I was tinkering with a Cobra 148 GTL this morning( side mic/PC-412 ) that works "fairly well" on the normal 40 channels, but still has some drifty issues that a 148 should not have.
The cause, someone has added a crystal/switch/for a extra band of channels.
When the extra crystal is switched in, the radio becomes even more unstable.
This is because whomever did the conversion did not take the time to secure the added wires/ crystal well and were sloppy.
Removing the covers from the radio and just placing your finger near the crystal/switch or moving wires around was causing the radio to shift frequency......
His "tech" gave up because after trying to get the radio to stay on frequency on the second band, he found that when the covers were placed back on the radio, it would shift again.
It is not a good idea to have a crystal hanging off of the side of the switch, with long unsecured/unshielded wires floating around.
Even more so in a mobile radio.
I moved the crystal, soldered it to a secure location, grounded the outside of the crystal case, re-routed and shortened up the wires, used some cable ties and a few dabs of hot melt to keep everything in place.
Much better and the frequency shift problem with the covers back on has gone away.
It pays to be neat.
73
Jeff