Motrac U64LHT-3100A UHF Radio

[Chris Simpson]

Greetings all,
I just purchased a motorola motrac radio to put in my 1960 American Lafrance. the problem I have it the relay inside the radio is a TLN-8427A negative ground only. I know there was a kit to make it positive ground... anyone know what the part number is, or ayny one have one? I have set up the radio and tested it and it works good. I just need to make it positive ground and change the Freq. it's tx is 469.150 and I am not sure what the rx is but I need tx 465.250 rx 460.250. if anyone can help me out I would appriciate it.
Thanks,
Chris

[WB6NVH]

As I recall, there is a polarity plug located on the power supply, which is basically a multi-pin proprietary connector with various pins jumpered. It would seem unlikely you would be able to source one these days since they were uncommon in the first place, so I would suggest prying the plug apart and rewiring it to be the positive ground version. I think the manual shows the polarity plug internal wiring.

The next thing is that this is not a broadband radio. It will have to be realigned to function right. 4 MHz is a bit too far to move one without touching things up.

Finally, this is going to be somewhat of a boatanchor in a couple of years, if not sooner, because of the narrow band FCC mandate, if you are actually planning on using it on a public safety channel.

[WB6DGN]

I'm not optimistic that you'll ever find one of these, but the part that you're looking for is TLN8482A. It is called a "Ground Reversing Kit". It can be used in place of the TLN8427A "Negative Ground Kit" for EITHER positive OR negative ground depending on it's inserted position in the radio, so, if you are lucky enough to find one, YOU STILL have to be careful how it is inserted in the radio. I looked briefly for a schematic of the Ground Reversing Plug without success. The manual does show the Negative Ground Plug and references the Reversing Plug but doesn't show that schematic. I'm getting kind of bleary eyed tonight but I will look further tomorrow. If I can find it I will make arrangements to get you a copy of it but so far it doesn't look promising.
Tom DGN

[Chris Simpson]

thanks for the info. I am not planning on Tx on this radio just basically using it a single channel scanner. The truck is an original truck from my fire dept. and I thought it would be awesome if while at events the actual radio would Rx. if any one knows anyplace to try to find the plug let me know.
Thanks again,
Chris

[WB6DGN]

Chris,
I have been unable to find a schematic of that Ground Reversing Kit in any of the Motrac manuals. As is typical with Motorola, accessories are usually covered on a separate sheet supplied with the accessory. Two possible solutions: 1. Astron makes a polarity reversal unit which is essentially a DC to DC converter with the output voltage the same as the input. If you're not going to transmit, you'd need a very low current one. Not sure whether you would have to isolate the whole chassis from ground or not; never had to use one, but a possibility.
2. Check with Ted at MDM Radio mdmradio@yahoo.com He just may have the plug or know someone who does. He has a lot of resources at his fingertips for equipment of all types. He's presently on vacation; you will probably have to wait until after the first of the year to reach him but, in my opinion, hes probably your best bet. Good Luck,
Third possibility, for receive only is just a full wave diode bridge. This would definitely require isolation of the chassis AND antenna from the vehicle but, in a pinch?????

Tom DGN

[Bigred]

Chris,
1. Astron makes a polarity reversal unit which is essentially a DC to DC converter with the output voltage the same as the input. If you're not going to transmit, you'd need a very low current one. Not sure whether you would have to isolate the whole chassis from ground or not; never had to use one, but a possibility.

Tom DGN

These Astron units do not require the radio chassis to be isolated from ground.

[Glen W Christen]

If you go the isolation route, don't forget the control head and fusing BOTH leads. Some functions are referenced to chassis.

[com501]

Make sure you check the one you have, it might already have that plug in it. Many did, when sold to public safety in those days....