Quick grounding question.

Grounding the radio will help, but if you can figure out a way to ground the antenna mount its self you will cure all kinds of problems.

 

14-16 ga. is normal. connect ground to the frame of the antenna bracket.

good luck.

 

Heard of people running a wire from the antenna mounting bracket to the negative post on the battery. Claim it solved their ground problem.

 

never ground the antenna to the battery !!! what you need is a chassis ground. run a ground wire from the antenna bracket not the stud. you want to locate a good ground as close as possible to the antenna mount

 

Puppy,
Folks have alluded to the fact that there are different "kinds" of grounds. It's important, if time and $$$ make a difference to you, to recognize the difference.

A D.C. ground is what you get when you run a conductor (like the radio's black power lead) to the negative post on the battery. That's made to carry the return path of the actual D.C. current that powers your radio's circuits, just like lighting grounds on the chassis. That will have nothing to do with how well your antenna works. D.C. conductors "make sense", as you just choose a wire gauge that's suitable for the current you draw and the length of the wire.

An RF ("radio frequency") bypass ground is as short as you can make it. It's the conductor you see on some circuits to give stray radio signal energy a place to go to kinda get it out of the way, so that it won't foul up other nearby circuits. It's why you use capacitors on devices on a vehicle that generate interference that your radio picks up via your antenna. It will commonly be seen on wiper motors and washer pumps, window motors, etc. Lightning protection grounds are a special kind of bypass grounds, because there are often more than one conductor to different ground rods, but the idea is similar, minus the capacitors.

What you need is really an RF counterpoise, so that the half of the antenna circuit that the outer shell of your coax and the antenna mount itself (not the antenna) connect to has a way to exist. Think of old TV rabbit ears. There are 2 conductors the TV to the antenna. Each of the two rabbit ears is connected to one of the conductors. It's easier to reason out if you see one that has older style twinlead instead of coax, but the coax has the shield and the center conductor. The signal that your radio pumps out through the center lead has its path completed at by having the shield of the coax connected to either a large metallic surface. Ideally it would be about 5% more than a "full size" quarter wave antenna, or ~106 inches + 5% for CB, in all directions, at the same height and immediately adjacent to the antenna's feed point on the bracket. And it would be conductive. For roofs, steel cab shells work essentially the same as aluminum, or copper or silver, etc.

Right off the bat, that's part of the problem on any civilian vehicle other than a trailer roof: if it's round, it's going to be somewhere around 19 feet in diameter -- sorta unwieldy on the highway. At least a trailer roof is long enough in two directions to provide a nice "ground plane", as the surface is referred to. Purists will maintain that the actual ground plane is the surface of the earth over which we drive, and the vehicle is coupling to that *actual* ground like a big capacitor. And the closer to ideal the vehicle's "ground plane" is, the more efficient the whole antenna system will be.

In plastic cabs (as I think of them) I've had good luck using self-stick copper tape stuck to the inside of the cab roof and radiating like a star in several directions from the through-roof mount. The ones that point towards the A- and B-pillars can actually extend down into the pillars so that a few of them approach adequate length. A drooping ground plane radial is better than a short one (or none at all).

And at RF frequencies, which is essentially just high frequency A.C., wide conductors do better than just simple round wires. The higher you go in frequency (CB is ~27,000, 000 Hertz, compared to the 60 Hertz in your wall socket), the more pronounced is a trait called skin effect, wherein the current is carried closer and closer to the surface of the conductor.

So I use copper tape that's a couple of inches wide. It's available from places like Georgia Copper, and some sizes are often available from stained glass shops, although you may have to put on your own adhesive. Thickness doesn't matter at typical operating powers up to a few thousand watts.

You *can* put the tape on the outside of the cab, if you don't mind answering endless questions from fellow drivers at the TS. Just make sure that the mount's ground is connected to the foil well, ideally by fastening the stud right through a hole in the foil.

Even a coat of conductive paint that's made especially for RF shielding, applied to the inside of your cab's roof, can simulate the same size metal roof, as long as you can electrically fasten the grounded part of the mount to the painted surface, same as foil.

As to the other points, you can probably figure out that a "ground wire" from the antenna mount's cold side (not the part that's hooked to the whip) to the battery won't make any difference in the antenna system's performance.

And lots of CB radios have DC isolated cases, so that they can run on positive ground vehicles by just swapping the red & black power leads.

Speaking of which, are there still any positive ground trucks? Is White still around? I dunno.

At any rate, a jumper from the case of the radio to the dash or body pretty much only supplies something else from which you can hang a mic hanger, but won't do anything for the radio, anecdotal evidence to the contrary.

Dunno if that's more information than you needed, but it should provide the tools to help you solve your lack of an RF ground at the antenna's feedpoint after making an informed decision.

Either that, or something else.® <----------- Handlebar's Universal Disclaimer (Handlebar Enterprises Int'l, 1981)

 

Wish I had read this before I attached a wire, with alligator clip, to the case and clipped to various points in cabs (I'm a 'slip seater'). Never helped. Oddly enough, sometimes, it added noise.? I finally detached the ground wire & got rid of it, baffled why it didn't work. Now I understand, thanks.