On Sun, Oct 17, 2021 at 2:15 PM Harold Hallikainen <harold@w6iwi.org> wrote:
On Sun, October 17, 2021 10:32 am, Nick England wrote:
> An interesting an informative article is here
> "Military Teletypewriter Systems of World War II"
> https://www.nonstopsystems.com/radio/pdf-hell/article-AIEE-1948.pdf
>
Thanks for posting! An interesting idea is on pdf page 8. They transmitted
two mark tones and two space tones on an SSB transmitter to get frequency
diversity.
Harold
 
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This was standard practice on the Navy's UCC-1 multiplex system. Called "twinning". Also the selector switch included 4 channel diversity as well as 2.
https://www.navy-radio.com/rtty-mux-ucc1.htm

IIRC, one of the Army's RATT TU's will do the same thing, simultaneously running 85Hz as well as 850 Hz shift.
MD-522 used with the GRC-106 maybe?
Nick