Top 10 Cobra 148 GTL 120-Channels Base CB Radio Questions & Answers

No audio out / low audio out....This is a constant problem with the COBRA 148 gtl....to get a good level of volume replace the
electro caps ...start around the two speaker wires and work back from there. I'm in the process of rebuilding a 148 gtl and have found caps that are leaky and dried out...after replacing nine the volume went up to a good level...now i need to fix the distortion
and background hash. Did you know that there are many posts
on FIXYA about this same problem I.E. great TX , great PA but poor , or no audio out. these sets have been made in sevetal countries...The sets made in Taiwan or China have poor quality
front panel pots (the carbon track is micro thin and simply wares through to the material the track is printed on) This has the same effect as removing a wire from a pot I.E. no audio. The good news is that 99% of parts in the radio are freely available and that includes the front panel controls. ONE WONDERS IF THE SET IS WORTH THE EFFORT !!!

CHEERS GUYS / GIRLS.

Hi,

I read through the specifications of this antenna and you were right in posting "no ground plane, no tune". Still, there are only three (3) possible reasons why the SWR would be high:
1. Cable/connector - loose, cold solder or improperly terminated;
2. Antenna - tuning and/or ground plane; and
3. Radio has been highly modified or defect in final stage.

Corrective procedures would call for:
a. verify that the coaxial cable is properly connected to the PL-259 connectors. You may need to use a continuity tester (or a DVM) to do so. Pls pay particular attention to the braided shield/grounding, they should be real tight/soldered good to the casing of the connector. Of course the cable should be 50ohms RG8 or 58 with thick shielding.
b. as stated the antenna doesn't need to be tuned then there's nothing that can be done since there is no provision for such, however, even if the specs says no ground plane needed, there is something you can try. Install a ground plane. this could be done by attaching 2 lengths of big gauge ordinary wire to both sides of the metal bracket of the antenna. They have to be 8' 7" ~ 9' long. It may help you further to install a grounding strap again from the metal bracket to any grounded metal portions of your house such as the plumbing.
c. radio problem would be unlikely if it is still stock.

Hope that this be of some help/idea. Pls post back how things turned up or should you need additional information.

Good luck and kind regards.

cobra 2000
am carrier 4.4 volts will not ajust...ssb carrier will 3.5 volt will ajust but max out put is only 3.5 volts.losses all voltage at ssd carrier when switched to usd r lsb

This is a complicated modification. I have never done it to a 1000 GTL, but its done basically the same in all radio's.

I don't recommend doing it, especially since I am not 100% sure on how exactly to do it. I have never been in a 1000 gtl. If I had one in front of me I could tell you for sure how to do it.

If the reason for Variable power is a linear, just a swing kit in for the dead key you need, most likely 2 watts, and leave it.

Here is how to do a variable power mod. this is assuming the swing mod is done the same to this as a cobra 25/29 or uniden 68/76 etc.

If you would like to try it, here it is.

You get a TIP31 transistor, Radioshack has them.

Where you put the swing mod in the radio, which is a cap and a resistor, you put the TIP31 and cap. A 47uf cap works fine.

With the resistor facing you, and the tab in the back away, solder the cap to the transistor. the leg with the black stripe goes on the right most leg. then the other goes to the center leg of the transistor.

Solder a wire on the left most leg, long enough to reach the front of the radio. Now solder the 2 legs that don't have the wire on it, in the place where you would put the swing kit, with the black stripe on the cap facing the back of the radio usually.

Remove the wires from the RF gain and solder them together.

Now solder the wire from the transistor to the center tab.

Remove VR6 and solder a wire from the top tag of the RF gain to the top connection of VR6 that you removed.

Then connect a wire from the bottom tag to a ground point. The side of a tuning can works fine.

Take a piece of shrink tube and put it over the TIP31 so it does not ground against the heat sink, that would be bad.

This is done basically the same in all cb radio's.

At a pinch you can use 5 x LR44 button cells, yes that does add up to 7.5 volts but that's near enough, the 5 cells on top of each other are exactly the same size height and width as the 7 volt battery. I am using them in a "Telex" mike
Gray

Most units do NOT allow modulation adjustment as any more than 90-100% modulation causes adjacent channel signal "Splatter" therefore is subject to restrictions, hence generally that is locked. Also there really is no reason to have more than 100% modulation..as well ... why? I would suggest a voice/speech "Compressor" would be more suited.

• Locate the MB8719 chip that is right behind the channel selector. Wire a SPST switch from pin 10 to ground and another from pin 11 to pin 12.
  

• Schematic http://minus.com/my8tfHQMD#1

• Channel Chart
  

• Position 1: sw1 down, sw2 down
• NORMAL CHANNELS
  

• Position 3: sw1 up, sw2 up
  

• 1=27.605 6=27.505 10=27.555 14=27.605
  
• 2=27.455 7=27.515 11=27.565 16=27.475
  
• 3=27.465 8=27.535 12=27.585 20=27.525
  
• 4=27.485 9=27.545 13=27.595 23=27.575
  
• 5=27.495
  

• Position 4: sw1 down, sw2 up
  

• 1=27.605 11=27.725 21=27.855 31=27.955
  
• 2=27.615 12=27.745 22=27.865 32=27.965
  
• 3=27.625 13=27.755 23=27.895 33=27.975
  
• 4=27.645 14=27.765 24=27.875 34=27.985
  

best way is to leave the radio in piece and obtain a linear amplifier to do the job a 10 meter ham radio amplifier will do nicely but you must re-tune it for the 27 mhz band 10 meter band is 28 mhz.
RF amps work best using side-band mode.

need to get a watt meter hooked up to then go the where the final is and look aroung for a tuning slug marked L38 and that is the baby you have to turn in order to power down this radio.

It is very likely that the reverse polarity diode inside the radio is shorted, usually because the radio was connected up incorrectly.