Those who operated CQ WPX SSB this weekend don't need to hear that conditions were not great, 20 meters was an impenetrable wall of QRM and every other QSO inflicted pain. WPX is commonly understood to be a runners delight where big power and antennas rule and everyone else scrounges for scraps. It really doesn't matter who you work so point the antennas where propagation is best and work what you can.
So rather than dwell on all of that I decided to do something different for this article. Phone contests bring out our personalities in ways that are not seen with other modes. Talking is the most natural thing for humans and phone contests provide a grand stage for the display of emotion, camaraderie, and human idiosyncrasies. Perhaps more than other modes it shows us at our best and our worst.
No contest is so busy that we can't indulge in a little people watching. Therefore with a wink of the eye let's delve into the humour of ham culture, contesting and the clash between contesters and everyone else. To protect the innocent and the guilty I will obscure identifying information.
We've worked before
I continue to be amazed at how many contesters are adamantly opposed to logging duplicate contacts. I heard several instances this weekend of the running station telling the caller that they've worked before, the caller insisting that they aren't in their log, and the runner still refuses to work them again.
This is foolhardy for the runner since it almost guarantees a NIL (not in log) penalty and wastes time arguing instead of conceding the insurance contact and moving on. I cannot imagine what these people are thinking. How can they not understand how this hurts their results?
When I informed one big gun that we've worked before and he said I wasn't in his log I made a didn't hesitate to make another contact. The dupes don't incur penalties and is the fastest way to dispose of the issue. If I truly wasn't in their log the dupe avoid a NIL penalty. On CW where the interruption cost more time I make the duplicate contact without raising the issue.
Schoolmarm
Speaking of incomprehensible behaviour, I heard one operator brusquely and repeatedly critique callers who did not use the minimum number of words to identify or complete the exchange. For example, "please copy" seemed to especially infuriate him and he'd make rude comments about their use of these superfluous words. I listened to a few minutes of this for my own amusement when my QSO rate was dreadful and I had time on my hands.
Of course "please copy" is unnecessary, but it is used by many casual operators since it seems a polite way to ask the other person to prepare to log what they're about to send. It's very natural and I hear it a lot during phone contests. Rather than complain I am thankful for the casual contesters and non-contesters who call me and add points to my log.
The last thing I want to do is scare them away. We need to encourage the casual operators for contesting to remain healthy. Even if they never develop a serious interest in contests these hams are eager to help us out and we should do all we can to help them along, including explaining the exchange and encouraging them to go forth and work others as well.
Schoolmarmish behaviour can scare them off and, worse, turning them against contests and contesters. What are these curmudgeons thinking?
Ocho
With increasing contest activity from South America I have gradually become aware that exchanging information with many of these operators on phone can be difficult. Many do not speak English and have only a thin veneer of ham English. Some English numerals are difficult for them. Eight seems to be the worst: I say 'eight' and they typically hear 'two', 'four' or 'six'.
I don't have this problem
with Spanish stations (EA) so it may be due to the different accents in South American countries. It
is perhaps comparable to the diversity of accents across English speaking
countries, and French between Quebec and France. Decades later I still remember how the Chinese exchange students in my university classes had good comprehension of English except in one class taught by an Australian.
On Sunday as I approached 800 QSOs in my log and 15 meters was opening to South America I decided to do something about it. My inspiration was the Americans speaking Spanish to overcome the difficulty, a country where Spanish is close to becoming their second language.
I already knew to use 'ocho' for 8, but mixing this with English numerals was caused confusion. I typed 'count in Spanish' into my browser's search box and studied the list of numerals from 0 to 9. This took all of two minutes.
With some trepidation I tried out my new knowledge on the unsuspecting South Americans (but not Brazilians, for the obvious reason). To my surprise it went very well. Some were surprised by my use of Spanish for the serial number and there were nearly zero requests for repeats. No one sounded offended by what must be my atrocious pronunciation.
Because of the prevalent use of English on phone by hams across the world native English speakers often fail to appreciate the effort that others are taking to communicate with us. Learning a few words in the other ham's language isn't difficult and can make a good impression. It also increases QSO rate which any contester ought to appreciate.
The non-contesters in our midst
Tune the bands any day of the week and there is a lot of activity by many hams around the world. Those people don't vanish during major contests. Some will switch modes, others will stay off the air and a few will casually partake in the contest. Many others will continue to do what they do. Conflict is inevitable, and that conflict can bring out the worst and sometimes the best in us, contesters and non-contesters alike.
Twice when I found a clear frequency and got no response to "is this frequency in use?" and proceeded to call CQ I was soon interrupted by callers requesting that I move. In one case I was on a (normally quiet) net frequency and in the other I was near but not quite on top of an active net. Both times the callers identified and briefly explained the difficulty, with some evident exasperation since I'm sure this happens a lot during a major contest.
Without hesitation I agreed to move. They sounded surprised and thanked me for my consideration. Unfortunately there are contesters that I know who balk at the request. While no frequency is sacrosanct it is possible for contesters to exist alongside non-contest activity. I was in part motivated by their politeness and that they identified themselves. It behooves us as contesters to be considerate despite being in the vast majority during major contest. Flexing our muscle -- sheer numbers and size of towers, antennas and amplifiers -- can be tempting. Avoid the temptation.
Sometimes it does not go well. Once when I was about to call a DX station on one of the low bands someone who was in a ragchew nearby began shouting insults at anyone and everyone calling the DX station. He did not identify. The DX station obviously couldn't hear this person. Out of curiosity I checked and found that the separation between the contesters and the other QSO was just shy of 3 kHz. I suspect this behaviour was more one of animosity than QRM. The callers kept calling regardless and the hurler of insults accomplished little more than raise his own blood pressure.
There is also the conflict that doesn't happen. It is interesting to come across an ordinary QSO among the massive QRM that was 20 meters phone in this contest. The QRM raged at the edges of the pass band while the QSO went unmolested. Most people are good and respectful of others, so it is no surprise that these non-events occur. It is far too easy to focus on the conflicts that do occur. There is something within many of us that wants to reach out and latch onto every perceived injustice just so that we have an excuse to be angry and complain. That is another temptation to avoid. Some are unable to do so.
Then there are the DQRMers. It happened to me a few times this weekend and I heard it many times on other contesters. It is best to ignore it and carry on. Frankly it has little effect during a major contest when the prevailing QRM is worse than the deliberate kind. I just kept working stations and in a minute the interference disappeared. DQRMers are a small minority and can have no effect on the countless thousands active in a major contest. I feel no anger, only pity for these benighted individuals.
How's my signal?
Among all the splatter, over-compression and poorly injected digital voice messages you hear there are the many with good and even great signals. Adjusting for the operator, microphone, digitally composed and stored messages, compression and amplifier drive level in a contest environment is not rocket science but it takes time and attention to detail. The truly great sounding signals are not accidental. Someone took the time to get it right.
When it is done right the talk power is high, the intelligibility is great and the signal fits within its spectral limits. The ones who get it wrong -- whether it is by error, laziness or in an effort to be loud at any price -- hurt their rate and results due to requests for repeats of unintelligible call signs and exchanges.
A few stations this weekend after completing the contest exchange asked me for an honest report of their signal strength, audio quality and whether their frequency is reasonably clear of QRM at my end. One operator of a well-known, high-scoring multi-multi station in particular comes to mind.
After telling him that his audio was perfectly intelligible though perhaps a little over-compressed with audible popping sounds he told me he was concerned because he was being asked for repeats more than was normal. He requested that I stay with him for a few moments while he adjusted the rig. After doing so the popping was gone and the audio quality was obviously improved without noticably reducing talk power. He was clearly pleased and thanked me for my help as we went our separate ways.
While we tend to remember the bad actors more than the good when it comes to signal quality we should appreciate those who make the effort to put high-quality signals on the bands we all share. The best contesters know that their results and their reputations depend on it. I appreciate the opportunity to help others improve their signals.
Who are you?
CQ WPX is a contest where many of your friends wear a disguise. That disguise is a special call sign of some sort. A few times this weekend I was greeted with "Hi, Ron!" by someone sporting a call I didn't recognize. My response would be friendly but necessarily vague since I didn't know who I was talking to.
One old friend did identify himself and another I figured out after the contest. As for the rest, I still don't know who they were. Perhaps they enjoy confusing their friends or have forgotten in the heat of the contest that they're wearing a disguise. Do they wonder why those they greet seem a little cool in their responses?
My audience
The readers of this blog are not terribly numerous but there are substantially more than a few. Mostly I know about this by the emails I receive and web statistics. Phone contests are another opportunity for me to learn who you are.
Twice this weekend the ham at the other end of the QSO told me that they read my blog and that they actually enjoy it. Although I don't aim for a huge audience it's nice to know there are indeed real people following the blog where I tell my story and pass along my experiences in the hobby. Thank you for taking the time to let me know who you are!
Race to the finish
The start of a major contest can be daunting. Ahead of you is 48 hours of hard work, risk of the unknown, angst, regrets, hastily eaten food and disrupted sleep cycles. It's hard on our bodies and our minds.
As the finish line approaches on Sunday there is anticipation of the coming release from the effort and an urgency to squeeze in a few last contacts and multipliers. There is a palpable adrenaline rush.
I closed the contest by running on 80 meters to top up the log with nearby American stations and perhaps a little DX. My rate was steady but not fast. Then in the final 10 minutes my rate shot upward. I could hear the enthusiasm and urgency in callers' voices as they strove to pack in as many contacts as possible before the bell rang.
It was brief but exhilarating. A few last Europeans also made it into my log. Then it was over. The mountain range on the band scope instantly turned into an featureless prairie as transmitters around the world went silent at the same moment. I got up to stretch with a grin on my face. I almost regretted not putting more effort into the contest.
Wrapping up
Early reports look good for me in this contest, which is quite a surprise since I made no attempt to turn in a competitive entry. When the going got too slow I stepped away the radio, had regular mealtimes and got a full night's rest. Conditions were not great and even with a big tower the QRM was too much for 100 watts to be heard well. That made this weekend an opportune time for people watching.
If anyone reading this sees themselves reflected in an unflattering light, I apologize. No offense is intended. Occasional bouts of humourous self reflection is beneficial to our continued sanity. I make enough mistakes on my own even when I try to get it right. We're all human. It's cathartic to laugh at ourselves from time to time and, respectfully, others as well.
Tuesday, March 27, 2018
Thursday, March 22, 2018
SWR and the Contester
An antenna with a low SWR is good; we all know that. What is not always understood is why a low SWR is good. I would hope that by 2018 most hams would no longer suffer from the lore of myths of long ago and have a technically accurate understanding of SWR. Even so there are bound to be gaps in our knowledge and a refresh can be helpful.
The headline benefits can be summarized as follows:
How low is low?
HF transmitters and amplifiers are most happy when the SWR is no more than 1.5. However this is a broad generalization. The importance of low SWR tends to be proportional to power. The culprit, as we'll see, is heat. When I contested with my KX3 at 5 watts I never worried about SWR; the KX3 rarely balked at an SWR as high as 3 or even 4. I didn't bother purchasing the ATU option.
Most 100 watt transmitters will not roll back the power until the SWR is 2.With the FTdx5000 at 200 watts it appears to reduce output when the SWR exceeds 1.5. This seems to be a sensible choice. Rare is the broadband kilowatt amplifier that will not turn down the power when the SWR is 1.5, and may go so far as to shut down until the problem is resolved. You don't want that happening in a contest.
Even if your equipment will comfortably handle higher SWR, with or without a tuner, there are still benefits to be had. High SWR affects more than just the transmitter.
SWR and impedance
I have always found that talking about reflections, reflected power and return loss not terribly effective when it comes to gaining a basic understanding of RF networks. For me it is far easier to approach the problem as about impedance: Z = R + jX.
Now we assume a generator that is optimized to transfer power to a load of 50 Ω, with an optional network in between. The network can be as simple as a transmission line with a characteristic impedance of 50 Ω. If we further assume the transmission line is lossless it essentially disappears. In fact for the purpose of this discussion I'll assume that we have a transmission line of this type. At HF with large diameter hard line, such as the Andrew Heliax I use, this is pretty close to reality.
For a load impedance that is not 50 + j0 Ω there is a mismatch. That is, power is reflected back toward the generator where, in our steady state case, appears as a complex impedance as determined by the transmission line length. This is easiest to see with a Smith chart.
At the centre is an SWR of 1, relative to a selected resistance, which although it can be any value we'll stick with 50 Ω. SWR circles (constant radius) are shown. For an SWR of 1.5 you can see that R ranges between 33.3 Ω and 75 Ω, and varies between -20 Ω and +20 Ω. At higher SWR the range of both increases. There is an infinity of points (R, X) for any given SWR.
Once you know the load impedance (and therefore SWR) you walk around the Smith chart to find the impedance at the generator end of the transmission line, with each completed circle representing ½λ of electrical length. Thus you can estimate the impedance seen by the transmitter.
Why broadband transmitters demand low SWR
An RF active circuit is a finicky creature. Departures from the designed load impedance (output port) change the behaviour of the circuit. Its efficiency will decline and it may have reduced linearity resulting in additional distortion products. Misbehaviour can increase for maximum excursions of R and X for a constant SWR. In years past it was not unusual for hams to change the transmission line length (values of R and X) to tame transmitter difficulties when faced with a high SWR.
If the load is 50 Ω all is well. The generator (our transmitter or amplifier) is happy, transmission line loss is as low as it can be and the load (antenna) accepts all the power. In real life it is never that simple.
Consider transmitter efficiency. Assume that our 1,000 watt transmitter operating in AB class has an efficiency of 60%, therefore generating 670 watts of heat. This heat which is produced in the active devices (tubes or transistors) and other elements of the circuit must be removed to prevent component destruction. This should come as no revelation to anyone who is not new to the hobby.
The challenge grows as the impedance at the output port moves from the optimum value. This is primarily seen as a reduction in its efficiency, meaning more heat produced for a constant output power, which is how most of our equipment is designed to perform. For example, if efficiency drops to 50% the heat produced rises to 1,000 watts, or 330 watts more than in the optimum case. In addition, high SWR (large R and X variation) can place high current or voltage at critical locations that can lead to component failure.
You can see how fragile our high power equipment can become when faced with a mismatch. Equipment size and cost (active devices, transformers, coils, etc.) can be increased to handle more heat, current and voltage, or we can lower the SWR threshold at which power is rolled back. Although efficiency depends on the specific values or R and X it is easier and more reliable to measure and trigger on SWR.
With that overview I have covered enough about mismatch behaviour to continue onward without exhausting my limited knowledge of the subject. I will leave the gory details to the engineering literature where you can indulge yourself if you want to learn more.
Agility
Any contester will know that operating agility is a competitive edge. When all antennas have low, flat SWR you can achieve the following:
The rest of us can pick our spots to improve our agility since we cannot do it all. There exist inexpensive shortcuts such as sticking labels on manually tuned amplifiers to mark the settings for each band, band segment and antenna. For my own station plan I have a lot to think about.
There are a variety of other benefits to contesters of low SWR antennas. I believe the time spent delving into SWR will show its value in the following sections.
Transmission line loss
I'll keep this brief since every ham ought to know that a mismatch increases transmission line loss. For contesters with long runs to reach antennas on high towers the impact can be worse. When the SWR is kept low the design loss objective can be met with less expensive transmission line.
Use software such as TLW (comes with the ARRL Antenna Book) and online calculators to quantify the loss of transmission line alternatives and the impact of SWR. On the higher HF bands and at VHF and UHF the results can be enlightening.
Power division for stacking
Equal power division for effective stacking can only be accomplished when the impedances of the antennas is equal. A power divider, whether done transformer or phasing lines, is essentially just loads connected in parallel, and we know from Ohm's Law that the power in each load element depends on the impedance of each.
The most common solution is to use identical antennas in the stack. It is certainly possible to use dissimilar yagis if the impedances are near equal, in both R and X components. This is typically only practical when the SWR is low for all the antennas. An alternative is to insert a network at the feed point of at least one antenna that is carefully designed to match the impedance curves of the other(s).
Failure to closely match antenna impedances will send most of the power to one antenna, undercutting the objective of stacking and may present a high SWR to the transmitter. When a transformer is used as a power divider the mismatch due to a poor SWR on one or more antennas in the stack can alter the transformation ratio and increase heating in the ferrite core on which the transformer is wound. When running high power that heat can permanently damage the ferrite core.
Filters and stubs
The band pass filters used by many contesters protect receivers and reception quality by removing harmonics and other out-of-band emissions from a second transmitter, whether SO2R or multi-op. Most often they are placed between transceiver and amplifier. Sometimes (and more expensively) they are placed between the amplifier and antenna. In the former case stubs may be used to notch harmonics since they are a low cost alternative to high power band pass filters. Triplexers for sharing tri-band yagis utilize both band pass and band stop filters.
A filter is a network element like any other; look at the picture up above and imagine that the filter is the network between generator and load. Some manufacturers provide excellent technical resources on how their filters work and should be used. Here's a quick quiz: where does the out of band energy go?
Even if you don't know the answer there are just a few possibilities: dissipated as heat; grounded; or reflected. In the latter case this would be a high SWR outside the pass band, while in the former cases the impedance would have to be near 50 + j0 Ω, which is that of a pure resistance. It should be self evident that within the pass band the impedance would also be near 50 + j0 Ω. As you can see, impedance is a useful way to think about filters. Provided that harmonic energy is a small percentage of the total transmitter power (as it should be!) how that energy is handled by the filter will not noticably affect the transmitter.
Be aware that the source and load are integral components of the filter design. The filter only does what you expect if these are close is those impedances are close to 50 + j0 as well. Depending on the filter design a high SWR at the antenna port can degrade filter performance both within and outside the pass band. If you want your filter to work at its best antennas with low SWR are desirable. A few decibels can be enough to cause grief on other bands.
Performance of transmission line stubs to reject (reflect) the harmonic energy they are tuned for is sensitive to placement on the transmission line. Although the SWR may be low at the fundamental that is typically not the case for the harmonics. For best performance a predictable impedance is required and that will depend on the generator, load and stub placement. Since K9YC covers this topic so well I'll point you there for the details.
Common mode chokes
Preventing antenna currents on the outer surface of transmission lines protects the pattern of directive arrays, ensure power goes where it is most effective and reduce noise on reception. Common mode chokes at all antenna feed points are needed. Chokes typically take the form of 1:1 current baluns or coiling the coax on a ferrite or air form.
In the case of a 1:1 balun there is less core heating when the SWR is low; as with stacking power dividers (see above) efficiency suffers for high SWR and reactive loads. Coax coils wound on ferrite toroids are less susceptible to high SWR. Air core coax coils are sensitive to frequency and therefore less effective, which is a shame since they can handle higher power even when the SWR is high.
Relays
The typical contest station has dozens of relays to manage antenna switching and sharing among operator positions. If an antenna has a high SWR the current or voltage at the electrical distance of a relay from the antenna dictates whether the relay contact see abnormally high voltage or current. These can affect relay reliability and lifetime by arcing or heating when using high power.
Although relays with wider contact spacing and current capacity can reduce the impact they are often not used in commercial antenna switches. You can build your own switches if you insist on operating with high SWR antennas. Keep in mind these relays are larger, a little more expensive, and the coils require 100 ma or more at 12 VDC versus ~40 ma for the ones typically found in these products.
Conclusions and suggestions
Non-contesters can get by using antennas with high SWR over parts of the band, for the most part not suffering from many of the problems discussed. Contesters should reconsider if they have not dealt with these issues. It is something that I am striving for in my antenna farm, although at this time I have progressed very far.
All my yagis are either tri-banders or have loaded elements, which results in high Q behaviour and therefore higher than desirable SWR over significant parts of every band. My wire antennas for 80 and 160 meters fare a little better. Since these antennas are temporary, power is limited to 200 watts and I don't yet do SO2R or multi-op I am able to get by without too much trouble. For the antenna with the highest SWR on a band I train the rig's ATU for it and then have to remember to switch the ATU in and out depending on the antenna in use. Of course I sometimes forget.
I propose the following suggestions for the contester with a growing antenna farm to achieve the lowest possible SWR:
The headline benefits can be summarized as follows:
- Minimize transmission line loss
- Transmitter (and amplifier) linearity and efficiency
- Reduce risk of equipment and component failure and, where protection circuitry is present, ensure full power output from transmitters and amplifiers
How low is low?
HF transmitters and amplifiers are most happy when the SWR is no more than 1.5. However this is a broad generalization. The importance of low SWR tends to be proportional to power. The culprit, as we'll see, is heat. When I contested with my KX3 at 5 watts I never worried about SWR; the KX3 rarely balked at an SWR as high as 3 or even 4. I didn't bother purchasing the ATU option.
Most 100 watt transmitters will not roll back the power until the SWR is 2.With the FTdx5000 at 200 watts it appears to reduce output when the SWR exceeds 1.5. This seems to be a sensible choice. Rare is the broadband kilowatt amplifier that will not turn down the power when the SWR is 1.5, and may go so far as to shut down until the problem is resolved. You don't want that happening in a contest.
Even if your equipment will comfortably handle higher SWR, with or without a tuner, there are still benefits to be had. High SWR affects more than just the transmitter.
SWR and impedance
I have always found that talking about reflections, reflected power and return loss not terribly effective when it comes to gaining a basic understanding of RF networks. For me it is far easier to approach the problem as about impedance: Z = R + jX.
Now we assume a generator that is optimized to transfer power to a load of 50 Ω, with an optional network in between. The network can be as simple as a transmission line with a characteristic impedance of 50 Ω. If we further assume the transmission line is lossless it essentially disappears. In fact for the purpose of this discussion I'll assume that we have a transmission line of this type. At HF with large diameter hard line, such as the Andrew Heliax I use, this is pretty close to reality.
For a load impedance that is not 50 + j0 Ω there is a mismatch. That is, power is reflected back toward the generator where, in our steady state case, appears as a complex impedance as determined by the transmission line length. This is easiest to see with a Smith chart.
 |
| Smith Chart with circles drawn for SWR 1.5, 2 and 3 (original figure from Wikipedia, by Wdwd) |
Once you know the load impedance (and therefore SWR) you walk around the Smith chart to find the impedance at the generator end of the transmission line, with each completed circle representing ½λ of electrical length. Thus you can estimate the impedance seen by the transmitter.
Why broadband transmitters demand low SWR
An RF active circuit is a finicky creature. Departures from the designed load impedance (output port) change the behaviour of the circuit. Its efficiency will decline and it may have reduced linearity resulting in additional distortion products. Misbehaviour can increase for maximum excursions of R and X for a constant SWR. In years past it was not unusual for hams to change the transmission line length (values of R and X) to tame transmitter difficulties when faced with a high SWR.
If the load is 50 Ω all is well. The generator (our transmitter or amplifier) is happy, transmission line loss is as low as it can be and the load (antenna) accepts all the power. In real life it is never that simple.
Consider transmitter efficiency. Assume that our 1,000 watt transmitter operating in AB class has an efficiency of 60%, therefore generating 670 watts of heat. This heat which is produced in the active devices (tubes or transistors) and other elements of the circuit must be removed to prevent component destruction. This should come as no revelation to anyone who is not new to the hobby.
The challenge grows as the impedance at the output port moves from the optimum value. This is primarily seen as a reduction in its efficiency, meaning more heat produced for a constant output power, which is how most of our equipment is designed to perform. For example, if efficiency drops to 50% the heat produced rises to 1,000 watts, or 330 watts more than in the optimum case. In addition, high SWR (large R and X variation) can place high current or voltage at critical locations that can lead to component failure.
You can see how fragile our high power equipment can become when faced with a mismatch. Equipment size and cost (active devices, transformers, coils, etc.) can be increased to handle more heat, current and voltage, or we can lower the SWR threshold at which power is rolled back. Although efficiency depends on the specific values or R and X it is easier and more reliable to measure and trigger on SWR.
With that overview I have covered enough about mismatch behaviour to continue onward without exhausting my limited knowledge of the subject. I will leave the gory details to the engineering literature where you can indulge yourself if you want to learn more.
Agility
Any contester will know that operating agility is a competitive edge. When all antennas have low, flat SWR you can achieve the following:
- Switch among antennas on a band without the need to adjust amplifiers or tuners
- With a broadband amplifier, switch bands without the need to adjust amplifiers or tuners
- No time wasted during band and antenna changes, and therefore more potential QSOs
- Quickly move multipliers to another band without losing your run frequency or losing the multiplier due to your delay in setting up on the other band
- Avoid mistakes that weaken your signal during band and antenna changes, either due to inadvertent high SWR, tuning error or amplifier dropping offline
- Broadband amplifiers with automatic band switching, or at least automated tuners that react to frequency changes
- OWA yagis, even at the expense of serious mechanical challenges on 40 meters
- 4-squares on 80 and 160 meters, which excel at broadband SWR and performance in comparison to alternatives
The rest of us can pick our spots to improve our agility since we cannot do it all. There exist inexpensive shortcuts such as sticking labels on manually tuned amplifiers to mark the settings for each band, band segment and antenna. For my own station plan I have a lot to think about.
There are a variety of other benefits to contesters of low SWR antennas. I believe the time spent delving into SWR will show its value in the following sections.
Transmission line loss
I'll keep this brief since every ham ought to know that a mismatch increases transmission line loss. For contesters with long runs to reach antennas on high towers the impact can be worse. When the SWR is kept low the design loss objective can be met with less expensive transmission line.
Use software such as TLW (comes with the ARRL Antenna Book) and online calculators to quantify the loss of transmission line alternatives and the impact of SWR. On the higher HF bands and at VHF and UHF the results can be enlightening.
Power division for stacking
Equal power division for effective stacking can only be accomplished when the impedances of the antennas is equal. A power divider, whether done transformer or phasing lines, is essentially just loads connected in parallel, and we know from Ohm's Law that the power in each load element depends on the impedance of each.
The most common solution is to use identical antennas in the stack. It is certainly possible to use dissimilar yagis if the impedances are near equal, in both R and X components. This is typically only practical when the SWR is low for all the antennas. An alternative is to insert a network at the feed point of at least one antenna that is carefully designed to match the impedance curves of the other(s).
Failure to closely match antenna impedances will send most of the power to one antenna, undercutting the objective of stacking and may present a high SWR to the transmitter. When a transformer is used as a power divider the mismatch due to a poor SWR on one or more antennas in the stack can alter the transformation ratio and increase heating in the ferrite core on which the transformer is wound. When running high power that heat can permanently damage the ferrite core.
Filters and stubs
The band pass filters used by many contesters protect receivers and reception quality by removing harmonics and other out-of-band emissions from a second transmitter, whether SO2R or multi-op. Most often they are placed between transceiver and amplifier. Sometimes (and more expensively) they are placed between the amplifier and antenna. In the former case stubs may be used to notch harmonics since they are a low cost alternative to high power band pass filters. Triplexers for sharing tri-band yagis utilize both band pass and band stop filters.
A filter is a network element like any other; look at the picture up above and imagine that the filter is the network between generator and load. Some manufacturers provide excellent technical resources on how their filters work and should be used. Here's a quick quiz: where does the out of band energy go?
Even if you don't know the answer there are just a few possibilities: dissipated as heat; grounded; or reflected. In the latter case this would be a high SWR outside the pass band, while in the former cases the impedance would have to be near 50 + j0 Ω, which is that of a pure resistance. It should be self evident that within the pass band the impedance would also be near 50 + j0 Ω. As you can see, impedance is a useful way to think about filters. Provided that harmonic energy is a small percentage of the total transmitter power (as it should be!) how that energy is handled by the filter will not noticably affect the transmitter.
Be aware that the source and load are integral components of the filter design. The filter only does what you expect if these are close is those impedances are close to 50 + j0 as well. Depending on the filter design a high SWR at the antenna port can degrade filter performance both within and outside the pass band. If you want your filter to work at its best antennas with low SWR are desirable. A few decibels can be enough to cause grief on other bands.
Performance of transmission line stubs to reject (reflect) the harmonic energy they are tuned for is sensitive to placement on the transmission line. Although the SWR may be low at the fundamental that is typically not the case for the harmonics. For best performance a predictable impedance is required and that will depend on the generator, load and stub placement. Since K9YC covers this topic so well I'll point you there for the details.
Common mode chokes
Preventing antenna currents on the outer surface of transmission lines protects the pattern of directive arrays, ensure power goes where it is most effective and reduce noise on reception. Common mode chokes at all antenna feed points are needed. Chokes typically take the form of 1:1 current baluns or coiling the coax on a ferrite or air form.
In the case of a 1:1 balun there is less core heating when the SWR is low; as with stacking power dividers (see above) efficiency suffers for high SWR and reactive loads. Coax coils wound on ferrite toroids are less susceptible to high SWR. Air core coax coils are sensitive to frequency and therefore less effective, which is a shame since they can handle higher power even when the SWR is high.
Relays
The typical contest station has dozens of relays to manage antenna switching and sharing among operator positions. If an antenna has a high SWR the current or voltage at the electrical distance of a relay from the antenna dictates whether the relay contact see abnormally high voltage or current. These can affect relay reliability and lifetime by arcing or heating when using high power.
Although relays with wider contact spacing and current capacity can reduce the impact they are often not used in commercial antenna switches. You can build your own switches if you insist on operating with high SWR antennas. Keep in mind these relays are larger, a little more expensive, and the coils require 100 ma or more at 12 VDC versus ~40 ma for the ones typically found in these products.
Conclusions and suggestions
Non-contesters can get by using antennas with high SWR over parts of the band, for the most part not suffering from many of the problems discussed. Contesters should reconsider if they have not dealt with these issues. It is something that I am striving for in my antenna farm, although at this time I have progressed very far.
All my yagis are either tri-banders or have loaded elements, which results in high Q behaviour and therefore higher than desirable SWR over significant parts of every band. My wire antennas for 80 and 160 meters fare a little better. Since these antennas are temporary, power is limited to 200 watts and I don't yet do SO2R or multi-op I am able to get by without too much trouble. For the antenna with the highest SWR on a band I train the rig's ATU for it and then have to remember to switch the ATU in and out depending on the antenna in use. Of course I sometimes forget.
I propose the following suggestions for the contester with a growing antenna farm to achieve the lowest possible SWR:
- Avoid multi-band yagis, and especially those with traps. Multi-band yagis with interlaced elements or, better yet, mono-band yagis should be used.
- Consider OWA yagis despite the complication of an additional element for a given boom length. Low SWR across the band can be readily achieved from 40 meters on up.
- An alternative to OWA yagis when boom lengths are long are the optimized yagis documented in the ARRL Antenna Book and elsewhere. These yagis can achieve low SWR across the band from 20 meters on up.
- If a 40 meter yagi is to have only 2 elements a Moxon is a good choice. Convert an XM240 or build a W6NL Moxon from scratch.
- On 80 meters you best choice for low SWR from 3.5 to 3.8 MHz is a 4-square. Many contesters use 4-squares on 40 meters with good results, and is a far less challenging project than a large yagi.
- Use good quality coax and test it periodically. Old coax, even Andrew Heliax, will wander away from 50 Ω as time passes. From the testing I've done a lot of this old coax tends to develop a lower characteristic impedance, reaching as far as 45 Ω. That's an SWR of 1.1 to a perfect dummy load.
- Matching networks, where required, should be placed at the antenna feed point, not in the shack. If necessary make the network switchable to change the low SWR range between band segments depending on the contest mode (CW, SSB, RTTY).
Wednesday, March 14, 2018
More Pile-up Techniques
After a period of relative quiet this month numerous DXpeditions are on the air. It's been a lot of fun. While only one new country made it onto my list (9M0W, Spratly Islands) quite a few new band slots have been filled. Particularly challenging has been the highest bands and the low bands, and in the case of 9M0W finding just the right combination and band and time to find effective propagation in this time of zero sunspots.
More so than in the past I am able to rely on brute force to get through the pile-ups. Antennas up high is a great help even without the aid of high power. About half the time I must still rely on agility and technique to get through the pile ups quickly. This is not strictly necessary since all these DXpeditions are one to two weeks long and eventually the depth of callers will thin and even those with small stations, and QRP, are likely to get through.
Jumping in early is more about the fun of the chase and honing my pile up skills. There is always more to learn. Some pile up skills apply equally to chasing contest multipliers, so this is good practice. In contests the technique must adjust for pile ups on the DX's transmit frequency; that is, no split.
This is an opportune time to review a few advanced techniques applicable to DXpeditions and contests. For many veterans there will be nothing new to read here. It can still prove helpful by reminding ourselves of what lurks in the bottoms of our toolboxes, digging them out and blowing off the dust. For some readers the information will be new and therefore of greater interest. Search this blog and you'll find similar articles covering a variety of pile up techniques.
Brute force
When propagation, antennas and power favour you it is best to rely on brute force to get through. Learn the DX operator's pattern -- listening frequency change between contacts -- then find the current lucky DXer and transmit where the DX is most likely to listen next. Don't worry about the presence of many others doing the same since you count on your superior signal to stand above them all. Or at least enough of them that you'll get through within a minute or two.
You may be thinking that this is hardly a pile up technique! Yet it is. Even if you have a modest station there will be times when propagation favours you and brute force works. When it does it is the most reliable and predictable way to get through pile ups fast. Spending time jumping around will only slow you down.
Leave the more advanced techniques for when you really need them. On the other hand, the big guns have to be wily when propagation is unfavourable and brute force doesn't work. For us in North America this is common when propagation favours Europe for DXpeditions such as Spratly Island. The reverse is true for Pacific Ocean DXpeditions.
Going below
Many DXers hamper themselves by collaring themselves the same as dogs restrained by invisible fences. On CW the spectrum within 1 kHz of the DX transmit frequency is avoided since it is a guard zone to prevent QRM on the DX who is operating split. There are times when the prohibition can be ignored to increase success if it is done respectfully and carefully.
Pay attention to whether the DX operator ever works stations below the edge of the 1 kHz guard zone -- listen and you'll notice that some use larger guard zones, such as 2 kHz, and on SSB it is typically 5 kHz or more. Should you probe below without that indication try to keep the split to no less than 800 Hz, and 900 Hz is a better limit if you want to be heard. I strongly recommend you never transmit closer to the transmit frequency even when the DX operator shows a willingness to listen there or bedlam can ensue.
This technique works because the majority strictly respect the guard zone regardless of the DX operator's observed behaviour. As I said, be careful when you do it. Don't QRM the DX!
Reset
A typical listening pattern for the DX operator is to shift the listening frequency in small steps. When he judges that the split is great enough he'll do one of two things: reverse direction or jump back to the edge of the guard zone. You usually notice this has occurred when your natural inclination to QSY up results in your inability to hear the station being worked.
When you determine that the listening frequency has been "reset" to the edge of the guard zone you have learned an important datum. The next time that invisible line is approached that is your signal to QSY to the edge of the guard zone and wait for the reset to occur. Should there be others doing the same it can help to move up slightly from the edge (say, from +1 kHz to +1.1 kHz). Also consider dropping into the guard zone slightly (+0.95 kHz) per the previous section.
There is another time when a reset can occur and catch everyone sleeping. This can be your opportunity if you stay nimble. The DX operator may show evidence of frustration when copying become difficult because the pattern is well understood by many and they then keep calling despite the attempt to focus on one identified caller. They may QSY randomly or they may do a reset.
Other indications of an impending reset include when they stop to identify several times or seem to be responding to no one for a while. In the latter case they may be changing operators. It is well worth the gambit of QSYing to the edge of the guard zone and calling there. I did this with one of the African DXpeditions currently active (I believe it was TN5R) and put them in the log with just one call precisely 1 kHz above the transmit frequency.
Calling in the hole
I discussed this item in the context of CW DXing. It can also be applied to good effect when encountering SSB pile ups. The technique also happens to be easier to apply.
A typical SSB split operation will announce a range of where the DX station will be listening. For example. 5 kHz to 10 kHz above the transmit frequency. On 40 meters and sometimes 80 meters the range will be similar but with a greater separation to take advantage of the frequency allocations available in different ITU regions.
What you will soon discover is that the bulk of the callers will transmit exactly at the boundaries of the range; that is, 5 kHz and 10 kHz up. In wider ranges, every 5 kHz. There is some sense to this behaviour because SSB requires greater signal separation to avoid an impenetrable wall of QRM. Many DX operators tend to jump in 5 kHz steps and we respond in kind, and so we all become accustomed to it.
Of course many of the pursuers are listening to learn the split of the last successful caller which results in deep QRM centred on these discrete frequencies. As often happens the DX station will work numerous stations at one frequency before listening elsewhere in the range, making the QRM worse for a while.
When brute force is not an option there is a way, obvious perhaps, to get through. That is to call in between those discrete steps. For example if the range is 14.195 MHz to 14.200 MHz, most of the callers are exactly at those two frequencies and you should call in the hole at 14.1975 MHz. Since this is 2.5 kHz from both those frequencies it is relatively free of QRM. Keep calling there. When the DX operator finally spins the VFO you'll be right there.
It's as simple as that. Even dogs have figured this one out. Ever notice how it is when they want attention that they're underfoot when you turn around? That's no accident!
The secret
Calling this next one the secret is a bit of a joke. It isn't much of a secret despite so many hams being unfamiliar with it. I don't mind sharing it since, even worst case, my readership is modest and, frankly, most won't use it anyway. Thus there will be little impact -- perhaps I'm being too cynical.
It is most useful in CW contests where even the most wanted multipliers operate simplex. When the pile up is on the DX station's transmit frequency the DX station has difficulty isolating one station (often it's the loudest one) and few in the pile up can hear the DX station underneath the QRM. Everyone's rate suffers. Discipline is usually good since otherwise no QSOs take place.
Unless you're that loudest of stations you are faced with a challenge. Since you aren't the loudest what you want to do is sound different. You do this by offsetting your transmit frequency. The shift must be enough to be distinctive yet still within the DX station's receiver pass band. Many DX stations are looking for that difference as well and will use their RIT feature to allow a wider shift.
In the former case a shift of at least 50 Hz is necessary but probably no more than 100 Hz. Aim for the high side (positive offset) since most receivers place the BFO at the bottom of the pass band (USB reception) and lower pitched tones are not as easily noticed. Don't be afraid use a negative offset since they may be using LSB reception (e.g. Elecraft transceivers).
Try it. You'll be surprised at how much of a difference it makes. If you've ever been on the receiving end of a pile up you'll know that all those zero beat callers are nearly impossible to separate, yet a shifted tone that's weaker than the others will be copied at least well enough to capture part of the call sign. It is for this reason that N1MM Logger contest software introduced jitter by default when clicking on a spot to minimize the risk of zero beating. Most rigs are so frequency precise that otherwise everyone clicking on a spot will end up 10 Hz of each other!
When the DX station is in on the game and you are paying attention you'll notice how he will split further and further, and then suddenly shift to the opposite offset. The vast majority of callers never seem to catch on. Get in the game and in moments you'll be trawling the bands for the next multipliers and leaving the messy pile up behind.
That's all there is to the secret. Have fun with it.
More so than in the past I am able to rely on brute force to get through the pile-ups. Antennas up high is a great help even without the aid of high power. About half the time I must still rely on agility and technique to get through the pile ups quickly. This is not strictly necessary since all these DXpeditions are one to two weeks long and eventually the depth of callers will thin and even those with small stations, and QRP, are likely to get through.
Jumping in early is more about the fun of the chase and honing my pile up skills. There is always more to learn. Some pile up skills apply equally to chasing contest multipliers, so this is good practice. In contests the technique must adjust for pile ups on the DX's transmit frequency; that is, no split.
This is an opportune time to review a few advanced techniques applicable to DXpeditions and contests. For many veterans there will be nothing new to read here. It can still prove helpful by reminding ourselves of what lurks in the bottoms of our toolboxes, digging them out and blowing off the dust. For some readers the information will be new and therefore of greater interest. Search this blog and you'll find similar articles covering a variety of pile up techniques.
Brute force
When propagation, antennas and power favour you it is best to rely on brute force to get through. Learn the DX operator's pattern -- listening frequency change between contacts -- then find the current lucky DXer and transmit where the DX is most likely to listen next. Don't worry about the presence of many others doing the same since you count on your superior signal to stand above them all. Or at least enough of them that you'll get through within a minute or two.
You may be thinking that this is hardly a pile up technique! Yet it is. Even if you have a modest station there will be times when propagation favours you and brute force works. When it does it is the most reliable and predictable way to get through pile ups fast. Spending time jumping around will only slow you down.
Leave the more advanced techniques for when you really need them. On the other hand, the big guns have to be wily when propagation is unfavourable and brute force doesn't work. For us in North America this is common when propagation favours Europe for DXpeditions such as Spratly Island. The reverse is true for Pacific Ocean DXpeditions.
Going below
Many DXers hamper themselves by collaring themselves the same as dogs restrained by invisible fences. On CW the spectrum within 1 kHz of the DX transmit frequency is avoided since it is a guard zone to prevent QRM on the DX who is operating split. There are times when the prohibition can be ignored to increase success if it is done respectfully and carefully.
Pay attention to whether the DX operator ever works stations below the edge of the 1 kHz guard zone -- listen and you'll notice that some use larger guard zones, such as 2 kHz, and on SSB it is typically 5 kHz or more. Should you probe below without that indication try to keep the split to no less than 800 Hz, and 900 Hz is a better limit if you want to be heard. I strongly recommend you never transmit closer to the transmit frequency even when the DX operator shows a willingness to listen there or bedlam can ensue.
This technique works because the majority strictly respect the guard zone regardless of the DX operator's observed behaviour. As I said, be careful when you do it. Don't QRM the DX!
Reset
A typical listening pattern for the DX operator is to shift the listening frequency in small steps. When he judges that the split is great enough he'll do one of two things: reverse direction or jump back to the edge of the guard zone. You usually notice this has occurred when your natural inclination to QSY up results in your inability to hear the station being worked.
When you determine that the listening frequency has been "reset" to the edge of the guard zone you have learned an important datum. The next time that invisible line is approached that is your signal to QSY to the edge of the guard zone and wait for the reset to occur. Should there be others doing the same it can help to move up slightly from the edge (say, from +1 kHz to +1.1 kHz). Also consider dropping into the guard zone slightly (+0.95 kHz) per the previous section.
There is another time when a reset can occur and catch everyone sleeping. This can be your opportunity if you stay nimble. The DX operator may show evidence of frustration when copying become difficult because the pattern is well understood by many and they then keep calling despite the attempt to focus on one identified caller. They may QSY randomly or they may do a reset.
Other indications of an impending reset include when they stop to identify several times or seem to be responding to no one for a while. In the latter case they may be changing operators. It is well worth the gambit of QSYing to the edge of the guard zone and calling there. I did this with one of the African DXpeditions currently active (I believe it was TN5R) and put them in the log with just one call precisely 1 kHz above the transmit frequency.
Calling in the hole
I discussed this item in the context of CW DXing. It can also be applied to good effect when encountering SSB pile ups. The technique also happens to be easier to apply.
A typical SSB split operation will announce a range of where the DX station will be listening. For example. 5 kHz to 10 kHz above the transmit frequency. On 40 meters and sometimes 80 meters the range will be similar but with a greater separation to take advantage of the frequency allocations available in different ITU regions.
What you will soon discover is that the bulk of the callers will transmit exactly at the boundaries of the range; that is, 5 kHz and 10 kHz up. In wider ranges, every 5 kHz. There is some sense to this behaviour because SSB requires greater signal separation to avoid an impenetrable wall of QRM. Many DX operators tend to jump in 5 kHz steps and we respond in kind, and so we all become accustomed to it.
Of course many of the pursuers are listening to learn the split of the last successful caller which results in deep QRM centred on these discrete frequencies. As often happens the DX station will work numerous stations at one frequency before listening elsewhere in the range, making the QRM worse for a while.
When brute force is not an option there is a way, obvious perhaps, to get through. That is to call in between those discrete steps. For example if the range is 14.195 MHz to 14.200 MHz, most of the callers are exactly at those two frequencies and you should call in the hole at 14.1975 MHz. Since this is 2.5 kHz from both those frequencies it is relatively free of QRM. Keep calling there. When the DX operator finally spins the VFO you'll be right there.
It's as simple as that. Even dogs have figured this one out. Ever notice how it is when they want attention that they're underfoot when you turn around? That's no accident!
The secret
Calling this next one the secret is a bit of a joke. It isn't much of a secret despite so many hams being unfamiliar with it. I don't mind sharing it since, even worst case, my readership is modest and, frankly, most won't use it anyway. Thus there will be little impact -- perhaps I'm being too cynical.
It is most useful in CW contests where even the most wanted multipliers operate simplex. When the pile up is on the DX station's transmit frequency the DX station has difficulty isolating one station (often it's the loudest one) and few in the pile up can hear the DX station underneath the QRM. Everyone's rate suffers. Discipline is usually good since otherwise no QSOs take place.
Unless you're that loudest of stations you are faced with a challenge. Since you aren't the loudest what you want to do is sound different. You do this by offsetting your transmit frequency. The shift must be enough to be distinctive yet still within the DX station's receiver pass band. Many DX stations are looking for that difference as well and will use their RIT feature to allow a wider shift.
In the former case a shift of at least 50 Hz is necessary but probably no more than 100 Hz. Aim for the high side (positive offset) since most receivers place the BFO at the bottom of the pass band (USB reception) and lower pitched tones are not as easily noticed. Don't be afraid use a negative offset since they may be using LSB reception (e.g. Elecraft transceivers).
Try it. You'll be surprised at how much of a difference it makes. If you've ever been on the receiving end of a pile up you'll know that all those zero beat callers are nearly impossible to separate, yet a shifted tone that's weaker than the others will be copied at least well enough to capture part of the call sign. It is for this reason that N1MM Logger contest software introduced jitter by default when clicking on a spot to minimize the risk of zero beating. Most rigs are so frequency precise that otherwise everyone clicking on a spot will end up 10 Hz of each other!
When the DX station is in on the game and you are paying attention you'll notice how he will split further and further, and then suddenly shift to the opposite offset. The vast majority of callers never seem to catch on. Get in the game and in moments you'll be trawling the bands for the next multipliers and leaving the messy pile up behind.
That's all there is to the secret. Have fun with it.
Tuesday, March 6, 2018
SSB Low Power: The Muddy Middle
I operated part time in this past weekend's ARRL DX SSB contest. This was a decision made before the contest since I knew that 150 watts, even with good antennas, would be a struggle in a SSB DX contest of this magnitude at this point in the solar cycle. However I left enough latitude in my schedule so that I could operate more if I changed my mind.
Of the several technical problems that appeared soon after the contest started most aggravating was a (still unexplained) distortion of the computer-based digital voice memories, making them unusable and CQing unpleasant. I ended up operating a little over 11 hours until I pulled the plug late Saturday evening. Although my alarm was set to allow me to catch the pre-sunrise low band openings I had no desire to continue and went back to sleep.
To explain my attitude let me start with an anecdote. Soon after Saturday sunrise 20 meters opened strongly to Europe. I positioned myself a little below 14.150 MHz, the edge of the US phone band, to call CQ to see what would happen. After a few CQs a German station replied. When we were done he said "I will spot you". I continued to CQ for another minute with no replies. Then bedlam descended. For the next 15 minutes I had a deep pile up of European callers at a rate of 4 to 5 QSOs per minute. It didn't last.
The rate abruptly dropped to no better than 1 QSO per minute and then died completely. It seemed I was done despite the good conditions. Never again was I able to effectively run to Europe, or to anywhere else for that matter. Further running attempts on any band rarely netted more than one QSO.
This is not necessarily a terrible thing and few would sympathize with my inability to run DX stations. Indeed from what I heard on the bands even the big guns in the US and Canada were not achieving high rates. For me and the majority of participants, even those with QRO, this was a primarily S & P (search and pounce) contest. Often a frustrating one at that.
It is an indication of the challenges anyone will encounter in SSB contests at this stage of the solar cycle. With 10 meters almost dead and 15 meters little better the main stage is 20 meters. The band is intensely crowded and the QRM overwhelming. The lower bands fare worse. On 40 meters the available SSB band segment is narrow, the noise higher and the MUF drops low a few hours past sunset. The lower bands are challenging for SSB DX at any time due to the higher noise level and the relatively poor antennas that are typical.
We must get used to this for the next few years in SSB contests. More stations are crammed into smaller spaces resulting in massive QRM as stations squeeze far closer together than 2.5 kHz. As I tuned across the bands it was difficult to hear any but the biggest guns. There are smaller stations to be found, if you can hear them underneath the tightly packed big guns. Highly directive antennas can sometimes help but on the low bands at least they are not practical for most.
As a result you can't run with low power and S & P turns only turns up the stations you've already worked. Smaller stations can't easily find each other. That is, unless you're the only one on from a country and can attract a constant stream of multiplier hunters. Entering an 'assisted' category alleviate much of the drudgery, which I may do.
Therefore QSO totals are low and hunting for multipliers becomes the primary pursuit. Those running QRO fare relatively better. Even for those with modest antennas the addition of an amplifier can deliver a large dividend. Low power combined with big antennas cannot do the same since it is quite difficult (and expensive) to deliver an additional 10+ db that an amplifier offers with the flip of a switch. Unfortunately when everyone is tempted to run QRO we get a tragedy of the commons where the sum of sensible individual decisions can ruin the bands for everyone.
Well, that's contesting. You play the hand you're dealt or exit the game. I choose a middle position, playing where I can excel or altering my objectives. This contest ultimately bored me since with a better antenna farm I want to do better than scrimp for QSOs the way I did when I ran QRP. Back then the high bands were great and I could run with 5 watts on SSB. Now I can't run with 150 watts and better antennas. SSB low power stations are in the "muddy middle" where they cannot effectively run yet must not stick with S & P since that will not bring success.
Propagation is determined by the sun and ionosphere, not our antennas and transmitters. We build what we can and adjust our objectives to the prevailing conditions. When it stops being fun it is better to step away from the radio, or at least change perspective and objectives. One cure that works for many is to join a multi-op. That way you share the burden of poor rates and you get to take frequent breaks without affecting the final score.
Long term burn out is a symptom of forcing yourself to stay when it isn't enjoyable. This weekend I chose to step away from the radio. Had I stayed for the duration perhaps I would have placed well, but I simply didn't care to do so.
Of the several technical problems that appeared soon after the contest started most aggravating was a (still unexplained) distortion of the computer-based digital voice memories, making them unusable and CQing unpleasant. I ended up operating a little over 11 hours until I pulled the plug late Saturday evening. Although my alarm was set to allow me to catch the pre-sunrise low band openings I had no desire to continue and went back to sleep.
To explain my attitude let me start with an anecdote. Soon after Saturday sunrise 20 meters opened strongly to Europe. I positioned myself a little below 14.150 MHz, the edge of the US phone band, to call CQ to see what would happen. After a few CQs a German station replied. When we were done he said "I will spot you". I continued to CQ for another minute with no replies. Then bedlam descended. For the next 15 minutes I had a deep pile up of European callers at a rate of 4 to 5 QSOs per minute. It didn't last.
The rate abruptly dropped to no better than 1 QSO per minute and then died completely. It seemed I was done despite the good conditions. Never again was I able to effectively run to Europe, or to anywhere else for that matter. Further running attempts on any band rarely netted more than one QSO.
This is not necessarily a terrible thing and few would sympathize with my inability to run DX stations. Indeed from what I heard on the bands even the big guns in the US and Canada were not achieving high rates. For me and the majority of participants, even those with QRO, this was a primarily S & P (search and pounce) contest. Often a frustrating one at that.
It is an indication of the challenges anyone will encounter in SSB contests at this stage of the solar cycle. With 10 meters almost dead and 15 meters little better the main stage is 20 meters. The band is intensely crowded and the QRM overwhelming. The lower bands fare worse. On 40 meters the available SSB band segment is narrow, the noise higher and the MUF drops low a few hours past sunset. The lower bands are challenging for SSB DX at any time due to the higher noise level and the relatively poor antennas that are typical.
We must get used to this for the next few years in SSB contests. More stations are crammed into smaller spaces resulting in massive QRM as stations squeeze far closer together than 2.5 kHz. As I tuned across the bands it was difficult to hear any but the biggest guns. There are smaller stations to be found, if you can hear them underneath the tightly packed big guns. Highly directive antennas can sometimes help but on the low bands at least they are not practical for most.
As a result you can't run with low power and S & P turns only turns up the stations you've already worked. Smaller stations can't easily find each other. That is, unless you're the only one on from a country and can attract a constant stream of multiplier hunters. Entering an 'assisted' category alleviate much of the drudgery, which I may do.
Therefore QSO totals are low and hunting for multipliers becomes the primary pursuit. Those running QRO fare relatively better. Even for those with modest antennas the addition of an amplifier can deliver a large dividend. Low power combined with big antennas cannot do the same since it is quite difficult (and expensive) to deliver an additional 10+ db that an amplifier offers with the flip of a switch. Unfortunately when everyone is tempted to run QRO we get a tragedy of the commons where the sum of sensible individual decisions can ruin the bands for everyone.
Well, that's contesting. You play the hand you're dealt or exit the game. I choose a middle position, playing where I can excel or altering my objectives. This contest ultimately bored me since with a better antenna farm I want to do better than scrimp for QSOs the way I did when I ran QRP. Back then the high bands were great and I could run with 5 watts on SSB. Now I can't run with 150 watts and better antennas. SSB low power stations are in the "muddy middle" where they cannot effectively run yet must not stick with S & P since that will not bring success.
Propagation is determined by the sun and ionosphere, not our antennas and transmitters. We build what we can and adjust our objectives to the prevailing conditions. When it stops being fun it is better to step away from the radio, or at least change perspective and objectives. One cure that works for many is to join a multi-op. That way you share the burden of poor rates and you get to take frequent breaks without affecting the final score.
Long term burn out is a symptom of forcing yourself to stay when it isn't enjoyable. This weekend I chose to step away from the radio. Had I stayed for the duration perhaps I would have placed well, but I simply didn't care to do so.
Thursday, March 1, 2018
Big Station, Big Maintenance
For those of you prone to vertigo I apologize for the picture. It isn't gratuitous; I have a point to make. This picture was in the second last slide in a talk I gave on station building earlier this winter. The topic was maintenance.The more towers and antennas you put up the more maintenance is required. Although also true for the quantity of equipment you have inside the shack there is an added component of danger, difficulty and expense with the former. Never forget that. There are substantial benefits to building your station with a eye on minimizing maintenance. It can never be eliminated so be prepared.
I was reminded of that this week when a problem occurred on top of my 150' tower. This was a potentially disastrous problem. On Monday I noticed that the top yagis were pointing towards an unexpected direction. As I gazed upward I noticed that the action of the wind was slowly turning them, first in one direction and then the other. Obviously something bad had happened.
Binoculars showed nothing amiss. I could not climb just then since it was immediately before sunset. The next day, with the wind howling but with unseasonably warm weather, I went up there to check it out. Before doing so I tried to arm myself with information by corresponding with another ham with extensive prop pitch motor experience and with the style of drive system I'm using.
Once up there I quickly saw what had gone wrong. The six sets of bolts, lock washers and nuts securing the motor flange to the drive platform had all unscrewed. The bolts fell out the bottom with the lock washers and nuts stranded up top. The loose motor allowed the mast to spin freely and yanked the motor wires out of the splices to the main cable run back to the shack.The two bolts that landed on the drive shaft bearing were enough to temporarily secure the motor. The next day I climbed up with new hardware and electrical tools and fixed everything. Tower time was 2 hours, plus 90 minutes the previous day. The wind was howling which made the job unpleasant and difficult since I had to fight that wind to turn the mast and antennas to a better position for attaching the wiring. You can be sure that this time I made certain to properly torque the grade 5 galvanized fasteners.
This was also an opportunity to fix the coupling to the direction pot which will save me some grief. The fewer times I have to climb the tower the better.
This fiasco was, of course, entirely my fault. I am not ashamed to say it. We are all human and we make mistakes. How I made this mistake I don't know other than recalling the urgency to complete the project in December as the weather deteriorated day after day.
Mistakes at the top of 150' tower in winter are not like a mistake on a 50' tower or inside the shack. All mistakes and failures are aggravating but most do not involve dangerous repairs. On the bright side the weather was warm and the yagis -- TH6 and XM240 -- are pretty well torque balanced and so did not turn hard in the wind. All coaxial cables were undamaged.
The bigger your station the bigger your problems. If you seriously want a big station prepare yourself. There is lesson in this: build it to last. That was the message of the slide in my talk with the vertiginous picture. The picture shows me climbing the mast of the big tower to release the coiled up coax from the XM240 feed point. Although impressive in a way not even I want to do it often!
It is well worth the expense to buy or build the very best up front to reduce maintenance events. Use the best parts and methods and you can increase MTBF (mean time before failure). The initial expense will be recouped many times over the coming years. You do not want to be climbing towers and making repairs every week or two. It not only puts you at risk it is expensive and, perhaps most important, it can put you off the air just as a major DXpedition or contest occurs.
If, like most hams, you do not climb towers you must factor that into your calculations. Educate yourself about materials and engineering needed to build survivable antenna systems. Otherwise you are at the mercy of others and their opinions, and you will not know enough to distinguish good advice and workmanship from bad. What you don't know will hurt you. Money spent in no guarantee of quality. It helps a great deal if you are able to climb although it is not mandatory.
Do it right and be careful out there. Spring antenna season is nearly here.
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