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Cobra 148gtl on USB/LSB the famous garble problem
- Thread starter dss56
- Start date
I did not check the vco voltage. The vco seems to be ok as I did a little adjustment to it and the radio has the full 40 channel band with no dropped channels and full power across the 40 channels. I will check that out for the voltage before I button up the radio.
thanks
thanks
The reason I ask , I had a radio that worked great on AM and on SSB it had a warble. Full power on all 40. Chased it for a year . Someone told me to check vco. It was right on the edge and just a little tweak stopped the warble. Nothing to lose by trying.
I did adjust the vco both ways and still the bad audio on ssb. Like I said I did the proper alignment with the bias and back off vr 11 for ssb. On vr 11 ssb if I back it down to almost no ssb power you can hear the audio clear up. So either the ssb power is over loaded or ssb is starving for power. And with your mod I did it did not make a difference. I'm going to give it 1 more going over and see if I can find the problem.
I check most forums and also youtube for this problem and not much info.
thanks Bob
I check most forums and also youtube for this problem and not much info.
thanks Bob
If lights are not dimming on AM but are on SSB peaks I would start at power supply, the power cord, then plug on back of radio and work your way down the power supply chain.
One thing you have not told us; have you adjusted the Mic Gain, or on a 148GTL, the Dynamike...does the Motorboating sound happen all the time?
If so, then you have some work to do, start looking for soldering blobs and potential shorts, even a cold solder joint on the foil/soldering side as well as burnt or blown/cracked open parts on the component side of the board.
Again, you may have to replace a lot of capacitors in there, in various locations, because as caps dry out - they make the radio act weird.
If turning down the audio tends to restore some stability - less garble, then your answer is in the power supply FEED in the radio - the things got one post from the power switch, goes back to the rear panel, over by the power choke and branches out, from that starting point 3 different ways.
One to light the meter lamp and dimmer function for the front panel, one to the regulator and one to the Final and Driver.
Two (2) of them are thru the power choke, the last one to the front panels AM/USB/LSB switch...
Each one of them, uses Electrolytic caps to filter their power feed to different sections of the board. If one of more caps are bad, they load down the board and the regulator doesn't work right.
If so, then you have some work to do, start looking for soldering blobs and potential shorts, even a cold solder joint on the foil/soldering side as well as burnt or blown/cracked open parts on the component side of the board.
Again, you may have to replace a lot of capacitors in there, in various locations, because as caps dry out - they make the radio act weird.
If turning down the audio tends to restore some stability - less garble, then your answer is in the power supply FEED in the radio - the things got one post from the power switch, goes back to the rear panel, over by the power choke and branches out, from that starting point 3 different ways.
One to light the meter lamp and dimmer function for the front panel, one to the regulator and one to the Final and Driver.
Two (2) of them are thru the power choke, the last one to the front panels AM/USB/LSB switch...
Each one of them, uses Electrolytic caps to filter their power feed to different sections of the board. If one of more caps are bad, they load down the board and the regulator doesn't work right.
I have had many cobra 148 GTL's and the problems you mentioned liked garbled speech and motor boating are not common problems.
The motor boating sounds all the time lowering power and the dynamike in front
if I start to lower the ssb power with vr11 it will show a difference for the better but still crappy on ssb
if I start to lower the ssb power with vr11 it will show a difference for the better but still crappy on ssb
Ok, then it looks like the various stages operating at the same time - this is a hit or miss problem.
To describe this in detail is a bit much, but to bring it into fewer words, the radio just can't take your audio and put it into an RF signal in one single action. It has to be done in steps, or stages.
The Motorboating sound can be a result of mixing the signals made in one stage of the audio chain - not being kept in one stage - instead it's being added to another.
This is what I caught from your post...
Now, knowing you have this sound basically all the time is not good. This symptom happening all the time now EXPANDS this into a potential blown diode problem, where more than one section is processing the signal at the same point in time, not as a separate stage from one into another. It's as if you have one MODE working in AM, but when you switch to SSB, you now have TWO MODES instead of just the one Mode you selected and want to use.
Here's what I would do, do you have a schematic of that 148 around? All I've got is one I've saved from CB Tricks site quite a while ago and I use it often to help me with other similar chassis like the Grant XL as well as Cobra 2000 and the Cobra 142 - but that is only because they use similar (that doesn't mean EXACTLY the same) boards...
Begin your study, don't know the symbols or recognize any of these symbols on this schematic? Then we may be in over our head. I may not be able to guide you.
But if you can - study this JPEG and see if you can locate their references, the Part Numbers on the Sheet - to the Parts on the board - it would be a great start in learning how this radio works.
Let me know how to proceed - if it's too much for you all at once, that's OK, we're here to help you to try and figure this out.
To describe this in detail is a bit much, but to bring it into fewer words, the radio just can't take your audio and put it into an RF signal in one single action. It has to be done in steps, or stages.
The Motorboating sound can be a result of mixing the signals made in one stage of the audio chain - not being kept in one stage - instead it's being added to another.
This is what I caught from your post...
Now, knowing you have this sound basically all the time is not good. This symptom happening all the time now EXPANDS this into a potential blown diode problem, where more than one section is processing the signal at the same point in time, not as a separate stage from one into another. It's as if you have one MODE working in AM, but when you switch to SSB, you now have TWO MODES instead of just the one Mode you selected and want to use.
Here's what I would do, do you have a schematic of that 148 around? All I've got is one I've saved from CB Tricks site quite a while ago and I use it often to help me with other similar chassis like the Grant XL as well as Cobra 2000 and the Cobra 142 - but that is only because they use similar (that doesn't mean EXACTLY the same) boards...
Begin your study, don't know the symbols or recognize any of these symbols on this schematic? Then we may be in over our head. I may not be able to guide you.
But if you can - study this JPEG and see if you can locate their references, the Part Numbers on the Sheet - to the Parts on the board - it would be a great start in learning how this radio works.
Let me know how to proceed - if it's too much for you all at once, that's OK, we're here to help you to try and figure this out.