On Jun 6, 2007, at 7:52 AM, Vic K2VCO wrote:
Julian G4ILO wrote:
On 6/5/07, FISCHER,GREG <[EMAIL PROTECTED]> wrote:
I believe the only time you will need some other external
interface would be for true FSK. The line for this is on
the ACC connector and should be keyed via an open
collector at less than 5 volts.
Why would one want to use true FSK if you are using for receive a
modern datamode program that is capable of AFSK anyway? With AFSK you
can net on a station by clicking on the waterfall. With FSK you have
to tune the radio to the exact frequency.
I must be missing something. I thought AFSK was an FSK signal
produced by feeding an audio tone which is switched between mark
and space frequencies to an SSB transmitter, resulting in a single
RF carrier whose frequency changes.
This signal, if the tones are clean sine waves and the transmitter
has good carrier and opposite sideband suppression, should be
*identical* to a 'true' FSK signal, which is produced by varying
the frequency of a VFO in the exciter.
If you mean that it's easier to tune an AFSK signal that has some
residual carrier, that's a poor signal.
It isn't necessary to have any carrier leakage. With the modern
software demodulators using a waterfall display one can fine-tune the
received signal by clicking on the waterfall display. This adjusts
the mark/space frequencies rather than tuning the VFO. The
transmitter mark/space audio frequencies are then matched to those
used to receive. Having previously (40 years ago) used a fixed-filter
TU with a "green eye" tuning indicator and a diode-switched shift
capacitor on my transmit VFO, I was a bit skeptical until I tried it,
but it works quite well.
73 - Bob, N7XY
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