Batboard

I've been given a project to wire a podium-style gooseneck microphone to an xtl1500 mobile being used as a base radio. The mic is 500 ohm dynamic. I am assuming the usual xtl1500 mic (hmn1090a) uses a small preamp (at least it looks like it does). When I hooked up the gooseneck mic, the most mod I could get out of it 1kc, and that was eating the mic and talking loudly. I was thinking about just taking the hmn1090 apart and putting the guts into the gooseneck. Unfortunately the mic element will not fit into the end of the gooseneck mic. Thoughts?

The problems facing you are twofold. First, every single Moto radio I've ever encountered places about 9V of DC bias on the mic hi line to facilitate driving the preamp in the standard Moto mics. This is a throwback to the days when carbon-button mics were still common. If you're going to try connecting a dynamic mic directly to the radio, you will need to put about a 1uF non-polar DC blocking capacitor in series with it.

This leads into the second problem. Even with the blocking cap, a simple dynamic mic may not have enough output to drive the thing to normal modulation. You will need a preamp of some sort. Examples of circuits for such can be found all over the place, including older editions (80's-90's) of the ARRL Radio Amateur's Handbook.

Happy tweaking.

Anybody remember those in-line preamps /\/\ot had that would interface a dynamic mic to a radio? They probably dumped those a long time ago. Check your hardbound silver partsbook...