Paul Keinanen wrote in message . ..
On 4 Jul 2003 23:21:05 -0700, (R C) wrote:

I'm working on a telemetry board and wish to include software FSK1200
(MX-614's are getting harder to find). The official Bell 202 spec is
out of print and hard to find as well, so I pieced this together from
what I can find. Multimon won't decode the output, so I'm likely doing
something wrong.

What is this Multimon thing expecting ?

Okay, I've figured some things out since I first posted. Multimon was
written by Thomas Sailer, who also wrote the soundmodem program.

It's available at http://www.baycom.org/~tom/ham/linux/multimon.html.

Documentation is lacking, but reviewing the source (don't try and
debug at 4 AM; I should've figured this out originally) the afsk1200
decoder expects hdlc encoding, and possibly AX.25 framing (didn't
trace that far). However, an undocumented option -v 10 yields the raw
bit stream.

In that case I assume you have mixed the polarity of the start and
stop bits.

In ordinary RS-232 asynchronous communication the start bit is "0"
SPACE, interrupting the idle MARK state, followed by the data bits
with LSB sent first. The stop bit is "1" or MARK, which then transfers
to a MARK idle state if no more characters are to be transmitted.

That part I figured out from APRS packets recorded off the air. Start
is definately 1200 hz, stop is 2200 hz.

Thanks for the suggestions,
R C
KG4MVB