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Converting a Uniden Scanner To Pick Up AIS Signals

by Stan Swan

These well-priced, wide-coverage and very popular hand held scanners further offer a valuable “close call” feature and have become well respected for general VHF/UHF work.

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The discriminator tap access is straightforward and fitting an external socket should make for a neat and professional enhancement to the set. However, your scanner warranty may become invalid!

All variants of the UNIDEN UBC72/73 & 92/93 use the 24-pin TOKO TK10931 discriminator IC, with base- band audio output at pin 12 (LND7). This accesses the unfiltered audio. A resistor soldered to a convenient pad on the PC board provides the tap without otherwise affecting scanner operation. In most cases a 10kΩ resistor suffices but with some sound cards we’ve had to go as high as 220kΩ to avoid overload. You could also use a 220kΩ trimpot in series with a 10kΩ resistor to make adjustment easier.

The resistor’s other end is wired to a 2.5mm mono chassis socket mounted on the back of the scanner. There is sufficient space between the stacked PCBs and case for this.

A short wire for the ground lead can be run to the antenna’s ground terminal – a 10nF capacitor between the resistor’s far end and ground may help remove residual higher frequency portions.

A 2-wire external lead then connects to a stereo 3.5mm plug to suit the PC soundcard’s line-in or mic input socket. The scanner squelch must be wide open (“hissing”) but the scanner’s internal speaker volume can be turned right down.

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