But Dave, the soundcard is doing that already!

Most Ham RTTY is in Baudot (Paul, take note), I've never seen any ASCII on
air although it was experimented with when machines became available. The
actual code is called Murray Code. Baudot is a bit of a misnomer as it
really refers to timing.

MMTTY will do all the timing/decoding of the characters in RTTY, the sound
card will perform the audio processing. For a good old fashioned TU, even
one in a PIC, you will need some good audio filtering and processing in
order to clean up the tones. My old unit was called an ST6 and might appear
on Google. It consisted of some audio filtering, then two tuned filters
using toroids (88mH) then a slicer and a level shifter.

This unit could only handle two frequencies 2125 and 2295Hz for a 170Hz
shift signal. Since RTTY is also being sent on the ham bands with 200Hz
shift, you will need to account for this. Since then, new chips became
available from Exar to decode the audio tones, based on PLL's, but it must
be said, the audio performance was never quite as good under noisy
conditions. The DSP in new soundcards now run rings around this old process.

To assist you in your quest I suggest you read some of the notes with MMTTY
as he refers to the signal processing in them. Also, there was a Greenkeys
website around a couple of years ago with a lot of information about RTTY
signalling which might help.

Nana (aka Brad VK2QQ)

wrote in message
ps.com...
I'm still open to what type of RTTY to use... and as far as
transmitting, I'm not using available software or a UART/USART chip.
My goal is to program a PIC so that it can control a FSK circuit and
transmit to my PC, which is receiving with MMTTY or something similar.
Thanks for the info all!
Dave