Just like it says on the tin, it’s phase shift keying, and a proper implementation uses a phase detection circuit or something similar. [Craig] thought it would be fun to build an analog BPSK31 ...

A variant of phase-shift keying, created by Magellan Technology, which operates at 13.56 MHz and complies with the ISO/IEC 18000 3 Mode 2 standard. PJM technology enables a write data rate of up to ...

The goal was to decode the frequency-shift-keyed (FSK) signal into an 8-bit parallel output, and maybe drive a seven-segment display as the characters came off the tape at a screaming 300 baud.