High SWR - Cobra 29LX w/ magnetic mount antenna

Ok, so I know I've seen similiar issues within this forum, but Im new to CB's and my situation is a lil peculiar. As the title suggests, I just recently bought a brand new Cobra 29LX and the Cobra 42" 300watt magnetic mount antenna. I installed it, taking both leads directly to the battery.

I installed the cb in my center console, and ran the antenna coax from there to the back of my pickup, and finally through a factory opening under the seat. Ran it through there, and up the bed of the truck to the toolbox. To do this, I had to disassemble the mount from the antenna to make it fit through the opening. (See photo of antenna).

To disassemble the mount from the antenna I had to remove the little screw on the bottom of the mount. When I removed the little rubber protector on the bottom it had this little metallic type film. I had to puncture it to remove the screw. Is this tear in this metallic film causing any issues? (See photo)

After I ran the wire, I made sure to assemble the antenna the same way I took it apart. The only noticeable difference was the little rubber gasket thing that goes between the antenna base and antenna mount. It fit around the bottom screw pretty tight, and I noticed the hole in the middle, where the screw goes, was a lil bigger. Not sure if that would cause any problems.

Anyway, I calibrate as the manual says; I goto a relatively open area, calibrate and I still get a high SWR. Between 2.8 - 3.5 or so. I run the "radio check" feature and get both "RF power failure" and "Antenna warning". After another calibration, adjusting the antenna a lil, those go away. And now, I still have a high 3+ SWR.

A little info - my antenna is sitting on the back of my toolbox. This toolbox has a
a few features that may or may not be related. First, it has a coating very similiar to a spray bedliner or rhino lined. Secondly, the toolbox is a"gullwing" style where the middle dips down, which is where I had the antenna. (See photo example)

Not sure if any of that is relevant. However, when I move the antenna to the roof I still get the same problem. I can hear people talking, but the quality is poor and I have to have the RF Gain turned nearly all the way up. I also have a handheld Cobra CB radio and while on the same channel, I can only faintly hear myself.

Oddly enough, before I fully installed this cb radio, I hooked the leada up to my truck battery to just test it. I used my handheld cb radio and I could hear myself very crisp and clear. I had the antenna just sitting on my the bed rail of my truck. But now I feel like no one can hear me at all on top of bad receiving performance.

So, I feel like the issue is either a ground issue or something went wrong when I disassembled the antenna from its mount.

One last odd thing was when I tested my ground under the hood. When I removed the ground connection the cb still worked. Is that normal? Does that mean that there's some sort of ground short with the antenna?

I have a multimeter but its a peice of junk, and I did get some fluctuations in OHM readings when I tested for resistance between the actual antenna and coax ground shield on the cb. That's a whole process Im not completely familiar with though.

If someone could please provide some info on how I can fix this. Unfortunately, I
cannot find one CB shop in the area I live.

 

Thanks porkchop, I'm still trying to learn the multimeter OHM displays. It starts off at 1 and then when I touch the terminals to something the #'s go up (or down) and then either ends in a negative number or positive #. So if I touch the terminals to the coax shield and the antenna bracket the # on the multimeter should say 0? Sorry, still learning these OHM stuff. I honestly feel like something is wrong with the antenna and the ground, caused by me disassembling it. If someone could provide some insight on that I'd greatly appreciate it.

 

Ridgeline, no I wasnt able to fully put the metal foil back completely. It wouldnt peel back so I had to pop a hole in the middle. There's a photo of it in my original post. I took the antenna mount off the antenna because I ran the antenna coax to the outside of my truck, through a small hole and the wouldnt antenna mount wouldnt fit through. I circled the area where it comes off the antenna and the mount.

When removed, it has a threaded stud on both ends. Bottom stud has the rubber gasket thing. Which I assume is some sort of shoulder washer to prevent the mount ground from reaching the antenna?? The top stud is where the antenna screws onto. I'll send a pic shortly.

Its my understanding that the mount is grounded by the magnetic, through something called 'capacitive coupling'. But the mount and the antenna are supposed to have seperate grounds, correct? Which that continues to confuse me if the entire chasis of the vehicle is grounded.

 

I did the tinfoil thing. I got some of the wifes tinfoil and cut the same size circle out. Now the SWR is higher lol. Even when I recalibrate. Another thing I notice is how, at times, when I select SWR on the SWR/CAL and do a test after calibrating, the SWR will read well below 1. But once I select S/RF and hold the mic down, the SWR is 2.5-3.5+

The rubber peice Im referring to is the rubber gasket on the bottom stud, not the protective rubber cover under the magnet.

So the antenna itself and the mount are to have the same ground? Wow, I read wrong then. I thought I had read how they are not supposed to have the same ground.

My multimeter is junk, I could be wrong about the negative #. I'll try again and send a pic.

Im also getting intermittent "antenna warning" on the display when keying up.

When I calibrate, are there any settings I need to adjust? Squelch setting? RF Gain? Deltatune? Etc.

Thx guys!

 

Not sure if any of these pictures help?


Torn foil


The tinfoil i added

The bottom stud that goes into the mount. You can see the rubber gasket/washer

Too stud where antenna screws on