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Making a MaxTrac and MTR2000 Dual-Purpose Programming Cable By Robert W. Meister WA1MIK

The MaxTrac programming cable is used on a lot of radios with RJ45 programming jacks, such as the Radius, MaraTrac, GM300, GTX, CDM, etc. You can make or buy a cable for about $7; it consists of an RJ45 modular plug, a piece of appropriate cable, and a DB-25F connector. The interface is a single shared line that carries both transmit and receive data. The cable must be used with a Motorola RIB (Radio Interface Box) and is wired as follows, using MaxTrac pin numbers.

RJ45 pin 4 (GND) to DB-25F pin 1 (GND).
RJ45 pin 7 (SCI+) to DB-25F pin 15 (BUS+).
DB-25F pin 4 (BIAS) to DB-25F pin 11 (BUS-). Don't forget this jumper.

The MTR2000 programming cable does NOT require a RIB. You can make a cable for about $7; it consists of an RJ45 modular plug, a piece of appropriate cable, and a DE-9F connector. (I've seen these sell for over $25US, which is ridiculous.) The station uses the RS-232 levels directly and only needs a simple three-wire serial connection. The cable is wired as follows, using MTR2000 pin numbers. This information came directly from the MTR2000 RSS Help screen.

RJ45 pin 5 (GND) to DE-9F pin 5 (GND).
RJ45 pin 6 (TXD) to DE-9F pin 2 (RXD).
RJ45 pin 7 (RXD) to DE-9F pin 3 (TXD).

Because the two radios number the RJ45 pins differently, you must be careful how you make these cables up. However, after a little thought, I realized that the two radios can utilize one RJ45 cable if you wire it up properly. First, let's translate the MTR2000 RJ45 pin numbers to match those for the MaxTrac.

MTR2000 Pin #	MaxTrac Pin #
8	1
7	2
6	3
5	4
4	5
3	6
2	7
1	8

It's said that a picture is worth a thousand words, so here's a graphical representation of the numbering schemes. These are views looking into the RJ45 programming jacks on the two radios.

If we stick with MaxTrac pin numbers from now on, we can see that the MaxTrac cable uses pins 4 and 7, and the MTR2000 cable uses pins 2, 3, and 4. Only one pin is shared (pin 4) and that's ground. We can actually hang a DE-9F off the RIB end of the cable and make one cable do double duty. When you plug the DB-25F into the RIB and plug the RIB into the computer serial port, you can use the cable on a MaxTrac or similar mobile radio. When you plug the DE-9F into a computer serial port, you can use the cable on the MTR2000 station.

I had an RJ45 to DE-9F cable that someone gave me. Turns out it's a Cisco console cable that can be purchased for about $3 on a popular auction site. I had previously snipped off the DE-9F connector and added a DB-25F connector, so I already had a working MaxTrac-style programming cable. All of the unused wires were still present inside the DB-25 shell, so I just spliced some new ones on and ran those to the appropriate pins on the new DE-9F connector. The wire colors were what my cable had and the wire I used; yours may be different. Go by the pin numbers, NOT the wire colors. Use an ohmmeter to make sure you've got the pin numbering correct. So now here's the wiring for this combined cable, again using MaxTrac pin numbers.

RJ45 Pin #	RJ45 Color	DB-25F Pin #	DE-9F Pin #	DE-9F Color	Signal Name
1	Black
2	Brown		3	Red	MTR In
3	Red		2	Yellow	MTR Out
4	Orange	1	5	Black	GND
5	Yellow
6	Green
7	Blue	15			SCI+
8	Violet

If your MaxTrac programming cable brings all eight wires from the RJ45 down the cable to the DB-25F (as mine did), you should be able to splice onto two of the unused wires and share the ground already on the DB-25F pin 1 (as I did).

Apply labels to the DB-25F and DE-9F connectors so you know what the cable can be used for. Here's my completed cable. I tested it with a Dell laptop and an MTR2000 and it works fine.

MaxTrac, Radius, GTX, GM300, MaraTrac, MTR2000, RSS, and a bunch of other model names and terms are trademarks of Motorola, Inc.

The author can be contacted at: his-callsign [ at ] comcast [ dot ] net.

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This page originally posted on 03-Jun-2011

Article text, photos, and hand-coded HTML © Copyright 2011 by Robert W. Meister WA1MIK.

This web page, this web site, the information presented in and on its pages and in these modifications and conversions is © Copyrighted 1995 and (date of last update) by Kevin Custer W3KKC and multiple originating authors. All Rights Reserved, including that of paper and web publication elsewhere.