PRO-2006 / COM-205
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The Realistic PRO-2006 and the Commtel COM205 are
similar. The scanner be opened by removing 4 screws on the back. Slide
the complete case half a centimeter back, and remove the lid. I also
disconnected the loudspeaker PCB-connector, which makes the scanner
easier to handle. |
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PRO-2006 (top) and COM-205
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There are 2 options for a discriminator output:
directly to pin 9 of the discriminator IC, a TK10420. Or to TP2 (test
point 2), which is connected to this IC directly. I chose for this last
option, so that I didn't have to solder to the IC.
To facilitate working on TP2, I temporarily displaced the cable tree
behind the big blue capacitor. |
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Two options for a discriminator output
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Close-up of the simple RC-filter
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TP2 consists of a 0 Ohm resistor, mounted vertically.
I connected a 12 k resistor to the free end of this resistor.
Because the demodulated audio contained a small IF component, I
connected a 2.2 n capacitor to the other lead of this 12 k resistor.
The other lead of this capacitor is connected to the PCB ground plane
around TP2. This creates a simple RC filter with a cutoff frequency of
about 6 kHz. |
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The inner connector of a piece of shielded cable is
connected to the RC-joint. The braid is soldered to the PCB ground
plane. The other side of the shielded cable was connected to a 3.5 mm
chassis terminal mounted in the back of the scanner.
After mounting the shielded cable, the cable tree can be restored to
its original position. |
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Overview
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