[GreenKeys] Single Tone Keying

[Jim Haynes]

As a matter of interest, note that the modem used by deaf people is
single tone for space.  The reason is so that when nobody is sending
the circuit is quiet, so there is no need for a send/receive switch.
The modem also sends a tone for mark, but turns it off after a short
interval to leave the circuit quiet.  The reason for the mark tone is
not FSK but to suppress echoes that occur on long telephone lines,
so the frequency is fairly arbitrary.


On Sun, 10 Sep 2023, B. Smith wrote:

> I've added another 555 board as a tone generator to send RY's Mark only to 
> the TU for "Make and Break" RTTY.
>
> http://k4che.com/Tempvideo/RY%20Comparison/RY%20Mark%20Only.mp4
>
> K4CHE
>