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Old 07-07-2013, 10:34 PM
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Default buzzing antenna

Today we were on 285 in the middle of South Park driving along in the 60 when one of the bikes was about to fall off so we pulled over...

It was pretty stormy and had been raining on and off with some big clouds, but no visible lightening or audible thunder.

I hopped out to re-attach the bike to the hitch carrier and realized that the 2 Meter antenna on the back driver's corner of the roof was buzzing loudly and vibrating. It sounded like the noise was coming from the tip of the antenna.

I assumed it was static buildup and that a lightening strike was eminent so I hurried up, hopped back in the truck and took off. I figured if lightening hi the truck we'd be better off in it than standing around it and that moving might be better. Anyways, nothing happened an we went about the drive.

Any ideas? The buzzing was about as loud or louder than High Voltage power lines buzz in the rain with a somewhat higher frequency. The radio was turned off and I checked it when i got back in the truck.

It was kinda freaky.
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Old 07-08-2013, 06:18 AM
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Well, if sounded like high tension lines then it could have been similar. Those make the buzzing, crackling sound from the corona.

I somewhat doubt it was an eminent lightning strike per say but rather just driving through the storm created a static build-up on the antenna. This is why some antennas are designed to be DC grounded, to dissipate static. I don't remember if your Larsen NMO150 is designed to be at ground potential or not.

Could also be the mag mount, which certainly does isolate the antenna from the truck body electrically, forcing the DC ground to happen through the radio. This is another reason why a solid NMO mount in sheet metal is preferred, no static build-up. :-)
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Old 07-08-2013, 10:02 AM
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Yeah it is one of the trunk lid lip NMO mount things. It is probably not grounded very well.

Nice work on remembering the antenna type. Dang.
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Old 07-08-2013, 10:32 AM
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I thought you had a mag mount. In any case it's not tough to figure out, measure the resistance of the whip to the body to see if there is conductivity or not. BTW, is the little ball by chance missing from the end of your antenna whip? Those are there to dissipate static, too. Their name is pretty clever, corona balls. :-)
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