RadioBanter - View Single Post

January 21st 05, 09:34 PM

On 21 Jan 2005 11:37:19 -0800, wrote:

I'm trying to write a program (for my own education) that will transmit
RTTY. I'm having some difficulty determining the exact format. From
what I've observed from MMTTY, an idle keyboard has a 22ms space tone
followed by a mark tone until the next space tone. I would have
assumed that a standard letter/8bit transmit would last 196ms (22*8),
but after recording it with a wav recorder and viewing it, it appears
to be shorter (168ms or so, +/- 10). I'm not sure if the recorder is
not accurate with timekeeping, or if I don't fully understand the
format.

I would like to believe the standard format for a letter/8bit transmit
is a start bit (space), data bits (marks/spaces), and two stop bits
(space), *ALL* of which are 22ms long. Is this statement correct?
Thanks in advance,
Dave

No. It's a 5-bit code, plus start/stop bits. google for Baudot and you
can find a code chart.

The stop bit may be 1.0, 1.42 or 1.5 units long, with 1.42 being the
value based on the most common mechanical printers.

Hence, you will often see it called a 7.42 unit code.

Jack K8ZOA