SWR high, but...

As previously stated you have no ground. Run a strap from the plate along the mirror arm to one of the Torx screws mounting the mirror to the door. Remove the wire link from the Wilson Silver Load to the plate (clearly visible in the pic) and do not cut it as many shops do (no point in ruining it for some other application where it may be needed), just zip tie it to the antenna above the ferrule out of the way. Readjust the tip to re-tune the antenna. Once you have added the ground strap you can keep the Wilson or pick another model, they will all work out much better now that the mount has a ground. Regardless of any ohm meter reading you may have made until you add the strap to bond the bracket to the door nothing else is going to work in that location. As to the lower readings when grabbing the hot center this is merely due to your body absorbing RF power.

 

BTW, that copper plate mount looks like it's hell for stout, but as a counterpoise, it's a bit on the short side for CB. Actually, at the center of a square that's 6x6", it's inadequate as a counterpoise ("ground plane") for any frequency lower than around 800 MHz. Think older AMRS cell phones, or SMR freqs, or the shared ham band between 902 - 928 MHz.

If only you could make it about 18 feet in diameter, you'd have a technically great counterpoise for CB. Of course, while it *might* not stick out farther than the legal limit towards the passenger side, you'd likely run afoul of anyone with a similarly tall vehicle passing you on your driver's side.....

73

 

Sorry for being late to respond. When your SWR reading is 3 or higher, this is an indication that you have an antenna ground plane [some prefer the term counter poise] problem. Tuning the antenna will not correct the problem.
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.What you need to do is interconnect the large metal components of the truck into one large antenna ground plane for RF [radio frequency] purposes. This is done by BONDING. It is not grounding. Grounding is for electrical purposes.
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.Using a multimeter on resistance, check for resistance betweeen the antenna mount and the door. This needs to be metal to metal contact. Paint is an insulator. If there is high resistance, run a short length of ground strap from the antenna mount to the door.
.Next check for resistance between the bolt that mounts the door to the hinge and the bolt that mounts the hinge to the cab frame. If high resistance, run a short length of ground strap from the bolt that mounts the door to the hinge across to the bolt that mounts the hinge to the cab frame.
.Finally check for resistance between the cab frame and the vehicle chassis. If high resistance, run a short length of ground strap from the cab frame to the vehicle chassis.
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.Keep all ground strap lengths short. Do NOT use a ground strap from the antenna mount to the battery. That is to long and could act like an additional antenna and cause additional problems. Remember, the purpose is to interconnect the large metal components of the vehicle (door, cab frame and chassis) together to create one very large antenna grount plane.
.Sorry for the long post.

 

If you don't see a dead short, I'd run a strap.

 

Zero ohms Is what you are looking for.
Good luck.

 

An SWR higher than 3:1 can also show a coax fault. I've seen this lots on VHF & UHF commercial and ham systems. Often the <insert derogatory descriptor here> person who installed the coax connectors didn't "ohm out" the cable before installing it, and never knew that he/she/it had made a short between the center conductor and the shell or braid inside the connector.

If Xcis will allow me to add a couple of steps to his fine DC Resistance checks above, please also check the coax. Disconnect both ends from radio and antenna (or anything else inline). Check for zero ohms between the two center pins (on the ends). Similarly look for zero ohms between the outer shells of the connectors (again, end-to-end). If they're both good, it shows there's continuity. So far, so good.
Now, the acid test. (No, don't spray/pour or drop any....) Put the ohmmeter's probes from either center conductor to the shell. The needle shouldn't move, or a digital meter will show something to the effect of "OF" (overflow) or some such indication that the resistance is "infinite", or too high for measurement. As long as your bare fingers aren't holding the conductors or metal probe ends, then *any* numeric indication says that there's a path between the hot lead and the shield on the coax. (The bit about bare skin is because a decent meter will show the DC resistance through your body, on the order of hundreds of thousands or millions of ohms.)

If the coax is either shorted or open (broken) at either end, the SWR will show as high, and no amount of manipulation of the stuff downstream (towards the antenna) will fix it.
If not sure, swap out the coax with a temporary jumper to reach from the radio to the antenna -- let it drape over the seats, dash, etc. -- it's only used for a test.

Just a thought. At my age, they happen infrequently enough that I try to write them down more or less as they occur. Too many years of high power UHF transmitters.....Mom, is that you? ;-O

73