Question about Cobra 148 GTL 120-Channels Base CB Radio

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148gtl, Taiwan when you modulate the meter swings backwards

Hello,I took this radio in for repair everything worked but there was no power or movment in the meters when keyed,so caps C95,109,173,174 was replaced and that brought the radio back to where it keyed up but only keys a 1/2 watt,the repair guy never finished it,he goes south for the winter.he said that the finals were putting out what they should,and the regulater also..Here is the specs on the radio..PCB 412,PLL is C1969 can you tell me what else I need to replace? on SSB it swings forward but its not powering up all the way.Can you help?

Thank you so much

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  • 3 more comments 
  • May 11, 2010

    yes more info please sounds like a dead key of 1/2 watts.

  • Tom Arsenault
    Tom Arsenault May 11, 2010

    1/2 watt deadkey or 1/2 watt swing? Has the power mod been done to the radio? Has a "modulator" or "super tune" been done?

  • Steve Tompkins
    Steve Tompkins Mar 14, 2013

    The idea is on AM Amplitude Modulation- You need full power to get high performance-its all audio modulation& antenna- AUDIO Mods make sthem super loud with only 1 1/2 watts of power- so the key is turned back some by old timers.

  • Steve Tompkins
    Steve Tompkins Mar 14, 2013

    Sorry I meant to say"You don't need full power of 4 or 12 watts SSB- You just need 100 to 130% modulation by Power Mics or Modification of Audio mod(swing)Setback dead key to 1 watt to 1 1/2 is the old timers way.

  • Steve Tompkins
    Steve Tompkins Mar 14, 2013

    Loudness is the result of setback 1/2 watt. But to clear it up& further range is to give it 3 watts deadkey.



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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%.

Posted on Jan 06, 2012


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Now as for the watt meter....

There are a few types of meters out there. The 2 most common are ones that read AVG, or average watts, or PEP or Peak envelope power, which in short terms is your Peak wattage. Some meters do both.

An AVG meter will not read peak wattage, or swing. So if you meter is an AVG meter, or is set to AVG, then it will not read swing, and will show you your dead key, and that's it. Some times the needle will move a little, but it is not showing your true swing.

All in all a PEP meter is a loose representation any way, because you really cannot get an accurate reading when there is modulation. But it's close enough. You would need a spectrum analyzer to really see what you are putting out with modulation. AVG with no modulation is a more accurate reading however you cannot see swing.

Now PEP while transmitting in SSB with modulation, would be accurate. Just not AM, but like I said, its close enough and is what every one goes by.

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I wouldn't run it past 80 watt dead key for long. With that radio you should really only run what you need. For instance, when I am using mine, I start at around 70--80 watts, and do a check, and if it's not strong enough I bring it up a little, until the audio sounds good to who I am talking too.

Like I said, you have to keep it from getting too hot.

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It sounds like you may have damaged the RF power amplifier stage of the CB. Since you were adjusting the antenna characteristics. Did you have a SWR (Standing Wave Ratio) meter connected while you were tuning the unit? If you did you might have noticed the needle go past the 1.2 mark when you were adjusting the antenna or the unit itself. In any event I think that the RF power Amp is shot.

Thank you,

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