Make sure your computer isn't cranking the gain on the line in.
Most shack audio line levels you want to keep at the 1V P-P level if at all
possible. If you're attenuating down to sub-millivolts (microphone levels)
to match "mic in" levels that's a very poor choice and makes you very
susceptible to noise from non-isolated grounds.
There are some conventions regarding "microphone audio is mono and line in
is stereo" with dual-purpose mic-in/line-in jacks that may be throwing you
off and resulting in your card treating the audio like mic in, not line in.
Some soundcard setting may result in AGC automatically being applied to
mic-in.
If you have no choice but to use millivolt microphone levels, you really
super duper need ground isolation via audio transformer. I have found
ground isolation via audio transformer to be unnecessary at 1V line levels.
Also... this may sound stupid... but make sure you are actually feeding the
decoder off of "line in" and not off of a microphone that may be plugged
into the PC. I have had some bizarro-world experiences where I start a
contest with the computer decoding audio that has leaked out of my
headphones, into the computer's microphone, and then into the decoder. It
kinda sorta works but not very well!!!!
Tim N3QE
> I am just running the AFSK simple set-up of computer line in / line out to
> K3 line out / line in.
> Didn't think I was having decoding problems.
>
> The other day I was using Google remote desktop to listen to the shack
> computer. To get the audio
> the "listen to line-in" box has to be checked. I was amazed at how noisy
> it was, crackles/pops, etc.
> I turned the K3 off and the noise was the same. There are a few ferrites
> on the line in cable.
>
> Does this mean I need an external usb soundcard? Better grounding? More
> ferrites?
>
> Maybe this is why I can't hear the VU's and 9K2's calling me on 80M rtty :)
>
> 73 Bill KO7SS
>
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