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New Cobra 148 GTL

O

OPCART

Member
Aug 19, 2009
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I just purchased a new Cobra 148 GTL, and just after i saw some blogs with complaints about the new 148. Namely a problem with people not being able to clarify the output of the new 148s SSB, due to a poor voltage regulator, so the voltage drop causes the variance in frequency in SSB.
Is this true and are there any fixes?

Any help would be appreciated, thank you so much
 

Yes, voltage drop causes Clarifier problems on SSB. Mostly on TX, where there is a "warbling" effect.

I am a SSB'er and am pretty demanding of my radio's SSB performance. One thing I always do when I am setting up a CB for myself is to put in a dedicated voltage source for the clarifier circuit. I will get a LM7808 and tap off of the output side of the hash filter. Add some capacitance (470uf/25v) and a .01 to the 7808 input. On the output, add another .01 and I then run it into the high side of the SSB TX VR (make sure you disconnect TX only voltage from it first). Hook the low side of the TX VR to the high side of the Clarifier. You don't have to but you can lift up the leg of the TX switching diode to take the TX side out of the circuit (circuit should be dead because the TX VR output was moved) and jump the RX switching diode so you don't drop voltage going through it (might give you a little more slide). This way I have "unlocked" my clarifier so it will "slide" on TX as well.

Center your clarifier and adjust the TX VR to "center" your frequency. This is easiest by listening to someone who is transmitting on frequency and adjusting the TX VR for best audio. If you have the equipment, you can always zero beat it.

Now you have a dedicated, constant, stable voltage source for the clarifier and you wont have any issues with warbling or frequency "shift" between RX & TX.
 
Wow, i dont think i have the ability to do what you are sugesting Dr DX
Thanks for the info though
I will open my radio as soon as i get it.

I paid 163 shipped, and i just want it so i can listen and some times trry a little DX in my car.
Maybe it was a big mistake.


DrDX where abouts do you live?......how much would you charge to do those changes on my radio?
 
I live down around the Alamo.

20 years ago, I would have told you to send it to my shop but I am out of the business now days and only work on my own stuff and a few old customers out of my house.

You should be able to take those instructions to any radio tech worth his salt and he can do it for you. Parts will run you $2~$3 tops, so don't get stiffed.

This mod will eliminate warbling and "split" RX & TX, but it won't eliminate "drift". If you find your self having to "re-clarify" as your radio warms up or cools off, then that is another problem. It can also be solved but it is more labor intensive.

The problem is that some radio manufacturers, in an effort to cut corners and save a buck or two, don't use NPO capacitors in the PLL and clarifier sections of the newer radios. NPO capacitors don't change capacitance as they change in temperature, regular ones do. Since many of the small capacitors are in the picofarad range in those circuits, even a change of only 1~2 picofarads makes a big difference. The fix is to go through and replace all of the non NPO caps with NPO versions and then re-align the PLL and clarifier sections.

This is fairly easy to do on the non-SMD radios, as the components are larger and easier to replace. If your radio uses SMD, then it takes specialized equipment to unsolder and re-solder the new NPO SMD caps in. Again, any radio tech worth his salt should be able to do this.

Generally speaking the older SSB CB radios (pre 1995) all use NPO caps.
 
For that kind of money I hope that radio is tuned. You could have gotten one cheaper at Sparkys cb, Custom cb, DTB radio, or Bob's cb. And all of those places will tune and align the radio as part of the sale.
 
Thats just a feature on the newer Cobra 148's....LOL. I will say this though, a larger heavier duty voltage regulator can be installed and does help alot of Export radio's. By this I am talking about the orange display 2950, Magnum Delta Force, Galaxy 88 & 99. I think the new Exports that are mosfet powered already have larger regulators.

Chop, thats a bad a$$ base set-up you have there. Very cool.
 
i think the old cobra radio company would have seen something as common as what DR_DX described as a factory defect and would have fixed it in future releases , if they didnt catch it befor it hit the market . stuff like this and the embarassments like the 100/200 not being able to work right even after multiple revisions lead me to believe cobra either can not or will not bother to build quality radios anymore .
 
i think it has to do with the old MB3756 voltage regulator IC being in short supply.
im pretty sure its a discontinued part.

so cobra took the easy cheap way out and decided that if the SSB quality suffered, that was something they could live with. LOL

LC
 
a buddy of mine got a new 148 and it just plain sucked on ssb AM was pretty good but we do mostly ssb over here ..he finally gave up on it and got a 2950..don't know what happened to the new 148
 
Thank you

Thanks for the help Dr DX

By all i read is it possible i may have a new version of this radio
where it has a better regulator?

is there a way to see?
 

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