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

wrote in message
ups.com...
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


You've got it all correct Dave, but for one multiplication error. Eight bits (1
start bits, 5 character bits, and 2 stop bits) of 22ms works out to 176ms, not
196ms.

73, de Hans, K0HB

Thanks, I realized after I posted... it's Friday.

Dave

I think you will find an "idle keyboard", no key pressed, will be a
continuous mark tone.

Paul, KD7HB

wrote:
Thanks, I realized after I posted... it's Friday.

Dave

wrote in message
oups.com...
I think you will find an "idle keyboard", no key pressed, will be a
continuous mark tone.

Paul, KD7HB

Quite right. The 'diddles' you hear are often Letters character being sent
to stop the machine from getting bored.
By the way, I saw it mentioned that a Stop bit was 2 units long? I've always
thought it was 1.5.

Nana

Thanks for the info. The "diddles" (LETTERS char) I was hearing wasn't
a continuous mark tone, which was what I referenced in my original
post. I assume this is to help the RX station stay in sync.

Dave