Freightliner M2 OEM 3/8 Stud Mirror Mount Antenna SWR

It looks like you've made some progress by bringing the SWR down some, but you still have a long way to go. Most of these mobile cb antennas use a 3/8 stud. I'm surprised that the mirror mount hole is larger. Is the nylon washer on the antenna a flat washer? I was thinking Firestick antennas used a nylon washer that had a molded part on one side of the nylon washer, that fit into the hole of the mirror mount. Sometimes people (including me) have installed the nylon washer on the wrong side of the mount. Although with a molded mirror mount, I don't think that would be an issue.
The professionals say to use 3/4 to 1 inch wide ground straps that are 10 inches long or shorter. Continue to do what Ridge is telling you. Here's a link about bonding. Just click on the basics.

Bonding

Hope this helps.

 

Is the driver still around > did you get this issue resolved?

I run an M2/106 with electric west coast mirrors, with twin 4' steel on coil spring.

That composite to door mount is what I believe my bit of cursing was from.

I ran a dedicated ground wire along with the antenna wire, from the the base of the antenna mount (using a ring connector) and all the way to a body bolt on the inside of the cab on the wall between the door and the firewall.

I forget what my final numbers were, but they were nice (there's a thread of mine about it here somewhere), all my radio checks get replies of loud & very clear, as is my receiving end.

 

Thanks for the replies guys..

I ran a ground cable from the base of the antenna mount to the engine compartment firewall ground stud. As for the nylon washer, it is pretty flat. That stud is a 3/8, I can probably fit a 3/4 stud in there. That's how big the mirror mount bracket is. I ordered some Nylon Shoulder washers hoping that might help. I replaced the original stud with a 3/8 firestik one. I think when I tightened the stud mount, it might be touching the mount base. can't tell. Did a resistance test and it says its grounded between the stud and PL-239 connector under the mirror mount.

 

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. For anyone who is reading this thread, let me attempt to simplify the solution to his problem. When the SWR is 3.0 or higher that indicates an insufficient Antenna Ground Plane problem. The problem can not be corrected by changing the coax cable or changing/tuning the antenna. It has nothing to do with electrical grounding. What is needed is to inter connect the large metal components of the truck for radio frequency(RF) purposes. Continued transmitting with a radio that has a SWR reading of 3.0 or higher can damage the final amplifer circuit and permantly reduce you output.
. Step 1: Using a meter check the resistance between the antenna mount and the door. Resistance should read zero. If not zero, connect one end of a short flat ground strap to the antenna mount and the other end to bare metal on the door. Paint is an insulator so a painted surface is not any good; it must be bare metal. Re-check the resistance to insure it is now reading zero.
. Step 2: Using a meter check the resistance between the door and the cab frame. Resistance should read zero. If not zero, connect one end of a short flat ground strap to the door at the hinge and the other end to bare metal on the cab frame near the hinge. Paint is an insulator so a painted surface is not any good; it must be bare metal. Re check the resistance between the door and the cab frame to insure it is now reading zero.
. Step 3: Using a meter check the resistance between the cab frame and the chassis frame. Resistance should read zero. Paint is an insulator so a painted surface is not any good; it must be bare metal. Re check the resistance between the cab frame and the chassis frame to insure it is now reading zero.

 

I agree, that's why I was referring him to read about bonding. You did a great job explaining the procedure. The only thing I would add, is to apply a thin amount of grease to the bare metal and ground strap connectors. Just to prevent future problems due to corrosion.

 

Well yes and no.

A high swr can also mean a problem with the feed line or the antenna itself. Bonding is the first thing that needs to be checked, but not because of a high SWR, it needs to be done regardless.

I won't get into the rest, it is good information but will say many trucks will have resistance showing more than zero on the door to cab and can to chassis, this is because the grounds for the systems are carried in the wiring harness.