Channel Board For Cobra 146GTL & Uniden PC-122XL: Low-cost AM/SSB radios with gPD2824 PLL chip. Expansion kits available to increase coverage but may void FCC approval.
cbworldinformer.com
The directions are for the Uniden PC122, all references in the web page are to this.
Pin 10 of the PLL is the 10.240/2 output, or 5.12 MHz. This through C67, goes to the Tripler coil, to generate 15.360 MHz, to mix with the VCO, the PLL locks on the difference frequency, of .910 MHz (CH1) to 1.35 MHz (Ch40).
It says to pull C67, tie the input of this add-on circuit to the Pin10 side of C67, the output of the add-on circuit to where C67 would go to the Tripler coil.
To make the VCO have a greater lock-up range, increase C72 (47pf) by replacing it to a higher value, or adding another capacitor in parallel to it on the solder side of the board. I'd use either a 100pf or higher. You should readjust the VCO coil for lock-up range after increasing C72's value.
By extrapolation, in the Cobra 146GTL or Uniden AX144, C72 is now the Tripler feed cap, and C75 is the VCO increase value cap, again, readjust the VCO coil.
In the Cobra 29GTL/LTD and other generations, C94 feeds the Tripler coil. and C89 needs to be increased in value or paralleled with to increase the VCO lock-up range.
