VOX Mod for APRS


Introduction: VOX Mod for APRS

About: I'm a physicist with a bunch of engineering experience, who likes to make stuff, and likes to get outdoors.

This is how you modify a Maxon VOX unit for use with a computer for APRS.

BOM (Bill of Materials):
Maxon VOX Unit $2
AA Battery Holder $1
3.5 mm to 2.5 mm Adapter $3
2x 2 m Mono Patch Cable $4 each

Step 1: Get the VOX Unit

I got mine from All Electronics. But there's a problem! The battery goes dead quickly, and is non-replaceable!

Step 2: Uncovering

Take off the back cover, and locate the battery connections at the bottom (here left) of the unit.

Step 3: Soldering

Solder the single AA battery holder as seen here: red to + on the PTT side, black to - (GND) on the other side. It's also quite simple at this point to take the soldering iron and melt a small channel in the side opposite the PTT for the battery wires to come out of.

Step 4: Connecting

Now connect the coiled wire to your HT, put in a AA battery, and connect the two audio cables to your PC: the Mic on your PC goes directly into the speaker jack, and the Headphone on your PC goes through a 3.5 mm to 2.5 mm adapter to the mic jack on the VOX unit. You may have to tweak the volume and vox levels, but mine worked right from plugging it in. Boot up AGWPE, start up UI-View, and you're good to go!



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    Voice Operated Xmit (Transmit). It's a term widely used in amateur radio and other telecom fields to denote a device that transmits, or turns on, after sound has crossed a certain threshold for volume. In other words, if you're not talking, it's not transmitting. If you are talking, it is transmitting. In this application, it's used to trigger a radio when data packets are coming from your computer, and to allow your computer to listen for data packets when it's not busy transmitting. Put another way, it's an automatic device for turning full duplex into half duplex so your sound card and radio can get along.