[SECC] N1MM Sound Card Interface

[Scott Straw]

Jeff,

I think I can solve both of your problems.  As a sound engineer wanna-be, my
first thought is that you have an impedance mis-match with your
speaker-level (8 ohm) audio feeding into to a mic-level (600 ohm) input.
This would possibly explain the distortion.  you need to impede the audio
output of the computer so that it looks like a microphone-level signal to
the radio.
A quick and dirty under $5 solution would be to use a RS 273-1380.  It is an
8:1K transformer.  It was probably in the blister pack on the rod next to
the 1:1 isolation transformer (RS 273-1374) that you bought. The red and
white leads go to the speaker, the blue and green leads go to the radio.
(The black center tap lead is unused.)
Normally this device is used to raise mic-level signals to speaker level,
but electrons inside the transformer are inherently lemming-like and will
"go with the flow."  In the process you will keep any and all of the nasty
ground-loop induced buzz or audio hum found on an unbalanced signal from
getting into your radio - the same job that the 1:1 transformer does without
the impedance change.

I hope this helps.

Scott Straw, CTS, EMT-I
KB4KBS

A/V Systems Engineer
SPL Integrated Solutions, Inc.
Norcross, GA

Firefighter/Emergency Medical Technician
Roswell Fire Department
Roswell, GA

Technical Director
Northside United Methodist Church
Atlanta, GA

(I have identity issues)