Tips on Correctly Copying Serial Numbers in Contest Exchanges
The last weekend in March and May each year, approximately 10,000 stations will be sending and copying serial numbers as the required exchange in the 48-hour CQWW WPX SSB and CW contests. Dozens of other contests use serial numbers, too, either as a standalone exchange or — as in ARRL Sweepstakes — as a variable part of a longer exchange.
How hard is it to copy a serial number correctly? In the log checking reports for almost 2 million QSOs logged in the 2022 CQWW WPX SSB contest, serial numbers were miscopied at a 3.0% rate; while callsigns were busted only about half as often, at a 1.6% rate. From a purely information-theory analysis, one might think that copying a serial number correctly would be easier than copying a callsign. After all, a callsign is often six characters, and each character in the callsign could be either a letter or digit, making 36 possible choices for each character. Serial numbers used in ham contests are shorter — four digits or less – and only made up of the 10 possible digits.
Contesters have a couple trick up their sleeves to copy callsigns more accurately. Foremost, a station calling CQ gives its callsign over and over on the same frequency, and this is a constant; contrasted with
