I have made myself a headphone splitter to use with my PRO-96 and PRO-97. It consists of 2 1/8" strereo plugs wired to a single 1/8" stereo jack. The tip of each plug is wired to the time and ring of the jack, and the ring of each plug is wired together to the shield of the jack. This allows audio from 1 scanner to feed the left headphone and audio from the other scanner to feed the right headphone. The "grounds" from the headphone jacks, which is actually the "ring" of the plug that has continuity with the common ground of the radios, are tied together. This arrangement works great when the scanners use dedicated duck antennas and battery power.
My question comes in when I connect a separate mobile antenna to each radio. These two antennas are both using NMO mounts. Obviously they are tied to the common ground of the vehicle frame. When both radios are connected to the mobile antennas, I start getting audio from both radios through both headphones. Somehow, the connection of the antenna grounds to each other somehow combines the audio circuits. It's like a ground loop or something.
Can anyone with a schematic of these radios and more technical knowledge than me explain why that happens? I haven't tried this yet, but my next step is to "lift" the ground of one of the antennas and see if that maintains separation of the audio. I might also try lifting the "shield" of one of the audio connections and see if that makes any difference.
Does anyone have any other ideas?
My question comes in when I connect a separate mobile antenna to each radio. These two antennas are both using NMO mounts. Obviously they are tied to the common ground of the vehicle frame. When both radios are connected to the mobile antennas, I start getting audio from both radios through both headphones. Somehow, the connection of the antenna grounds to each other somehow combines the audio circuits. It's like a ground loop or something.
Can anyone with a schematic of these radios and more technical knowledge than me explain why that happens? I haven't tried this yet, but my next step is to "lift" the ground of one of the antennas and see if that maintains separation of the audio. I might also try lifting the "shield" of one of the audio connections and see if that makes any difference.
Does anyone have any other ideas?
