I dug a bit deeper into the Paragon II, and the Paragon II Operator's
Manual. I found that the schematic for the RS-232 board is incomplete.
Some little details which someone may have thought were non-essential
were left out, such as the Vcc to the big ACIA chip. There is no ground
wire included in the cable running from the RS-232 board to the DB-25
connector board. I thought adding a ground here would fix the problem,
and maybe it would have, however before it tried that, I noticed the
single wire used for the CI-V interface. This wire, which runs from
connector W on the RS-232 board to connector W on the SIDETONE BOARD,
also does not have a ground wire with it. Unplugging the wire at either
end eliminated the noise (or at least put it below the noise floor of
the radio.) I left it disconnected at both ends, as I do not intend to
use the TTL level CI-V interface.
DE N6KB
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