Huh! So what in laymen's terms does this do? Isolate the scanner ground from the audio input's ground?
I used to plug my scanner headphone jack into a phono or other RCA audio input on my stereo amp in order to listen to the scanner over my stereo speaker system...
Are you guys saying we can't do that anymore? Thankfully I never tried it on the TRX, YET!!
Ground loops have been a problem as long as I've been tinkering with this stuff, nearly 40 years.
The issue comes when you have a scanner powered off the household electric circuits connected to something else that is also powered off the household electric circuits. The multiple paths to ground from these various devices create a loop which can pick up electrical interference by induction. A handheld scanner powered by batteries is probably not going to be affected.
In addition, some devices (like a good quality stereo amp) will have impedance transformers on the inputs, which also serve as effective ground loop isolators. Most computers, however, do not have any kind of impedance transformer on the sound card input or output, and are fairly poorly shielded to begin with, so you end up with a ground loop.
The outboard ground loop isolator (a small transformer) simply isolates one device from the other, breaking the loop while still passing the audio.
And thanks to the folks who provided the links for the inexpensive isolators. I've been making my own with little surplus audio transformers for years and mounting them in 35mm film cans, but I'm out of transformers and these are much neater and cleaner.