1. They send a bit as one of two tones using frequency-shift keying . 2. Data is transmitted using 4-level frequency-shift keying ( FSK ) modulation. 3. AFSK differs from regular frequency-shift keying in performing the modulation at baseband frequencies. 4. Signal encoding uses Phase-shift keying ( QPSK or GMSK ). 5. Originally, Gaussian frequency-shift keying ( GFSK ) modulation was the only modulation scheme available. 6. In the 1, 200 bit / s and faster systems, phase-shift keying was used. 7. The unit can also generate and sync to frequency-shift keying signals from a tape recorder. 8. Instead, a form of frequency shift keying was employed. 9. X-COM is the holder of multiple technical patents including "'Time-Shift Keying "'and other related technologies. 10. DP-QPSK refers to Dual polarization-quadrature phase shift keying .
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