malaysia 148 GTL sideband transmit problem

dizgolfer · Post by **dizgolfer** » Thursday 11th Dec 2008, 3:43

Radio Make and Model: cobra 148 GTL
PCB Number:
PLL Number: RCI8719
Test gear available: multi meter,swr/power meter, dummy load, signal generator
Symptoms: When I transmit on LSB/USB it sounds like I'm transmitting with a bird chirping under water. USB/LSB recieve sounds great. Radio works well on AM.

What is working: Everything except sideband TX

What has been tried: nothing

Did it suddenly happen ?: Was like this when I bought it used
Anything else that may be of help?:

http://www.youtube.com/user/TheDefpom · Post by **The Defpom** » Thursday 11th Dec 2008, 23:20

Warbling on TX SSB can be caused by poor voltage regulation, this can happen if the clarifier has been modded, the extra current drawn in TX puts more strain on the regulators, so it effects TX a lot more than RX.

My first port of call would be to see if the clarifier has been modified to give TX slide, and if so I would see if it is using a good stable 8V supply, which does not change voltage between TX and RX (otherwise your TX and RX will not be on exactly the same freq).

dizgolfer · Post by **dizgolfer** » Friday 12th Dec 2008, 6:14

The clarifier only works on recieve so I guess that part is stock. Thanks for the reply. Any other suggestions are greatly appreciated.

Flash · Post by **Flash** » Thursday 18th Dec 2008, 19:07

Check voltage on the AN612 IC5 I think. I have seen several with 12 volts on pin 7. Should be about 7 or 8 volts. This lets AM work OK but SSB sounds terrible.
If this is the case change the MB3756 switching regulator.

Flash