[GreenKeys] Tri-tone RTTY

[Harold Hallikainen]

On Thu, November 16, 2023 11:31 pm, William Wuttke wrote:
> You also have to watch your power output.
> Don't forget you've got another DSP TU available for live QSOs. It would
> be
> an interesting experiment.
> When I was in the Air Force, we used the Collins TE-204, 4 tone modem
> which
> also had time diversity between the two sets of tones.
>
> Bill
> KE3BK
>

I see a description of the TE204-A at
https://www.worldradiohistory.com/Archive-Catalogs/Collins/Collins-Communications-Equipment-1964-1965.pdf#page=121
. It's complicated! And it relies on synchronous transmission instead of
async.

Thinking further on time diversity, I think I could run each tone pair or
DDS output (mark and space) through a FIFO to delay that tone pair as
desired. On the receive side, the tone filter outputs would also go
through FIFOs to put all the tones back in time alignment, then full wave
rectified, summed (mark amplitudes summed and space amplitudes summed),
then threshold detected. This would require the FIFOs to hold 8,000
doubles per second of delay. I could also full wave rectify each of the
tone filter outputs and run them through the data LPF before the FIFO,
then reduce the sample rate down to perhaps 1,000 per second (1
millisecond resolution) and convert the double to a float reducing the
bits per sample by half.

More stuff to play with!

Harold
https://w6iwi.org