Uniden pc 122 xl drifting off frequency

[captain_caveman]

Radio Make and Model: pc 122xl
PCB Number: pb 122
PLL Number: 2824
Test gear available: vom,freq counter,rf wattmeter
Symptoms: drifting off frequency

What is working: most function working correctly ,receive is a little scratchy

What has been tried: tried changing 10.6975 crystal

Did it suddenly happen ?: no
Anything else that may be of help?: I'm not a tech

[13EL121]

Hi!

How much does it drift? And in which time after switching on?
Does it drift on RX and TX same time?
73s!

[captain_caveman]

Hi
The radio drifts about 250-300 khz on both rx and tx more on tx ,normal operating temp
thanks caveman

[13EL121]

250khz-300khz???
Wow, that is very much. 250-300Hz are normal. Send it to a rig doctor. He can check all oscillators. Without a good frequency counter it is very difficult to find the reason for this extreme drift. Is it sometimes "on frequency", maybe after switching on? Does it drift down or up? I had a similar problem on a Alan87. There was the PLL blown. After changing it, the problem was fixed.

[captain_caveman]

Sorry Ralf my mistake i ment hz

[13EL121]

Hi Joe!
200-300Hz are okay! That's normal for these transceivers. Often they drift a lot more. I have a "newer" Magnum S-9 which drifts nearly 500Hz or more and a Midland Alan87 (SS3900) which drifts nearly 800Hz during warm up. Here you can find the specification of your Uniden: http://www.cbradiomagazine.com/Radio%20 ... Review.htm
The frequency tolerace is 0,005% which means that it can drift up to 1350Hz! These types of cb radios are never stable!
You can align it when it's warm (maybe half hour after switching on) for center frequency. That's the best way.
There is video about the Uniden. There you can see the alignment points inside of it.

73s from germany, Ralf

[captain_caveman]

Gday Ralf thanks for responding to my post and giving me a helping hand i didnt realize that this much drift was within acceptable limits it's just a little annoying getting radio reports that i'm off frequency i align the radio when its warm then it decides it will drift further, the reports i get are from ham radio operators that might explain things
thanks for your time
joe

[13EL121]

Hi Joe!

No problem at all. Yes, if a HAM gives you the report, it explains all . So tell him that you "only" use an old CB radio. You can align it when it's warm, but you will always have a small drift. Btw that's the reason to use the clarifier on SSB radios . The person in the video says that the Uniden has nearly no drift. All radios have a little drift. It's normal, and especialy when the radios become older. The parts in the radio become older too (the condensers, chrystals, resistors etc.). So realign it that you are on frequency when it's in normal use.
In the video you can see where you can bring it back on frequency.
Good luck and 73s,
Ralf

[lbcomms]

These radios (and almost any other SSB radio) can have the drifting fixed by keeping the two (reference and carrier oscillator) crystals at a constant temperature.
Minikits in south australia sell a component designed just to do this:

50 degree C PTC thermistor suitable for using as a Crystal Heater.
Suits TS07S 50 deg QC50 case style crystals only
Suitable for stabilizing the Crystal frequency of local oscillators
8 – 14volt supply.
30mA @ 12volts typically
Order No: 50DEG PTC Thermistor
Each: $2.35
Supplied with a length of Heat shrink to attach the heater to the crystal.

http://www.minikits.com.au/doc/section4.pdf

Added a pair of these to mine (cost under $10 including postage) and they cut the drift from 350Hz town to about 20Hz, always on "12 o clock" now...

When you wire them up, connect them directly to the radios DC power socket, don't power them from the board, otherwise your radio will drift like crazy for about 3 minutes when you first turn it on.