20 Most Recent Cobra 148 GTL 120-Channels Base CB Radio - Page 4 Questions & Answers

What problem are you having with Receive?

If you have the manual that came with the equipment it should show you a diagram of plug on the mic with colour code.

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.

I had a similar problem with another brand radio. My power supply I was running it on was not rated high enough in the amp category. Are you running on a power supply or battery?

In the back is where power mods have been added...It sounds like a swing kit 1/2 watt deadkey to 25 watts which is a powerful modulation exceeding 100%. Its a 220uf capacitor in place of a jumper J1 or J(x) J something in some radios. if you replace the jumper and remove the capacitor 220uf or 470uf one.(near finals it will return to around 4 watt dead key) The result of 4 watts is modulation is flat;where if you adjust it to 2 1/4 watt to say 20 watts it will be very loud and modulation is at 100%.

take off bottom cover and see if the speaker wire came off.make sure its on cb and not on pa and make sure its plugged into the right port

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.

you would probably want at least a 4watt continuous power supply or better. do not use as switching power supply.

Your power supply is providing 20 volts? THAT is the problem. This radio should be connected to a power supply capable of providing anywhere between 12 ~ 13.8 VDC. Twenty volts is WAY too much. You may have cause significant damage to the radio if it was connected to that voltage for any period of time.

if your in the uk your limited to 4watts, but if you add a power mike it will help...don't think anyone will tell you how to get yourself into trubble;-)

http://www.cbtricks.com/radios/cobra/148gtl_dx/index.htmNice choice of radio i have the Grant LX Uniden which is roughly the older version.This site may be of interest also if you choose the channel mod make sure you have the right PLL. http://www.radioaficion.com/HamNews/mods/mods-cb/2428-uniden-grant-xl-mods-pll-agc-power-clarifier.html

clipping the limiter should not have prevented tx on sideband are u sure u didn't do something more accidently. r 131 is the correct limiter for the 148. just out of curiosity what year 148 is it?

There should a small diode located near the power input line, "black in color with band on the one end" chances are it is shorted, blowing the fuse. This is a protection diode preventing a positive/negative mix up, if this turns out to be the problem check to make sure the audio is working, if not! you must replace the ic chip.

replace AM regulator transistor 2SA1012 !

can you be more specific please ?TX meter or RX s meter ? check power supply voltage is stable, obviously on RX its essential to use a constant signal, of course,if you're doing it without test gear & just doing a quick 'tweak' comparing with a good know s reading off a known set - a s9 signal is usually the standard point they calibrate to. although on a CB set its not a greatly important. on TX you may first want to check RF power out is constant first, so a dummy load (in case aerial swr is changing while on TX) needs to be used. If actual RF power is changing, suspect drying electrolytic capacitors, these sets are 30 years old, so its not unlikely. dying driver or PA transistors or dry joints are also possible. or if everything checks out, possible voltage regulation probs, so check 2SA1012 AM reg isn't dying and the other ****** too.If you're lucky, its just the variable resistors giving up.

without more detailed info, quick suggestion - thermal fault, if all TX audio works when in this fault condition, it may be fair to assume audio IC is ok and check electrolytic capacitors and dry joints.

Hi, my name is John. Welcome to Fixya. Try turning your MIC GAIN to MAX and see what happens. Let me know how it goes, may have further. Thanks for choosing Fixya.....John

check voltage regulator

Several questions. 1) do you have it connected to antenna with good coax?2) did you check your match on the radio with an SWR meter? What kind of match do you have,is it below 3.0? If it is that high get down to around 1.5 - 2.0 and others should be able to hear you.

1audio. 1red
2shield. 2shield
3receive. 3blue
4switching. 4white
5transmit. 5black

Hope this helps