount and stack. This wire is 18" in diameter, which is approximately equivalent to a 20" face triangular lattice tower. The objective is to test for interactions between yagi and tower as the yagi is rotated around the tower.

The tower model is truncated and made resonant on 15 meters. There is no easy way to fully model the tower, or to arrive at results that are at once both specific and general. Instead I chose to pursue a worst case result by centering the tower segment with respect to the boom and making it long enough and resonant to excite interaction modes.

To this end I adjusted the tower "wire" to resonate ~40 meters, with the third harmonic at 21.2 MHz. That is, it's a 3λ/2 vertical dipole. The model is placed in free space to isolate the interactions from other environmental factors, including guy wires, ground and other antennas. If I can reduce interactions in this model there should be none of this type in the real world. Of course other interactions must also be addressed, but those can be done separately. In antenna models, as in other types of problem solving, it is best to vary one variable at a time.

In this antenna the mid-point of the 380" boom is 190". The positions of the first and second directors are 106.5" and 239", respectively. The second director is 49" from tower centre, but can come as close as 39" when parallel to a tower face. Clearly the design and construction of the yagi enters into the equation. However in this instance I will only focus on this particular antenna, not yagis in general. I need to keep this work focussed so that I don't get too far afield at this time.

With the model built I proceeded to "move" the position of the tower to different points and measure the resulting impedance and far-field pattern changes. These moves were in the X direction (parallel to the boom) and in the Y direction (parallel to the elements), but always staying within the space bracketed by directors 2 and 3. Without being exhaustive or comprehensive I was able to discern a few general trends that I found helpful.

Note that in the referenced diagrams above I truncated the yagi elements (green) to fit the illustration. In reality directors 2 and 3 or the 5-element 15 meter yagi are ~134", which is several times longer than drawn. The swing arm is also not quite to scale.
  • When the tower is adjacent to the boom there is negligible interaction, even where the tower gets as close as 6" to one of the directors. This is good news, and ameliorates that particular concern. It also tells me that fixed side-mounted yagis are not in general compromised when one or two elements get close to the tower. This is increasingly concerning at higher frequency bands where yagi elements are closer together and the tower is larger (wider) as expressed in wavelengths. Interaction could become significant on higher bands, but I did not test this.
  • The further the boom is from the tower (that is, in the Y direction, parallel to the elements) the greater the distance required from the adjacent elements to manage interactions. For example, when the separation is 24" (60 cm) the tower should be a minimum of 9", and preferably 12", from the directors of this 15 meter yagi. At double this distance (48" or 120 cm) the elements should be kept a minimum of 18" from the tower, and preferably 24". This is unsurprising since (capacitive) coupling becomes more pronounced toward the element tips; this is the same mechanism used in a Moxon rectangle and also confounds the tuning of fan dipoles.
  • Tower resonance by itself has a negligible impact on yagi performance. However when there is interaction as described in the previous point the presence of a resonance exacerbates the problem.
  • It takes a severe interaction to reduce gain by greater than 1 db. When this occurs the main lobe and rear side lobes become asymmetrical. SWR also increases due to the shift in impedance. From the model it appears that impedance deviations are a strong indicator of interaction; that is, you'll see the SWR increase, especially high in the band, before pattern distortion becomes significant.
As I said above, these cannot be taken as general rules. With different towers and yagis the situation will differ, at least in its details. NEC2 can also give misleading results for closely spaced wires. Even if interactions are discovered at some points along the rotation arc of side-mounted yagis that may be acceptable if not severe. Perfection is impossible.

If you play with a pen and paper you'll notice that the worst case for tower interaction is with the swing arm since it places the tower further in Y direction with respect to the yagi. Any rotation from the orientation show in the diagram above brings the tower closer to the boom and therefore will tend to reduce any interaction. Except, perhaps, when at the ±60° points where a direction will most closely approach one of the other two tower vertices. Keep that in mind when designing the yagi and side mount.

Next steps

The girts on the LR20 tower are every 5' (two per 10' section) and are ideal for attachment of hardware to support side mount yagis. I took measurements of the bolt holes on the girts to get an idea of how to proceed. It is also possible to use commercial clamps that attach to triangular tower legs (e.g. Trylon). However my current plan is to build my own supports.

Out of prudence I will undertake some rough calculations of the loads the yagis will impose on a swing arm, rotator, bearings and mast under wind and ice loads. The tower appears up to the challenge (from talking to other LR20 owners) but that still leaves all the side mount hardware. Because of the array's size and weight I may opt for a bottom thrust bearing so that the rotator can be serviced more easily.

Since the stacking height on 15 meters is quite large there will need to be a bearing mid way. An alternative is to use two independent rotator and swing arm assemblies, but I prefer to turn the antennas as a single unit.

To minimize interaction with the tower I may shift the yagi mount off centre. Weight and wind load compensation may be needed to avoid added mechanical stress. The boom truss will help to avoid boom oscillations due to any remaining imbalance.

Depending on time I may first fix the antennas towards Europe, then build the simple mast system, and only later add swing arms.

Friday, February 5, 2016

Personalization and the Multi-op Contester

In our own stations we all have a tendency to arrange and configure equipment as we like. There is no one else to please but ourselves. Put the display above or beside the transceiver? Do what you like. Set the keyer to iambic A or B? Do what you like. Selection and position of windows for your favourite logging program? Do what you like.

All this customization flies out the window the moment another ham sits down to operate. Their station ideal is very likely different from yours. There is the possibility of endless argument over which arrangement is better -- there are quantifiable differences -- but in the end it almost always comes down to personal preference. Arguments over what's right and what's wrong go nowhere, and stress friendships.

This approach of agreeing to disagree becomes difficult in a multi-op contest. There is one station and two or more opinions of how to set things up. I was strongly reminded of this truth when this past weekend in the CQ160 CW contest when I operated as part of a multi-op (VE2OJ) for the first time in 25 years. I like to pride myself on my flexibility, my ability to accommodate other station setups.

Accommodate is what I did since I was the newest team member. Yet there was lingering discomfort because I've become a little rigid, like most hams. I got by just fine other than a few small things that I could quickly adjust when I sat down to operate. Others could change these back just as easily, which they sometimes did. But I did leave a few things the way others like since that is a great way to experiment.

In this article I'll discuss some of the differences I found and explore arguments in favour of one arrangement versus another.

Centre of attention: rig versus screen

A common approach is to put the rig front and centre at the operating position. In modern contest stations with fully integrated rigs and computers this should be reconsidered. The best operators have already decided, and pushed the rig off to the side. Sometimes almost completely out of sight. It is a question I first pondered in this blog soon after my return to contesting. Later I discussed how I changed the arrangement for the better.

The difference is a simple one yet profound in its effects. In contests you are either running or hunting. When running the radio has little utility. Filters and RIT to tune in callers are accessible from the keyboard. Call sign and exchange entry involve only the screen and keyboard. When hunting, with assistance, the screen shows the spots and needed multipliers, which you (typically) click on with a mouse to QSY. All sending is by keyboard, microphone or paddles.

Only when hunting stations unassisted is the rig of more direct interest. In particular the VFO knob. Operating QRP I do more hunting than running than higher power participants. Even so I find that it is better to place to rig off to the side. It was easy to train myself to operate the rig with my left hand, type with both hands and send CW with the right hand. Give it a try. I'll think you'll like it.

With the rig up front your hands and clothing may brush the keyboard when reaching for and using rig controls. When the screen is above the rig the eyes can tire from constantly jumping up and down; in ergonomically designed computer desks (for general use) the screen is low, not high. Touch typists like myself can escape some of the effort of having to look up to a high screen, but not nearly enough.

Above is my current experiment with going SO2R QRP (the KX3 is only posing since it isn't connected to anything). The laptop screen is small for two entry windows, which I will eventually deal with. Some reaching around the mouse and paddles is required to reach the second radio. Since the operating table will remain as is for the time being I will have to be creative. However the screen and keyboard will remain at the centre.

Sinister effects

I am in the majority in that I am right handed. A mix of left and right handed operators in a multi-op can be awkward in a CW contest. The problem is the location of the paddles. Either have two sets of paddles or configure the operating position to allow rapid paddle placement during operator shift changes. Our left-handed operator made do with the paddles on the right, but that is unfair to him.

Operator profiles

N1MM Logger supports operator profiles. When you sit down you type Ctrl+O and enter your call. The QSOs you make are tagged with your identity, and can be used to configure the software to your personality. This may include small things such as screens and screen positions, and important ones such as messages in your own voice (SSB contests).

We experimented with profiles during the contest. This is something worth setting up before the contest: each operator sits down, makes desired adjustments and saves the profile. It may seem unimportant to customize the operating position this way, but it can make a difference over the course of 24 or 48 hours. For example, do you use iambic A or B keying? That was a popular item to switch when sitting down for one's shift. How about CW and CW-R (reverse)? Again, it's a small thing that can affect operator efficiency.

Logging software

We used N1MM Logger+ integrated with the WinKeyer and K3 transceiver. This is the same as my own station, other than the rig (mine came along as backup). This difference is mostly immaterial since N1MM abstracts rig functions so that they function the same for all rigs, provided the rig supports the function. This is valuable in a multi-op where each operator may have a different rig in their own station. It's the logging software (and other contest-related software) that is key, and everyone's familiarity with it.

In run mode some liked to tune stations by rig control, others by keyboard RIT and others by filter width and shift. N1MM is compatible with all of them. It is only important to reset or check settings when switching operators.

We had ESM enabled (enter sends message), though not everyone used it, or used it for only select situations. Happily N1MM mostly acts sensibly when function keys are used when ESM is enabled. Mistakes were made but were usually easy to correct during the (many) quiet times. The software can't read minds and so may not do what one expects. I use ESM almost exclusively in my home station, only reaching for the paddles and function keys to say hello to a friend or to struggle through a difficult QSO.

Receiving antenna

Serious low band operation benefits from one or more directional receive-only antennas. These may be magnetic loops, beverages, phased verticals, among other options. We had a beverage (BOG) towards Europe. It is necessary to select the antenna to receive on, as often as every QSO.

I hadn't given the problem much thought since I do not have a receive-only antenna at home. There are two distinct approaches: manually switch the receiver between the transmit antenna and the receive antenna; or, diversity reception, with one antenna for each receiver in the K3 (or similarly-featured rig). We used diversity with a balance control to adjust how much of each was fed to the headphones. Alternatively each receiver could be fed to each earpiece of stereo headphones.

I have not made up my mind which approach I prefer.

Be flexible

Running a team by consensus sounds nice in theory. Except that getting to consensus on every issue is time-consuming and often fails anyway. Recognize that personalization of the operating position cannot suit everyone all the time. Although I had an opinion on most everything I was always ready to modulate my expectations. This was a fun, social weekend, and that was paramount, not the final score.

Would I have arranged the operating position differently? Yes. This should be apparent from what I've written in this article. I could claim that with my contesting ability and experience that my views ought to be suitably weighted in the discussion. However that is not right since all team members should be equal.

It is better to use one's skills to make the best of the situation as presented. Arranging the station to my vision of what works best is not necessarily the best for others, and I am just one operator among many.

Indeed, flexibility should be in every contester's toolkit. Look upon inefficiencies as a challenge, the same as a geomagnetic storm or other external events. Being inflexible leads to conflict and animosity, not a better score.