drivingfool

So I have 3:1, and I think it's common mode currents.

I have a cobra 75, on 18' of rg8 going to a ball mount with spring to a 24" firestik2 that's through the driver quarter panel, between the tailgate doorjamb and turn signal. The 6" spring mount is good. As the ballmount is cut through the quarter panel, I would think this is a good ground?

Removing the tune screw does affect SWR in a good way, but it's still 3:1.

Moving/grabbing the coax affects SWR, so I strongly thing I need a choke of some kind. I know 6-8 congruent wraps around a pill bottle will solve it, but I'd like to use some 'clip on' sort of deal because I have the coax running down the side away fro the drivetrain/exhaust which is where I'd like to keep it.

I also have a 102" whip, and that has no affect on SWR at all, further reinforcing my suspicion that my coax is radiating.

I'm thinking about running a ground wire from the inside of the mount down to the frame, just for shits and giggles.

My coax is tough to pull, for the above mentioned reason and because I have a tuffy security console and the coax comes in up front, so I'm looking for 'clip on' ferrite chokes like the ones old pc monitors use.

What do you guys think?


Common Mode Currents

feuerdog

I am not a fan of firestik type antennas, and especially not short 24" ones, but if your 102" whip shows 3:1 then it's gotta be another issue.

1. Confirm your grounds, and add if needed. Body panels are usually grounded, but i'd bond to a roll bar and/or main body to be sure.
2. Ensure you ball mount(is it new or old?) is properly isolating the whip, and test without the spring.
3. Make sure the coax isn't kinked, cut, or damaged anywhere.
4. Run short ground straps on the radio/module itself to the nearest body ground,...AND the negative battery terminal.

Good luck.

JK-jeepit

I think you need to work on your ground system (or call it the counterpoise).
My experience is when the SWR changes the way you are describing the ground needs work, or your coax shield has issues, not built correctly.

102" has no effort on SWR ... meaning it also is 3:1??

The best ground is to use braid.
you might want to bond your body to the frame also.



here are the ferrite beads you'd want.. but i'd say 99.9% that this isn't your problem.
//www.dxengineering.com/Products.asp?ID=182&SecID=152&DeptID=25&KeyWords=T rue&ShowAllProductLines=&ShowAllParts=&ShowAllArti cles=

drivingfool

where did you do that yellow pastic covered strap? Is that in the back above the muffler?

JK-jeepit

you could start with a ground 12-10 awg wire from the antenna bracket to a good point on the frame. If your SWR still drifts when you touch the coax or the SWR meter look at the shields on the cable and make sure they are connected correct. a high and solid SWR will be a different problem then a high SWR that changes with your bodies impedance.... so my experience tells me anyhow. either way you want the frame and body to be connected in several places for the best results.

Yes, I put one on each side of the rear. I used a tap and star washers.
I have one strap on the driver side, side panel to frame, two straps to the tailgate. and another running very close to the OEM engine strap, and then one more to the tranny.

here is more info on what I ended up doing.
I will say this was needed more for the higher power HAM HF freqs then the CB. but it will help you also.

https://www.jk-forum.com/forums/jk-c...nstall-154850/