GMRS grounding question

[MiamiC70]

Hi guys,

Newbie GMRS user question. Installed a Midland MXT275 radio along with the Midland Stealth antenna using Rago Fabrication ditch light mount and bracket on my 2019 Subaru Outback wired directly to my battery.

The antenna bracket and ditch light bracket are powder coated, do I need to strip back the coating to assure proper grounding of the antenna? Unfortunately, I don’t have a GMRS SWR or access to one near me.

 

[DaveInDenver]

This is the antenna and basically what you're intending for mount?

It's called a 5/8λ and that means it would be a good idea to have a counterpoise. Even with an antenna such as a 1/2λ (which is usually referred to as ground plane independent in marketing) having the mount grounded is still good to do.

In your case, yeah, it would be best if you expose bare metal under the NMO base and under the bolts holding down the ditch light bracket so that you're not relying completely on the coax to provide that path.

 

[MiamiC70]

Yes, that’s it And mounted same.

What is a counterpoise?

Thanks, will grind that off tomorrow.

 

[DaveInDenver]

Yes, that’s it And mounted same.

What is a counterpoise?

Thanks, will grind that off tomorrow.

Counterpoise is the dorky precise term for an antenna's RF ground. It just means the other half of an antenna.

Technically the whip you see is only half of an antenna. A full antenna is two legs known as a dipole. The whip is just a monopole and something has to stand in for the other half, e.g. the counterpoise to the radiating element.

That can be the Earth itself, e.g. real "ground", or a vehicle body, lengths of wire, a flat sheet of metal or in the case of a handheld radio the person, an artificial "ground".

If you don't provide it the radio and antenna will try and find their own to complete the RF circuit. Often that's the coax shield but could be anything, unintended vehicle wiring often does it, which is how interference occurs and you get weirdness like alternator noise, digital noise from processors, etc. So you want to do things right so you radiate RF where you want and not where you don't.