***** Moderator's Note *****
>
>Trivia question: when first establishing contact, the stations would
>often send a series of "RY" characters repeatedly. Why?
>
"RY" is a popular test pattern because the two characters feature alternating mark and space bits and are the opposite of each other. R has 2 and 4 marking, Y has 1, 3 and 5 marking. So if there is anything sluggish in your machine, or adjacent parts that are stuck together, the RY test is the one it is most likely to fail. Other than that, any repetitive pattern is useful for tuning in the receiver when you are establishing contact, and with the earlier radio gear that drifted so badly you were always retuning the receiver to compensate for drift.