Saturday, October 4, 2014

Pile-ups: Zig vs. Zag

Getting through the larger DX pile-ups with QRP and small antennas can be challenging. This is even more true on 40 meters and below where the atmospheric QRN makes it difficult for the other station to copy you even without the competition of a pile-up.

Sometimes it's better to just step away from the radio and not waste the time trying. But if you have some time to burn it doesn't hurt to try. I faced this choice with ZD9XF on 40 meters, after having worked him on 30, 17 and 10. An inverted vee and 10 watts versus the pile-up is not a fair fight!

For those willing to make the effort this is the story of how one QRP'er did, eventually, get through. Since I am no longer so focussed on the absolute need to work every country on every band I was able to look at the problem with some dispassionate analysis. That is, I don't have to work him, I just want to work him.

Be realistic

Even if I were the only station calling ZD9XF on a clear frequency the QSO would be marginal at best. I've been working QRP for long enough to gauge my chances. When you add to that the depth and breadth of a pile-up on a rare DX station the little guy's chances can dwindle to nothingness.

Only when you realistically assess your chances and the competition can you make a plan. Sure, you can just jump in and call anyway, if you have time to waste. However if you want to actually make the QSO you will benefit from a plan based on honest self assessment.


Good DXpedition CW operators establish a pattern designed to not only make it easy for them to work more stations but also to help out those in the chase. They need to encourage callers to spread out, creating enough separation so that their receiver filtering can, ideally, isolate one signal. When callers are bunched together the QSO rate can dramatically drop, to the detriment of everyone.

The typical pattern is for the DX to keep shifting his or her listening frequency by a small amount on every QSO. This can range from as little as 100 Hz up to several times that. Perhaps more frequently they'll drift higher until a signal can be picked out, either by its strength or lack of immediately adjacent signals. Eventually they'll reverse direction or jump to the lower end of the listening range, again moving upward.

Learning the pattern can be helpful, though not always. If too many callers adapt to the pattern it no longer works since too many callers will be packed tightly together. As part of learning the pattern it is important to further discover how the DX breaks the pattern. This can involve a sudden frequency shift or even a period of randomness. Either way you need to learn the pattern the DX station follows. That is the basis of all that follows.

Zig and zag

The caller's response to the DX station's pattern is to zig and zag. Here is what I mean by these terms:
  • Zig: You QSY after every QSO according to the observed pattern. For example, when the DX QSYs up 200 Hz after every QSO you QSY the same amount. If your signal is competitive with respect to the other callers, or if they are simply less observant, you make the QSO. Repeat as necessary. When the pattern changes, so do you. If the pile-up is successfully zigging, you should occasionally do a big zig. Per the above example, QSY up by more than the pattern typically exhibits. This is in the hope or expectation (by observation) that the DX tries to out-manoeuver the horde.
  • Zag: When the pile-up is on to the DX station's pattern and you cannot compete by signal strength alone it makes sense to anticipate pattern changes. For example, at some point the DX will reverse direction or abruptly QSY to the other end of the range. So instead of zigging you do the opposite of (you hope) of everyone else. This I call zagging. For example, if the DX QSYs up 200 Hz after every QSO you QSY down 200 Hz. Most of your calls will be fruitless but when the pattern reverses you are there and (hopefully) few others are. Similarly, you can plant yourself at the other end of the range and lie in wait for the abrupt QSY.
Whether you zig or zag it is important that you listen carefully to the frequency of every successful caller. That is how you establish the pattern, and changes to the pattern. If you can't hear the other station that is a sign that you should zig (or zag) regardless, as if the caller was at the predicted frequency, or the pattern has reversed or shifted. Go ahead and call anyway but you need to find out where the DX is listening now so that you can have a chance.

Luck = Chance + Planning

Zigging and zagging are all well and good, and is well-established practice among DXers. But if your signal is uncompetitive you are going to miss out unless you try something different. The reason is that the listening range is going to be full of callers who neither zig nor zag, but camp on any old frequency and call away. They often will do so during each QSO and even when the DX is transmitting!

Sure, you can laugh at their futile behaviour but that will not help you. Your QRP signal is weak and will be covered up by their blather. In other words, as ridiculous as it seems they have a better chance of working the DX than you. After all, regardless of the DX station's pattern they will occasionally be listening on the frequency where these stations have camped. You lose.

Consider what it will take for you to make the QSO with a marginal and uncompetitive signal:
  • Time: You need to be calling at the time the DX is listening. It may seem obvious yet many don't do this. You know, you've heard (and cursed) them.
  • Frequency: The frequency you call on must not only be where the DX is listening but must also be reasonably free of other callers. If there's even one other caller near your frequency you will almost always lose. And then then DX station QSYs for the next QSO.
  • Attraction: Even if you succeed at time and frequency if your signal is unattractive you will still lose. For example, if you are sending at 30 WPM you will likely be passed over. Copying high speed CW when you are so weak is very difficult. Do not send faster than the other station, and consider going quite a bit slower. A pile-up is not a CW speed competition. Once you get the operator's attention you may want to slow down further to make his or her job easier. You hold their attention by at least trying to make their job easier.
All of this will still fail if the other operator is averse to weak signals. You may just have to wait for better conditions or for when the competition is spent. The latter occurs when the DXpedition has gone on for a time, after all the big guns and even most of the little pistols have made their QSO. If the DXpedition is a short one, well, be prepared for disappointment.

Getting through a pile-up is more like poker than a lottery. It's a stochastic process composed of random variables and more deterministic factors. For little pistols the weighting of the random variables is higher than it is for others. It is therefore important to bolster the factors under your control so that when the chance comes you are ready.

The contact

When my chance came I was fully aware of it. I also knew if it didn't pan out I might not get another since the clock was rapidly running down on this DXpedition, as was the time I could devote to it. It did indeed turn out this was the last evening ZD9XF was active on 40.

The operator was sending more slowly than previous nights, perhaps in recognition that all the stations with larger antennas had been worked so signals would be weaker in both directions. The pile-up was still deep and wide but less so than before. It was under similar conditions that I worked FT5ZM on 40 so I reasoned that I had a chance.

The chance didn't appear to be working for me. After an hour of calling I got nowhere. There were just too many others calling for me to be heard. I even tried the strategy of ignoring the pattern and camping out on a frequency in his listening range that was mostly clear of other callers. That is not only time consuming it failed since when his listening frequency approached my camping spot the ziggers and zaggers covered me up anyway.

What finally happened is that during a descending frequency pattern the DX went lower down that before. When he worked a station with a small split of only 1.4 kHz I noticed that the frequency was otherwise quiet. And so I saw my chance. I QSY'd down to a 1.2 kHz split and called. The frequency was clear except for me. But would he keep tuning down or, more likely, QSY up or simply not hear me?

He sent "R3". I took it as a hopeful sign and called, knowing that if I was wrong I was unlikely to be interfering with a potentially real R3 station. Then I heard "R3FN". The turnover timing between my transmission and his was further evidence that it might be me he was hearing. I slowed the keyer and got "K3VN" in reply. That's when I was certain I had his attention. I slowed all the way down to 17 wpm and sent my call twice. That succeeded and with a quick "599 TU" he was in the log. This was later confirmed in his online log.

In the grand scheme of things this was no great accomplishment. What it did was to demonstrate that a combination of chance and skill can achieve results for small pistols with DX ambitions. If it can work for me it can work for others.


No, not mine! This contact would not have been possible if not for the skill and dedication that G3TXF put into his operation, including making the effort to pull out and work the weakest of signals.

It takes two to QSO, so always remember that. Tell them "thank you" when you have the opportunity.

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