I have a 2' antenna on my third brake light. You can see my install at the following link:

https://www.jk-forum.com/forums/jk-write-ups-39/budget-overhead-cb-install-101747/

Bad news is I just hooked up my buddies SWR meter to it and I am reading 5

I have no idea how to tune it because it doesn't have the set screw at the top like the fire stick. Does anyone have any ideas?

 

Try this........

https://www.jk-forum.com/forums/jk-cb-ham-radios-128/if-you-have-fiberglass-antenna-high-swr-read-101902/

 

I don't have a ground strap so I don't think this is going to help. I red online that antenna's without the tunable tip you have to trim to adjust the swr. I also read that you should check the swr in an open area and I checked it in a parking garage at work so maybe it isn't as bad as I think it is. I will recheck it tonight.

 

Ok, so I hooked up the swr meter at home in the yard and got much better results. I now see 3 on channel 20 and slightly lower at channel 40 and slightly higher at channel 1. What I found said that his means the antenna is too short. I can't add any length to my antenna but the numbers are so close I don't think this is an issue.

I also found the following link:

http://groups.google.com/group/113-d...95827e48d0a3cb

This site makes me think that I might not be grounded enough on the third break light. When I mounted it I didn't run a ground strap and there is paint between the bracket and the third brake light. I am going to try and run a ground wire temporarily and see if this brings my numbers down anymore.

 

I am starting to feel like I am talking to myself but here it goes anyway.

I ran a temporary ground from the antenna to the frame and now my SWR is at 1.7 on Ch 20, 1.6 on Ch 1 and 1.8 on CH 40. I think this means I need to trim the antenna.

So I went ahead and put the permanent ground in and had to run an errand before I could test it. My wife and I took our baby so I put the top up and when I got back and checked my SWR it was 1.9 on CH 20, 1.8 on Ch 1 and 2.25 on ch 40.

Should my top being up make that much of a difference in the SWR or do you think my new ground is bad?

I didn't think it could be the top so I tried rerunning the ground to a better location. I drilled a hole in the wheel well and scratched through the paint and used a self tapping screw to mount it. So now using an ohm-meter I have less then 20 mOhm difference between the mount and anyplace on the body I checked and now I know the ground is good.

It got dark before I could recheck the SWR so I will do it in the morning.

 

So I rechecked the SRW this morning with the new ground in and the value changes depending if my ragtop is up or down. It goes from 1.8 (top up) to 3 (top down) on ch 20. What causes this?

 

Maybe the antenna is too close to the soft top frame. You just got me thinking. I want to get a reading top down.. I'm getting 1.4 channel 19 top up. I'll post a pic of what I did tomorrow. And I'm not using any ground. But the antenna is mounted to a LōD carrier.

 

It is close, about 3 -6 inches maybe. But the swr seems good with it up. I would think that if it was too close that the swr would be higher wiht it up not lower.

 

If you already know this, I apologize. SWR stands for Standing Wave Ratio. Basically, standing waves are not desirable because the are RF energy that is not moving out the antenna. They are caused when RF energy that you send out the antenna gets reflected back to the radio. Ideally, every bit of RF you send out to the antenna is radiated because that increases the strength of your signal to the distant receiver. To effectively radiate, the antenna must be of the proper length for the frequency that you're operating on. That's why you're seeing different SWRs on different frequencies--you don't have a tunable antenna (one with a built-in antenna tuner), so the antenna is going to be perfect on just one frequency (channel), and slightly off on others.

Now, place the antenna near any kind of mass that reflects the radiated signal (garage, vehicle body, etc), and some of the reflected signal will get back into the antenna, and travel back down the RF cable (thus increasing your SWR).

CB operates around 11-meters. That means a full wavelength antenna is about 33 feet long. That's obviously not very practical on your Jeep. So we use shorter antennas--one-quarter wavelength is very popular, but is till a bit too long for a Jeep. So we "electrically lengthen" the antennas with coils built into the device. These are not perfect--far from it. The shorter the antenna, the more electrically lengthening the antenna will require. And there will be a reduction in consequent performance. That's why 2, 3 and 4 foot antennas are offered--4 footers will generally work better and be easier (less critical) to tune. Two footers are the opposite.

My suggestion: There are antennas that have a setscrew and a small stub that can be adjusted to get the best possible SWR. I use a K-40 that has such a feature (not one of the truck monster antennas, but rather a 3-foot whip). I suggest that everyone get something like this, as opposed to an antenna that requires physical cutting.

I hope that helps you better understand what you're working with.

 

Mark, I appreciate your input. The only reason I went with a 2' was because I wanted to clear the garage with it and the only reason I got an antenna without a tuning tip was because I didn't know they existed when I bought it. I am about ready to give up and order a new antenna and abandon the cheapy from Fry's.

The one thing I don’t get is why is the swr higher with the top down then with it up? This seems completely backwards to me.