Riddle me this??? A CB tuning question

[preacherman]

Ok, here is my dilemma. I was switching out CB's in my truck (a 1994 Isuzu trooper). The PO had a firestick installed on the ARB bull bar with a midland brand CB and a good cable. I was switching out the CB with a Corba model with weather stations. I installed the corba and tuned the antenna with a good SWR meter. With the firestick installed and tuned I could not get the CB to transmit or receive very far (less than a mile) so experimenting a bit I grabbed a no name wal-mart brand 1 foot tall mag mount cb antenna I had laying around and connected it up. I mounted the mag mount ********** dab in the middle of my roof. Un-tuned I was able to pick up the weather band from the airport 20 miles away and talk with and hear truckers talking on the interstate 7 miles way.:Wow1:

So here is my question, I know the ground plane on the roof is better but THAT much better??? Am I doing something wrong? Is the ARB that bad of a mounting place?

 

[soonenough]

What was the SWR of the Firestik when you tuned it on the bumper? If it was high (as in > 2.0) then most likely the bumper is not grounded well at all, so you basically had no ground plane.

 

[preacherman]

it was at 1.o does that help???

 

[UNI]

It could be your antenna is just bad. (It could be you just wacked it one to many times on a tree limb.)

Is your coaxial cable 18ft. long?
Does your CB have a good ground?

 

[SunTzuNephew]

Or the connection wasnt good.

 

[preacherman]

I should have said, I thought the antenna was bad so I put a new one on and got the same result... I am wondering if the cable is bad or nicked somewhere.


Is there any special trick to getting a proper ground on the ARB???

 

[gary in ohio]

SWR is just a ratio of power transmitted vs power reflected back. Its not an indication on how good an antenna is. I can take a resistor and get a 1:1 SWR but it would make a poor antennas. What is more likely the case is directivity. An antenna on the roof will be pretty much omni directional. One on the bull bar may favor a directional pattern. Try you bull bar antenna but put the vehicle in a different direction.

 

[PhulesAU]

Ground strap to the ARB, And you DO NOT need 18 ft of coax. is this the front or rear? if the antenna is right up against the sheet metal, it'll be hard to maintain SWR unless you're sitting still.

 

[UNI]

PhulesAU (Posted): Ground strap to the ARB, And you DO NOT need 18 ft of coax. is this the front or rear? if the antenna is right up against the sheet metal, it'll be hard to maintain SWR unless you're sitting still.

I'm assuming your using a FS-Series FireStik Antenna. Under a pefect condition you might not have to use a 18ft. cable, but you need a impedance match with the coax and antenna. This antenna is designed to perform at maximum capacity with 18ft. of cable.

Click Here: FireStik Website

 

[soonenough]

I'm assuming your using a FS-Series FireStik Antenna. Under a pefect condition you might not have to use a 18ft. cable, but you need a impedance match with the coax and antenna. This antenna is designed to perform at maximum capacity with 18ft. of cable.

Click Here: FireStik Website

Keep in mind that Firestik also happens to sell 18-ft sections of coax, so it's in their best interest to convince you that you need exactly that. I'm not saying they don't have some great Tech information on their website, because they do; just keep in mind that they're in busines to make money.

Read this link before convincing yourself that 18 feet of coax is an absolute necessity. Heck, Firestik even admits in their Tech section (link) that the length of the coax doesn't matter if your radio system is properly set up; they simply recommend 18 feet because of the vast variety of customer installations:

About the length: This is a testy subject with many engineering types. They have argued with us on many occasions regarding this matter. They say that if your system is set-up properly that the length of the coax is irrelevant. We agree! However, mobile installations have so many variables that a perfect set-up is the exception, not the rule.

 

[gary in ohio]

regardless if you need 18ft or not. the signal loss between 10ft and 18ft at 27mhz are pretty much the same. Not enough to make any difference.

 

[SunTzuNephew]

And if you're not going to set up your radio correctly with 10' (or whatever) of coax, what makes Firestick think you're going to set it up correctly with their magic wire?

 

[UNI]

Soonenough,

Your probably correct, its to there best interest to have that added $ale! :coffeedrink:

 

[762X39]

So here is my question, I know the ground plane on the roof is better but THAT much better??? Am I doing something wrong? Is the ARB that bad of a mounting place?

A couple of points from a former radtech...
The centre of a metal roof is the very best spot for an antenna.
18' of coax is about 1/2 a wavelength for a cb radio, this is the best match for a CB radio all other things being equal.
The bumper is one of the worst places for an antenna but that is where I mounted it on my MOG, the difference being that I used a full 1/4 wavelength antenna (108 inches long).

 

[Scenic WonderRunner]

Mobile Antennas:

The Compromises of Placement vs. Performance

http://www.olypen.com/craigh/antennab.htm






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