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Chinese Cobra 148gtl distorted ssb

I

Inquietude

Member
Jul 5, 2014
21
20
13
Hi,
Does anyone have a solution for the infamous newer 148gtl "D" made in China? I have the usual highly distorted transmit audio on SSB. The radio will run about 1-5 watts PEP and sound clean, but any more will sound horrible. Tried running the clarifier from an external regulated power supply at 7.5 volts and didn't help. Also changed C172 to 2200uF and that didn't help. The little 7809 regulator gets its 13.8 volts directly from the power switch, no hash filters inline here. Not sure it was a voltage sag problem but tried those things to eliminate them. Any help will be greatly appreciated. Tnx.
73,
Inquietude
 

A little more background.... This appears to be one of the newest 148's and bone stock, so no butchers or wizards have been inside it to "help" it. The factory did a fine enough job messing it up on their own from the sound of it. I'll check the rest of the things listed in the link above not already checked, but that is an old link. Thanks again for the help!
73.

"To date I have traveled far and have seen so many wonderous things that have left me in awe. Majestic mountains, cold rushing streams, intriguing tribes of indigenous peoples. But I must report that I have found the quality of citizens band radio equipment produced today and in most recent years to be thoroughly disenchanting and atrocious."
 
After purchasing 2 of these when they first came out, did not take me long to realize that Cobra really made a mistake and the cobra was no longer a quality radio. The problem is the voltage regulator. There is no regulation on ssb.

To my understanding no one has ever came up with a real solution for this. It will not be just a part swap either. What it will take is a new designed circuit to wire in with a real regulator and feed back circuit.

I long got rid of my china made 148's but this is on my to do list one day.
 
Radio Tech said:
After purchasing 2 of these when they first came out, did not take me long to realize that Cobra really made a mistake and the cobra was no longer a quality radio. The problem is the voltage regulator. There is no regulation on ssb.

To my understanding no one has ever came up with a real solution for this. It will not be just a part swap either. What it will take is a new designed circuit to wire in with a real regulator and feed back circuit.

I long got rid of my china made 148's but this is on my to do list one day.
Click to expand...
Interesting; like to see what you could do to see if that is true.
Imagine that a zener diode would be used to make that happen.
 
Robb said:
Interesting; like to see what you could do to see if that is true.
Imagine that a zener diode would be used to make that happen.
Click to expand...


Oh yes, there would be a zener in the feed back circuit as well as the regulator.
Idea is to get a constant current source there to the voltage while in ssb mode. The problem with it's current design if you look at the voltage source while transmitting in ssb mode you will see it is all over the shop. That voltage source is also less filtered than the original. Nasty signal.

A circuit could be built up on a small board and mounted inside the radio to feed voltage to the ssb side of things.
When I get another test radio I will start on this.
 
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Radio Tech said:
Oh yes, there would be a zener in the feed back circuit as well as the regulator.
Idea is to get a constant current source there to the voltage while in ssb mode. The problem with it's current design if you look at the voltage source while transmitting in ssb mode you will see it is all over the shop. That voltage source is also less filtered than the original. Nasty signal.

A circuit could be built up on a small board and mounted inside the radio to feed voltage to the ssb side of things.
When I get another test radio I will start on this.
Click to expand...
Cool stuff.
There are a LOT of people that own these NW/ST 148's that would like to see it finally fixed right.
Wish you all the best . . .
 
Last edited:
  • Like
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Radio Tech said:
Oh yes, there would be a zener in the feed back circuit as well as the regulator.
Idea is to get a constant current source there to the voltage while in ssb mode. The problem with it's current design if you look at the voltage source while transmitting in ssb mode you will see it is all over the shop. That voltage source is also less filtered than the original. Nasty signal.

A circuit could be built up on a small board and mounted inside the radio to feed voltage to the ssb side of things.
When I get another test radio I will start on this.
Click to expand...

We'll be awaiting your feedback on a potential fix. I'd do it in a heartbeat. I've got one here I will begin on with proposed changes.
 
I almost tried that myself but didn't have the time to play with it. The guy needed it back in a hurry. I only ran the clarifier diode on an external regulated supply but that does not help the oscillators. It would be nice to find one cheap or a loaner with "carte blanche." Then maybe yank the stupid 7809 completely out and build a small zener driven regulator on an experimenter board with a TO-220 pass transistor of some sort (a la Galaxy 949) and see what happens. If you couldn't bolt the pass transistor back where the regulator went then maybe somewhere on the frame with some wires soldered to it might work. Anybody out there have one and feel like collaborating?? Give it a try.
73.
 
Inquietude said:
I almost tried that myself but didn't have the time to play with it. The guy needed it back in a hurry. I only ran the clarifier diode on an external regulated supply but that does not help the oscillators. It would be nice to find one cheap or a loaner with "carte blanche." Then maybe yank the stupid 7809 completely out and build a small zener driven regulator on an experimenter board with a TO-220 pass transistor of some sort (a la Galaxy 949) and see what happens. If you couldn't bolt the pass transistor back where the regulator went then maybe somewhere on the frame with some wires soldered to it might work. Anybody out there have one and feel like collaborating?? Give it a try.
73.
Click to expand...

Shoot me schematic of what you believe to be a better circuit and I'll give it a go.
 

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