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Intermittent Squeal From Cobra 29 With KL203P

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GigaFish
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Intermittent Squeal From Cobra 29 With KL203P

Post by GigaFish » Friday, 29 September 2017, 10:30 AM

Hey all,

Recently did the variable power on my Cobra 29, and installed a KL203P amp in my truck. I am having an intermittent sound that comes from the radio on TX that I think is a result of the extra RF produced by the amp. It's kind of like a squeal, but a but lower ( I think heard it referred to as a growl somewhere online). It only does it occasionally, and is not caused by the talkback (Verified it comes over the air to another vehicle). I am using an Astatic 636, and it seems like if I hold the mic differently then it will not do it. Additionally, it only happens when the amp is on.

I have been reading online, and just wanted to get some input on various solutions before I go trying all sorts of stuff.
My Radio and amp are run straight to the battery leads (red and black) if that makes a difference. SWR is below 1.5 on all channels (tested without amp), and the only thing I have done to the radio is the variable power. Dynamike is at approximately 12:00 position, and power is right at/under 2 watts. I also read that some had success with putting some ferrite chokes on the mic cord, and since the issue seems to be with how I hold the mic, would this be a viable solution? Or if I open the mic up, is there anything I should look for to isolate the issue?

Sorry for the broadness of the issue, just trying to narrow it down some! Thanks in advance.


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Re: Intermittent Squeal From Cobra 29 With KL203P

Post by MDYoungblood » Friday, 29 September 2017, 10:43 AM

You could try a separate ground wire from a case screw of the radio to a good ground source under the dash, do this only if the radio's case is not attached to metal already. Same with the amp. The case ends on the KL203 is plastic so it does allow some RF to escape, ferrite bead, the snap type, you can try as well, a 5mm on the plug end of the mic cord might help and it definitely won't hurt. Last try to get the SWR down as low as possible.

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Re: Intermittent Squeal From Cobra 29 With KL203P

Post by GigaFish » Friday, 29 September 2017, 11:13 AM

Awesome, thanks for those tips. I've got the radio sitting on a sawtooth hump mount so it is not in contact with any other metal, and the amp is sitting directly under it on the carpet. I bet I have some ferrite cores laying around somewhere, I'll give those a shot too. I really appreciate the help!

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Re: Intermittent Squeal From Cobra 29 With KL203P

Post by jon6667 » Saturday, 30 September 2017, 10:00 AM

sounds like a grounding problem

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Re: Intermittent Squeal From Cobra 29 With KL203P

Post by MDYoungblood » Saturday, 30 September 2017, 16:24 PM

I think you will see an improvement in the SWR as well when you add a separate ground wire to the system.

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Re: Intermittent Squeal From Cobra 29 With KL203P

Post by sonoma » Saturday, 30 September 2017, 21:15 PM

also make sure the ground wire inside the pl259 connectors is making good contact. I have seen it more than once the shield inside the coax is not making a good connection and when you put power on it rf escapes and you get a squeal. the speaker wire could be picking up the RF if you are using a external speaker and the wire is close to the coax. so many variables with ground will cause this. start with what MDY said to do 1st then check farther if needed.
MDY always has good ideas just some extra info if needed.

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Re: Intermittent Squeal From Cobra 29 With KL203P

Post by GigaFish » Saturday, 30 September 2017, 21:47 PM

Awesome, thanks for the help so far everyone. I swapped out the jumper between my radio and amp, making sure to tighten all connections snugly. That helped probably 30%, also just got done putting a snap on ferrite on the mic cord and that seems to help big time. I can slide the ferrite on and off while keyed and it’ll squeak and then stop. Still definitely gonna add a ground soon to try to drop my SWR some more.

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Re: Intermittent Squeal From Cobra 29 With KL203P

Post by RodinKy » Saturday, 07 October 2017, 8:27 AM

There are several people using the Cobra 29 around here and they are squealing also, it is usually fixed by turning the dynamike to a lower setting.

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Re: Intermittent Squeal From Cobra 29 With KL203P

Post by MightyMo » Sunday, 08 October 2017, 0:05 AM

Here is a couple of issues I've run into lately. Take it for what its worth. It may not be related at all.

1) I had a Cobra 29 that squealed on transmit. I could not hear it, but those I was talking to could hear it. I took it to the local shop and put it on a freq counter. The radio was slightly off frequency. A quick alignment fixed it.

2) I had a Galaxy Pluto that was not on the correct frequency and would not respond when the band switch was changed. Took it to the same shop. A new crystal fixed that problem, but he couldn't get it to align correctly. It took him a full hour to find a single bad capacitor that was causing it. ($0.50 part cost me $95 in labor).

Maybe check your alignment and verify it's staying aligned. Once again, all this could be completely irrelevant to your situation.


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