OK. That standard mic clip is the HUB Hang Up Box. When the mic is attached to the HUB, it activates the PL. When its off the HUB, it de activates the PL. No sensors or extra buttons needed. Its a spring clip mounted to the inside of the clip and when it contacts the HUB it completes the circuit.
The old-style HUB was a little metal box with a slide switch on it; had to be wired to the control head. I'll just bet I still have one or two in a box out in the garage.
If I recall correctly the newer radios work through vehicle ground; if the mic hook isn't properly grounded (and the circuit completed through the hang-up button on the back of the mic), the HUB function won't work right. if you have trouble, try grounding the mic hook and see what happens.
By the way, it also works for scanning on some radios; when the mic is in the hook the radio scans, when it's out of the hook scan stops and the radio goes to the selected channel.
I haven't used HUB programming since we got away from the days of co-channel interference (neighboring agencies being on the same frequency); PL is always on for anything I program these days.
