Maxtrac mic connector

W6JK · Post by **W6JK** » Sun Feb 19, 2006 10:42 pm

Over on Batlabs, there's a cryptic comment about the mic connector on 900 MHz Maxtracs being wired differently from the others. This raises more questions than it answers. Are the mic leads different, or is it other signals that don't match? Is it dangerous to connect certain mics to certain radios, or will they simply not work? Which mic(s) are 900 MHz compatable? Is there a known reason why M would do this? Are these issues documented somewhere that has escaped my attention? In short: Help!

Jeff

kb0nly · Post by **kb0nly** » Sun Feb 19, 2006 10:50 pm

As far as i know all Maxtracs use the same microphone pinout and mics for that matter. Never come across one that was different.

W6JK · Post by **W6JK** » Sun Feb 19, 2006 11:15 pm

So how come on this page...

http://www.batlabs.com/maxrad.html

it sez...

Linking Maxtracs for Repeater/Crossband Use

Need to connect a couple of Maxtrac/Radius radios together? Here is a schematic of the R.I.C.K. to get you started. Order the service manual part number 6880901Z79 from Motorola.

An alternative method of linking 2 Maxtrac/Radius type radios together can be found here. DO NOT USE THIS WITH 900MHz RADIOS, the pinout of the microphone connector is different!

kb0nly · Post by **kb0nly** » Mon Feb 20, 2006 12:19 am

No clue, but i know guys that are using the same mic on their 900Mhz that i have used on VHF and UHF radios.

kcbooboo · Post by **kcbooboo** » Mon Feb 20, 2006 4:39 am

On VHF/UHF/800 MaxTracs, MIC connector pins 1&2 are normally spare and run to unused pins on the logic board. Myself, and others, usually bring a COR signal out via pin 1. The schematic that is brought up when you click "here" (not on this message but on the maxrpt page), shows the COS (COR) signal on pin 1.

900 MHz MaxTracs have HearClear components mounted on the mike/vol circuit board in the control head. To enable/disable HearClear, they use the spare wire that used to go to pin 1 of the MIC jack. So you can no longer use that pin as the COR pin.

COR can just as easily be put onto pin 2 of the MIC jack, then it would probably work with all MaxTracs.

Other than that, the pinouts of the MIC jacks are identical, for the signals that Motorola brings out to them (pins 3 thru 8).

Bob M.

W6JK · Post by **W6JK** » Mon Feb 20, 2006 10:09 am

Ah, so I don't have a problem after all. Thank you both for the help. I think I'm going to use the accessory connector in my project.

This is a case where a few more details on that page would have been a good thing.

'JK

kb0nly · Post by **kb0nly** » Mon Feb 20, 2006 11:38 am

The Batlabs site really needs some updating and editing but for whatever reason it hasn't been touched in a long long time.

Max-trac · Post by **Max-trac** » Tue Feb 21, 2006 10:42 am

If you plug in most DTMF mics into a 900 unit, they knock down and distort the speaker audio.
You have to go into the mic and snip the wire (blue, I think, but better check) that goes to the "unused" pin. See the schematic on batlabs.

There were a bunch of DTMF mics in that vintage, they all seem to be very similar inside, you just have to figure out things like the Mostar hang-up went to another pin and not to ground.
IE it is simple to put a new plug on a mostar mic and change 2 things inside and us it on a maxtrac.

n2knc · Post by **n2knc** » Wed Feb 22, 2006 9:08 pm

they work good for my icom 706mk2g gives it some good hot audio

train_radio_guy · Post by **train_radio_guy** » Sat Apr 15, 2006 7:16 am

Speaking of microphone audio issues, I've noticed something rather interesting on GTX900s. Using regular (non-DTMF) microphones, and the same mobile radio, I've measured different audio levels, depending on which microphone is used.

Most of the mics are the standard black type, with the rubber gasket separating the two halves, which are held together by several Phillips screws. A few of the mics have the RX/TX LED built in.

Is there an impedance difference in the radius/maxtrac/gtx series microphones? Several have muffled audio, while others have especially clear audio. Did /\/\ change something in their mics?

Thank,

trg,

Max-trac · Post by **Max-trac** » Sat Apr 15, 2006 8:25 am

I have a bunch of older Mostar DESK mics that have muffled audio when I converted them over to Maxtrac.
We replaced C2 (a .022) with a .0047 for crisper audio.

There are variations in the scematics, but maybe you can figure something out...

Sometimes the mic element is just bad.

kcbooboo · Post by **kcbooboo** » Sat Apr 15, 2006 8:32 am

Many of the Motorola mobile radios use a 560 ohm resistor to +9.6V to provide current to operate a preamp in the mike, or even work with an old carbon microphone (that'll date me). For the most part, the input impedance of the radio is nominally 600 ohms. This should let it work with most microphones, but some might not be happy about the DC present on the audio line.

Bob M.

train_radio_guy · Post by **train_radio_guy** » Sat Apr 15, 2006 4:20 pm

Well, it looks like I'll need to compare the mics with decent audio, to those with poor audio. As it just so happens, the mic with the best audio came with a GM350 from the UK. I'm not quite sure how that will play into things, but I'll pass along anything I find out.

Hopefully it's just a component difference or a dirty mic hole. How often do these mic elements fail? If it's the mic element itself, I'll need to find replacements. It seems like Radio Shack used to sell electret mics, but I seriously question their quality. Any recommendations or suggestions.

Thanks,

trg,

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