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2.
a digital mode of transmission used by Amateur Radio Operators
I interfaced my computer to my high-frequency (HF) transceiver and now I operate PSK31 from my keyboard.
by Rod C. VA3ROD December 09, 2003
 
1.
A digital transmission mode -- Phase Shift keying with 31.25 baud rate
PSK31 is one of the better HF operating digital modes.
by IrishRepublicanArmy January 01, 2004