Serial port permissions -

Brian Mury brianmury at
Tue Oct 18 21:43:21 UTC 2011

On Tue, Oct 18, 2011 at 10:30, g <geleem at> wrote:
> what you have not communicated, are you connecting to a modem, or to
> another computer?


He is trying to use a RS-232 control signal as an input to a simple
transistor or optocoupler circuit, which will ground the "push to
talk" input to a radio transceiver in order to toggle it between
transmit and receive modes.

The sound card is being used as a modem, but that is not relevant to
the serial port issue.

It'll usually look something like this: (not my image,
just a Google Images search result).

It's a very common amateur radio (a.k.a. ham radio) setup for digital
modes. The computer modulates a data stream. The modulated signal (at
audio frequencies) is fed from the sound card line out to the
transmitter's microphone input. On the other end, the receiver's
speaker output is fed into the sound card's line in or mic input,
where it is demodulated back into the original data stream. Bob wants
to use PSK31, but there are quite a few other digital modes as well
(PSK31 just happens to be one of the most popular). If you're
interested, a Google search for PSK31 is a good starting point to
learn more, or email me off list and I'd be happy to share what I


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