[GreenKeys] HAL ST-6 Manual needed

[Jim Haynes]

Not to nit pick, but some of the AFSK generators use a crystal oscillator
and an IC frequency divider, so shifting is accomplished by changing the
divisor.  Which should result in a phase continuous signal.  Then the
modern DSP implementations - I don't know what they all do, but one
possibility is to quickly fade the amplitude down to zero, shift frequency
and then bring the amplitude back up again.  I know something like that is
done in PSK where they don't want to have an abrupt change in phase.