Jeep Wrangler solution for VHF/UHF performance

kc2rgw · #1 (**permalink**) 11-16-2009, 9:17 AM

So I don't have pictures up as it was raining all weekend...but an experiment I've wanted to try for a long time has paid off quite well.

I have an 05 Jeep Wrangler Unlimited that I run with the hard top full time.

I've had my VHF/UHF antenna side mounted on the tub because the roof is fiberglass. The performance on the side mount just plain sucked. I like to work VHF simplex frequently too so this was even more of an issue vs the high density of repeaters in the area. 440 performance was particularly horrible with the side mount.

I'd run a Larsen 2/70B and that was useless without a proper counterpoise under it. I upgraded to a Diamond SG-7900 high gain and that improved things quite a lot, though it was still very sub-par for what it was due to the mounting.

So to fix this, I took a 30" square 3/32" sheet of aluminum plate, through bolted at each corner through the fiberglass top. The plate is on the inside. I used a thick mount NMO and put that through the plate and the roof.

The performance increase has been dramatic. A 440 machine from my driveway that is S1-S3 with a lot of flutter is now S6+ and DFQ. The local repeater on 2m, I would run out of coverage at about 15miles in varying terrain. I tested the new configuration out to 25-30 miles and could still hold a full conversation on the machine. Simplex is less definitive, but I'm able to hear the usual crew when I just plain couldn't before and the range is 15+ miles to most of them working on home antennas and 25W or so.

Just plain seat of the pants, audible improvements with generally strong machines is high too. Machines that were solid and usable are now completely DFQ. Courtesy tones sound like they are in high def sound heh.

Time will tell how it holds up in cold and hot weather, but I used shoulder washers top and bottom, 1/4" stainless bolts with lock washers as well. The worst part of it is bending the 'kick' into the plate to get around the internal reinforcing rib that was in the way. I used cabinet clamps and a piece of landscaping tie as a makeshift break. It worked, though a proper metal break would have made it look a lot neater.

I used some silicone caulk at the top and with the rain all weekend, things remained nice and dry on the underside, so that is promising too.

If you are a hard top sort of Jeep owner and like to play radio, I can't recommend this enough. For HF/10/11m use, you could put a sheet that is the full size of the roof in and bond the corners to the windshield and the rear corners of the tub too. I already have a ball mount on the right side and for HF it doesn't matter as much for the location of the counterpoise. I get decent 20m and up performance already.

mancow · #2 (**permalink**) 11-16-2009, 9:42 AM

This is exactly the situation that I face and I've been thinking about doing something like this for years but I can't seem to bring myself to drill holes. I've been using an L bracket NMO behind the 3rd light and like you mentioned, it pretty much sucks.

I've been thinking more about installing a thin piece of sheet metal on the outside that is painted to match. If a guy could seal it and conform it so it's perfectly flat against the top it would be basically invisible and then you slap a mag mount or whatever on it.

DieselFF918 · #3 (**permalink**) 11-16-2009, 9:48 AM

When I had my 01 Wrangler, I took a piece of sheet metal and bent it 90* and bolted it to the tub behind the driver side tail light.

Had a NMO mount with a dual band antenna, it worked great for me. I was able to reach machines 30 miles away on 2m.

wcr20 · #4 (**permalink**) 11-17-2009, 1:32 PM

I've been considering a wrangler and have had the same question in the back of my mind - but was wondering if you could make use of one of those off-road light mount bars that attach at the top of the windshield. I realize that you wouldn't be able to do a 30" square ground plate up there, but you might be able to get a 4 or 5" dia.round or similar size square plate mounted up there, then put in say a 2m and a 70cm quarterwave NMO. You could then probably even still get in my garage.

Anyone ever tried this? Results?

James04TJ · #5 (**permalink**) 11-17-2009, 6:41 PM

You can do pretty well also if you have a decent rear tire carrier. I had both a 2' CB antenna and dual band NGC SBB-2NMO mounted in a custom standoff bracket that I built on the back of my TJ. Both performed very well for what I wanted. While I did have a hardtop for it, I didn't run a top at all most of the time so it left me with the bumpers, tire carrier, and hood to mount things on.

http://lh3.ggpht.com/_-y5gOOY_HTY/Rp...0/DSCF0687.JPG

DieselFF918 · #6 (**permalink**) 11-18-2009, 6:36 PM

Quote:

Originally Posted by wcr20

I've been considering a wrangler and have had the same question in the back of my mind - but was wondering if you could make use of one of those off-road light mount bars that attach at the top of the windshield. I realize that you wouldn't be able to do a 30" square ground plate up there, but you might be able to get a 4 or 5" dia.round or similar size square plate mounted up there, then put in say a 2m and a 70cm quarterwave NMO. You could then probably even still get in my garage.

Anyone ever tried this? Results?

I had one on my TJ and considered doing the same thing, but decided to mount mine lower.

If this is the direction you want to go, Diamond makes antenna mounts that are designed to clamp on to a tubular roof rack, or even possibly a light bar like you mentioned. I would look into the price of those.

MOTEX · #7 (**permalink**) 11-21-2009, 9:45 AM

Your Larsen NMO 2/70B must have been improperly installed
I have used the NMO2/70B on the rear tire carriers of jeeps with virtually no conterpoise at all with GREAT results.

The NMO2/70Bs electrical design enables it to work with or without a good counterpoise.

kc2rgw · #8 (**permalink**) 11-21-2009, 2:29 PM

The mount was fine, used their flappy metal side mount bracket. Analyzer was happy but performance sucked.

It took trimming almost an inch off the whip to get it resonant high enough in both bands too.

I've since put the 2/70B back up on the roof with the proper counterpoise and a stock length whip and it works very well. Larsen themselves told me that antenna needs a proper counterpoise by its design. As a matter of fact, their measurements for counterpoise size were a guideline on the size of the sheet I used.

When you say it worked great, what did you compare it to? Mine worked, but the performance sucked compared to other antennas on the same mount and side by side with other friends' vehicles on simplex tests with the same distant station or repeater.

kc9buh · #9 (**permalink**) 11-24-2009, 10:35 AM

on my 04 wrangler I mounted a " L" bracket high on the windshield post(driver side) and ran the cable by the rubber ot the top ,inside and hidden behind the postdown to the radio
Mike

N1BHH · #10 (**permalink**) 11-25-2009, 12:06 AM

First of all, antennas side mounted tend to not work very well, due to the fact that there is no ground plane beneath it. To have a good quality antenna installation, it should always be mounted on the roof. I know some people don't want it there for some vanity reason, like it will hit trees, or my garage door is too low and other similar stories. Trunk mounting is a secondary location, while mounting on the cowl is really the worst place, since it is close to the engine. With today's electronic/computer controlled engines, and all vehicles, it's really wise to mount any antenna as high as practicable and with good ground plane.

The aluminum plate is really an excellent choice. There have been installations that I have seen of radios in chair cars with the fiberglass roof, where the installer has placed the antenna on the roof, with an aluminum plate and it works really well. As an alternative, using a small piece of thin copper plate, doesn't have to be big, with several wires attached in a ground plane configuration, tucked up in the headliner. With either of these installation alternatives, you should have no problem accessing your favorite repeaters and have fun with simplex mobile.

I have a real metal roof on my van, so no problems with putting antennas up there. My Larsen NMO-2/70B does just what I hoped it would, giving me good dual band operation with either a hand held or mobile rig.