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High swr on GMRS box



I have a radiodditty GMRS mobile radio that I built into an ammunition box for portability and connected to a lithium battery. The battery box is plastic/nonmetal. When I checked the SWR of the antenna, I get a very high reading, between five and 10. Is there any way to reduce the SWR? Do I need a ground plane? Is there a way to add a ground to the system, such as a wire connected to a post in the ground? The radio box was intended to be used as a mobile unit to coordinate multiple smaller GMRs radios. Thank you 


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I have never used one of these setups, but you probably need a metal ground plane (even if it a 1/2 wave, ground plane still helps). It looks like your antenna attaches directly to the top plate which looks like plastic (maybe make that top cover oit of metal?).

The Midland "Ammo Can Base Station" recommends using the supplied mag mount antenna on the ammo can lid (separated from the can) as a ground plane.

As suggested above, maybe try the UT-72G or similar mag mount antenna for GMRS on the lid.

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