Homemade quarter-wave ground plane base antenna

[222DBFL]

Yep. You most likely don't need 3 watts of dead key. Just like JJD is stating. About 1-2 watts is normally all that is needed. A proper or close as possible ratio of 1:4 power output is what is really needed. So if the amp is producing 150 watts pep then your dead key should be about 30-45 watts. This should help the backwards swing issue. It's not hard to turn down the AM power and achieve what you are looking for. Also you most likely need to adjust the modulation as well. A tech should really perform this work if you don't know what you are doing as you can damage your radio very quickly using the wrong tools!! Use only plastic tip screwdrivers, or something that is electrically non conductive. Ceramic works as well but you have to be careful using a ceramic tipped screwdriver as well due to being able to damage parts in the radio. Like I said. Best bet is to send or take both the amp and radio to a good tech and have them matched up for each other. Or at least have the radio done. A variable power knob can be added or placed where the delta tune is located at now. Don't use the pot with the delta tune on it. Have a proper one placed in its spot. And have the dead key set to be able to go from about .5 watts to 4-5 watts max. This will help with using most any amp you want. Just some food for thought. But at any rate, yes you need to get the dead key dropped down on your radio to at least 2 watts or less. No 2 watts isn't a standard, it's just an approximation of where you need to be. The amp May need as little as .25 watts. Hard to tell without having the amp in front of you and keying into it with a radio that can go that low in power. That is why I said a variable power could or might be a good way for you to go. This way you can run the radio without the amp if you wanted, or use a different amp.

[JesseJamesDallas]

Yep. I would back off the dk to 2w, that "should" make the amp happy and not swing backwards...however on the Cobra 29 lx and lxle models it will probably cause a RF POWER fail when your in test mode because the radio from the factory was set for 3w...just have to ignore that fail warning.

[mattsowders1989]

Cool. Thanks guys. You all have been a big help.


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[mattsowders1989]

Does how much the radio swings matter or is it mainly the dead key that I should be concerned with?


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[JesseJamesDallas]

Does how much the radio swings matter or is it mainly the dead key that I should be concerned with?


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It can, but unless that Cobra has had some serious mods done to it, it shouldn't mater in your case. I would just deal with the DK.

[mattsowders1989]

Ok cool. Nope. It's all factory on the cobra.


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[mattsowders1989]

I'm going to do some research and see which pot will turn down the dead key


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[JesseJamesDallas]

I'm going to do some research and see which pot will turn down the dead key


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Not real sure, but I don't think there is a pod on the Cobra's, I think you have to add a resistor to lower the dk on the 29's. And if that 29lx has the new SMT board, "good luck"...Those resistors are tiny little critters.

Last 29lx I bought, I got from Bells CB, and just had them install a variable power knob where the Delta Tune was so I could lower the dk down to 1/2w and up to 5w.

[mattsowders1989]

Well I do have a SMT rework station that I use for laptop and game system boards. I'll do some research and see what I can find out.


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[222DBFL]

That is the best way to go JJD. Having variable RF power added. No real need for Delta Tune on an AM only radio especially if it's pretty well on frequency. Have them align radio and add variable power and some other things, and they are great AM radios. My 29lx le has a 1969 final mod done to it. Limiter still intact and it does well. Good audio and works well.