I have 3 Uniden scanners. I wanted to mix all the audio via an audio mixer panel. I had problems that I traced to a lack of audio isolation in the scanner(s). I measured a 3 volt potential between scanner audio ground and mixer ground. So I put 600:600 Ohm audio transformers on all external speaker lines before they go into the mixer. That provides complete DC isolation. So for my 3 scanners I needed 3 transformers. The ext spkr line goes to the transformer primary. And the transformer secondary goes to the audio mixer.
Everything works great now!
Everything works great now!