"Tom, N3IJ" wrote in message
...
I want to interface the audio from the Small Wonder Labs PSK20 to the
mic input in the Toughbook CF27 laptop. The computer has no line
input, and I plan to use the mic input via the port replicator. The
Toughbook reference manual doesn't give any specs for the mic input.
The user manual does contain this caution:

"Use only a monaural condenser microphone (miniature jack). Using
an input source other than a monaural condenser microphone
may not allow audio to be input or may damage the equipment."

Reading suggests that an L pad in the 40-60 dB range is required, but
I would like to narrow this down before experimenting. Any experiences
using the Toughbook on PSK would be helpful.

Thanks, Tom, N3IJ

Microphone does work well if you have a decent one. Also has the advantage
of being able to record both sides of conversations for logging purposes.

The inputs are usually 500-2000 ohm impedance and have a DC bias for
powering the mic.

I have always used what is in the junk box to make the transition. The
speaker output is fed to a low impedance audio transformer. It may be 8 ohm
to 2000 ohm or 500-500 ohm or whatever in that range. Such things are easily
obtainable at RS and other sources. The output of the transformer is loaded
with a resistor of 1k-10 k and a series resistor of 100k or more feeds the
mic input. This will usually reduce the input to mic level and the
transformer will break up any common mode potentials between the chassis of
the computer and the radio that tend to bring hum and noise. You will also
see a flatter response than with acoustic coupling. You should be able to
reduce the mic level in the mixer applet to normal level. You may have to
play with the 100k and may need to shunt the mic input as well but you will
find this by experimentation to get it right. A purist might also series
the input with a 1uf to 10 uf capacitor to completely block the DC
component but the series 100k should limit that sufficiently. Some
experimentation could be done for more precise equalization if you still
have time on your hands.

This should work with any sound card mode.