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Reports of crackle/popping sound from cobra 29

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mushr00m

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I am helping a friend get a cb setup working, I think we've decided it must be something strange with the ground / electrical. The radio will transmit crystal clear one minute, then it will be so crackle sounding you can't even understand him. My question is, what types of filters should I now install, as last resort options? I have installed many cb's in the past and never encountered this problem.

Thanks


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mmckenna

mmckenna

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Before you purchase filters, I'd recommend checking the power and antenna connections thoroughly.

Start with the power feed. Any connection/joint should be suspect. Any crimped connector should be inspected, make sure it's not loose, corroded, damaged, etc. Work through from the power source all the way to the radio. Check the fuses, too. I've often soldered any connections. Not a lot of solder, but just a touch on any crimped connectors. Marine grade heat shrink tubing can help seal things up too. When in doubt, cut the connectors out and redo them.

Same with the antenna. If possible, try a known/good mag-mount antenna in place of the original. Go through everything from end to end, paying close attention to the connector at the radio and the antenna.

I've seen commercial radios do weird stuff like this. Usually I found a badly corroded antenna connection. Cleaning it up or replacing it fixed the issue. Biggest issue I've seen were NMO base antennas that either were not properly installed, or were so corroded. I had one VHF radio fry the power amplifier section due to a corroded connection.
 
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JayMojave

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Hello M+8: Yeah What mmckenna said.

One other suggestion is to replace the antenna with another antenna or dummy load, and listen to the transmit that way. Using a near by radio. This should indicate if the existing antenna is working or not, or there is a radio problem.

Jay in the Mojave
 
kc8kek

kc8kek

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All good points...I would just add checking the mic connection, and preferably trying a different mic as well, might be a simple solution.

Antenna would be my next thing to check as well...with the antenna and radio disconnected, check for continuity between the shield and center of the cable (shouldn't be any, of course). If you find continuity, stop here and replace the cable. Next, meter it. If the SWR is high, or spikes, this can cause audio distortion. If the SWR is high enough to produce audio distortion, it's high enough to produce final transistor distortion, so don't try and "work through" the noise.
 
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SCPD

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You running any other radio equipment besides the cb? If so proper spacing of antennas? After checking already mentioned it's possible there is interference. Make sure your grounded to a good ground point to the vehicle. Your power should be direct to battery Avoiding any path of components that will cause interference in newer vehicles.
 
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MONITORING247

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sounds like a bad cap or a cb final braking down will cause that sound or the audio ic is getting to hot and doing the same thing and rarely its the audio transformer opened up those are your culprits but first check antenna system from coax to antenna with a mfj antenna analyzer to eliminate a bad antenna system a another way is hook his radio to a 50ohm dummy load and see if you smell anything burning while he keys it and talks if you do its more then likely thermal breakdown of a component on the Bord
 
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XTS3000

XTS3000

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There were MANY years the cobra 29 had a defective dynamic (mic gain) control. Try turning the dynamic control up and down 10-20 times and see if that fixes the problem. 2007-2009 production dates were the worst for these dynamic mic pot controls, but any date from 2002 to current are cheaply built.
The mic switch could also be dirty. I've seen the OP's problems from new radios out of the box.
 
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