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.

• Get a 6-pin mini DIN extension cable, typically sold as a PC keyboard or mouse extension cable with "PS/2" connectors.

• Cut it in two.  Take the half with a male plug and strip the insulation from each of the wires.

• Using a Volt-Ohm-Meter (VOM) to check continuity, for both cables, and document which color wire is connected to which pin. (Simple trick: open up a paper clip and insert that into a connection spot, then check with VOM between the clip and the wire.)

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:

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.

• Get a 16-pin Motorola accessory plug (on eBay, search for "Cable 73 Motorola 16-pin Maxtrac")

• When plugging the connector into the radio's accessory socket, the odd-numbered pins will be closer to the bottom of the radio; if you get the Cable73 on eBay, there's a plastic latch that faces down.  Pins 15 & 16 are closer to the edge of the radio, 1 & 2 closer to the center of the radio.
• Cable 73 comes with a jumper on pin 15 & 16, enabling the MaxTrac's speaker.  Most people will want to cut that jumper, since turning the audio volume control all the way down does not completely shut off the sound.
 (A hotspot or repeater doesn't need the RX speaker to function.)

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:

• DSub-1 (Radio Mic) ==> Moto-5 (Tx Audio into radio)
• DSub-2 (Radio COS/squelch ==> Moto-8 (COS/SQL) - optional
• DSub-3 (Radio SPK) ==> Moto-11 (RX Audio - flat)
• DSub-4 (Radio PTT) ==> Moto-3 (PTT)
• DSub-5 (GND) ==> Moto-7 (Ground)

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:

D-Star® is a registered trademark used for communication equipment (repeaters and transceivers) for amateur radio communications, and owned by Icom Incorporated.