Phase one is complete. The 470 ohm resister and jumper are installed and I improved the grounding substantially.
Before:
After:
As you can see there was an almost 12dB drop from doing those two simple mods. There is still quite a bit of room for improvement, and since I can't stop tinkering with things I will probably try and do more. 12dB is nothing to sneeze at though that is 4x quieter than before. That in theory should make a noticeable improvement on decode.
Here are some pictures of the mods installed on my Signalink USB:
You can see the green jumper that snakes around the circut board with black heat shrink. There is the 470 ohm resister in there somewhere
I used green because that was the first color hookup wire I could find. The length is longer than needed but for the sake of experimenting it will work fine. I will eventually replace it with a more appropriate color and shorter length when I am truly satisfied with the results I am getting.
The USB port is now grounded to the chassis. I am not completely sure I like the way I did it, but it looks neat enough to work for now.