Ah, I see David G3YYD has beaten me to the draw on most of it :-) :-)
He also wrote:
> Many rigs which have too large a AFSK input signal will produce 2nd harmonic
> output that will cause QRM to other amateurs. This is totally avoidable by
> attenuating the sound card output by about 20dB, a 10K series resistor and a
> 1K resistor to ground will do this for you.
Allow me to add just one thing to David's sound [sic] advice: place that
attenuator as close to the transceiver's line input as you can, and not at the
sound card end. This way, when the cabling is long, the noise that is picked up
is also attenuated before reaching the transmitter.
(This is like the sage advice when traveling by airline -- instead of just
wearing a pair of headphones to remove the engine noise, use foam earplugs, and
over that, a pair of headphones. You then crank the volume of the headphones
high enough so you can hear the music through the ear plugs. This way, you
will hear the music, but the engine noise is now much lower. David's 20 dB
voltage divider serves the function of the foam earplugs.)
73
Chen, W7AY
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