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(U)BC180XLT and (U)BC280XLT



The Uniden Bearcat 180XLT and 280XLT are rather recent scanners. In spite of that, adding a discriminator output to these scanners is not a big deal. I would like to thank Ronald and Ron who trusted me to abuse their brand new scanners.

From the inside, the scanners are similar. The discriminator IC is an 'ordinary' SMD. The challenge is in the mechanical work: to bring the shielded cable from the IC to the chassis terminal, some milling or filing is necessary inside the housing. Luckily, there is just enough room for a 3.5 mm chassis terminal.





The opened scanner

The output is made to pin 9 of the MC3361

The discriminator IC, an SMD MC3361, is located at the back of the PCB that becomes visible if you open the scanner. The unfiltered audio can be found at pin 9. One leg of a safety resistor of 5.6 k (I use values between 5.6 k and 15 k) is bent so it follows the IC pin. To prevent possible mechanical strain to pin 9, the resistor is fixated to the IC with a drop of glue from a glue gun.

There is hardly any room between the case and the PCB. That's the reason why I used the thinnest shielded cable I could find. The core of the shielded cable is soldered to the 5.6 k resistor. The braid can be soldered to the middle solder pad of a component on the other side of the PCB. This pad is grounded.



Close-up of the discriminator output

Location of the 3.5 mm chassis terminal

The chassis terminal is mounted in the back of the case. The terminal just fits between the housing and the shield of the RF part that is visible in the picture of the opened scanner. I milled a trace in the inside of the case to facilitate the shielded cable from one side of the PCB to the chassis terminal mounted on the other side.

The demodulated signal contained a small IF component at 455 kHz. This is filtered by mounting a 4.7 n capacitor over the lugs of the terminal. Together with the 5.6 k resistor, this creates a simple low-pass filter with a cutoff frequency of about 6 kHz.


The result

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