The best and easist way to tune swrs.

Bootymonster, what can I say, except that I was not as educated as I tout I was.
I would speculate that the radiation pattern for cophase is much better than with single. I now feel I need to cophase.
Thanks for the edgemacation

 

Tune each antenna seperately using a seperate 50 ohm coax then hook them up to the cophased coax and fine tune them both at the same time.
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If you ar going to run a single setup then placing the antenna on the passenger side is perfered because your ground plane gives you a better pattern to the drivers side. Just make sure the antennas are long enough so that over 2/3 of the antenna are above the roof line or unobstructed by the cab or you will have some serious reflect problems and poor performance.[/quote]

This would be true on a car or a van or even a flatbedder or tanker, but not one a 18 wheeler pulling a High Cube Van trailer. The trailer will act as a reflector not has a groundplane.

The right antenna will actually use the side of the tractor to ground plane off of. So you would actually have a tendency to not hear stuff to the left side so well. I have checked this theroy with a Motorola R2000 Service Monitor using the specturm analizer to verify it. A big rig actually need to run a cophased setup ot gain a omni-directional recieve pattern. For a while I had 2 radios installed into my truck, each using a single antenna on opposite mirrors. I could actually hear things on one redio that I could not hear on the other, swapping coax would change what I couldhear, proving the omni directional capabilities.


You are absolutley correct on the tuning proceedures for the antennas, as long as they are tunable. I have used francis antennas, and alway found them below 1.5 to 1, which is certainly more than acceptable.

Get rid ot the tee connector this should be used as a test connector only, For instance I use a tee connector to connect my scope or Service Monitor to the radio for making audio adjustments. Sorry for the lenghty answer.

 

I dont know where you got these pretty pictures, they are close, But they are not correct. If you mount a antenna on a car on the left rear the strongest signat will be to the right front, with a null directly out the left rear, Your signal will alway reflect out the largest area of unobstructed ground plane. Also when you copahsed as pictuered you will not be omni you will end up with to cariod patterns with a null between them where the signals cancel them selves. There is no advantage to running a co-phase on a car or pickup, unless the pick has a overhead camper obstructing the signal. If you can tollerate a ugly antenna right in the center of the roof that is the best place for them. Antennas are tool proper use and understanding and they you increase your radios performance.

I worked for Motorola Communcation solving coverage problems for over 10 this is the stuff I know.

 

I found that it is very important to ground the truck body, preferably with a braided ground strap, to the frame and with mirror mounted antennas to ground the door to the body with a short braided strap. I got immediate improvement with sending and receiving.

 

I've occasionally seen them in truck stops. But the best bet is trucker supply stores, electrical supply, or marine supply, auto/motorcycle parts store, and of course a good CB shop. As for location, I don't think it is that important. You want to find a spot where there is a pre-drilled hole in the frame (it's illegal to drill holes in a frame, also extremely difficult) and a spot where you have easy access to a bolt on the body, metal of course. The braided strap from frame to body should be of the type used for auto battery ground straps. The door to body should be of a size that won't interfere with the door. Coax is commonly used by drivers instead of braided ground straps, but as another driver previously said, it is a poor substitute. In the meantime, the door to body ground can be achieved by using the heaviest copper-stranded wire you can find.

As I mentioned before, I got great results from this easy fix. The CB repairman showed me the difference on an ohmmeter and it was impressive.

 

Speedy,

I found that you can order the straps online from Google groundstrap. The straps are exactly what you want. Good luck.

 

TNspeedy:

Here's an image file of the straps for you:

View attachment Straps.pdf

Now, just Google "ground straps" and you can order them on-line.

 

WHOA! This topic takes me back over 30 yrs. when I had a 17' beam sitting next to the house and a shoe that I could switch over from my ham rig. I thought that you guys would have found something better by now.

I was prepared to write a dissertation but found this site http://www.signalengineering.com/ultimate/antenna_basics.html that saved me most of the work.

You can co-phase on a car, I've done it and the distance would be approx. 4-1/2 ft. or 1/8 wavelength. Mine were short center-loads mounted through the roof just ahead of the rear window. That way the roof, hood act as your forward ground plane and the trunk lid as the rear. Add some mono fishing line to keep everything vertical and you're ready to cannonball in the '70's.

BTW, a big thanks to all of the guys that got me from SoFL to Phoenix in 34 hrs. in '76 and SoFL to San Diego in 35 hrs. in '78. That's truckin'!