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Grounding mobile Ant. Fiberglass Body Car

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Chris0381

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I am installing a small Diamond mobile antenna on the rear of my Saturn with an L bracket for use with a mobile Pro-97 scanner. I just realized the body were Im attaching the bracket is Fiberglass any need to run a special ground and if so what would be a way to ground the antenna.

Thanks
 

ka3jjz

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Which Diamond? Some of the antennas they sell are no-ground needed (I have one, and it's pretty good from about 120 mhz up to about 170 mhz and 430-500 Mhz or so).

Probably the best way to ground the bracket would be to put a copper braid strap from the bottom of the mount that should bite into the trunk (or whatever you're putting it on) to a known ground point - and that will take a little hunting with a VOM. I'm not familiar enough with a Saturn to say where that might be found - but wherever you do this, the shorter the braid, the better. Since this is a receive only app, I can't imagine where more than 1 or 2 would do the job nicely. 73s Mike
 

Chris0381

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Thanks Mike

Im not sure which antenna Im getting yet its just a run of the mill wideband antenna that is fairly small about $23.99
 

RevGary

Senior Tropical Storm Analyst, TSRC, in Alabama
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IF the antenna that you choose does not have to be grounded, take a page from the Marine industry and use overlapping metallic tape on the underside of the fiberglass surfaces near the antenna's mounting position to create an artificial signal ground plate. Just remember to use an actual ground strap from the metal tape to a frame or steel body ground. It does make a difference in performance. The tape can be purchased at any home center - and is normally used to seal A/C ducts. (NOT duct tape!).

This may not be necessary depending upon which antenna that you select.
 

Chris0381

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Thanks

I guess my next question is should I place the antenna on the side of the car opposite were the fuel pump is since the fuel pump is electrical and my cause interference ?
 

gcgrotz

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Chris0381 said:
Thanks

I guess my next question is should I place the antenna on the side of the car opposite were the fuel pump is since the fuel pump is electrical and my cause interference ?
Couldn't hurt, if you have that option.

OTOH, it may not help, OR, it may not even be necessary depending on the fuel pump.

There's a little luck and/or black magic involved in radio, ya know?
 

n8chb

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Chris0381 said:
I am installing a small Diamond mobile antenna on the rear of my Saturn with an L bracket for use with a mobile Pro-97 scanner. I just realized the body were Im attaching the bracket is Fiberglass any need to run a special ground and if so what would be a way to ground the antenna.

Thanks
Electrical grounding and RF grounding are totally differant things.
If the antenna is mounted on a bracket it will not react the same as a ground plane.

A ground plane type installation causes the pattern to be directed towards the earth. The radiation pattern will travel outward increasing the gain more than going up into the sky.

Follow the manafactures specs about ungrounded antennas. Most fiberglass boat installations use a ground more for lightning protection than controling the RF pattern.

Putting a jumped wire at the base of the antenna can degrade the signal so I would go without it.

73

Roger
 
N

N_Jay

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The ground plane or "counterpoise" does NOT need to be grounded to the car frame.

It only needs to be connected to the shield of the transmission line at the base of the antenna.

The fuel pump may or may not be a source of noise, but being further away can't hurt.

There is no "black magic" in RF, only misunderstood science!:lol: :twisted: :lol:
 
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