[RTTY] AFSK-to-FSK Circuit

[Doug Hall]

Hi All,

There has been some discussion in the past about how to generate an
FSK signal if you don't have a serial port or if your RTTY software
doesn't support FSK. If you find yourself in this situation and you
want or need to run FSK I have created a fairly simple circuit for
creating an FSK signal from the AFSK output of your sound card.

This circuit is a very simple AFSK demodulator, with the demodulated
output driving the FSK input on the radio.  A PTT signal is also
generated, so this can also be used as a general purpose sound card
interface if you are so inclined. But the main purpose is to provide a
way for those who can't otherwise run FSK to do so.

There are details (schematic, firmware, source code, and
theory/operation documentation) at
http://k4dsp.homeip.net/~doug/regenerator/index.html  I have toyed
with the idea of laying out a little circuit board, but I just don't
think there is that much demand. If I find out otherwise I'll get some
boards made.

I hope it's useful for someone. I have been using this circuit for a
while now and it works very well. If you have questions or comments
please feel free to drop me a note. And if you're looking at this and
asking yourself "Why the heck do I need that?" then you probably don't
need it :-)

73,
Doug, K4DSP