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  #1  
Old 04-15-2008, 03:01 PM
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Rezarf Rezarf is offline
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Default CB antenna placement...

Howdy-

I know this isn't HAM per'se but I bet you folks are in the know!

I want to move my antenna to my tire carrier, to get it up a little higher than the roof. I have a spring and quick disconnect mount. Isn't there something I need to do with the groud to make it work correctly? This will be on the swing out. I will get about 3' of clearance above the roof if I go this route.

Right now it is located on the lower bumper and doesn't reach above the roof line even an inch.

FWIW, it is a Cobra CB with the weather stations wx-18 or somethin' like that And a Wilson 1500 antenna... maybe

Any help would be great, thanks!
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Old 04-15-2008, 04:22 PM
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I couldn't find a Wilson 1500 antenna.

However, there are a couple of things to keep in mind when installing an antenna on a vehicle.

1. (And I know Dave will disagree) NEVER, EVER, USE A MAG MOUNT. They are bullets waiting to fly off and kill someone.

2. Keep the feedline (coax) clean and short. No big loops of extra coax bundled up anywhere. These become loading coils that will mess with the resonant effects of your antenna. Don't kink the coax. It too will mess with the impedance.

3. Unless your antenna is a shorted-to-ground like the homebrew antennas we made for 2M, keep the two conductors from shorting out. That means that your antenna needs one of those fancy little plastic washers with the shoulder. This keeps the center conductor and the shielded conductor (ground) from coming in contact with each other before the electromagnetic waves get a chance to be resonated on the antenna.

4. Mount the antenna securely. Mount it as high and over as much metal as possible. If your feedline is not shorted like , and you follow these simple guidelines, you should be able to use your CB as a trail radio no problem.

Any questions?
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Old 04-15-2008, 06:10 PM
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Nathaniel, you my friend are a wealth of information!

Should I still ground this little wire? Here is a pic of what I have. Also I think it is the Wilson 1000, 4 ft, with adjustable tip.

How high above the roof line will this start to become a problem? I am seeing myself putting it on and off for trail riding only.

One more question, where does the little nylon washer go? Between the antenna mount and the antenna itself? In terms of the pic, does it go above or below the mount? I am assuming it is some sort of insulator?

Thanks!
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My rig... "Maude"
1976 FJ40 with some stuff and some leaks.

2001 Sequoia Limited with heated seats

My camping trailer build up thread.

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Old 04-16-2008, 08:22 AM
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Default Here is some more help

Most folks have no idea what the insulating washer is supposed to do. Hopefully this .pdf can illustrate it better.

If you notice the cross section of coax, the thing to remember is that the inner copper wire (inner conductor) and the outer shielding are important for keeping SWR consistent. The distance between the inner and the outer must be a specific value for the impedance of the coax. If you have 50Ω coax, the distance will be different than 75Ω coax. Any fluctuation in that distance will change the impedance, and thustly change the SWR. That is why coax should never be smashed.

The way to "coil" up any excess coax is to loop it and then tie iit together in the center of the loop to form a kind of figure "8". That way, you minimize the effect the coil will have on the antenna. (Basically the coil would aid in "matching" the feedline to the antenna, so the impedance is the same at the feed point of the antenna and the coax.) Without knowing what your impedance is at those two locations, you don't want to coil up your wire.
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File Type: pdf antenna mounting help.pdf (426.9 KB, 101 views)
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Old 04-16-2008, 09:06 AM
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Quote:
Originally Posted by Groucho View Post
Most folks have no idea what the insulating washer is supposed to do. Hopefully this .pdf can illustrate it better.
Great diagram. I do think the little plastic shouldered washer in your sketch is shown on the wrong side of the mounting bracket, though. It does depend on how the whip-side connector is designed.

Here's the Firestik style:
http://firestik.com/Tech_Docs/mkfr-instl_nohook.htm

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Last edited by DaveInDenver; 08-26-2010 at 09:16 AM.
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Old 04-16-2008, 09:31 AM
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That is what I get for trying to draw a sketch without much sleep.
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Old 04-16-2008, 09:37 AM
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Thanks Fellas!

I am going to get on it tonight and get the CB/antenna installed and finished.

Rezarf <><
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My rig... "Maude"
1976 FJ40 with some stuff and some leaks.

2001 Sequoia Limited with heated seats

My camping trailer build up thread.

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Old 04-16-2008, 10:01 AM
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I should have looked at my mount. Now THAT'S an antenna mount!


Quote:
Originally Posted by DaveInDenver View Post
Great diagram. I do think the little plastic shouldered washer in your sketch is shown on the wrong side of the mounting bracket, though. It does depend on how the whip-side connector is designed.

Here's the Firestik style:
http://firestik.com/Tech_Docs/mkfr-instl_nohook.htm

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Old 04-16-2008, 10:17 AM
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TIG-O-licious.
Wish I could lay down microscopic stack-O-dimes like that.
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Old 04-16-2008, 10:18 AM
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That's ridiculous. Ridiculous crazy cool fool
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