[RTTY] AFSK to FSK converter

[Joe Subich, W4TV]

 > Joe, it is actually solvable if you can modify the program to put out
 > only an on-off keyed tone instead of an AFSK tone -- i.e., either
 > shut the transmit mark tone off, or shut the transmit space tone off.
 > Then use an OOK decoder like the USB Interface III to turn it into an
 > FSK keying signal.

Correct - but that requires cooperation from the program's developer.
OOK tone is one of those ways of supporting FSK I specifically listed.

A fourth approach would be to code a "frequency agile" version of the
K4DSP board.  It would require a one or two character delay, measuring
frequency and duration of both tones, determining which is mark and
which is space (most likely by looking for a "long" 1.5 bit tone) and 
then generating the appropriate output.

If one could reliably count on the software to start with mark, the
job would be easier but given current programming practices one can
not even be sure that the lower of the two tones (e.g. inversion due
to LSB operation) is MARK!

73,

    ... Joe, W4TV


On 9/17/2012 3:47 PM, Kok Chen wrote:
>
> On Sep 17, 2012, at 12:09 PM, Joe Subich, W4TV wrote:
>
>> If the software author insists on "all AFC, all the time" then
>> Bill's dilemma is essentially unsolvable.
>
> Joe, it is actually solvable if you can modify the program to put out
> only an on-off keyed tone instead of an AFSK tone -- i.e., either
> shut the transmit mark tone off, or shut the transmit space tone off.
> Then use an OOK decoder like the USB Interface III to turn it into an
> FSK keying signal.
>
> There is also another way around the "AFC problem": instantiate two
> copies of the software modem.  Use one modem for transmit and the
> other for receive.
>
> 73 Chen, W7AY
>
>
>
>
>
>
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