High SWR...whats next?

check your ground, ground the antenna maybe

 

Please try to avoid the all-too-common "ground your antenna" using various lengths of different types of wire to bond to random bolts at door and mirror mounts. Since there's a huge difference between a DC (battery) ground and an antenna's counterpoise (commonly, yet mistakenly, called a "ground plane" on a vehicle), most success that's been reported by short jumpers are merely anecdotal and, I believe, largely based upon the belief that "Well, I done sumpin' to ground this mount, so I think it's better now."

Do a search in the forum for "copper foil" or "aluminum foil" and you'll probably find a couple of hits from posts that I've made over the years. Self-adhesive metallic foil can be applied to the inside of the roof (directly against the "plastic", above the headliner & such). Make a star pattern, kinda like a Star of Life EMS symbol, with the mount at the center, penetrating the roof so that the grounded part of the mount goes through the foil. Extend all the spurs of foil as far as you can, down the A- and B-pillars, and as far as you can towards the tops of the doors. Yes, I know that the doors are much closer, and while ideally you'd want each of the radials you're installing to be somewhere around 9 ft long, nearly any substantial surface area of metal that has its origin near the feedpoint (mount) of the antenna will be a benefit. Aluminum and copper are nearly equally conductive at the relatively low frequency that CB radio uses, and the phenomenon known as "skin effect" dictates that the higher the frequency, the greater the tendency of energy to occupy the outermost surface of the conductor. And FWIW, adding a separate ground for the case of your radio really does nothing; in many radios, the black DC wire is isolated from the case of the radio, to allow for radios to work in legacy positive ground trucks. A lot of my lightweight gear is mounted via industrial strength Velcro, but I've also got filtered DC power and professional grade mounts that have been correctly installed (I'm a commercial radio tech and old-school -- 20 words per minute Morse -- Extra Class ham).

Since the "radials" will almost certainly be too short to be tuned, the entire array of foil will act like a capacity hat, which is more typically seen on the top of "bug catcher"-style ham antennas. Because it's adding capacitance, your whip may actually have to be longer, rather than shorter, which might be the intuitive tuning direction.

Antenna Specialists (now part of some larger conglomeration -- PC Tel maybe?) sells (or sold) rolls of just such adhesive copper for use on the inside of Fibreglas® roofs, like in ambulances and fire apparatus. I get mine now from a stained glass supply shop. You can also use ordinary aluminum foil, if you've got the patience to cut/tear it and apply contact cement, or maybe rubber cement. The actual dimensions of the strips are not critical at 27 MHz -- the more, the better. Just make sure that the mount grounds solidly *through* the foil at the roof penetration. Having the antenna mount 18 inches up on a pipe, then expecting the radial array you've just made to couple correctly to the shield side of the coax won't happen. You may be able to "ohm it out" with a DC ohmmeter, but radio waves don't act very much like DC.

If that method is too impractical, also do a search in this forum for "vertical dipole". I've put such a solution into a couple of threads that started out the same as yours. Users have reported varying degrees of success, but a lot depends upon how large the radiating elements are (like on any CB antenna, but doubled now because there's a downward-facing one, too).

On the off chance you're not sure where to search from (not Yahoo -- just here there's a search box at the top left of the page on the forum pages.

HTH

73

 

Sounds like you don't have a good enough ground plane or counterpoise. A CB antenna needs metal all under it to send the signal out properly. They do make CB antennas for fiberglass boats and Corvettes. They're called "no ground plane antennas". Might want to look into one. `

 

OK you first need to check the ground with a multi meter and determine if the truck chassis is grounded at the battery if chassis is grounded then run a 12 gauge wire from the antenna ground point to the chassis if this is not good then take a shortened antenna and invert it upside down from the mirrors you might have to make or buy a small flat bar to do this with but it works in most situations hope this helps

 

There still remains some confusion about this so-called grounding of the antenna. If you have a high [3.0 or above] SWR reading, the problem is NOT electrical grounding. The problem is often an insufficient antenna ground plane. It ain't got nothing to do with the electrical system or electrical grounding. I repeat, this has nothing to do with the electrical system or electrical grounding.
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.Your solution is to interconnect the large metal surfaces of the truck into a single large antenna ground plane for RF [radio frequency] purposes.
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. You check the resistance with a volt ohm meter [commonly referred to as a multimeter] between first the base of the antenna and the door and then between the base of the antenna and the door frame of the cab and finally the cab and the truck chassis/frame. You DO NOT run a long wire anywhere because it would act like another antenna. You do use short ground straps or large diameter wire from the antenna base to the door. Another from the bolt that connects the door to the door hinge to where the door hinge connects to the cab of the truck.

 

Is this a pete with dual antennas?

Or is this a setup you are using the "factory" coax?

 

The fact is, unless you do like handlebar said, which will help, getting really good performance on late model trucks is a tall order. I mentioned the counterpoise solution several years ago and have experimented some with it. So far I haven't had much success using it. I do have another plan for more experimentation though. For most of us, not owning the truck, or like me, slip-seating every week. The solutions for a decent working radio are about nil. Thank goodness for XM radio!

 

I'm curious, are these trucks fiberglass cabs or are the using fiberglass doors or what is fiberglass on them other than the hood and sleeper parts?