Antenna Ground on Rover

[SwampMonster]

Forgive me guys, its been 15 years since I have delt with CB's. I picked up one of the new Bearcat Digital CB's. Got it all installed went through the setup inside the radio and it says the antenna ground failed. The SWR was calibrated and was 1.7 which the radio said good. Do I need to run a new wire from the frame and ground the mount? if so how? its a 4' firestick with 18' of Wilson Coax, to a Al mount with a spring.

 

[4x4junkie]

I'm not familiar with how or what those radios do to self-test the antenna ground, however typically what you want is to have is the antenna (it's bracket) mounted directly to a substantial mass of metal to act as a ground plane (it doesn't necessarily have to be the center of the roof, though that would be ideal). If you have a large metal roof rack, typically that can work well for mounting an antenna, as can mounting it to the vehicle's rain gutters or a hood-lip mount or to the side-panel of the body (preferably with at least 60% of the antenna's length clear of the body in any case).

What usually doesn't work well is mounting the antenna's bracket onto a metal mast or post sticking up from your bumper or spare tire carrier, nor does mounting the antenna directly to the bumper itself (the rear one in particular, due to the body blocking most or all of the antenna). Similarly, mounting to a tire carrier swingout itself can be hit or miss as well (same goes for tail light brackets).


If you can post a pic of how it's actually mounted, I or someone else might be able to provide you a more direct answer.

 

[SwampMonster]

 

[SwampMonster]

 

[4x4junkie]

Hard to tell, is that a ladder (for roof access) mounted onto a rear door?

What I suggest is make sure the antenna bracket has a good mounting connection with the ladder (scrape any paint off if needed), and then do the same where the ladder is mounted onto the vehicle (both at the top & bottom mountings). Use of star washers under the bolts should help establish a better connection also. Then take a short length of grounding braid or strap and attach it right from the door to the door post at each door hinge. Should hopefully solve your issue (this assumes your door is made of metal not fiberglass, not familiar with what Rovers use).

Looks like your antenna is up high enough and in the clear, so you're good there.

 

[SwampMonster]

Yea its on the back ladder. The body is all aluminum.

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[4x4junkie]

Should be good to go then once everything has a good electrical bond.

Good luck with it

 

[Mashurst]

1.7 to 1 SWR is not generally considered a good match. Your radio will not be happy with that. You want to get it down to 1.2 -1.3 max. I don't see a problem with your setup overall so I think as others have said you should look a the electrical resistance between the outer braid of your coax and the body of the truck. It should be low. Those mounts like you are using are kind of good at not marring the paint. That is both good and bad. You may need to mar the paint for it to get a good connection.
Also, resistance between the center conductor and the braid at the radio end should be high. With 1.7 this is not likely your issue but just in case...
Let us know what you find.

 

[SwampMonster]

The radio will allow me to adjust the swr. I will drop it lower this aft. Thanks for the help.

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[Mashurst]

Swamp, Now you have me very curios. What is the model of radio you have? Does it have some kind of tuner built in? I can't imagine the radio can actually change the SWR because SWR is a property of the antenna system including the coax. It is possible for a radio to “put up with” a poorly matched antenna by way of a tuner, but I have never heard of a CB that can do it. It does sound like a cool setup and I would like to learn more about it.

 

[SwampMonster]

Radio is a Uniden Bearcat 880. Its is a big change over my years with a old President Jackson and a Texas Star 667 linear. That was when I was still in high school. I'm 38 now.

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[Mashurst]

So I looked up the manual for it. Looks like a cool rig. I see where it has the calibration feature and it says you want between 1.5 and 2. I am not sure what they are doing with the calibration but I would be looking to bring your SWR down anyway. I would consider 1.5 and absolute MAX. There is no reason you can't do better than that. A few things came to mind looking over it. Do you have the radio mounted with its bracket such that it is electrically connected to the vehicle chassis? Is the negative wire running back to the battery or to the frame? A real SWR meter would be a big help too if you know anyone that would have one. I guess I am a bit skeptical of this calibration feature. I wonder if it is just hiding any problems.

 

[4x4junkie]

You had my curiosity as well, so I downloaded the manual for that radio... I don't seem to be seeing anything in there about it being able to compensate (tune) for a poor SWR, all I see is that it has a simple meter built in to check what your SWR currently is, along with a "Pass/Fail" diagnostic test (maybe this is where you got confused about adjusting the SWR from the radio?).

As was said, SWR is governed solely by your antenna system (the antenna itself, the coax cable and connections, and your antenna's ground system (the antenna bracket and the structure it's mounted to)). Once you have everything grounded good and your door bonded to the rest of the vehicle body, it should drop your SWR to less than 1.5:1. If it doesn't then you might check that you don't have a cable problem (poor shield connection at the connector) or that the antenna itself isn't faulty (somewhat rare).

Edit:
Looks like Mashurst was looking it up at the same time lol

Yeah it appears to be just a normal everyday SWR meter... You key the transmitter, "calibrate" the meter by adjusting the indicator to the "CAL" mark on the meter, then set it to "SWR" and key up the xmit again to read your SWR. Uniden's wording in the manual seems a little off for some reason, like maybe whoever wrote it wasn't sure exactly how to word it. No matter how may times you do it, nothing will change if you don't also adjust the antenna itself each time (maybe is the part they forgot).

 

[SwampMonster]

The bracket for the radio is mounted in to plastic trim. After many hours of digging through the Rover Rave Manual I have found the problem. Its the ground I tapped into. Its some weird relayed ground, dont ask its those odd Brits. I just had it installed the easy route, should have worked a little harder. I just ordered two Odyssey batteries and the blue sea gear to run dual batteries. Ill just run it off the house battery when my 1K upgrade is done. Man this forum is getting expensive. Just need to put the two other CB's up for sale to help pay for this all. Thanks for all the help guys.

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[unseenone]

It could be that mass of electronics / light next to the coil, try removing the light. You should just run a flat ground strap to the body ground, maybe near the hinge bolts on the rear door.