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RF Power blew my amp?

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Mattkuhar

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hi everyone, im not sure if im posting in the right place (admin feel free to move it to the proper place)

heres the story:

my friend and i were testing out distance using my truck's mobile (Kenwood TK-780) and a Baofeng UV-5R Walkie. the Kenwood is hooked to a mag mount right now with power coming right off the battery. also in the truck i have an audio amp for the radio, after testing the radios, i noticed that my audio feed from the amp was VERY broken up sounding like blown speakers (brand new speakers). so my main question here is, is it actually possible the RF Energy from the Kenwood actually toasted my Amp? ive never heard of something like this occurring to anyone before. it wasnt an expensive amp at all but it was nice, just dont want to replace if itll happen again. i believe the Kenwood was pushing out 45-50w of power.

Thanks, Matt
 

jonwienke

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It is possible. If the antenna is using the feedline as a ground plane, the shielding of the coax becomes an active antenna element, and you can have RF feeding back from the antenna to the radio. This stray RF can can feed back through other devices electrically connected to the radio and damage them, and in extreme cases, (more common at higher power levels) create a shock/burn hazard.

If you make a coil of several turns of coax (the exact number needed depends on the TX frequency) right next to the antenna, you can block this stray RF. (See BUILD AN AIR WOUND 1:1 CHOKE BALUN FOR HF - THE UGLY BALUN! for some examples) But this should be a second line of defense--your first should be to make sure your antenna has an adequate ground plane, and that the coax is not part of the ground plane any more than absolutely necessary. For vehicle mounting, you want the as much of the coax inside the vehicle as possible, consistent with placing the antenna in the middle of an unobstructed expanse of vehicle roof. The coil should be just inside the vehicle; in the case of the mag-mount, it should be the inside the vehicle right next to the door/window where it goes outside.

Getting this done right will also lower your antenna SWR.
 

Mattkuhar

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Oct 3, 2013
Messages
137
Location
New Haven County, CT
The radio with the amp was the AM/FM radio, not electrically connected (until everything meets at the battery anyway) so it looks like i really need to get off my butt and do my NMO mounts ive wanted to do for close to a year now lol. Just a shock to me as im still getting my feet wet with the radio hobby. Hmmm maybe the radio is also the cause of ECM failure in my truck too?
 
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