Having a problem with my antenna for the CB I was hoping someone smarter could help me out with. I had a pretty janky mount set up temporarily with:



It worked ok, but eventually got bent back pretty bad from low branches. I was able to tune the SWR pretty well with that set up.

However, today I made a new bracket that was less shitty & added a spring to the mount to account for the low branches in the future. Here's the new mount:



The new one uses a small aluminum plate for better stability, versus the small stainless steel strip the first mount had. But now I can't get the radio to tune worth a damn regardless of how much raise or lower the tunable tip on the antenna. Channel 1 & 40 both read 3+ on the SWR meter. Any CB gurus got any guidance for me?

If I remember correctly, aluminum does not act as a ground plane. You need steel. I may be off, because there is a giant steel roof a couple inches below the aluminum. I would try making a piece of stainless the same size and shape as the aluminum piece and see if you have any better luck.

Or run a ground strap to the body of the truck. Isn't the roof rack isolated from the X by the plastic mounts?

I have always referred to the Firestik f.a.q. page. They have tons of info on antennas and mounts and cables.

Good luck.

Anything conductive will act as a ground plane.

Jordan, he's right about the ground wire though. You need to run a wire from the mount itself to something conductive on the truck. Just crimp two rings terminals onto some large gauge(14-16) wire and run it to both locations.

That's what I figured was needed, thanks for the help!

I'm missing something or this doesn't make sense. You have the exact same set up, coaxial cable and antenna in the same location. The small SS strip is replaced by a larger aluminum plate and a spring was added between the plate and antenna. And nothing else changed? If this is normal ground plane antenna then it shouldn't have worked before without a ground connection from the mount to the Xterra. If it's a NGP antenna it didn't need to be grounded and it still wouldn't. but it does have to be hooked up correctly. Did the coaxial cable get damaged? Is the cable mounting to the mount and antenna slightly different, like it runs to the underside of the plate and there is a plastic washer in the system breaking the ground? Why did it work then and not now? The spring will affect it some but it should be in the adjustment range of the antenna.

I do hope the added ground wire works for you!

Scott

The only thing that's changed is the aluminum plate & the spring. Everything else is the same. I actually put the old stainless steel strip back on to see if the aluminum bit was the issue and I was able to tune it again. It's really weird, but I don't know too much about radio stuff. I'm going to rig up a ground this week and try to tune once more.

Assuming that the antenna is in electrical contact with the plate (i.e., creates a circuit through which electricity is conducted), the plate acts as part of your antenna system. It may have the effect of increasing the length of your antenna system, which could adversely affect the SWR. You may want to try isolating the antenna from the plate. Also, adding the spring would definitely change the length of your antenna system, as if you adjusted your antenna to a longer length (as might have be done in tuning the antenna's SWR).

Also, adding an electrical connection from the antenna to the the vehicle by way of a wire or cable can have the same effect of changing the length of you antenna system and adversely affecting SWR. As I have previously noted elsewhere, "ground plane" does not mean an electrical ground. Instead it refers to a horizontal plane (like the ground on a radio tower) which reflects the transmission signal up and away from the antenna. The roof of the Xterra provides and adequate ground plane without any electrical connection of the antenna to the vehicle.

k_enn

I'm glad people that know more were able to comment. I know enough about antennas to know that I wanted a no ground plane setup for this reason among others. I know wherever I place it, as long as the cable is not damaged or rolled into a loop I shouldn't need to retune it.

The antenna center conductor should NOT have electrical connection to the mount. The Firestik spring stud comes with a flanged nylon washer that is meant to insulate the antenna from the mount itself. In this case it's actually insulating the spring base from the mount.

See here for the spring stud mount install, paying close attention to the nylon bushing. http://www.wearecb.com/images/watermark ... ik-k4a.jpg

The bottom of the spring stud mount will conduct to the mount, but that's okay since there's a concentric nylon insulator around the center conductor. The cable shield, and the bottom of the stud mount need to be tied into the ground plane with the grounding wire.



This is true, however the mount still needs to be grounded.

Firestik specifically states that here: http://www.firestik.com/Tech_Docs/rack-mnt.htm

Grounded the mount to the hatch strut bracket, did the trick!

Thanks everyone.

Nice!