COBRA 139XLR POWER DIFFERS BETWEEN LSB AND USB

[TonyV225]

I was talkin witha guy tonight thats working on a Cobra 139XLR the problem is that on Lower LSB hes only getting 16 watts PEP but when he switches over to USB its about 22-23 watts. Has anyone here ever seen this happen before or does anyone have any ideas on what would cause this or where to start as far as looking to solve it? Thanks in advance .......Tony

 

[loosecannon]

maybe try cleaning the AM/USB/LSB switch.

just a thought.
LC

 

[TonyV225]

No thats all done and this is something inside or internal I brought up carrier balance and he said he looked at that and thats not it either. Ive never seen this before and neither has the other guy with the problem so even though is has nothing to do with me I am now curious myself!! LMAO and just have to know for myself incase I ever see this myself. I also am hoping to help this guy before he rips all his own hair out!!

I thought this would be a good place to start with so many other good knowledgable people involved here.

 

[unit_399]

Tony -

Have the guy check the adjustment of VR4 (balance adjustment). With the mike gain turned all the way down, keyup the unit and adjust VR4 for minimum RF in USB. Switch back and forth between LSB and USB and readjust so that the readings in each miode are the same. Use a scope for this. If no scope is available use an swr meter set in the CAL mode. You're looking at really small rf readings here. If the set has an unlocked clarifier tell him to use a counter to make certain that the clarifier is set to center. If it isn't it will screw this adjustment up. Good luck. 73s

- 399

 

[Dodgem250]

It's a pretty common "that's the way it is thing" with side band units, a lot of them will read different outputs on lsb & usb, especially newer units.

 

[TonyV225]

I know this is older its the old 139 and Ive seen a power difference on radios but maybe 2 watts or so but this things 16 pep on one and 22-23 pep on the other thats to much of a gap but as you said it is what it is and may just have to stay that way its an old radio .

 

[RiverRat]

yep, I have seen as much as 10 watts difference on some radios, I currently am using a Cobra 148GTL ST and there's a good 6 watts difference between USB and LSB on this thing, and this is a fairly new radio compared to some I have worked on in the past.

 

[TonyV225]

Im thinking hes gonna have to just deal with this Ill have him try the above metioned with a scope and see if that doesnt fixer up. Other than that it is what it is I guess.