Midland Mic on Motorola XTL 2500

[Dogwelder]

I have a customer who has a need to attach a remote mic and speaker to an XTL2500 remote mount radio.

I know that I can pull PTT, Mic audio, and RX audio from the accessory connector on the back of the control head. I won't have any problems connecting mic audio and RX audio, but my concern is with PTT.

IIRC, ptt is provided by sending ground to the pin on the xtl radio. However, the mic that they want to use is made by midland. I took the connector apart. All that I can find is a shield, and two conductors which are normally open, and then go to about 700ohms when the button is pressed. I'm guessing that the midland radio senses the load from the microphone and uses that as ptt.

Any thoughts on how I could make this mic send out a connection to ground?

[Jim202]

I have a customer who has a need to attach a remote mic and speaker to an XTL2500 remote mount radio.

I know that I can pull PTT, Mic audio, and RX audio from the accessory connector on the back of the control head. I won't have any problems connecting mic audio and RX audio, but my concern is with PTT.

IIRC, ptt is provided by sending ground to the pin on the xtl radio. However, the mic that they want to use is made by midland. I took the connector apart. All that I can find is a shield, and two conductors which are normally open, and then go to about 700ohms when the button is pressed. I'm guessing that the midland radio senses the load from the microphone and uses that as ptt.

Any thoughts on how I could make this mic send out a connection to ground?

Find another model mic.

Another point to consider, depending on what the output level is of the mic you end up with, you might have to adjust the "EXTERNAL MIC" gain settings. In the radio software, there is a place where you can adjust the external mic gain. It comes from th4e factory set to "AGC". You can go in with the software and uncheck the box and adjust the gain to the right.

Jim


Jim

[Dogwelder]

I have a customer who has a need to attach a remote mic and speaker to an XTL2500 remote mount radio.

I know that I can pull PTT, Mic audio, and RX audio from the accessory connector on the back of the control head. I won't have any problems connecting mic audio and RX audio, but my concern is with PTT.

IIRC, ptt is provided by sending ground to the pin on the xtl radio. However, the mic that they want to use is made by midland. I took the connector apart. All that I can find is a shield, and two conductors which are normally open, and then go to about 700ohms when the button is pressed. I'm guessing that the midland radio senses the load from the microphone and uses that as ptt.

Any thoughts on how I could make this mic send out a connection to ground?

Find another model mic.

Another point to consider, depending on what the output level is of the mic you end up with, you might have to adjust the "EXTERNAL MIC" gain settings. In the radio software, there is a place where you can adjust the external mic gain. It comes from th4e factory set to "AGC". You can go in with the software and uncheck the box and adjust the gain to the right.

Jim


Jim

Yea that's kind of what I figured. I would consider mic gain control a "high class problem" at this point. I just need to get there =).

[Dogwelder]

OK. The customer is not dead-set on using the midland mic. Would it be possible to use a mic from say a CDM mobile and interface that into the rear accessory jack?

I've seen some information about interfacing with these types of mics. It seems that they use some sort of pre-amp in the mic itself. I've found this, which seems to be pretty common among these types of mics:

Red = Mic high (must be fed with power though a 600-1.2K ohm resister to filtered B+ to run the pre-amplifer)

Green = PTT (it may be an open collector sink to ground)

Black = Ground

Blue = Hook switch



So excuse my ignorance, but there is b+ voltage on the accessory connector. I would connect that to the red wire with a resistor, black is ground, green would provide ground with ptt, and blue is the hook switch, which I don't really care about. Where does the mic audio come from?

Thanks in advance for your help.

[Jim202]

OK. The customer is not dead-set on using the midland mic. Would it be possible to use a mic from say a CDM mobile and interface that into the rear accessory jack?

I've seen some information about interfacing with these types of mics. It seems that they use some sort of pre-amp in the mic itself. I've found this, which seems to be pretty common among these types of mics:

Red = Mic high (must be fed with power though a 600-1.2K ohm resister to filtered B+ to run the pre-amplifer)

Green = PTT (it may be an open collector sink to ground)

Black = Ground

Blue = Hook switch



So excuse my ignorance, but there is b+ voltage on the accessory connector. I would connect that to the red wire with a resistor, black is ground, green would provide ground with ptt, and blue is the hook switch, which I don't really care about. Where does the mic audio come from?

Thanks in advance for your help.

The mic high in most Motorola radios has a DC bias on it to run the mic amp circuit. Don't worry about it and just connect it up to the mic high input.

Jim