Antenna Install Tips

First of all, I'd like to say thanks to all the great folks who've helped me with my questions in the past, you guys and gals have been wonderful. Now, I'm looking to upgrade to a 102" Stainless Steel whip, mounted on a mirror mount to my driver's side rear tail light on a Jeep Grand Cherokee. My question is this, Do I need to ground this setup to my chassis? Also any tips for antenna install would be wonderful. Thanks!

Yes. 1/4 wave antennas need a ground. The mount for the antenna should have a point you can ground to. Do NOT rely on any connection that involves painted metal. Run a dedicated short ground strap from the mount base to the vehicle body. Clean the paint away from the grounding point, down to bare/shiny metal. Use a star washer.

Since 27MHz frequencies require big antennas and an equally big ground plane, it's a good idea to make sure ALL body panels are bonded (connected) together. A while back there was someone on here that had a Jeep Wrangler with a CB antenna that was having a difficult time getting the SWR low enough. It turned out it needed a good ground between the tailgate and the body.
I'd recommend making sure you install short lengths of grounding strap between your tailgate and vehicle body, hood and vehicle body, and if at all possible, each door and body.
Having a good RF ground will improve performance and help you achieve a low SWR.

Mirror mounts would be difficult with an antenna this size. Not impossible, but not easy. The length and momentum can be hard to control, and the Jeep's mirrors might not be up to it. I'd recommend something off the rear bumper, spare tire carrier, or a ball mount off the rear quarter panel.
Install a spring between the antenna and the base.
Invest in a reliable SWR meter if your radio doesn't already have one.

I never really saw a benefit to running a 102" whip on 11m. Compared to my other antennas, performance was always comparable. Much simpler to get a 48" low band NMO antenna and mount it to the roof but that's just me.

Yep, that's good advice.

The trouble with 102" whips is the mounting. Difficult to mount them in the center of a vehicle ground plane to give them good omnidirectional coverage. The compromise usually involves mounting them on the bumper or on a ball mount. While that works pretty well, it usually results in a lopsided radiation pattern. Good if you are trying to talk in that direction, not so good if you aren't.
To me, it really doesn't make a difference on CB.

After a few failed attempts at using 102" whips or loaded fiberglass whips mounted in the bed of a pickup, I got smart and went to Larsen NMO-27's.
The big benefit here is that you can do a much better job mounting the antenna. It's fairly easy to place an NMO mount in the center of a vehicle roof. Having the antenna in the center of the ground plane is going to help a bit.
Bonus is that if you ever decide to get your amateur license or replace the CB with a scanner, you already have an excellent antenna mounting point installed.
Personally, I'd much rather install an NMO mount than trying to hang a 3/8x24 mount or ball off the side of the vehicle.

I ran NMO-27's for a long time when I still used CB and they work really well. I installed many on friend/family vehicles back in the early 90's.
I found the 102" whips were just too long for my taste. They do work well, though, if mounted properly.
The fiberglass whips were always failing me. Got tired of replacing those.
After I switched to the NMO-27, I never had to replace any of them. They'll take tree branch strikes and low parking garages without issue.

Worked out well when I was finally able to get others into GMRS. Just pulled the NM0-27 off and installed a 1/4 wave UHF antenna. When they started getting their amateur licenses, pulled the UHF antennas off and installed VHF antennas.

If you are mounting it by drilling holes in the body of the vehicle, since you mentioned it would be on the "rear" tail light, that should be sufficient ground as long as the body is made of metal, although a grounding strap to the frame never hurts either, you can never have too much ground,

On my Dodge Dakota I run a 102 inch whip, and I just drilled a 3/8" hole in the bed rail on the passenger side just about 6 inches forward of the back end, and ran a stud through that hole the same as if I was putting it through a mirror mount bracket. I've attached a photo for reference. The other holes are from trying a bracket and a first attempt at doing this (drilled it too close to an uneven surface first try), but it has ran this way for about 2 years with an SWR of about 1.2:1. The stud has dielectric grease all the way through to prevent water from getting into it. However, this is a pickup truck bed which is bolted directly to the frame. On a Jeep/SUV, I'm not sure how well the body panels are mounted; if you have high SWR, try running as short a grounding strap as possible straight to the frame or some other solid piece of grounded metal.

ZJ/WJ/WK/WK2 Grand Cherokees are unibody vehicles like their predecessor, the XJ Cherokee.

Taillight housings are plastic (JCR Offroad has had some success with a tail light bolt on mount for the XJ...) so anything coming off there would have be using the factory mounting bolts.

Thanks all for the replies. What about a hitch mount? Yay or nay?

Kommissar73 said:

Thanks all for the replies. What about a hitch mount? Yay or nay?

Click to expand...

I wouldn't personally because I use my hitch quite often to haul trailers around, and it would be kind of annoying to have to disconnect or move the antenna every time you need to haul something. If you don't use it though, and have no plans of ever using it, then sure, go for it. If you've got a steel bumper, you might try putting it through the bumper toward the end where the hatch doesn't hit it when opening. That would also hide the lower end of the stud behind the bumper and let you run the coax through the frame without having it exposed. That would put the vehicle right next to the antenna for 3 or 4 feet, so you may have some SWR, but I've seen other people run their antennas like that without much of an issue. You could also just get one of those large magnetic bases with a stud mount and put it on top of the vehicle, but you might hit low hanging phone lines and stuff. Even with mine on the bed rail I smack the overhangs at the local banks and fast food drive thrus,

Again, placing the antenna at the edges of the ground plane is going to make it directional. Using the rear trailer hitch mount will make the antenna perform better in the direction of the rear of the vehicle.

Also, having it down that low, most of the antenna will be blocked by the vehicle body.

I'd really recommend getting it higher up. If you can't/won't do center of the roof, then at least mount it up high enough on one of the corners or side to keep the antenna away from the sheet metal.

I have a tailgate which I open at least 5 times a day…so no on the hitch mount.