Batboard

On the 40W 450-482 Spectra, is the VCO board on the top or the bottom of the radio? There is a small ceramic slab on the bottom of the radio, but it has a shield on it that appears well soldered or welded on. However, there is a small window in the top of this shield, directly above a laser cut trace. Is this the VCO board? And do I have to work through this little window, or is there some way to remove the shield?

Why do you want to modify the VCO. The spectra works great in the 440's in the UHF range 3 bandsplit. You should be able to lock until about 441.0000 without a problem.

Yes, the open-ended track with the laser cut visible thru the slot is the VCO resonator microstrip.

If your VCO wont quite get to the frequency you want, you'll need to add a little electrical length or capacitance to that line. It is almost impossible to solder across the laser cut but you can buy silver loaded conductive ink, by the pot or in a pen dispenser. With care you won't need to unsolder the cover, which by the way is a dog of a job.

The best way to tackle this job is to use a digital voltmeter to monitor the VCO loop voltage. You don't want to drop much below 0.5 volts at your lowest frequency while keeping your highest frequency at or below about 8.5 volts. Keep also in mind that as you reduce the low end you also reduce the overall tuning swing.

If you try and drop the low end too far you'll start reduce your receiver sensitivity as you go outside the passband of the front-end resonator block.

Cool, that's what I was looking for. As it is now, the radio will give FAIL 001 below 448.0, so I'd like to get it down to 442.0.