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Just came up on a Desktrac base

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Josh380

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Through some bartering, I came up on a desktrac base last night. Radio has 32 channels. I also have a Radius m120 (2 ch), that I'd like to add to it to make this thing a repeater.

There doesn't seem to be any step by step instructions for adding a second radio to it. Does anyone have any experience with these radios that could help me? I don't have a clue here and I want to make sure it's done right.

I can provide picures as I'm sure they will be needed. Thanks!
 

Josh380

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Here are some pics:
 

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Josh380

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A few more:
 

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Josh380

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And btw, I've already looked at repeater builder and there's just an overview of the desktrac. No step by step instructions. There's not much help for how and where to make connections.
 

Project25_MASTR

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Interfacing should be the same as a regular 5 pin/16 pin Maxtrac/GM300/Radius. To the best of my knowledge, the Desktrac was never offered in a repeater configuration (that is what the GR300/500 and different RIB assortments were for). You may have to trace wires coming out of the radio to the console interface but that should be about all. Now to fit a full repeater inside of there...you may need to find a smaller receiver to put in there. Personally, I'd go with a Hamtronics reciever and a ComSpec PL board (for decode)...high end receiver though. Or maybe a Saber, GP300, or HT1000 as a receiver with a battery eliminator for less investment.
 

mikewazowski

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To the best of my knowledge, the Desktrac was never offered in a repeater configuration (that is what the GR300/500 and different RIB assortments were for).

The Desktrac was available in a repeater configuration.

Another Maxtrac mobile was added in the front right of the cabinet as a receiver.

I would start with this wiring diagram:

http://www.repeater-builder.com/motorola/maxtrac/desktrac-pix/rptr-wiring-diagrams.pdf

The part numbers for the various cables are included on the diagram. Once you've made or bought the cables, it's probably just a matter of programming the accessory connectors correctly for repeater operation.

I doubt there was ever a step by step guide for converting a regular Desktrac into a repeater. Most people just bought them as a repeater.
 

Project25_MASTR

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The Desktrac was available in a repeater configuration.

Another Maxtrac mobile was added in the front right of the cabinet as a receiver.

I would start with this wiring diagram:

http://www.repeater-builder.com/motorola/maxtrac/desktrac-pix/rptr-wiring-diagrams.pdf

The part numbers for the various cables are included on the diagram. Once you've made or bought the cables, it's probably just a matter of programming the accessory connectors correctly for repeater operation.

I doubt there was ever a step by step guide for converting a regular Desktrac into a repeater. Most people just bought them as a repeater.

Interesting. Good info to know as I've never seen one (seen some of the Spectra based consoles in repeater configuration but never a Desktrac).
 

mikewazowski

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Here's an eBay auction for a UHF unit which gives a pretty good picture of the guts:

Motorola Classic Desktrac UHF Base Repeater L24SUM7000AT | eBay

Looks like they sell for just over $100.

A friend had some VHF units that he dragged down to Dayton every year. I don't recall tossing them under the truck during the rainy periods so he must have sold them at some point.
 

cmdrwill

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You will have to make up a cable to connect to the front pins, control head, connector on the receiver. The cable is NLA from Motorola, so we built our own 'receiver interface' cables. They are soldered on the control board behind the front panel. I have some photos of the cable if you need.

The receiver radio does not even have to have the 16 pin connector as it is not used.
 

Josh380

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Hmm. Interesting. Looking at what I have it seems all that's in this thing is a power supply, a radio, and the desktrac control head. I know that if I remove the outer casing and control head from the m120, the second radio WILL fit. My questions are:

How do I connect the receiver radio (m120) inline with the rest, so that this thing works as intended..i.e. programs both radios through the control head, operates both radios through the control head, repeater/base button works as intended. Where does the receiver get it's power from? Where do I make those connections?

To be honest with you all, I have some technical know-how, and I'm no stranger to a soldering iron, but as far as radio technology is concerned with respect to repeaters, I haven't the foggiest idea what I'm doing.

I know I need a controller (which one, I have no clue), and I know I'll need a duplexer. If I could find someone to hook this all up for me for a fair price, I'd go that route. But if it's gonna cost more than the setup is worth just to get the insides wired up, I'd rather do it on my own.

I know building a repeater isn't cheap by any means, but I need it done as cheap as possible. I've got nothing but time, so if it has to be done piece by piece, little by little, so be it.
 

Josh380

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Ok, so I've had some time to look at the diagram, and I'm starting to get it. Turns out I have the "B" version front panel. I'm assuming the diagram is depicting a maxtrac as the receiver. I have a radius M120 (and the service manual for that) that I want to use for the receiver, so I have to match up the wiring diagram for the m120 control head with the diagram for the "maxtrac (desktrac)" receiver..unless they're the same in which case would make my life much easier. I still don't understand where the receiver draws power from..I read somewhere something about the receiver taking power from the control head..not sure where I read it though.

And the line control board (frn5351b)..is this supposed to be the repeater controller? I don't have that board in the desktrac....

Cmdrwill: Pics would be extremely helpful. I've got the receiver apart and in the cabinet (loose) and I think I'm ready to start soldering.
 

Josh380

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Here's a pic of it mocked up. I left the boards connected for the time being. Can I just use the existing connector and wiring from the radio? Extend the wires....of course leaving a little left to reconnect later if need be?
 

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cmdrwill

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The M120 does not use the control head connections. It is just the receiver and you have to build the cable I mentioned. The receiver gets power from the front panel circuit board of the desktrac.

Maxtrac receiver cable:
 

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cmdrwill

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The above Desktrac repeater had local control full duplex split for a dispatch application. You can see where the receiver cable attaches to the front panel board in the upper right in the first photo. The grey cable under the blue connector in the second photo is the receiver antenna cable.

The cable for the M120 is even simpler.
 

Josh380

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Ok. So can you tell me where I can get said connectors? You say the cable for the m120 is simpler..could you possibly provide me with instructions..with detail to where the connectors should go (like here's which pins on jumper (J**) the wires attach to, where the other end connects to the receiver, etc)?

I realize I'm asking for a lot, but I need all the help I can possibly get with this. I can follow instructions easy, but stuff like figuring out what goes where is kinda hard for me.
 
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Josh380

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Only asking because it seems by what you said the m120 wiring might be slightly different than a maxtrac. Anyway, I've decided to use one of the existing connectors to wire this to the front panel. It's a 15 pin connector, and your picture shows a 13 pin connector. So, I suppose I'll just wire it up as if it were a 13 pin connector and leave the last two on the end null. What Guage are these wires?

Of course, I'll take a pic of the connector before I pull the wires from it. So all I need to know now is what pin on the connector goes to which pin on the board. The wiring diagram I have isn't going to help much if wiring between the maxtrac and m120 is different, and I'm assuming the diagram is showing a maxtrac.

There are a few wires I see on your connector that I can't see where they're going..

Then after that's all done, I just need to know how to wire up a controller (and which one to get) and I'm good.
 

Josh380

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Update

Cmdrwill--I just found a post by you in another thread..been doing a ton of reading:

The desk trac does not havea controller per se. It does have a interface from the receiver to the transmitter that passes the RX audio and PTT to the TX radio.

TOT is in the Transmit radio, left side.

The receiver provides RUS/ PL/DPL plus carrier squelch to the front panel board. This passes thru a Drop out delay and becomes the PTT for the TX.

So it seems obvious now that I don't need an external controller for this to work. Insert foot in mouth.

I just need to know exactly where to solder the wires on the board. Some of the spots are hard to see in the pic, and two wires the same color doesn't help either. And then there are the wires that I can't see where they go at all.

I'm going to copy how you have your connector setup and await your (or anyone else) response.
 

cmdrwill

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Josh,

I will get you a connection diagram for a M120 receiver. The connections are different than Maxtrac radio in the Desktrac diagram/ wiring. Send me a PM.

I just sent a PM to you.
 
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