GMRS antenna question

[AirborneSilva]

Hi guys, sorry if this has been asked and answered but I recently installed my Midland MXT275, while installing the antenna the mount came with a plastic spacer that wouldn't fit in the mount, my question is will it harm the radio if the part of the antenna that goes through the mount touches it? I have the ghost antenna for reference. Thanks and I hope that makes sense.

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[Zapper]

I'm not an expert on the ghost antenna but I am a Ham so I can provide a general answer that might help.

If it allows the center conductor on the bottom of the antenna to connect to the metal of the vehicle in any way (e.g. via the mounting bracket) that would be bad.

If it is touching the threaded metal ring around the antenna it should be fine.

 

[AirborneSilva]

I'm not an expert on the ghost antenna but I am a Ham so I can provide a general answer that might help.

If it allows the center conductor on the bottom of the antenna to connect to the metal of the vehicle in any way (e.g. via the mounting bracket) that would be bad.

If it is touching the threaded metal ring around the antenna it should be fine.

Thank you for the reply Zapper, if I'm understanding your reply the conductor you mentioned appears to be insulated by plastic around it so I should be fine then?

 

[Zapper]

Yep that should be correct. The center conductor is attached internally to a coil of wire and that wire terminates to "free space" aka nothing. That coil of wire is the antenna radiator itself.

In this antenna design (as I understand it, without actually having one in hand), there needs to be another "half"- what's known as a ground plane. That half is the body of the vehicle. The inner conductor of the feedline cable goes to the antenna itself (the coil) and the shield of the feedline ends up connected indirectly to the vehicle body - usually via the mounting bracket.

If the antenna half and the ground half are connected together it won't work properly. The radio might have decent enough protection circuits to avoid damage but you will have zero or near-zero power on transmit. Receive will be severely attenuated.

In any case, connecting it up and just listening won't damage anything. So a test if you have a walkie-talkie available would be to get a friend to walk a few blocks away and transmit. If you can hear them fine you should be OK to transmit. Or if you turn on the radio and can hear one or more conversations going on that's a good hint that things are connected OK. If the ground and antenna are directly connected those received signals will be attenuated and you will likely hear nothing.

 

[AirborneSilva]

Thank you for that explanation Zapper. I did turn it on and had it scan through the channels but couldn't hear anything, that could just mean there's no one broadcasting in my area, which I think is likely. I'll have to see if I can get a walkie talkie to test it out.

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