RadioBanter - View Single Post

November 19th 03, 04:38 AM

(Dave Platt) wrote in message ...

Getting proper, fine control of the volume level might be very
difficult with this approach.

Even if it "works pretty well", I'd be concerned about shoving audio
distortion products out well away from the signal. This might not be
too much of an issue for SSTV, which is using voice-grade bandwidth,
but I _really_ wouldn't want to do it when working PSK31. One of
PSK31's benefits is its extremely narrow spectrum width, when tuned
properly.

you are quite right. about the intermod levels. i just ran a check on
my PC sound card and this is what i have to report:

1) audio output from the PC sound card is 1V v p-p. The mic input
required is 10mV (unless there is a built-in preamp in the mic, this
is common to some japanese rigs). Thus, u need a 1:100 attentuator. A
10K and a 100 ohms resistor in series would do the trick. I suggest
100 ohms so that the impedance into the mic remains low and noise
free. further, i would also suggest that u place a 1000pf across the
mic input close to the mic jack.

2) audio input required into the PC sound card is 10mV. This is as per
the PC sound specs in the web. If we assume about 50mW audio from the
transceiver across an 8 ohms load, we are looking at V = sqrt(0.050 *
8 * 2) ~ 500mV. I think that a similar attenuator will suffice at this
end too.

- farhan