Freightliner M2 OEM 3/8 Stud Mirror Mount Antenna SWR

One question and one comment

are you checking the swr at the antenna or coax in the truck?

this is important.

so here is the thing, you need to have both sides of the feed line (coax) acting as a means to transmit the signal.

this means you need an RF ground otherwise you get what is called a common mode current problem and a high swr.

the resistance reading shows only a very little part of the issue, so you need to start bonding the antenna mount to the chassis to create that other half of the feed line (coax) to have the antenna to work better.

 

Pull coax to the mount, one peice.

The ground you mentioned is an electrical ground for the mirror motors and the heater element if it has one.

it is not a proper ground.

you need to properly build an rf ground through bonding and/or use of braided straps.

is this your truck or a company truck?

 

I am having the same exact issue with mine. Have you found a solution?

I tried the grounding straps and the SWR has gotten worse .

 

Are the mirror mounts pop metal or something similar? The picture makes them look like they are plastic. Unfortunately the manufacturers don't care or don't understand the principal of how a mobile CB antenna works. These trucks might be a good candidate for the dipole antenna using two 4 foot firestick antennas. A dipole antenna won't be the best performance wise, but it would be better than nothing.

 

Hey Night Stalker10 just saw this.

Yes, the mirror mount is some kind of metal, but not enough to carry a ground from chassis. I used a 4 gauge wire, with copper connections, ran that through the mirror mount, cab door, into the firewall at a ground "manifold" that was connected to the frame. The SWR went down to 2.6 across the board. I can't get it lower than that. But.... When I hold the base of the mount stud, it drops to 1.21 or lower. I don't think it's the RF ground or the chassis ground. My next thing is to replace the Nylon shoulder washer in the stud. The Firestik stud I used is smaller than the hole that the Freightliner mirror mount is mounted in. I think the ground at the stud is the problem. that's my only hope.. fingers are crossed.

 

That's your problem. Anything other than zero is a problem.

 

holding the antenna stud shows that it is an RF ground issue.

You are providing a capacitance to the system that completes the ground. You don't need 4 gauge wire, that's really thick, you need to get a good copper bonding strap and use that.

The RF ground is really a misnomer, it is the other half of the antenna system which is inheritantly balance.