Trouble Tuning Hood Mounted Wilson Flex CB Antenna

I installed my cobra 75 last week and am using a 3' wilson flex antenna with it. The antenna is mounted on a relentless fab hood hinge mount. I keep getting high SWR readings. 3:1 on channel 1 and 2:1 on channel 40.

I've checked my grounding and everything looks fine. I've also tried a variety of adjustment tip lengths and they I still can't get the SWR low enough. Anybody have any ideas?

 

I've already done that. I've checked everything with a multi meter. The cables are good, the antenna is good, and the mount is grounded.

 

just try putting it on the roof of the cab and see if thats any better. it just might be too short for your aplication and isnt above the cab enough

 

try grounding with a very large cable...like a set of jumper cables, see if you get a better reading. ive heard of people having problems because their ground wasn't strong enough. i also recently talked to someone at firestik, and they told me a little 12ga wire/grounding to the thin body metal doesn't cut it (in most cases).

 

Ground the antenna itself or the mount? In the antenna's directions it said to only use the ground on the antenna with certain types of radios. When I grounded my antenna itself it raised my SWR. My mount is grounded through the hood hinge bolts. Should I try putting an actual grounding cable on the mounting bracket?

 

Just hooked a jumper cable from my antenna base to the frame, made no difference in SWR. Also checked with a multi meter, the base has a good ground to the body

 

hm, im not sure then. if youre using a 3' antenna, the problem (as UMBCrew said) could be you arent getting it high enough above the cab...i know a lot of companies recommend the antenna be at least 2/3 about the cab. good luck, let us know what you find out.

 

This is what I've been thinking. I just figured I'd try every option before I go out and buy a 4' antenna but that's looking like that'll be the case.

 

Hey, use copper braid ground straps and ground your hood to the front quarters (I used the hood hinge bolts), the rear quarters to the frame, the front quaters to the frame. Make sure to scrape/sand down to bare metal to insure good connectino. The body panels on these trucks are not grounded well, I went through the same thing and got my swr to 1.2 or so. I mounted my antenna in the front passenger corner of the bed, a Wilson 2000.

 

this is what i was thinking.

do you have pics of your setup, specifically the ground wire location? ive been wanting to run a thick copper braid ground from my behind the cab mounting location, but dont know where to run the wire/how i want to ground to the truck.

 

wouldn't running a jumper cable from the mount to the frame have tested this though? I did that to be sure it was grounded well and it made no difference in SWR.

 

There is a difference between grounding for DC and grounding for RF (radio frequency AC current). Usually you go for short runs of wide copper braid or foil to make an effective RF ground. To make a good RF ground sometimes I'll strip old coax and just take off the braid and put ring terminals on the ends.

You also want to bond the body panels together and bond them to the frame and negative battery terminal. Hood to body, fenders to body, frame to body, body to battery. Again, RF bonds, not just DC grounds.

In fact, you usually want to bond the rest of the body panels together too, including the bed, and if you get interference from the ignition system or other engine electronics, you bond the engine and exhaust system to the frame and body too.

 

anybody know where I can get some copper braid? I'm going to try grounding all the panels tomorrow

 

JKD hit it - the antenna needs a ground plane to work properly and bonding the body panels together provides such a plane.

I don't have any pics, i did ground my mounting bracket first, but it didn't give me any better SWR. The bonding process took care of the problem. Keep in mind this took me a few weeks of trial and error to get right.

I grounded my cab to the frame with a ground strap, too.

I bought my ground straps at a battery store, they were 8" long.

 

Did you ever get this figured out?

 

you should check the cable that you are using going from your meter to the cb. I had a similar problem with tuning and as a desperate last resort I swapped out this cable and discovered that the initial cable was bad.

 

take it to a local truckstop and seek help there.