(U)BC180XLT and (U)BC280XLT
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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. |
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The UBC180XLT
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The UBC280XLT
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The opened scanner
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The output is made to pin 9 of the
MC3361
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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.
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Close-up of the discriminator output
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Location of the 3.5 mm chassis
terminal
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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. |
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The result
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