Even when SNR (signal to noise ratio) is high there can be asymmetries in copying. On SSB this may be due to language and accent for the majority of hams who are not using their native languages, or simply by poor enunciation by those who fail to realize that a communication channel with limited band width and dynamic range makes copy more challenging than talking in person. There is also the all too common practice of poorly adjusted audio. On CW it may be poor sending, deviations from standard code element length and spacing, or sending faster than the other ham can comfortably copy.
Putting those situations aside I want to focus on QSOs between operators who are doing their utmost to get the message across: in this case call signs and contest exchanges. I'll focus on CW and SSB since I don't have sufficient experience to discuss digital modes.
Run versus S & P
Let's imagine we are tuning across the band and run across two adjacent signals, one strong and one weak. Which one do you tune in first? Even if you are disciplined enough to focus on the weak one I bet that you are still strongly drawn to the strong one. This is perfectly natural since it is less work to copy the stronger station well. Struggling with a weak signal costs time and time costs points. We are more inclined to do the hard work late in a contest when all the strong ones are already in the log.
However, it is not quite so straightforward. When you tune in a strong signal in the clear you will most likely copy the call sign the first time it is sent. You will most likely easily copy the exchange. The same is often not the case on the other side of the QSO. You may be running less power and a smaller antenna; they may be experiencing strong QRM from other callers and adjacent signals near to you that you don't hear because they are in the skip zone or off the side of the beam.
It should therefore be no surprise that for stations you copy perfectly while you S & P that less than 100% of them will copy you as well. Some of the time or much of the time, depending on many variables, they will ask for repeats or you'll have to correct their copying error. During the two years my contesting was exclusively QRP the percentage of running stations that could copy my call sign and exchange the first time was not high. On the low bands it was often no better than 25%.
Now let's return to the weak station you earlier skipped over. More S & P operators than you might imagine won't pay any attention to the ones that are hard to copy. I'll assume you're not one of those, since as a contester you should never overlook potential points (and multipliers).
So you listen and listen, perhaps taking a little time to completely copy the call sign and perhaps you'll also note the exchange being sent. For many it is only at that point you make your call.
Consider what's going on here. You spent time to copy the full call and ensure it is not a dupe. You have already had one or two opportunities to copy the exchange. Even if it's a serial number you know what number comes next and you'll be ready for it!
The running station has not had that opportunity. Their probability of correct copy on the first try is perhaps, on average, no better than yours. Yet you've already gotten past that obstacle. Now it's their turn. The weak running station is even less likely to copy your call and exchange on the first try.
The lesson here is that when you S & P you should not be surprised that the running station will need repeats of your information. For the running station many callers will not be readily copied and you'll have to spend time to correctly solicit their information.
Example: Ontario QSO Party
As an experiment I did 100% running in the recent Ontario QSO Party. That is, sitting on a frequency calling CQ and never hunting other stations. The contest has light activity and I wasn't concerned about my score, only giving out QSOs to others. This is not a bad way to make it easy for non-VE3 participants to find me, and my perhaps uncommon county multiplier. Many of the active VE3 stations spent much of their time running as well, perhaps for the same reason.
The objective of my experiment was to see just how often the callers were difficult to copy. Well, it was surprisingly often. While a sample of n=1 is not statistically significant my results do fit well with my thesis and my recollection of past years of contest experience at larger stations.
My springtime QRN levels on the low bands was quite high during the contest, with several electrically active rainstorms passing through or nearby. That could have contributed to asymmetrical listening ability. Asymmetrical power wasn't a problem since I kept to the low power limit of 150 watts, which is on par or less than the majority of callers.
On 80 meters I found I had to use the Beverage all the time even though it favours Europe and almost all callers were off the side or back of the Beverage. The SNR was almost always better than the inverted vee. This worked less well on 40 meters, partly due to the Beverage's sharper pattern on that band. The 2-element yagi's directivity is not very good, which is typical of this type of antenna.
There were many callers I could not copy at all, while with other I would only catch a letter or two of the call. It seemed surprising they were copying me. Perhaps they had lower atmospheric QRN, more directive antennas or there was power asymmetry.
One obvious problem was looking west on 40 meters soon after my sunset. At that time the other station's band noise will be lower than mine. This is typical of the low bands. As soon as propagation is enhanced by the arrival of darkness the noise level rises along with the signals from the dark hemisphere.
Stations west of the terminator hear me fine while I struggle with the atmospheric QRN accompanying that of signals from the east and south. This is the same phenomenon responsible for the difficulty of working clearly heard Europeans before sunset on this side of the Atlantic Ocean.
In many cases I could not come up with a good explanation of why copy would be difficult. QRN would be low and QRM absent. Obviously I can't know what is going on at the other side of the QSO. Maybe they were driven there by a spot (or skimmer) or maybe they had already spent some time copying me before calling. All I can know for sure is that copying asymmetry was common.
Let's face it, for the upwardly mobile contester it is necessary to run a lot to improve scores. That guarantees you'll be struggling with many callers that are difficult to copy. Since you must do it there are things you can do to be best prepared to deal with it to your (and their) benefit. Scores will improve and frustration levels will decline as abandonned QSOs are reduced in number.
- Directive antennas: One sure way to improve copy on the low bands, and even on the higher bands, is with highly directive receive antennas. This can be as simple as a small loop, or can be a Beverage or phased vertical array. Transmit antennas are typically not highly directive on 80 and 160 meters so a more directive receive antenna is a good addition. The results can be surprisingly profitable. Since directive antennas are directive you'll need more than one, or at least an antenna with 2 or more selectable directions.
- F/B: Antennas for all bands should have strong suppression off the back and sides, preferably with minor lobes that are no more than -15 db than the main lobe, and preferably much better. On the low bands phased vertical arrays are often the best at this, while on the high bands a Moxon rectangle or similar critically-coupled 2-element yagi, or optimized yagi with 3 or more elements.
- Hunt down noise sources: Any noise source -- power line, Ethernet, USB, appliance, electric fence, etc. -- is a potential killer of QSOs, especially on an otherwise quiet band. Do everything you can to locate and silence noise. If you can you should place your antennas as far away from buildings and power lines as possible, or where productive directions for QSOs are over quiet zones.
- Filters: Learn how to alter your filter settings quickly so that you waste little time asking for repeats. This include bandwidth, centre frequency, noise reduction, notch, and RIT. The last is important since you are less likely to hear a weak caller unless you tune above and below your frequency. You don't want to overlook them just because they failed to zero beat properly.
- Partial call database: This one can be controversial. Many contest loggers will search for calls that are similar to the partial or full calls that you type in. This can help you to deduce that the caller is one of those, either a known contester or a call you've worked before in this or a previous contest. The technology exists and it's your choice whether to us it. Whatever you do, confirm the call with the caller. Never assume.