I dont know if this is what you are running into or not, but we ran into the same thing when attempting to use the Motorola Maxtrac/Radius series with an external controller. We use the ones without the 16 pin accy connector because they can be had very reasonably. All connections are thru the front panel mic connector.
The Motorola amplified mic uses a bias resistor inside the radio and supplies around 10V thru about a 500 ohm resistor to the mic element. This is probably a holdover from the days when they used a carbon element. When converting a station such as the Micor, we would usually remove this resistor. The input impedance is now much higher and there is no pesky voltage on the line to reverse bias electrolytics etc. In the Radius, the resistor is a surface mount on the bottom of a board. In addition to being very diffucult to remove we would lose the microphone functionality. We opted to use a self powered FET circuit mounted either in the controller enclosure or in the connector shell of the cable. Click below for schematic. http://webpages.charter.net/k4hal/amp.jpg Click below for photo of the the amp mounted in a DB9 connector shell that plugs into a NHRC-2 controller. http://webpages.charter.net/k4hal/cable.jpg The amp has a modest amount of gain (around 4 or 5). We use it on all our link/remotes and APRS. Henry, K4HAL --- In Repeater-Builder@yahoogroups.com, "Rob" <[EMAIL PROTECTED]> wrote: > > Anyone know if the schematic for an amplified Motorola Mic is > available on the net? > Still trying to get this autopatch going and having some real level > issues. My patch just doesn't have enough drive for the radio. > TIA -Rob- Yahoo! Groups Links <*> To visit your group on the web, go to: http://groups.yahoo.com/group/Repeater-Builder/ <*> To unsubscribe from this group, send an email to: [EMAIL PROTECTED] <*> Your use of Yahoo! Groups is subject to: http://docs.yahoo.com/info/terms/
