Questions from a newbie...

[Bailey228]

Hello all,

I work as a race controller at a motorsports park and we use the CM300 series radios.

The current setup has 5 radios with 5 mic's lying around. I'm trying to incorporate 1 mic for use with 5 radios.

I've built a 'switch box' which has an (1) RJ45 INPUT and then using five simple momentary on/off switches to transfer the mic to (5) RJ45 OUTPUTS.

When using the standard mic with the unit, everything works well. However, I'm trying to replace the std mic with a headset type and am encountering issues.

I'm somewhat electronically savvy, but I'm not up on my 'radio' terms (SPI, Hook etc...)

Can anyone provide me with a 'layman' description of the RJ45 pinouts? Specifically, which wire colours for audio to the earpiece and mic output.

Any help would be greatly appreciated, and again, please keep it simple.

Thanks... Glenn

[Bill_G]

Glenn - Batlabs has a gif of the Maxtrac / GM / CM mic jack. You need just four wires - ground, PTT, mic hi, and handset audio. PTT to ground for xmit. Mic hi supplies DC to bias mic amp. Handset audio is fixed level not affected by vol control. You will have to determine wire colors based on the cord you use.

[Bailey228]

Bill,

Thanks for the quick response. That is the GIF I used to originally wire the plugs / switches.

I've 'straight' wired all the wires in the RJ45 and introduced the switches between (6) PTT and (4) GROUND to transmit.

This seems to work well, although the actual 'audio' from the mic doesn't seem to work with any mic other than the original handheld mic. Any suggestions as to why any other mic won't work?

I suppose the first question should have been; what mic specs do I need to meet to use on a CM300?

Again, thanks for the quick response.

Cheers... Glenn

[Jim202]

Bill,

Thanks for the quick response. That is the GIF I used to originally wire the plugs / switches.

I've 'straight' wired all the wires in the RJ45 and introduced the switches between (6) PTT and (4) GROUND to transmit.

This seems to work well, although the actual 'audio' from the mic doesn't seem to work with any mic other than the original handheld mic. Any suggestions as to why any other mic won't work?

I suppose the first question should have been; what mic specs do I need to meet to use on a CM300?

Again, thanks for the quick response.

Cheers... Glenn

The original Motorola mic is using the bias voltage on the mic pin to run an audio amp inside the mic. Using another type of mic, you could be even shorting out the bias and as such, killing the mic audio.

Jim

[Bill_G]

I agree with Jim. You need a headset designed to work with the radio.

[Bailey228]

Ok, that makes sense... thanks.

Does anyone know of any lightweight headset that will work with the CM300.

Ideally, I'd like something like this;
http://www.novacommunications.com/Two-W ... _info.html

Or most preferable, this;
http://www.novacommunications.com/Two-W ... _info.html

Any way to make use of either using a pre-amp?

Thanks for all your help... Glenn

[Bill_G]

You can contact Setcom. It is a niche market. Not much off the shelf for mobiles. I've always had to McGuiver the customer's chose of headset to their radio.

[HLA]

if it's a condensor mic make shure the radio can power the condensor and that the polarity is correct

[Will]

The mobile radio requires a lot more output from the mic, upwards of 180 mV. The headsets for portables have a much lower output and way different voltages and impedance.

I have a amplifier that works to use a portable/handheld headset with Motorola mobile radios. It uses the headset ptt.
Let me know if the circuit for the amp would help. Not too hard to build.

The amp even works for Heil headsets..... And Bob Heil said "it was impossible".

[Bailey228]

Will,

I assumed that was the problem, and yes, I'd love to have a circuit for the amp. If you could see your way clear to send it my way, I'd be very appreciative.

On another tangent, and this is just throwing it out there... would the audio output from a PC sound card work? My thinking is that it would open up a lot of possibilities. Just thinking outside the box.

Another thought is to steal the circuit board from a RMN5068 that I have kicking around. Possibly taping the mic into the circuit and eliminating the actual 'mic' from the RMN5068.

Any thoughts on these options?

You folks are great, and I do appreciate your help!

Cheers... Glenn

[Bailey228]

Will,

That's what I was beginning to suspect as well. I would definitely appreciate any schematic / circuit design for an amp that would allow this.

Thanks... Glenn