"Michael Black" wrote in message
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I actually don't know what the common scheme for FSK is these days.
If the transmitter is using DSP, the fsk can be done digitally.
I assume that DDS-based VFOs in current rigs may actually be able
to be reprogrammed at a fast enough rate that one just keeps loading
the two frequencies into the synthesizer as the shifting is needed,
but I've not kept track of recent rigs to know if that's what's being
used.

This is pretty reasonable at low bit rates. But some more recent DDS chips,
for example, TI's TRF4900, actually have a data pin, and the two frequencies
are programmable, so the chip has the two divisors onboard making it a
simple matter to switch between divisors.

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