Monday, March 27, 2017

Struggling with CQ WPX SSB

CQ WPX contest is not a favourite of mine, especially the SSB weekend. The CW weekend, although more preferable to me, comes at the end of May when I'd rather be outdoors than indoors. Apart from the reasons I expressed in that earlier article here is one more thing I don't like about the contest.

Since prefixes count once and not once per band there is little incentive to pursue contacts on bands with marginal conditions. A quick review of top claimed scores on 3830 reveals little activity on 10 and 160 meters. There was nearly as little activity on 15 meters despite the presence of modest openings, including from here to southern Europe (EA, CT, I), and some good openings to South America. I heard many down south calling CQ on 15 with few takers.

Making it worse was a low solar flux that further concentrated activity onto 20 and 40 meters. The resulting heavy QRM limited the chances (and enjoyment) of little guns.

I put in a part time effort this past weekend if only for practice, to casually experiment with the station and operating technique and to ensure that recent repairs held up (they did). Not being serious in a contest is a good way to try things without worrying about the impact on your score.

Voice memories

I have used voice memories in SSB contest in the past. The KX3 has room for two messages in its on-board DVK (digital voice keyer). Because I was QRP the memory I programmed with a CQ was not very useful. The one I used most often was for my call sign. I sent that one a lot! The DVK was fairly easy to program by pressing lots of buttons and speaking into the mic connected to the rig. Levels and equalization were automatically the same for live voice and memories.

Editting of messages wasn't possible, making it vital to time button presses and recording to avoid silence before and after the message content. Macros programmed into the contest software (N1MM+ in my case) are used to simulate button presses on the rig to play the messages. This is a bit arcane but doable. I saved the function key file in case I decide to use the KX3 in a future SSB contest.

The FTdx5000 has an on-board DVK. Unfortunately it is, to be blunt, a joke. Too often manufacturers load up modern rigs with features that are unwanted and in any case are not designed for use in their intended applications. Again, there is no editting of messages. I can live with that. What annoyed me was playback.

The FH-2 accessory keypad could be quite handy to use the DVK. Recording isn't too cumbersome, once you get used to the sequence of buttons to be pressed. As with the KX3 and many other rig-based DVKs silence at start and end of the messages cannot be editted and so good timing during recording is mandatory.

Playback requires two button pushes and then activating the transmitter if you aren't using VOX since the rig will not automatically key the transmitter when a message is played. This is absurd and useless. What were Yaesu thinking? Indeed, were they thinking at all or just didn't care?

I therefore resolved to record messages on the computer and have N1MM play the Wave files (.wav) just as for CW memories using function keys. PTT is done with the WinKeyer interface, which offers perfect timing. This attempt was perhaps foolhardy since I haven't done software voice memories before and I undertook the task 3 hours before the start of the contest and only spent an hour at it. The experience was interesting.

In my first attempt I used N1MM's rapid programming technique of connecting the mic to the computer and pressing CTRL+Shift+Fn to record a message direct to a function key associated Wave file. It is similar in concept to direct programming of a rig DVK, with the same challenges. The played back files were noisy and the voice level was low. It seems that more work with sound card settings is necessary to make this feature perform properly.

I next chose to use Audacity, a popular free software application for recording and editting sound files. It is used by many contesters. I downloaded and installed the software and was soon happily recording and editting message files and exporting them to Wave files for playback by N1MM. Oh, if only it were that easy!

Playback requires connecting the output of the computer sound card to the rig. Unfortunately I am using a laptop where the mic and headphones jacks (sound card ports) are at the front where my hands rest. Although I have the integrated CAT/audio/data interface SCU-17 it is not yet installed on the FTdx5000.

The rig connection is as simple as a 3.5 mm Y-connector to join the mic and sound card into the mic jack. Not only did I not have a Y-connector in my junk box (I plan to order a few) I hesitated since I didn't know if the sound card output was AC or DC coupled. This matters since I wired the mic jack for my new headset with an electret microphone and it would put DC onto the sound card if there is no blocking capacitor in there.

Instead I routed the sound card output to the rear panel mic jack on the FTdx5000 which, according to the manual, is mixed with the mic jack on the front panel. Luckily I had a 3.5 mm stereo to phone mono cable in my junk box; Yaesu should have used a 3.5 mm jack on the rear panel.

That worked, sort of. The playback level was different from the mic and the audio didn't sound as if it used the same equalization setting I programmed into the FTdx5000 for the flat response mic. There wasn't time to trace the schematic and there was nothing I could do about it anyway just then. Instead I editted the sound files to add equalization and adjust the levels. Not being able to satisfactorily adjust these in time for the start of the contest I went with what I had.

When I set the mic level to best suit live voice the memories often clipped. During the contest a couple of hams helpfully informed me, thinking I had RF getting into the mic. I had to explain, briefly, what was really going on. Occasionally I gave up on the memories altogether to avoid the issue.

The experiment was instructive and pointed me towards what I need to do to get it right for the next time I enter an SSB contest.

Crowds = QRM

By concentrating most activity onto 20 and 40 meters the QRM was dreadful. SSB makes the problem far worse because of the bandwidth consumed. Unlike in CW you need at least 2 kHz separation to keep QRM managable even with the receive bandwidth dialled down to 1.5 kHz. Activity was so dense the separation was often only 500 to 1,000 Hz between stations.

There is thus little room for the little guns to run or to hear those lesser signals. The big guns were in reality not much better off since they had great difficult copying anything other than the strongest signals. The request for repeats of call signs and exchanges was routine, and rates suffered as a result.

It became comical at times. Here is a fictionalized QSO between me and a big gun. It is typical of some of my QSOs and many I listened to while waiting for my turn to call.
Him: "CQ contest QQ9XYZ"
Me: "Victor Echo 3 Victor Norway"
Him: "Victor Echo?"
Me: "Victor Echo 3 Victor Norway. Victor Echo 3 Victor November"
Him: "Victor Echo 3 what?"
Me: (repeat as above a couple more times)
Him: "VE3VN 59 1 2 3 4"
Me: "QSL. 59 3 2 4"
Him: "Your number?"
Me: "3...2...4..three hundred twenty-four"
Him: "381?"
Me: No! 3 2 4...3 2 4"
Him: "224?"
Me: No! 3 2 4...1-2-3 1-2 1-2-3-4"
Him: "Is it 3 2 4, roger?"
Me: "Roger roger roger!"
Him: "QSL. QQ9XYZ"
That final and successful method of communicating a serial number is sometimes known as horse counting. It is how purportedly intelligent horses answer math questions. For example:
Human: "What's 7 minus 3?"
Horse (stomping the ground with one hoof): clomp-clomp-clomp-clomp.
Very amusing the first time but increasingly aggravating when frequently resorted to in a contest to combat the ever present QRM.

One final note on QRM is that of F/B (or F/R and F/S). This is something I have sometimes lightly mocked since I am more often pursuing gain rather than directivity in my antenna designs. Yet this is a prime example of a contest when good directivity is useful to combat overwhelming QRM.

Often in contests there is some advantage in having only modest F/B so that stations in other directions can be worked without resorting to multiple antennas and frequently trying different directions, especially when running. It is occasionally useful in DX pile-ups as well so that the successful station can be quickly located.

In an SSB contest like this one with such intense QRM more directivity can be very helpful. My yagis -- short tri-bander and 2-element on 40 meters -- do not have great directivity. I will have better by this autumn. On 80 and 160 meters directivity can be less important in a high-efficiency transmit antenna if the antenna is supplemented with a high directivity receive antenna such a Beverage or 8-circle array. I used my Europe-facing Beverage even on the high bands in tough situations since it often helped just enough to make a difference, whether or not the station was in that direction.

Tragedy of the commons

Despite being called the dismal science, economics does contain many interesting concepts. One of these is useful for understanding CQ WPX and other contests: tragedy of the commons. In brief it explains how over-exploitation of a resource can occur by individual choices based on self interest. There is no need for a conspiracy to explain the phenomenon.

By over-exploitation in CQ WPX I primarily point to the unreasonable abundance of prefixes. As a result there is little reason to pursue prefix multipliers during the contest since you'll work new prefixes at a high rate by simply making QSOs. No one is special; when everyone is a multiplier then all QSOs are equivalent. Multiplier hunting becomes superfluous.

The implications on the contest are profound. The object becomes to work as many QSOs as possible, with only a preference for intercontinental and low bands for the higher QSO points. The bulk of the action is therefore between Europe and North America. Intra-continental QSOs are supplements to prefixes and QSO points. The rest of the world is largely excluded when yagis don't point their way. I heard many rare DX stations calling CQ without answers and even good signals from JA and VK had few takers.

Another example is power. To fight the incessant QRM inherent to an SSB contest during a solar minimum more stations are inclined to enter the high power class. That is, if you can't fight them, join them. When the majority do this the situation becomes the same as when everyone runs 100 watts: the QRM is the same and nobody really wins. It then comes down to who has the bigger antenna, a potential resource not so easily exploited by the majority.

One of the few reasons high power stations do so well relative to low power stations is that there are low power stations. Power can quite easily turn into another tragedy of the commons since amplifiers are easier to acquire and use than big towers and antennas. It can get uglier when ever more contesters choose to run illegal power.

Prospects

Get used to a high level of QRM for the next few years until the solar flux resumes its climb. Consider it one more aspect of the challenge of a contest like CQ WPX and take comfort in knowing that everyone is dealing with it as well, from little gun to big gun. Contesting is a competition so don't expect it to be easy. Use the QRM as motivation to build better antennas and improve operating tactics.

Although CQ WPX has its unique problems that drive my dislike of the contest this is one aspect of it that will apply to many contests for the next few years. With sunspots the QRM will once again relent as activity spills over onto 15 and 10 meters.

Tuesday, March 21, 2017

Perils of Expediency

As I wrote my series of articles on tower construction and antenna raising in the midst of a Canadian winter I downplayed the difficulties. Trust me, it is no fun at all standing atop a tower when the temperature is -5° C and the north wind is blowing while I am propping 20 kg of antenna on my shoulder and threading nuts on bolts to (hopefully) finally get a yagi securely attached. Of course I have to do this with gloves off.

I am thus reminded of just how driven hams can be in the pursuit of what is essentially just a hobby that we would undertake these challenges. It is little wonder that those around us sometimes think we're just a little bit crazy.

Considering the conditions it should be no surprise that I took shortcuts. I deliberately did sub par work to minimize exposure to the winter weather and the associated hazards. Although I am not proud of that I did what I felt needed to be done to get me on the air this winter. Expediency has its price, a price that I am now paying. My hope that all would survive until spring did not come true.

Here is my list of things that went wrong. Some have been briefly mentioned in preceding articles.
  • What I had at first thought was an inexplicable interaction between the XM240 40 meter yagi with the 80 meter inverted vee turned out instead to be an intermittent connection in the coax rotation loop. I had tested the coax on the ground and I taped the coax such that there were no connectors within the loop. It needs to be fixed to keep the yagi working at all times.
  • The rotator wiring has suffered two failures, both caused by reusing the only cable I had on hand that had connectors on it was long enough. The cable has several splices, the wire ends are frayed and the connectors are difficult to waterproof. One of the splices sagged onto the ground just before a heavy snowfall and subsequent thaw. This caused a few days of unreliable direction indication. I dried and cleaned the splice and made sure it was properly supported above ground. Then the rotator failed entirely due to a broken connection. Jiggling the cable and re-securing the connector at the rotator was only a temporary solution. Now I have to remove the rotator from underneath the mast to do a proper repair.
  • The mast and tower are overloaded for my wind zone. I did this to have yagis on 40 through 10 meters through the winter. For the second time the mast has slipped in the rotator clamp in high winds.
  • The galvanized muffler clamps securing the XM240 to the mast are not up to the task. These fasteners are not designed to withstand axial loads. The formed sheet metal saddles can bend under axial load. The saddles ought to be solid and have a large gripping surface. I already knew this when I chose what was locally available: inexpensive and easily acquired under a tight schedule (expediency).
  • The Trylon is almost but not quite vertical. Fighting with the gin pole and splice bolts has in a few resulted in a couple of instances of an improperly seated section. Although not a serious problem and only noticed when looked at closely -- it's about 1° out of true from about 25' above ground -- it irritates me.
  • Running cables on the ground risks damage with the amount of house renovation and construction that has continued through the winter and now into early spring. There has been one instance when a contractor spread out a bunch of tarps to dry over the cables, which means they walked over them, not noticing them due to the light snow cover. Luckily there was no damage.
  • The wire of the Beverage antenna sags in a few places low enough to reach up and touch. There is risk of wildlife damage, especially bucks being chased by coyotes (yes, this sort of thing really happens on my property). Since the antenna looks like a keeper I'll have to redo the support system to keep it high enough to prevent injury and damage.
Despite this litany of woes the station has performed very well over the past few months.

Repairs

The immediate problems that needed fixing were the coax to the XM240 and the rotator wiring. All the other problems can wait for spring.

It took a couple of trips up the tower once the weather cooperated. The first climb was to assess the problems better than I could from the ground and to haul up the things I'd need to complete the job. These items included a power cord for soldering, clamps to support the mast and antennas when the rotator was temporary removed and cords from yagi to tower to limit mast rotation during the repair period.

I slightly loosened the bolts securing the mast to the rotator and the rotator to the tower plate. This was done to ensure there would be no delays when the work was to be done. A new method of raising the mast and antennas (200 lb) was experimented with and discarded. Better to get that dealt with beforehand rather than wasting time later.

Before descending I fiddled with the rotator wiring and connector, purely out of curiosity to see if it would work again (it did). Locating the source of XM240 misbehaviour was quickly determined to be an ancient nickel-plated PL259 UHF connector on the 40 meter run of RG213.

The braid had broken off the solder to the connector body. I had mistakenly secured the coax to the tower below that connector instead of above. The connection experienced rotation stress, especially severe in cold weather when the coax is stiff. Never place a connector within a rotation loop. This is the price of sloppy work when the north wind is howling.

The next day a ham friend arrived to serve as ground crew. The forecast was promising to effect repairs, including soldering a new connector onto the main run of rotator cable. Unfortunately the weather stayed cool and turned windy making soldering too difficult; I had a small soldering torch, but that can't be used on a multi-pin connector since it'll melt the plastic body. Nevertheless I did get much of the work done.

I used a car scissors jack under the XM240 boom-to-mast clamp plate to raise the mast about 1 cm, which is enough to allow the rotator to be removed. Clamps at both bearings served as insurance in case the jack slipped. Of the many methods to lift 200 lb of mast and antennas off a rotator using a car jack is simple and fast but has the serious disadvantages of being unstable in a wind and placing undue stress on the antenna clamp. It was desirable in this instance since it was fast and easy.

With the rotator sideways on the tower plate I scraped off the old silicone sealant and then removed and discarded the wiring harness. The new one I had prepared was quickly attached and the rotator reinstalled. I then removed the jack but left the mast clamps in place in case the wiring was faulty and the job needed to be redone. Before retiring for the day I secured the XM240 coax from motion during rotation, thus protecting the broken connector.

I planned to return to the job later when the weather improved. Not only did it not improve the forecast was for moderately high winds. The next day I cut down the full length of rotator cable, brought the end indoors and soldered on the new connector there. Then back up the tower to reinstall the cable. In the end it was easier and faster this way. I then removed the mast clamps so that the full weight of the antenna systems rested on the Tailtwister once again. I left them on the mast, just in case!

Since the XM240 worked fine as is I decided to abandon repair of the coax connector for another time. The wind speed was rapidly climbing and it was time to finish up and descend. Fortunately the new wire harness and connectors worked placing the rotator back in service. If nothing else I am now prepared for CQ WPX SSB this weekend should I decide to enter: it is not a favourite contest of mine.

Spring follow-up

Since my weather associated fiasco in attempting to plant the 150' tower last fall my 2017 plans have been adjusted in accord with that event. We are now waiting for the ground to thaw and dry out enough to allow the foundation work to be completed. I predict that will happen in early to mid May. With luck the tower should be up by the end of June. I'll write up the full woe-filled story once the foundation for the tower is complete.

Until then I have the one tower for my antennas. I will need to make some compromises on operating since I need to raise the refurbished 6 meter yagi for sporadic E season starting in May. I will likely have to take down the XM240 for that and put it aside at least until the new tower is up. So I will likely have reduced capability for CQ WPX CW at the end of May. Perhaps I'll temporarily put up one of my old 40 meter inverted vees.

I can then leave the Explorer 14 where it is for a while longer, stacked on the mast with the A50-6. July will be when the major antenna work can begin.

Final

Expediency comes at a price and I paid for it this winter. I'd do it again. The success I've had in contests and DX chasing for the past 12 weeks was well worth it to me.

Should you ever do anything similar be honest with yourself. Put the risks up front, assess them and prepare accordingly. Do not fool yourself. That is a sure path to disaster. Avoid expedient choices except in a pinch. Even then don't do it unless you are comfortable with the risks.

Wednesday, March 15, 2017

I Hate Running

It is not possible to be competitive in a contest without running. You can of course have a lot of fun by cruising the bands and calling who you want, but you will never "win" that way. The greater your antenna farm and power the more of your contacts will (must) come from running. Top contesters are almost always running, using a second radio (SO2R) to concurrently S & P on other bands. Even for the QRPer or those with small stations running is an indispensible tool to run up the score.

The reason is simple enough: rate and reaching out. No matter how fast you S & P (search and pounce) the runner will consistently achieve a higher rate. At my best I can S & P up to 3 per minute on CW and 4 per minute on SSB. However that is unusual, fatiguing and unsustainable. As for reaching out, most participants, casual and semi-serious, focus so much on S & P that unless you call CQ you will never work them. So that is what you must do.

So why do so many contest participants avoid running? Some have convinced themselves that their stations or their skills are inadequate for running. That isn't true: anyone can run. I won CQ WW SSB in 2014 as QRP because I ran. True, calling CQ does not always work out. If the QSOs aren't happening switch bands or do S & P for a time. Just be sure to keep trying at intervals to get a run going. A slow run (1 to 2 QSOs per minute) can be exceedingly boring and seem unproductive yet be better than S & P. If you do not use the clusters and skimmers (assisted category) you will find it difficult to exceed an hourly rate of 30 or 40 QSOs/hour in the latter part of any major contest.

Queuing theory

I like to lean on my academic and practical mathematics experience to explain some of the challenges of running in a contest. There are aspects that are directly explainable by referring to queuing theory. In particular its stochastic nature wherein a fairly predictable hourly rate is not at all predictive of arrival rates of replies to QSO solicitations.

Let's say that your hourly rate is 180. Not only will you not typically log a QSO every 20 seconds, if you did it would be a sure sign to the log checkers that you're cheating! In reality the arrival rate of callers is stochastic: a equation with one or more random variables. In telecommunications we used the Erlang distribution to give the probabilities of intervals between events with a known or estimated long term rate.

What this means is that in that hour you can have a few minutes with no callers at all and at other times you may feel as if you were signing /P5. Even so you can predictably put around 180 QSOs in the log each of several consecutive hours (provided propagation and other factors are roughly equal, and you have not worked out the band). Each CQ or signing TU brings a surprise. You have to be prepared for anything, including typing the call in correctly when you have a caller sending at 32 wpm after two minutes of boring nothing.

Queuing theory is not so reliable these days to predict what you'll experience when you run. Rather than others coming across you as they scan the bands many of the callers are driven there by spots, whether human input or by skimmers. There is a correlation between spots and rate over the next few minutes, except late in the contest when you've worked nearly everyone. Unless of course your call is spotted incorrectly, in which case be prepared for a flurry of dupes! Yes, it really happens, so learn to deal with that as well.

Why I hate running

You don't have to enjoy running to get the benefit. This is as true of contesting as it is of the sport of the same name -- I do both, and hate both. It's about challenging yourself to reach the next level of performance. Even if you dislike the process you can appreciate and enjoy the results. So if contesting matters to you yet you avoid running you need to practice it and do it. There is no alternative if you want to improve your scores.

Everyone has their reason for avoiding running in a contest. My reason can be summed up in the following Youtube clip of a classic comedy skit by Lucille Ball:


Running during a contest is very much like that! Or if you prefer it is like sitting behind the cash register taking customer orders at a fast food restaurant or a cashier at a grocery store. Although you have some control over the situation your performance is measured by how fast and accurately you process customers, and smile while you're doing it. Running is akin to being in a front line service job.

Some love it and some hate it. I am somewhere in between. It's nice to be so well heard and wanted that stations step all over each other in a bid to get my attention. It is incumbent on the runner to process the callers fast enough that they leave satisfied and put points in your log and theirs. As the running station you have a responsibility to do it well.

Others love the attention so much they spend large sums of money to travel to exotic locales and create their own personal contest: the DXpedition. DXers such as myself appreciate that they do this and love doing it, even though I am ambivalent on whether I'd care to be on the DX end running pile ups for hours and days on end.

I feel the same way about those who build super-stations and run continuously throughout a contest. I am building a big station and I know very well that becoming good at running, and doing it lots, is what I will have to do. But I don't have to like it.

It is rare than any hobby or vocation that anyone chooses to pursue is 100% enjoyable. There are always tasks to be done that are not enjoyable. As with contesting it is the net enjoyment that counts. Therefore I can continue to enjoy contesting even though I must run. For others the task no enjoyed might be CW proficiency, SO2R, computer logging/interfacing, tower and antenna building, etc.

Because we enjoy the overall contest experience we accept the need to do the tasks that are not so enjoyable. The willingness to step up makes us better contesters.

Getting accustomed to running

If your antennas and power are good enough and the band is open you will find it easy to start a run. Just find a reasonably free frequency and call CQ. The trouble starts when stations answer. Here is the typical litany of things to watch out for:
  • Multiple callers
  • Multiple callers on the same frequency
  • Callers at the edge or outside your filter pass band
  • Weak callers
  • QRM
  • Hostile takeovers
  • Boredom
Running takes a lot of practice to do it well. Doing it well means putting QSOs in your log and theirs as quickly and as accurately as possible, and doing so without being evil. An example of the latter is not signing your call often. It is not my intent to explain or teach technique -- there are tools such as Morse Runner for that -- only to provide some guidance on what to expect before you dive in.

Multiple callers

First, about those multiple callers. Pick one and stick with it. If you only get a letter or two send that and, hopefully, only that station will respond. Of course in a contest time is valuable and many are not willing to wait. Just work them one at a time and don't worry about the others: they are not your problem. Should they become impatient and leave they'll soon be back; they want the points, too.

Picking out anything when the callers are zero beat is harder. Often you can latch onto a letter at the end of one call since they typically have different length call signs. Latch onto that when you can. Or send '?' and try again.

About pass bands

A surprisingly number of stations will be below or above your pass band. Try to keep the bandwidth as wide as possible if conditions allow. Otherwise make a point of using the RIT to check from off-frequency callers.

Reasons for the problem include: different pitch/offset preferences for CW; VFO overshoot as they tune you in; USB vs LSB CW receive; someone forgetting that their RIT is enabled; antique rigs, etc. Don't complain; deal with it.

Weak ones

Since you are now a big gun, or even just a medium gun, many of the callers will be weak. You must work them. There are some operators with big stations who refuse to work weak ones. You will never see them at the top of the contest results. I've heard a few so-called contesters telling weak callers to get lost or get an amplifier. They are the losers at that game since they lose the most points, not you. Ignore them, move on and never emulate them. Assuming, that is, you want to do well and not become a laughingstock.

The point is that you must get used to digging stations out of the noise, QRM or whatever receive challenges you might be facing. If you don't dig those marginal signals out for the noise you will lose points, and losing points loses contests. It can be hard work and it take practice. When you can't pull them through after a reasonable time thank them for calling and suggest they try again later. Then call CQ and resume your run.

Even when I ran QRP in the major contests I was surprised at how many weak stations called me during my occasional runs. Sometimes they were also QRP, driven to me by a skimmer spot or they simply had a lower noise floor than I had in my suburban neighbourhood.

QRM and keeping those elbows up

Finding a clear frequency in prime real estate (the lower end of the band) during a major contest is not easy. Nestle too close to a big gun and your CQ won't be heard and you'll have to move. Some runners don't even bother to check if the frequency is clear and will try to set up shop almost on top of you. Don't despair too quickly, but also don't stay with a no-win situation so long they you lose valuable time fighting for the frequency.

The big guns will always win when they persist at taking over 'your' frequency. That's rough play that you have to get used to. Just like in hockey the elbows always come up in the corners. Don't yell at the cat or bang your fist on the transceiver. It won't help. Move and restart your run, whether on the same band or another.

Fighting boredom

Finally, there is the matter of boredom to contend with. Late in the contest or in poor conditions the rate will slow down. Sometime it'll slow down dramatically. You must decide when to stick with the run when you only log a QSO less than once per minute. Depending on the particular situation this may still be better than changing frequency, changing band or switching to S & P.

As in baseball there is a whole lot of nothing happening most of the time. Then when something does happen you must react quickly or you'll miscopy the call or make some other time wasting mistake.

This may be a good time to learn how to do SO2R. Construct your antenna and rig switching accordingly, so you can search for QSOs during those times CQ elicits few responses. Get really good and you can interleave CQ on two bands at once.

At the very least you can feel you're doing something productive when the runs are not very productive. It's better than vaguely worrying that your run might be better done elsewhere or that you are missing an opening or a rare multiplier while you sit there waiting for something to happen.

I have never properly done SO2R. It is on my list for 2017, starting with antenna and rig switching. The setup is very similar to a multi-single operation. Then it's a matter of practice. Not only will the boredom of poor runs be eliminated it can add a lot of excitement when you try to CQ and work a needed multiplier at the same time!

Learn to love it?

As I said: I hate running. Not so much that I avoid it; it's a necessary skill for a contester, even a QRP contester. Years ago when my contest activity was more often as a member of a multi-op team I often volunteered for the graveyard shift when runs were very difficult to establish (this was during a solar minimum). That way I could spend my time S & P for new multipliers and digging weak ones out of the noise. While it might surprise some that was my idea of fun.

When dawn broke and the daytime crew arrived I would step away and watch them start the European runs on the now opening high bands. I felt little regret seeing them log more contact in 5 minutes than I did in any one hour overnight. I would of course do some running later in the day since it was unavoidable when operating as a big gun.

I suppose this is why I am more of a DXer in some respects than I am a contester. Besides, most of the time there is no contest, or one I care to enter, and I can dig away for the rare DXCC entities quite contentedly. Even so, as my new stations grows I will run more, and I will do SO2R. I have to do it and I intend to do it well.

It's results that I want and that drives me to do things I may not love. As our mothers used to tell us, "eat your vegetables, they're good for you."

Tuesday, March 7, 2017

Beverage Comparison: ARRL DX SSB

Due to circumstance I was unable to make a serious effort in this weekend's ARRL DX SSB contest. The major reason was (another) rotator wiring failure a day before the contest. It happened just as I was turning the yagis toward Europe right after working VP6EU on 40 meters Since this is not my favourite contest and the weather became bitterly cold I was unwilling to climb the tower and undertake the work. Instead I chose to tackle a slew of small chores I'd been putting off.

With the pressure off I decided to play on 80 meters Friday and Saturday nights to get a better understanding of how my new Beverage performs and to see who could hear my 150 watts to an inverted vee. I received an important education about not only my Beverage but also how well others hear. What I learned is important enough that it is worth another article, even coming so soon after the last one.

The method

It is no simple matter to compare the Beverage to alternatives. I have none. But other stations do, and it is them I must compare against. In this case it is easier to compare a receive antenna than a transmit antenna since we are both listening to the same stations.

It was quite easy to do. On 80 meters I would find a known big gun in the US northeast (reasonably close to my location) and sit on their frequency to listen for a while. If they listened split so did I with the second receiver in my FTdx5000. Conditions were poor so their rates were slow. I had to be somewhat patient, especially on Saturday evening when they had pretty well worked out the band.

When a weak European station called them I would pay close attention. The challenge was to copy the station better than the big gun. It is not unlike watching a quiz show on television where you try to outguess the contestants as they try to answer difficult questions. That can be quite a lot of fun, and so was this game I was playing.

What I found was that in most instances I could copy the really weak ones about as well as most of the big guns. Only rarely was I outgunned. In a surprising number of cases I could copy the DX better. This made me very happy since it means that my receive capability on 80 meters in that direction, but only in that direction, is comparable to the best contesters. Of course it is possible the operators were not as good as their antennas, however knowing who these folks are I highly doubt that!

On 160 meters my task was more difficult since activity was lower and rates worse. My sample of comparisons was far smaller than on 80 meters. I can only tentatively claim the same result on 160 meters.

What am I comparing against?

Perhaps the biggest unknown with my method of comparison is what antennas other stations are using for receiving on 80 and 160 meters. Even when I know they have separate receive arrays, whether those be pennants, flags, or more elaborate arrays such as Beverages and 8-circles, I don't know which they are using on any given contact. It may even be that they are sticking with transmit 4-squares on receive.

Since I can't know the answer to that question I have to assume that these operators, who are among the best around, would in each case choose the antenna best suited to getting the other guy into the log. In which case I am comparing against their best towards Europe. This is likely though not absolutely certain.

Off the main lobe

A directive antenna attenuates QRM and QRN, which is at least as important as its (relative) forward gain for copying weak signals. I had ample opportunity to test that as well during the contest. Of course I already knew perfectly well that the F/B, F/S, F/R or whatever metric you prefer had to be reasonably good or I would not have experienced such a favourable comparison. However that comparison alone is not the full story, nor should it be.

The test is to see how much signals and noise off the main lobe are attenuated. This can be precisely quantified by RDF and DMF figures used by W8JI and ON4UN, respectively. On the air a quantified measurement is not easy when the comparison signals weaken and strengthen in response to ionospheric changes, even if only Faraday location, and I don't know the precise direction of stations.

Instead I did a rough statistical assessment using as many signals as possible, thus reducing the impact of unknown factors in each comparison. DX stations were a little easier to assess since in many cases their bearings are known to within a few degrees. While I cannot easily measure the RDF or DMF of the Beverage there is the possibility of getting an approximate idea of what it might be by careful listening.

When there was QRM on frequency the benefit of the Beverage was greatly enhanced. Since in almost every instance the interfering station was in North America, and therefore far off the main lobe, the attenuation of QRM ranged from good to remarkable. The remarkable cases were most likely those that fit neatly into one of the nulls between the several minor lobes to the side and back of the antenna. For DX stations in South America, the Caribbean and Central America the results were the same, which is to be expected from my QTH.

The Beverage is a great QRM fighter. Calibrating the attenuation of signals required some quick work with the RX antenna switch and pre-amp (IPO) toggle switches on the FTdx5000. This is absolutelynecessary due to the unequal signal levels from the two antennas yet can never be perfectly accomplished. There is also the matter than my comparison antenna is an inverted vee which is horizontally polarized, while the Beverage is vertically polarized. Faraday rotation is a factor.

The worst case rejection of QRM was in the vicinity of -15 db and in the best cases was -30 db or better. Most times it fell somewhere between. I am very happy with the Beverage performance in this respect on 80 meters. On 160 meters it was more difficult to assess since the main lobe is broader and activity was less. Early indications are promising. I'll have to keep listening. I expect that a deep pile-up on a DX station will provide the best test conditions.

Higher bands

Beverages work on bands higher than 80 meters, and can work quite well. I tested mine on 40 meters and 20 meters during the contest with variable results. The main lobe becomes quite narrow on higher bands since it is long in terms of wavelength: 4λ on 40 meters and 8λ on 20 meters.

I couldn't see any benefit of the Beverage on 20 meters at all, even with the yagi fixed on north due to the faulty rotator, and therefore receiving Europe quite poorly. This may be because the 2.5 meter height of the Beverage is a substantial fraction of a wavelength. It would have to be lower to perform well since a Beverage works in part due to the lowered velocity factor caused by ground proximity.

On 40 meters it worked though with signal levels that were weaker than expected. Some European signals were received very well though not all benefitted from the Beverage. Performance was not consistent for some reason, perhaps the narrower main lobe. Once the yagis can again be turned I'll do another evaluation.

Proceeding with receive antennas

Before committing to building an array of Beverage antennas I would like to experiment with a couple of smaller receive antennas such as the K9AY or a type of flag or pennant. These are not difficult to build if there is no provision for direction switching. I would like to try them pointing southwest (US and South Pacific) and north (Asia).

I could of course build these in addition to more Beverages and have the luxury of doing extensive comparisons. That's a lot of effort that I really need to devote to other antenna farm projects this year. Perhaps the most profitable comparison will be a switchable directional antenna for 80 meters, whether a 4-square or a parasitic array. A transmit antenna with directivity is, after all, a type of receive antenna. Although these are typically not highly directive they have enough directivity to be effective, especially a properly adjusted 4-square.

Whatever path I do choose I will definitely have more receive capabilities on the low bands when fall rolls around later this year. My immediate need is better transmit antennas so that I can finally work the many stations I am now able to hear. It has been somewhat frustrating calling stations that cannot hear my puny signal on 80 meters.

SWR chart

Since my attempt to take a photograph of the analyzer display for the earlier article was so poor I decided to take one from inside the shack where I could control the light conditions. I'll close this article with that picture. You can see how nicely the SWR is from 1 through 15 MHz. A Beverage is truly a broadband antenna.

The periodicity you see is due to the termination resistor not equalling the antenna impedance; they differ around 10%. The impedance appears to be rising with frequency resulting in greater SWR swings.

Thursday, March 2, 2017

Building and Using an Experimental Beverage

Directional receive antennas for the low bands are a must in my antenna plans. It is, however, not an immediate need since I do not have good transmit antennas for 80 and 160 meters, nor do I run a kilowatt. Considering my low noise rural location it is unusual at present that I cannot copy a station that can copy me.

With the lull in tower and antenna work until spring arrives this is an opportunity to experiment with one or more low band receive antennas. My first is a unidirectional Beverage antenna pointed at Europe. I have the space for several moderately long Beverage antennas should I wish to do so.

This antenna is a trial run to see how it works and how much effort it'll be to build Beverages through bush, bog and forest. I will not run these antennas over open fields since those have better uses. The land I've chosen has no use other than for antennas like these.

Since I'm coming from a position of ignorance I have relied on several experts in the field of Beverage antennas. One is Low Band Dxing by ON4UN. The other is W8JI. Those are my primary sources. I have also spoken to and read material written by other hams with theoretical and practical Beverage experience. I especially like ON4UN's book because it is a compendium of material from many reliable sources. One of best sources he heavily relies upon is W8JI.

There are, of course, many hams with experience and opinions, but be careful. Too many of those voices are not reliable. As with other antenna topics there is a great deal of myth being promulgated about low band receive antennas. I strongly suggest sticking with reliable sources.

Model

As W8JI, ON4UN and others have demonstrated a Beverage can be successfully modelled with NEC2 despite being so low and connected to ground. The ground proximity is not a problem for NEC2, however the ground connections require special provision in the model. These connections are simulated with two equal length radials that run orthogonal to the antenna and close to the ground. The source and load are placed on wires that connect the antenna wire to the radials.

The radials in my model are 20 meters long and are 0.1 meters (10 cm) above EZNEC medium ground. The The antenna is 2.5 meters high.

I was originally intending the antenna to be 120 meters long, which is enough for good directivity and not so long as to make construction in the bush too onerous. It turns out that is a very poor choice since there is a significant minor lobe directly rearward. So I went longer, trying to get reasonably close to ON4UN's suggestion to make the Beverage an integer multiple of 89 meters.

The following azimuth pattern is for a 170 meter long and 2.5 meter high Beverage at 3.5 and 1.8 MHz with a 500 Ω termination resistor. Although the modelled source impedance is closer to 550 Ω the pattern is stable for small deviations.

The 2.5 meter height was chosen to ease construction and to reduce the risk of wildlife incidents. One local top band enthusiast (VE3QAA) says his Beverages are 1.5 deer heights so that a running stag does not break the wire with its antlers. Mine is perhaps not quite high enough. I'll deal with that if the antenna becomes permanent.

As the Beverage length approaches 178 meters (2 x 89 meters) the most rearward lobe shrinks to a very small value. This is useful to attenuate QRM from that direction. The other minor lobes change only a little for small length excursions.

The length of my Beverage is approximately 175 meters, close to the ideal, and which is the longest I could fit in the location I chose. The F/B should therefore be 20 db versus the 16 db shown above for 80 meters.

The chosen 45° bearing covers all of Europe, from northern Scandinavia to the Mediterranean, within the fairly broad main lobe. On 160 meters the lobe is even wider. The azimuth plot is an overlay of the patterns for 160 and 80 meters.

Location,  location, location

When I first laid out my plans for antennas and towers on my property I looked at the easternmost bog and forest as the best location for receive antennas. This area has no other use and it is furthest from dwellings and power lines, particularly in the direction of Europe. This matters for contests since that is the most productive path for QSOs and multipliers. I want to catch as many European signals as possible.


The scaling of my 50 meter graphical "measuring rods" is not perfect. When the wire is extended at both ends right to the property line (upper left) and the southwestward large tree the Beverage is ~175 meters long per the map scale -- I used a higher magnification of the satellite view for my calculation. Only the most eastward 10 meters is bog. The rest is bushes and scattered trees. It is not that easy to walk and work in. Snow cover and winter clothing makes it easier and safer. The countless thorn bushes are a serious hazard. I did not bother to with an actual measurement since the length is not overly critical for my purposes.

I originally considered the bog area at the lower right for a northeast Beverage. Although there are stunted trees that can support the Beverage wire it is unpleasant to work in and requires a far longer transmission line in order to avoid the hay field. Although bulk RG6 is cheap the routing of such a long cable is more work is because it won't be buried there is additional wildlife hazard.

The trees in the selected field are sparse enough to allow stringing Beverage wires without being so dense that it becomes unreasonably difficult. The large trees lining the field boundaries are not as handy as it might appear since, close up, there is dense underbrush. Even so I may try to use those boundary lines for north-south and east-west Beverages.

45° bearing corrected for magnetic deviation
The source end of the Beverage is fairly close to one of the anchors for the big tower. It is not close enough for significant interaction, but even so I may break up the upper guys with insulators to further reduce that risk. I am also considering moving the 80 meter transmit array from the north field to the area east of the big tower. If I do that and decide to build more Beverages I will keep the distance between it and the Beverages sufficiently large to minimize interaction.

Blazing a trail

Satellite views are comfortably clean. You don't see the reality of what it's like on the ground. Starting from the source I found it impossible to walk in the northeast direction without routing around the many obstacles and losing my way. It really is that difficult.

What I did was carry a bunch of wood stakes under one arm and a compass in the other and blaze a trail. As I reached an obstacle (often doubling as a wire support) I would pound a stake into the ground, walk around the obstacle and use the compass to orient myself. I would then continue onward to the next obstacle.


Through the camera lens the path doesn't look too bad. That is deceiving. Many of those innocent looking twigs are covered in thorns, some 2" (5 cm) long and needle sharp. Old clothes are recommended! Doing this in winter helps since you can comfortably wear heavy, thick and warm clothing.

You can see the imprint of my snowshoes in the snow. Snowshoes can easily get caught in the brush so some care is needed. The termination is in the trees at the edge of the bog behind the final stake. In the background can be seen the rotting logs of the fence marking the eastern boundary of my property. There is more bog and bush towards the northeast for at least 1 or 2 km. Man-made noise is not an issue.

Labelling the ground in this area as "EZNEC medium" is perhaps optimistic. For a Beverage ground quality is not critical so I didn't fret about it in the model.

Running the wire

This was the hardest task in the construction of the Beverage. After surveying and staking the path for the wire I had to run an enormous amount of wire through the bush. Although my path was selected to take advantage of high bushes and small trees to which the wire could be attached I still had to remove all the foliage at the height of the wire so that it had an unobstructed space around it.

My equipment for running the wire is shown in the photograph: ladder and a crate of electric fence insulators, gardening tools, plastic ties, nails, porcelain insulators, rope, ground rods and wire clamps. It was very strange being out in the bush and carrying all this stuff with me. I discovered that it is difficult to climb a ladder with snowshoes.

An example of a tree attachment can be seen in the picture. I took the picture while walking back from the end of the line. This was one of the easier attachments. Most required extensive pruning of branches and twigs that covered the targetted tree trunks and branches so that nothing would touch the wire in windy weather.

I took along two types of fencing insulators: those that could be screwed in and those that took a nail. The nailed variety were used for the smaller branches and were attached with UV-resistant plastic ties rather than nails. The screw in type were easier to attach on tree trunks.

The wire is AWG 17 aluminum electric fence wire. It is quite inexpensive. The downside is that if it breaks the splice repair cannot be soldered. For an experiment it is perfectly suitable. Should I go all in with Beverages my wire choice will change since I want something more robust, and preferably twinned for reversible Beverages.

Terminations

I tried a few mechanical termination techniques until I settled on one that allows tension to be finely adjusted and which does not interfere with the electrical terminations. Large trees serve as anchors at both ends. The wire ends at a porcelain egg insulator, securely twisted and dangles down for electrical connection. A short rope ties the egg insulator to the tree.


Rather than wrap around the tree and tie a knot I hammered two 3-½" galvanized nails into the tree at Beverage height and used them as an improvised rope cleat. No knots required and the tension is easy to adjust.

The electrical termination at the far end is simply a resistor connecting the Beverage wire to ground -- the ground rods are 4' copper clad steel and were hammered in with a small sledgehammer. On the near end there is a transformer to match the RG6 transmission line. The high-impedance primary attacjes to the Beverage wire and a ground rod. The low-impedance secondary attaches to an F connector. I used a barrel connector since I could not find a suitable bulkhead female connector locally. I wasn't prepared to wait for a mail order delivery.


Both were put into small plastic "hobby" boxes. The hardware for wire connections is stainless steel. The boxes are not waterproof so (not shown) I lined the rim of the boxes with good quality electrical tape to reduce the map between box and cover. The screws pierce the tape to add some protection there as well. This amount of precaution is sufficient for an experiment. I did not protect the screw heads from rusting.

The transformer is the very same one I built as an experiment last year, in preparation for this very project. It better matches 50 Ω coax than the RG6 I am using, however the SWR and consequent transmission line loss that is not a serious concern.

Measurements

Sorry that the display isn't readable (see text)
As soon as I had the termination resistor installed I measured the feed point impedance on 160 and 80 meters with an antenna analyzer. I did not yet have the transformer installed so that the "raw" impedance could be measured. It is approximately 540 - j100 Ω.

On his Beverage page (link at the top of this article) W8JI demonstrates how to calculate the radiation resistance with a range of analyzer readings. Ideally you should insert a termination resistor of that value. My (very old stock) carbon composition resistor measures 495 Ω, a little higher than its nominal 470 Ω value.

I was happy with that so I attached the transformer box and again measured the impedance. The SWR was fairly constant at around 1.7 from 1.5 to 4.0 MHz. Of course that is relative to 50 Ω. The actual resistance component of the impedance varied between 65 and 75 Ω, with a small amount of reactance. This is higher than expected for the 9:1 transformation ratio. The good match to RG6 is a fortunate accident.

Transmission line

Bulk RG6 is cheap. I bought a 500' (150 meter) roll at a local big box store along with some twist on male F connectors. I pulled the coax from the feed point west along the tree line until I was north of the Trylon tower. I then crossed the stone wall and ran the coax toward the tower and laid it next to the cables running from the towers to the house. Cables will eventually be buried or elevated by messenger wire from the tower to the house.

I used trees and carefully selected weights at the two corridors where people are likely to walk and elevated the RG6 over them. This reduces the chance that it will be accidentally stepped on or tripped over. Apart from that I'll take my chances with the wildlife. Other hams have varied reports whether animals will gnaw at coax lying on the ground. Now I get to find out.

The total amount of RG6 I played out was ~400' (130 meters). This is perhaps 50' (15 meters) longer than necessary. The extra length is to wind a common mode choke at the feed point and for future consideration in regard to cable routing and Beverage switching. As I said, the cable is very cheap.

Once routed into the shack I attached a UHF connector and remeasured it on the analyzer. Apart from some attenuation from the long transmission line it was fine. Since it was nearly sunset I connected it to the FTdx5000, pressed the RX antenna switch and proceeded to tune the low bands.

Early impressions

It works very well. In fact it works very, very well. As soon as I had it connected I heard European and west Asian (4X, 4J, EY) stations on 80 meters, despite being before sunset and a disturbed geomagnetic field. The gain is low so it is necessary to use the highest pre-amp setting on the rig to ensure that the antenna noise exceeds the receiver noise. An external pre-amp would only be required to equalize gain with the transmit antenna for operating convenience when switching between antennas.

On strong signals it is not easy to tell if the Beverage is helping at all. It is on weak signals that it shows its effectiveness. Many signals that are inaudible on the inverted vee are solid copy on the Beverage. I could listen in on European stations working each other and Asians long before they were workable here. Of course they might be workable with a better transmit antenna and more power.

A couple of other indicators are when an American and a European are on the same frequency and copied on both antennas. On the inverted vee the European signal is heard but covered up. Switching to the Beverage reverses the situation so that the European is solid copy and the American signal is knocked down enough that it is no more than an annoyance. The other indicator is SSB. The wider bandwidth makes many signals a chore to dig out of the noise. Even unheard SSB Europeans on the inverted vee are perfectly copied on the Beverage.

The beam width is noticable for stations that are somewhat off the main lobe. EA8, for example, is 88° bearing from my QTH. This is 43° off the peak direction of 45° bearing. From the pattern this should only reduce the signal by -7 to -8 db, yet that is enough to make the Beverage little better than the inverted vee. It is for this reason that hams I know with Beverages of similar length (2λ on 80 meters) opt for 8 directions rather than just 4. Often this is accomplished with 4 reversible (2 wire) Beverages.

On 160 meters the antenna also performs well. The most significant difference is that the beam width is broader -- see the pattern comparison above -- since the Beverage is only 1λ long on that band. A proper comparison will need to wait for a full-size transmit antenna. The 80 meter inverted vee is not an ideal basis for comparison. For now all I can say is that I can copy more stations and copy them better on 160.

What comes next

What the Beverage teaches me is that there are many more stations out there that I cannot work. I can hear them but they do not hear me. I expected that. This is why the Beverage is not especially needed at this time. Apart from experimenting with it I can copy more stations with far less QRM and QRN. It isn't merely directivity. The antenna is so much further from local noise sources that there is (so far) no evidence of the electronic and power line noise that occasionally make an appearance on the inverted vee.

After I build a high performance transmit array later this year I will have to decide on permanent receive antennas. If I choose to go with Beverages I will likely need to emulate others and go with 4 reversible Beverages (8 directions). They could all fit in the same field, crossing each other (this is perfectly fine) and with transmission lines brought to a single point for switching. ON4UN has a lot to say on this topic in his book.

Although Beverages work on both 80 and 160 it is desirable to have two receive systems for SO2R and multi-op contests so that 80 and 160 antennas can be separately steered. The secondary receive array can be simpler and only 4 directions -- operators can have a friendly fight over who get the Beverages. Of course if I build a directional array on 80 that reduces the need to use a Beverage antenna except for the weakest signals and to reduce QRM with its superior F/B.

This weekend is the ARRL DX SSB contest. Since I do not plan to be too serious in the contest it is an opportunity to play with the Beverage under conditions of heavy activity and QRM. I have high expectations for it.

Monday, February 27, 2017

New Antenna: How They Play

When I completed the Trylon tower and antenna construction and put it on the air I promised to report about how the station performs in regards to my technical assessment of what to expect. With close to two months of experience, one major contest and several DXpeditions I am now ready to come to some conclusions.

I've done this before from my previous station in Ottawa. I believe that this kind of analysis is something any ham should do. However it must be done honestly. The task is not easy when there is no possibility of a direct A-B comparison due to the previous antenna, tower or complete station being removed. Yet this is quite typical, and the source of much uncertainty or outright error. While I am not immune to misleading myself I try to keep my skepticism intact when I undertake such a comparison. Whether or not I succeed you will have to judge for yourself.

Perhaps the greatest tests of my current station were the ARRL DX CW contest and working the A5A and XX9D DXpeditions. Early indications from the contest are that I placed highly among the W/VE entrants in the SOAB LP category.

20, 15 and 10 meters with the Explorer 14 up 23 meters

Modelling showed a modest though far from insignificant improvement of 3.5 to 4 db compared to its 14 meter height in my previous station in Ottawa. In practice I definitely notice it, and so do those I call.

Running 100 watts I can enter any pile up with confidence. Sure I don't get though immediately when the big guns are in there. But I do get through sooner than I did before. In contests I can establish runs on 20 and 15 meters without any real trouble as long as the propagation cooperates. There is little on the high bands the big guns work that I now cannot at least hear. That was often not the case beforehand.

Another 3 db with 200 watts and my results have only gotten better. A higher antenna will be needed to capture those marginal openings that only the big guns can take advantage of. That is of course in my plans. For now I am cruising the bands with more confidence and success than I have in a long time. QRP and little antennas are challenging and fun, and so is this. It is just that the nature of the challenges changes.

40 meters with the XM240 up 21 meters

This antenna full meets my expectations. The modelled 10 db of gain over the inverted vees I used back in Ottawa is certainly present. Without high power I am now competitive in the pile-ups. If I hear a station I can work it. Long path openings to VK and Asia in the early evening yield many QSOs, including VK6 and XX9D.

In contests I can get a run going without much difficulty. Any evening if I call CQ there are Europeans who answer. After signing with another station who had called CQ I frequently get called by others (but of course I QSY). This is a level of performance I have not had before on 40 meters.

Front-to-back (F/B) on any 2-element yagi is poor, and this antenna is no exception. I can often work stations off the back without any difficulty. When I point to Europe during contests I can continue to work the US. Off the back it is much like what I previously had with an inverted vee. Not great, but good enough for contests when I do not have the option of a second antenna for diversity.

Because of the high SWR at the bottom of the band I operate with rig's internal ATU. The SWR is not so high that the transmission line losses are a worry. The XM240 will make for a good secondary antenna once I have a bigger antenna installed on the 150' tower.

Structurally I can see that I need to make changes to the antenna. The galvanized muffler clamps that secure the elements to the boom and the boom to the mast do not have the best gripping strength. They get their grip in part by the edges of the formed sheet steel saddles dimpling the boom and mast. Worse, in the case of the boom-to-mast clamp the saddles bend under the axial force. Solid saddles are a must for at least the boom-to-mast clamp.

80 meters with an inverted vee up 19 meters

An inverted vee with the apex up only λ/4 is not a good DX antenna. Even so it works. Sometimes it's because the elevation angle is at times higher than expected on the low bands and other times because verticals are deployed in a way that the ground loss is high: inadequate radial system or high-density suburban environment.

My country count on 80 meters has surpassed 100, starting from my DXCC "reset" in 2013 when I returned to the air after a 20 year absence. In reality my country count is ~200, if I were to bother with the paperwork. I won't because I don't care: I like working DX, not QSLing or award chasing.

The latest additions were TX5T and VP6EU during this morning sunrise opening. In ARRL DX CW I worked 65 countries, which is quite good for 150 watts and an inverted vee. I would say that the inverted vee has surpassed my expectations despite being merely a convenient and easy temporary antenna until I can put up something more substantial later this year.

With a better antenna or more power I will be pushed over the threshold where I will often not be able to hear many stations that can copy me. Directive receiving antennas are a must. As I write this my first Beverage antenna is nearing completion. I will say more about it in a future article.

160 meters with the 80 meter inverted vee

This should not have worked at all, yet it did. Modelling estimates an impedance of 6.5 - j1000 Ω. With 40 meters of RG213 the calculated loss is -22 db. Measurement with an analyzer tells a different story, perhaps only -6db of loss. This measurement is misleading since the 1:1 balun at the feed point will behave unpredictably under such a severe mismatch -- this is typical of baluns and RF transformers. From on the air experience the loss is substantial.

In the January NAQP CW contest I used an external tuner and unscrewed the outer ring of the connector. That seemed to work pretty well. In ARRL DX CW I did not bother. The FTdx5000 ATU found a match (to my surprise) which made me lazy. With the help of excellent conditions I worked an unbelievable 20 countries on top band with this ridiculous antenna system. Running 150 watts out my effective power was no better than QRP.

While interesting it is unacceptable, with or without the connector half unscrewed. I will have something better when fall arrives. But for those running QRP it shows what can be done with low effective power on top band, assuming a decent antenna is used.

6, 12, 17 and 30 meters

I have no antenna for any of these bands. On 12 meters I use the rig ATU with the Explorer 14, on 17 meters I use the XM240 the same way, and on 30 meters I use the third harmonic of the 80 meter inverted vee, but also with the ATU in line. At least 6 meters hasn't been a worry since sporadic E season is still a couple of months in the future.

Despite this improvisation I have had little trouble working many DXpeditions on 12, 17 and 30 meters. It is just a little more work than would otherwise be the case. I don't mind that. After all if I can reach DXCC on 17 and 30 meters with QRP and simple wire antennas my present situation is not so bad!

I briefly contemplated putting up my old multi-band inverted vee back up just so that I would have a resonant antenna on 17 and 30 meters. After considering how much trouble that would be I decided against it. While not ideal the use of the ATU with judicious selection of a non-resonant antenna is adequate to my needs for the next several months.

FTdx5000

The new rig is a delight to use. The receiver is top notch and I am exploring its features as I tune the bands through contest congestion, DX pile ups and QRN. I can narrow the DSP down to 50 Hz to copy the weakest signals and not experience any objectionable ringing. This has proved invaluable numerous times in contests, certainly improving my score with QSOs that would otherwise not make it into the log.

The noise blanker seems to create fewer artifacts than others I've used. The notch filter attenuates interference without unduly affecting fidelity of the desired signal. Split operation is smooth, and since it functions identically to that of other Yaesu rigs there was no learning curve. Dual receivers works just as it did in the FT1000 MP I previously owned. Except now I have far better filtering on the sub-receiver. I have yet to try SO2V operation in contests.

Since I have only 3 antennas at the moment the ability to connect 4 antennas to the rig makes band changes a breeze during contests. I do not need or use an external mechanical switch and I can defer a sophisticated system such as 2xN switches and band decoders until later. I connect a dummy load to the fourth antenna position.

The monitor scope (SM-5000) is, as many report, mostly a toy. It did come in handy once. During the ARRL DX CW contest openings on 10 meters were elusive. Since I operated unassisted I would briefly change bands, look at the band scope to take in activity across the entire CW segment at a glance. Any blobs present were tuned in and copied to see if it was something I wanted to work. If there were no blobs the bands was either dead or the signals were very weak. I could always check again later.

The extra 3 db from the 200 watt output is noticable and welcome. I am definitely no longer QRP! However I was disappointed to learn that the power can only be turned down to 10 watts. This is not a rig I can easily use to enter the QRP category in contests, which I likely will still do from time to time. Perhaps that'll be the time I return to using the KX3.

Of course the biggest problem with this rig is the weight. At 42 pounds (19 kg) it is difficult to carry and move. It isn't portable, and unlike many other rigs does not have a handle. For my purposes it is not really a problem. If you need portability in a high performance rig buy a K3S.

Troubles

Putting up a tower and antennas mid-winter is not without its difficulties. When I'm fighting with connections, bolts and heavy and unwieldy antennas while the north wind is blowing is not really a lot of fun. Shortcuts were taken. That has caused problems, some of which I've had to fix and others I have decided to let be until the spring. I'll run through these quickly.
  • My ancient rotator cable sprung a leak. Due to an injudicious placement of a splice when I routed the cables into the new house entry conduit a large snowfall followed by a thaw appears to have caused a conductance path between wires inside the splice. That is, water infiltration. That it happened during the ARRL DX CW contest added to the misery. I had to run into an adjacent room to see where the yagis pointed. At night I needed a flashlight. The next day it settled down. I redid the splice and moved it out of harm's way.
  • If that wasn't enough, a day after fixing the splice the rotator suddenly turned slowly or not at all. Within minutes it wouldn't turn at all. With DXpeditions on the band this was unwelcome news. With an ohmmeter I quickly discovered one of the motor winding wire showing over 2 kΩ resistance. I retested the splice, which was fine. So up the tower I went. Two trip later it was fixed. The connector off the wire tail from the rotator, while nicely sealed was not fully seated. I looked it over, twisted it closed and the rotator resumed full function.
  • My ancient Vista laptop kept crashing early in the ARRL DX CW contest. It is a known network hardware fault that rears up occasionally. Since I was operating unassisted I turned off the WiFi card and pulled the Ethernet cable, and it didn't crash again. This computer is on my priority list for replacement.
  • Intermittent power line noise has appeared, affecting the high bands only. The noise is impulse, slow or rapid depending on the weather, and can be silenced with a noise blanker on 6 and 10 meters but not on 15 and 20 where the impulses are poorly defined. After a heavy rain the noise vanished and has yet to return. I was able to pin down the direction which narrows my suspicion to two pole transformer and several other poles. I can do this since this rural area has few power lines. I'll be watching this one.
  • I purchased a large quantity of cylindrical ferrite RFI chokes to place on Ethernet cables between equipment and on the cable coming down from the terrestrial wireless internet access antenna. In some places it helps while in others it does little more than more the noise around as the resonance of the cable between chokes and terminations changes. There are other options I will explore.
  • I purchased a new headset to replace my old Heil headset on which the mic cable is intermittent. It's old and needed replacement anyway. The new one has an electret element which I had planned to build an interface to the rig, which only supports dynamic mics. But used as headphones they either need better adjustment or they simply won't work out. First, they are uncomfortable after several hours, and so are bad for contests. In the middle of the ARRL DX CW contest I tore them off and went back to the Heil. It was then I noticed the audio quality on the Heil headphones was better.
Looking ahead

There are few easily determined quantitative results that can validate my subjective observations. Propagation, activity levels (mine and others) and even mood can dominate objective measurements. I can only point to what I have to show, and in this case it is contests and DX chasing. The indications are good.

Spring is rapidly arriving and with it a new season of tower and antenna work. I have much planned for this year. As I plan and anticipate the list of project ahead I can also sit in the shack and work the world with a better station than I have had in a very long time.

After a busy fall and winter with the move, tower and antenna work, and house renovations I can finally sit down in the shack and profit from that hard effort.  And I am. Look for me on the bands.

Wednesday, February 22, 2017

Scaling a Yagi: NW3Z 20-15 Meters Interlaced Yagi

There are many excellent yagi designs in the amateur literature. With modern modelling and optimization software tools it is possible to design yagis that perform exactly to specified performance metrics. This was not always the case. In decades past yagi design was often hit or miss, relying on laborious trial and error measurements and adjustments in the field.

The difficulty of the task is due to the complex non-linear relationship of mutual coupling between close-spaced elements, defying efforts to finding analytical solutions. Numerical solutions only became effective in the 1980s with the evolution of computing technology and the concurrent evolution of algorithms and their software implementations.

My first exposure to the problem of yagi design and optimization was in the late 1980s. I and several other hams interested in building more competitive contest stations were unhappy with many of the commercial antennas we were using. Some with downright dreadful, relying more on myth and reputation than on measured performance. Yet the tools available to design something better were lacking. Then along came John Lawson W2PV and his excellent book Yagi Antenna Design (out of print), formalizing his analytical and experimental work on yagi design over many years.

With that book in hand I implemented several of his algorithms and designed realistic yagis for several of my friends. Aside from performance was the difficult problem of scaling the design to the mechanical specification of telescoped tube elements and the effects of clamps and boom. W2PV's algorithms provided an excellent analytical approach to solve those difficulties.

Stepped Diameter Correction (SDC)

There has been progress in the past 30 years. MiniNEC and then NEC2 engines arrived and were incorporated into many commercial and non-commercial antenna modelling applications. However neither engine correctly models tapered elements using telescoping tubes. NEC4 does handle it but it is an expensive solution for most hams. I have not seen fit to pay up for it.

It was long ago determined that NEC2 can be manipulated to give correct results for tapered elements. W2PV did it long ago (I don't know if he was the first) and then W6NL codified it for NEC2. EZNEC and others incorporate W6NL's SDC algorithms. They have been amply verified in the field so that we can confidently employ those algorithms and know that the results will closely match NEC4 and real antennas. The algorithms do have limitations on their application (e.g. loading coils). EZNEC 6, for one, has improvements in this area but I do not know how reliable those are.

Problem statement

Someone approached me with a request to model an optimized dual-band yagi for their custom tubing schedule and element-to-boom clamps. The antenna is a long boom, wide band interlaced yagi for 15 and 20 meters with 6 active elements on each band designed by NW3Z. The antenna is an intriguing one. It is in the class of OWA yagis that achieves excellent performance along with exceptional low SWR across both bands.

There were ample design challenges which you can read about in that document. In fact you must read the details of that antenna there since I will not repeat any of it. Otherwise the discussion that follows could be confusing in several important aspects. You can read some commentary about this type of antenna by Cebik. There is another discussion of the design principles starting on page 18-22 of this book extract.

The antenna has separate feeds for each band. Simultaneous operation on both bands absolutely requires very good high power filters. Otherwise you can use a remote switch to use one transmission line for both bands. No matching is needed for 50 Ω coax.

Certainly an antenna of this type would be best modelled with NEC4, and that is what NW3Z did. NEC2 with SDC can give accurate results although not without additional effort and some residual uncertainty. I use EZNEC+ version 5 (NEC2 engine) with the standard W6NL SDC algorithm. There were many challenges to overcome yet in the end the result matches the performance quoted by NW3Z.

This article is about how I did it. There is nothing here that is novel -- it's all been done before. The point is to guide readers along should they wish to do something similar. Being hams we are often likely to want to build yagis based on a proven design while using hardware that is locally available or cheaper than that specified in the design. Once you know how to scale the design to the chosen hardware you can proceed with construction confident that your actual performance will be a close match.

For me the interest was the interlacing of yagis. You cannot do this with tools such as YW, YO and some others, and is still quite challenging with a comprehensive modelling tool such as EZNEC. There was more to my initiative than doing someone a favour: I wanted to learn something about a subject I care about.

The antenna is already optimized

One important thing to state is that the NW3Z design is already thoroughly optimized. That is, it is optimized to its performance objectives. The antenna is not a maximum gain design, giving up around 0.5 db on 20 meters and perhaps 1.0 db on 15 meters. Its F/B is similar or better than mono-band designs of similar size. The SWR is exceptionally low by design, and is in part responsible for the lower gain. Despite giving up some gain it is a great antenna and will fare better than a multi-band antenna using traps or other element loading techniques.

Model view and currents when excited at 14.100 MHz
While an exceptionally low SWR -- well under 1.5 -- is not needed for most operators it is of great benefit to contesters. High power broadband amplifiers are not tolerant of even moderately high mismatches. For the competitive contester who must quickly and repeatedly change frequency and band during a contest the time avoided adjusting an amplifier's output network can give an operator a winning edge.

Other operators, even competitive DXers, can get by without this feature. For them a slightly higher SWR at the band edge (say, 2 to 2.5, or even 3) should be an acceptable trade off for an additional decibel of gain. If that's you there are other designs from which you can choose. Do not try to "optimize" this antenna since you are almost certain to make it worse. Small departures from the published dimensions will do just that. I experienced this when the ham asking me to do the model made a small calculation error on one of those 12 elements.

In accord with these points I am accepting the NW3Z antenna as is; I am scaling the antenna, not optimizing it or changing it into an antenna with different performance metrics.

What needs to be scaled

In this article I will not publish dimensions of the scaled antenna. That would be pointless since every ham is likely to use their own set of materials, in each case producing unique scaling results. It's the scaling procedure that is at issue here. If you want this antenna and do not want to bother with scaling you are best advised to adhere to the exact dimensions provided by NW3Z.
  • The tubing sections must decrease in diameter toward the element ends, the element halves must be identical and no loading elements. This is easy to achieve in a mono-band yagi, and EZNEC will warn you when you make a mistake. Clamps at the tube boundaries can be ignored at HF.
  • Element-to-boom clamps must be converted to an equivalent diameter which is then specified in the model. 
  • Depending on the clamp style the effect of the boom may need to be included. For example, in Hy-gain yagis where the element effectively pierces the boom. In homemade yagis with the more typical rectangular plates and u-bolts (with or without a saddle) the boom effect can be ignored.
Effective diameter of plate style element-to-boom clamps

The yagi I modelled uses plate style element-to-boom clamps. W2PV in his book presents equations for this style of clamp and for those where the element pierces the boom. I will only cover the first. However the boom effect for the latter style is small, being the equivalent of electrically shortening the element by about 10% the boom diameter.

I am using W2PV's equations despite more accurate models that are more recent. For example, there is the improved model promoted by W6NL. Unfortunately I don't his book Physical Design of Yagi Antennas (out of print) where this is discussed. The difference from what I can tell from my limited ability to compare results is within ±2% for HF size material, which is not significant. Note that the error is in the effective diameter of the clamp, not the element length.

There is lots of software around that will calculate the effective diameter of several common element-to-boom clamps if you insist on that degree of accuracy. One I feel confident recommending even though I don't own a copy (or at least not yet) is AutoEZ by AC6LA, which does this for you and much more when used in combination with EZNEC.
Example clamp here

However the W6NL and related models don't appear to model clamps where a u-bolt saddle is placed between the tube and plate, or at least not that I know of. W2PV's equation does, and that factor is not insignificant. So I put his model into a spreadsheet and used it in this antenna design, with the resulting effective diameter placed into the taper schedule in EZNEC.

The screen capture of the spreadsheet with my implementation of the W2PV equation for a tube over plate style clamp includes the specs of the antenna I am scaling. Although in this case the units are centimeters any units can be used provided it is used consistently throughout. The cell with the W2PV equation is shown so that you can replicate it.


The saddle height is equal to the distance between the tube and plate. The height is zero when there is no saddle. The calculated values are: a1, radius of the tube; S1, circumference of the tube; a2, effective radius of the plate (width / 4); S2, perimeter of the plate cross-section; d, centre-to-centre distance between tube and plate. The effective diameter is twice the calculated effective radius. This is the number to use in the EZNEC wires table. The wire length is simply the length of the plate.

In all case the effective diameter should be intermediate between the tube diameter and plate width. If it isn't you've made a mistake.

The effective diameter calculation does not work for elements clamps that electrically isolate the element. This is common in driven elements in many antenna, including the NW3Z design. Although the calculated effective diameter, or no correction at all, will be in error it is not of serious consequence. The reason is that tuning of the driven element(s) in a yagi does not affect gain and F/B performance. Once constructed the driven elements can be adjusted, if needed, to get the desired match. By using the actual tube diameter rather than the effective diameter the required adjustment should be less.

Segmentation and tubing schedule

Nearly end-on view showing the segment and tube alignment
For yagis with such close spaced element, even though resonant on different bands, the segments must be equal length and ends aligned with respect to the boom (line orthogonal to the elements) for best accuracy using NEC2. You can play with this in a model and you'll quickly see why.

I used a segment length of 10 cm (4"). This adds up to over 1,000 segments in the model and so can be quite slow to calculate on older computers. The length works well for 20 and 15 meters and being a round number it is relatively easy to align tube junctions, which is also desirable for model accuracy. Luckily the builder provided a detailed tube schedule with all this taken care of. I believe his intent was cost and convenience, yet it also helped make for a good model.

The element-to-boom clamps must also follow the plan since it is in effect the centre tube. Happily the clamps in this instance are 20 cm long -- two segments. However I used one 20 cm segment for the driven elements in order to avoid using a split source, which in my experience can introduce errors.

To build the model I worked up the wires for one element on each band and copied it until I had a full complement of elements, moving each into position. Then it is a matter of adjusting the tip lengths on the elements to match the spec. It is necessary to be inspect the segment length of the tip so that each is as close as possible to, in my model, 10 cm. The work is bothersome yet necessary, and must be repeated several times during the scaling procedure.

Even with the extensive segmentation work there was still a residual error in the model. This shows up using the average gain test that W7EL describes in the EZNEC manual. Since all other potential error sources were covered to the best of my knowledge the solution is to adjust the gain figures by the average gain. That is, if the average gain is -0.32 db you subtract this value from the calculated gain. For example if the calculated gain in a particular direction is 3.79 dbi the true gain should be 4.11 dbi.

Making this adjustment brought my model's gain almost precisely equal to what NW3Z got with NEC4. That's a good indication that my model is correct. Unfortunately the average gain adjustment is a function of frequency so the true gain must be uniquely adjusted at several points on each band. The F/B does not require this adjustment, so you can read F/B directly from the pattern plot. The reason should be clear when you realize the average gain error affects every point on the far field plot.

Scaling the element lengths

In the discussion of segmentation I said that it is only the element tip lengths that are adjusted during the scaling procedure. I took the element length spec from the ham I did this for and simply ran the model once I had everything else taken care of. I compared the SWR, gain and F/B curves with those published by NW3Z to see by how much the antenna's frequency range.

However it wasn't quite that easy. I eventually discovered why on one band the performance was unexpectedly poor: the length of one element was miscalculated. I adjust this to conform with NW3Z's spec and the expected performance immediately emerged. Just at the wrong frequency range.

When scaling a yagi all lengths are geometrically adjusted, not arithmetically. This means all elements for one band are multiplied by a constant. The constant is determined by the ratio of the calculated frequency to the desired frequency. Never adjust elements by adding or subtracting. The geometrical adjustment ensures that the resonant frequency ratios of any two elements is unaffected by scaling. That relationship must be preserved to maintain the performance metrics.

It can be argued that even this scaling factor includes an inaccuracy since we are only scaling the tips of the elements and not each tube in the schedule. This is a quibble since the introduced error is very small for the degree of scaling we are doing, which is only 1% to 2%. The error can be very significant should you attempt to scale the antenna to a different HF band.

Now we can proceed. Assume, for example, the calculated frequency of maximum F/B is 14.250 MHz. Yet it ought to be 14.100 MHz. To pull the yagi's frequency range down by 150 kHz all six 20 meter elements must be lengthened. The scaling constant is 14250 / 14100 = 1.01064. You can round this off to 1.01. After every scaling operation remember to adjust the segment count of the tip sections to keep it close to the selected value, and then confirm that the gain, F/B and SWR are where they should be. If not, repeat.

It is important that in a multi-band antenna like this that you first scale the elements for the lowest frequency band (the longest elements) and then do each next higher band until you're done. Do it the other way and the higher band will be incorrect after scaling the lower one. In this antenna that means you first scale the 20 meter elements. Even so, check 20 meters again after scaling the 15 meter elements since there is a possibility that another adjustment is necessary. If it is you will of course also have to redo the 15 meter elements.

SDC works on only one band at a time

The W6NL SDC algorithm only works within 15% of the resonant frequency. EZNEC will perform SDC on the 20 meter elements or the 15 meters elements, but not both at the same time. Resonant frequency is the frequency you select in the main EZNEC window. Check in the wires window that SDC is being applied as it should.

To measure the antenna you must set that frequency for the band you are calculating. This is in addition to moving the source to the corresponding driven element. It's a bother but you must set the frequency for the correct band when you do an SWR plot since SDC is not selected per the frequency range of the plot. Otherwise some error will be introduced into the impedance calculations.

The failure to perform SDC on both bands simultaneously affects the higher band of a two band antenna more than the lower band. Therefore the 20 meter results are very reliable while there may be some error on 15 meters. As far as I can tell for an antenna of this type the error ought to be very small, and so I ignored this limitation of the SDC algorithm. That isn't always advisable since every antenna is a unique case.

If you have NEC4...

SDC corrections are not needed in NEC4. That eliminates many of the modelling precautions I've described above. But not all. You must still calculate the effective diameter of the mast clamp and, if a concern, adjust for the boom.

NEC4 is not perfect, nothing is. Its usable domain is greater than NEC2, which is very helpful provided you keep in mind its limitations and constraints. For straightforward mono-band yagis it is certainly easier than NEC2 with the supplementary extensions in EZNEC and some other software tools.

Should you happen to have a friend with a NEC4 license by all means ask them run the model for you. It is a good way to see how well you've scaled the antenna and the accuracy of NEC2 plus SDC and other modelling precautions.

Comparing results

NW3Z modelled his antennas using NEC4. How close can we come to his results using EZNEC? Very close indeed as it turns out. It is so close that I was hard pressed to find any differences after completing the scaled model and tuning it so that the frequency ranges matched the curves in his document.

Here are a couple of examples. The first is an azimuth plot at the 20 meter frequency where F/B is greatest. Due to the average gain issue described earlier it is necessary to subtract -0.31 db from the gain in this particular plot. This brings the actual gain to 10.3 dbi. The F/B is correct as is.


The second example is the SWR curve across 15 meters. The impedances are a good match. This is telling since even small deviations from equal segmentation and total element length and position can cause significant miscalculation of impedance by NEC2.

For an antenna of this type I would aim to have the measurement correct to less than 1 cm (½"), which works out to 0.1% on 20 meters and 0.13% on 15 meters. In many cases that may be more accuracy than needed since the presence of cables, guy wires and other antennas even some distance away will introduce errors of at least this amount.

Beyond this modelling you can only build the antenna and do a field strength test to measure the performance. Since few hams will undertake that amount of work it is important that the scaling be done correctly and that the antenna is built as exactly as possible. However there is the alternative of finding the frequency of maximum F/B with the assistance of a friend within ground range. Don't try this with stations via ionospheric propagation since signal strengths change faster than you can rotate the antenna.

Conclusion

For my primary interest of HF contesting this type of antenna is a poor choice. Using one effectively would require a tri-plexer, just as one would use with a tri-bander shared among two or more operating positions. I prefer to aim for more separation and directional diversity which requires independent mono-banders.

Where it does enter my plans is for the WARC bands: 12, 17 and 30 meters. These bands are not used for contests but fit well into my DXing activity, either for country chasing or casual operation at any time. I will use my experience with scaling the NW3Z to play with some configurations that provide up to 3 elements on 30 and 17 meters on a single boom.

The importance of this is that I can get good performance on these bands while occupying the minimum amount of tower space, space that is a priority for the HF bands used for contests. Maybe not this year, yet I will have to do something eventually.