Saturday, 25 November 2017

New Toys

As my main interest in general utility listening is more geared towards intercept and identification rather than content, I decided I would finally treat myself to a bit of new kit. I looked at the cost of DMR and dPMR capable scanners, but they are still very much out of my range, and besides, SDR is in many ways a more fitting system for such modes.

So I dropped on a Uniden Bearcat UB125XLT handheld scanner, 2nd hand for a good price. The attraction of this device is Uniden's 'Close Call' feature - a strong signal intercept mode.

The above of course is a stock photo (the giveaway is the model number which has clearly been over-typed! I suspect the original photo was of the US market 125AT version!).

One very useful modification that can be made to scanners is to provide a high impedance raw audio tap from the discriminator. This is very easy to do on the 125 as the headphone output connector is stereo but the unit of course mono - giving an available connection. It just requires the removal of the L- and R- balance resistor, and the addition of a 10k resistor and wire between the discriminator and the audio socket. Rather conveniently, all the important signal paths in this receiver have nice big test points!

 All the photos above show the receiver in various states of dismantlement. The photo of interest is the one bottom right, this is the RF board. The big chip to the left of the IF filter (the big cream block on the lower right) is the IF subsystem IC, to the left of this is a large test pad for the discriminator output, marked DISC. At the top of the board between the BNC socket and the volume pot, can be seen the 3.5mm stereo jack socket. Just below that the balance resistor.

Later today I will perform the discriminator mod. But only once my workshop has warmed up!

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