anviljk

I installed a firestik fire-ring cable a few weekends ago going to a Cobra 29lx. I was getting an SWR on all channels of around 2.0 I figured it was a grounding issue due to the mount being on the tailgate. I added a ground wire and noticed that there was a cut on the coax cable. It's not big but it looks like it is only the shielding that is stripped off. I don't think it go into the center section of cable. I put a few wraps of electrical take around it and called it a day. Anyway, I had to replace the radio and when I installed the new 29lx It shows a SWR of still around 2.0 but "antenna warning" on radio. Any idea's what is up? Should I replace the coax cable? Im going to check the ground again on the mount but I really don't want to spend another $20 on something I just got.

Untitled by anviljk, on Flickr

ShawnInPaso

I doubt it's the cable. As you began to suggest, you can check for continuity on the cable to be sure ground-to-ground is good and center conductor-to-center conductor is good by using a continuity checker (can find them cheap at Lowes, etc., in the electrical dept.). As you may know, there is a difference between electrical ground and RF ground. Based on the info you provided, I'd presume it's the lack of an RF ground causing the SWR issue (common on 99% of Jeep installs). If it worked before with an SWR of 2.0, things should be the same with the new rig - except of course it has the little warning that shows up. HTH.

blockrockin

seems to be a common problem with that model cb i have the same one.. and i get that warning also at times.. even though i have a low swr.. i read about a internal adjustment you can make to make the light turn off if it continues to be a issue .

anviljk

I have the pdf file of how to adjust the sensitivity of it. I have to take some readings first and see what I can improve.

Mark Doiron

That bend through the grommet looks rather tight. The minimum bend radius for RG-58 is 1 inch. The reason for that is because as the radius becomes smaller, the inner conductor is pulled tighter to the inside of the bend (same effect that the differential on your axles is working against, but there's no diffy in coax cable). The damage can take time as the inner conductor cuts into the dielectric (that part of the cable that separates the inner and outer conductors). Heat can make it happen faster, especially with higher power radios (not usually an issue for a CB radio). As that bend becomes tighter, it introduces an impedance lump, which will show up as reflected power (higher SWR reading).

BTW: My several decades working in aviation radio, if an RF cable is damaged, it is replaced, never repaired except as a temporary expedient to get an aircraft back out for a mission. Also, I strongly recommend buying cable and cutting it to the needed length rather than buying the standard 18' pre-made cables. That way you can avoid tight bends like that, as well as excess cable laying around. If you've stumbled across anything that says an 18' cable is optimized for CB frequencies, that is a bunch of nonsense written by people who obviously know nothing about RF, RF velocity, and RF cable dynamics (and, yes, I know that Firestik is out there promoting that nonsense--which is a good enough reason to not buy Firestik).

anviljk

I actually cut about 2ft off the 18ft coax cable because it was too long. I'll pull some more cable through the grommet to cut back on the angles and see if that helps.

MD GP

Hi. The bends from the antenna connection and through the tail gate look tight. I would replace the cable. Your SWR shouldn't be the same on all channels; it should be lowest on your best channel (1.2 to 1.5 is realistic), and should be higher on all other channels. There is no such thing as an SWR less than 1.0.
Mark is correct that cable length is not an issue, but I disagree about Firestick products; they are high quality and have excellent customer service.

genesbro

If I were you I would remove the antenna mount from the tire carrier and then use something to remove the paint from the mounting holes where it attaches to the tire carrier. Also remove the paint from the bottom of the mount where the antenna attaches to it. The top side should be insulated anyway so that side doesn't matter. If after doing this and your swr still isn't less than 2:1 then the antenna you bought might have to have a spring to get its length correct. And by the way if the coax is cracked then replace it and be sure and leave a little loop at the bottom so water doesn't follow it into the Jeep.

maxspongebob

Sounds like some good advice. I would add that if you are replacing the cable, then you might consider using RG-8X instead of RG-58. It has much better shielding and is a bit tougher. Also make sure that the antenna is well grounded. You have to scrape some paint off or the connection will not be good enough. Lastly, if you have added a ground wire, it should be between the tailgate and the tub itself and a single wire will not work nearly as well as an actual ground strap.

Amazon.com: Ground Strap, Tinned Cu, 8in, PK2: Home Improvement

BTW, if you want to minimize the amount of paint you need to remove, at least use internal tooth lock washers with a little conductive grease so you get good electrical contact with a bit of weather protection.

These things will help to ensure that you can get the best that your antenna can give.

maxspongebob

I just noticed that that antenna has a proprietary Firering connection. OK, with that you probably can only get the cable from Firestick. It is $18 on Amazon.