Antenna Grounding Question

It sure won't hurt. I was struggling with my Pete door mounted mirrors after doing a lot of bonding, antenna and coax changing, different brackets, etc. I ended up having to tilt my antenna forward quite a bit and it lowered my SWR a bunch. For all the nay sayers I didn't do it to look cool and know it isn't the ideal positioning but I went from 1:5 - 1:6 to 1:2 across the board, so it worked for me.

 

I agree that adding to the amount of RF counterpoise near the same level as the mount certainly can't hurt. One of the huge tradeoffs that's come from using lighter materials in modern truck cabs is that it's become extremely difficult to make an antenna system that radiates efficiently.
Keep in mind that SWR is only the least expensive antenna parameter to measure, aside from adjusting the physical length according to just a frequency cutting chart. SWR doesn't really let you know if the antenna is resonant on the frequency you think you're on. With that RFX assembly, you might very well be transmitting spurs which are out of the antenna's passband, so the antenna "rejects" them, which then shows as a higher SWR. It doesn't mean the antenna is at fault.
Since it would be easier than tearing into your door, the first thing I'd do (if I didn't have easy access to someone with an MFJ or similar antenna analyzer) would be to test the SWR with a stock (untuned, out-of-the-box) CB. If the SWR is appreciably better than with your existing radio (and without changing anything else), your existing radio ought to be seen by a shop with a spectrum analyzer and staff trained in its use. A sad fact is that an awful lot of build-on power amps are tuned by the installer with nothing more than a wattmeter.
An antenna analyzer will show more valuable information, such as the resonant frequency and what kind of reactance (capacitive or inductive) and how much exists on your system, assuming the impedance isn't purely resistive. That data can guide you towards fixing problems if the problem lies in the antenna system.
It's possible that a dirty radio is coupled to an inefficient antenna system. That's too many variables to solve for at once.

The only problem with tilting an antenna is that it skews the radiation pattern, so that the energy in front of the truck is pointing downward into the road, and up into the sky to the rear, and at an odd angle toward the horizon out to the sides. But it might let an outboard amplifier with inadequate SWR protection run without power foldback, as long as the compromise in where that power is pointed, and the loss of received signal strength, is acceptable.

But to reiterate the answer to the OP: yes -- adding some *correct* RF bonding to the mounting point of the antenna can help. Even if it's not done well, it sure cant hurt, especially if everything around it is essentially plastic now.

73,
Handlebar

 

I can't see any way that grounding the cab would cause engine computer issues. In fact, I could see how not grounding it to the frame would cause problems due to static buildup.

 

What you need to do is called "bonding". Bonding is connecting the metal components of the truck [ mirror mount, door, cab and chassis] into one very large antenna ground plane for RF [radio frequency] purposes. If you have either a very high SWR reading or tuning the antenna does not change the SWR reading, then bonding could be the way to correct the problem. While it may look like grounding, bonding has nothing to do with electricity. Therefore bonding has nothing to do with the computer system in the truck.
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You want to keep the wires or straps used to bond the components together short in length. Do not run a wire from the antenna mount directly to the frame or the battery ground. That may cause the wire to act like another antenna. You want to run a wire from the antenna mount to the door. Another wire attachs one end to the bolt that mounts the door to the hinge. The other end attachs to the bolt that mounts the hinge to the cab. Finally, a wire from the cab to the truck frame chassis. This method interconnects the metal components of the truck together to form a large antenna ground plane.
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I suggest that you do a search for "bonding" in the cb-radio-forum. This topic has been handled extensively before.

 

http://www.k0bg.com/

More than you ever needed to know about grounding and bonding.

 

Hiya. I'd looked up as much as I could without being a Mack dealer about that cab's design originally, and saw the bit about the "rubber bubby buggy bumpers" (say that four times quickly). I don't think they were necessarily intended to be electrical insulators, but rather they are supposed to be physical shock isolators, to take out some of the high frequency road shock jiggles that would otherwise make hardware (and bones & eyeballs) fatigue or loosen faster as the miles accumulate. They're teamed with the obliquely mounted shock absorbers to the frame that I believe are for longer-period motions, like sway. Actually looks like a nice ride; Seagraves never thought of that for their old 70-foot aerial ladders, apparently (ouch!)
But I agree with MsJamie: it would seem that anything to help dissipate static would be a blessing for the whole shebang (technical term).
73

 

Shebang?

http://www.youtube.com/watch?v=0d5eP0wWLQY

 

Ahhh........ a/k/a "When Engineers Go Bad"

On another note <groan!> as a semi-pro musician, I dunno whether to be worried that I've neither heard of that tune nor had to play it for a gig.

Perhaps it's just one of those universally good things.
Yeah, that's what I'm going with.