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Building Your Own Hotspot Cable

It's easy to build your own cable, but I'll be honest, when I got into Hotspots, I purchased two cables that were professionally manufactured -- one because I was in a hurry, and the other because I demonstrated my hotspot at a hamfest and I wanted a perfect cable.  I've also made up cables on my own.

GMSK Node Adapter end of the cable
Many boards use a 9-pin DSub connector, including those from  Fred KA4YBR and the Matrix Circuits Star*Board(tm), so I'll describe that.

I tend to buy pre-made cables that fit the radio end (see the sections below), cut the cable to a good length, strip the wires, and use a VOM (volt ohm meter) to determine which color wires go to which connector pin.  I buy the parts to make the female DSub9 connector that plugs into the GMSK Modem and solder that up, then fit the shell onto the connector:

DSub9 Female connector

DSub9 Shell

Use the following pin numbers, looking at the 9-pin DSub female plug facing you, wires coming out the back:

1 - Radio MIC (audio input)
2 - Radio COS (squelch)
3 - Radio SPK (audio output)
4 - Radio PTT
5 - GND
Documentation shamelessly stolen from DUTCH*Star

Radio end of cable for Radios with 6-pin Mini DIN connectors
Most radios with a 9600 baud Data jack, or similar access to discriminator and modulator audio, use a 6-pin Mini DIN connector. The pin-outs have been standardized, making it easier for us.

Use the following pin numbers, looking at the 6-pin mini DIN plug with the pins facing you, wires coming out the back:

1 - TX audio into radio
2 - Ground
3 - PTT
4 - RX 9600 audio out of radio
6 - COS/Squelch

Solder wires as follows:

  • DSub-1 (Radio Mic) ==> DIN-1 (Tx audio into radio)
  • DSub-2 (Radio COS squelch) ==> DIN-6 (COS/Squelch)
  • DSub-3 (Radio SPK) ==> DIN-4 (RX 9600 out of radio)
  • DSub-4 (Radio PTT) ==> DIN-3 (PTT)
  • DSub-5 (GND) ==> DIN-2 (Ground)

For more information, please check out section 3.1 of the DUTCH*Star Construction and Reference Manual, which also documents the DSub plug's pins.

Radio end of cable for MaxTrac Radios
Many Hotspots are using Motorola MaxTrac radios that have come out of commerical service.  It's highly recommended you get the version with a 16-pin accessory socket (not the 5-pin socket).  The info below should be sufficient to make up a cable, but for more detail, check out
http://www.repeater-builder.com/motorola/maxtrac/maxtrac-option-plug.html.

Use the following pin numbers, looking at the 16-pin plug facing you, wires coming out the back:

3 - PTT
5 = TX Audio
7 = Ground
8 = COS/SQL
11 = RX Audio - flat

Splice/solder wires as follows:

On UHF, you need TX Invert but not RX Invert. Refer to http://www.repeater-builder.com/motorola/maxtrac/maxtrac-intro-stuff.html for how to set radio's jumpers.  The default jumper positions normally work, but if your MaxTrac and GMSK node adapter can't receive a D-Star radio, reverse the position of the JU-551 jumper.

Radio end of cable for Alinco DR-x35MkIII radios
The Alinco DR-135MkIII and DR-435MkIII radios work well in normal Hotspot service, though they need the "Simple Mod" (easy to do).  To connect to a GMSK Modem, the Alinco's packet data connector accepts a male DB9 rather than the more standard 6 pin mini DIN.

The easy way to build this cable is to get a pre-made cable from a PC or electronics store with a DB9 male connector on one end.  Cut off the other end, strip the wires and use a VOM to discover which color wires go to which pin.

Use the following pin numbers, looking at the 9-pin DSub male plug facing you, wires coming out the back:

1 - COS (squelch)
2 - 9600 RX audio out
3 - 9600 TX audio in
5 - Ground
7 - PTT

Solder wires as follows:

  • DSubFemale-1 (Radio MIC audio input) ==> DSubMale-3 (9600 TX audio in)
  • DSubFemale-2 (Radio COS squelch) ==> DSubMale-1 (COS squelch)
  • DSubFemale-3 (Radio SPK audio output) ==> DSubMale-2 (9600 RX audio out)
  • DSubFemale-4 (Radio PTT) ==> DSubMale-7 (PTT)
  • DSubFemale-5 (GND) ==> DSubMale-5 (Ground)

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Copyright © 2009-2016 James M. Moen. All rights reserved.
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