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Author Topic: Jeep Antenna Application  (Read 10657 times)
GRADY
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Posts: 14




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« on: March 05, 2011, 11:18:04 AM »

I have a late model soft top jeep, and am wondering which way to jump as far as an antenna for 2m 70cm and mount. Does anyone know if there is any improvement mounting it on the rear bumper on one corner vs mounting one say at the center of the rear bumper or spare tire mount? Since the top is fabric I would assume that the ground plane could be better. I intend to make sure all 4 door have ground straps back to the body to try to help as much as possible. I have read antenna reviews until I  am blue in the face but realize the location is most likely every bit as important. Looking for input.

Thanks
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KF5KZX just the new guy on the block!
KC7YRA
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« Reply #1 on: March 05, 2011, 11:50:45 AM »

I have read antenna reviews until I  am blue in the face but realize the location is most likely every bit as important.

That is a very good realization to come to at an early point.

As for Jeep VHF mounting, I absolutely cringe when I see VHF/UHF antennas mounted on the bumper.  There is a lot of metal in close proximity to the antenna and a screwy pattern.

Invariably, some jeeper will come on here and "correct" me about how he works a repeater a bajillion miles away with his bumper mounted wet noodle.  But the fact of the matter is that bumper mounting of these antennas sucks.  You need to get them up high with a decent groundplane.

Now, on a jeep this is hard.  The best performing antenna I ever saw on a Jeep was a properly fitted NMO mount, right in the center of the hood, with a decent antenna on it.  This may not be your forte though.

I have another friend who has an antenna mounted on an angled "L" bracket, attached to the body above the rear taillight.  This gets the antenna above the metal of the cab, and provides of a GP similar to a fender mount on a car.  That is probably how I would do it.

Brad
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GRADY
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« Reply #2 on: March 05, 2011, 12:51:04 PM »

I appreciate your speedy reply. I currently have a fabricated bracket for a CB antenna that does just that. It is mounted to the spare tire carrier and it brings the base of the mount up about a foot from there. This puts the tip of the antenna about  18 inches above the height of the top. I have plenty of steel laying around and a welder to fabricate something of the nature for a NMO mount. I guess I will proceed with this idea and start my search for an antenna. I saw one on here in the reviews that was by Comet that actually got a 5. I will have to go back and find it again
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KF5KZX just the new guy on the block!
K0BG
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« Reply #3 on: March 05, 2011, 03:00:32 PM »

If you want a dual band antenna, that will last as long as you will, then buy a Larsen NMO2/70BK. Smack almost any of the Pacific Rim antennas, and it will break. Do that to a Larsen, and all you'll do is bend it. Whatever you buy, don't get caught up in playing the Gain Game. There is virtually no difference in performance between a 1/4, 1/2, or 5/8 wave. Fact is, place is much more important than gain. Read this: http://www.k0bg.com/images/pdf/mobile_vhf_ant.pdf
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K7RBW
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« Reply #4 on: March 06, 2011, 08:13:45 PM »

I found this: http://www.larsen-antennas.com/docfiles/ASB7/MobileIntro.pdf on the larsen-antenna.com site that illustrates what they think about antenna placement.

Mag-mount in the center of the roof doesn't look that bad. Interestingly, if I'm reading that diagram correctly, a mag-mount in the rear corner of the roof is slightly better than a fixed-mount in the center.

In any case, higher is clearly better.
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GRADY
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« Reply #5 on: March 06, 2011, 08:23:34 PM »

I read both links with great interest. However, I assume my situation with a Jeep with a soft top is not unique. I guess I will start with an antenna mounted to some type of simple mount that I can clamp various places and see what responds best. From what I see on the road it appears the rear of the Jeep is by far the most common. I have seen some mounts on front fenders and front bumpers, but not many. With my old CB setup, I was mounted dead center on the rear gate and was able to get SWR from 1.1 to 1.4 across the band. I am sure I will be adding to the bonding that is existing to include all doors, back gate and exhaust to help as much as possible. But, that's half the fun, tinkering til you find out what works best. I may have a deal hooked up on a FT-8900 which would give me a quad band setup. The price is right, if the rig is not gone. If not, then I will go with the FT-8800 dual band.
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KF5KZX just the new guy on the block!
KE5PPH
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« Reply #6 on: March 15, 2011, 06:27:13 PM »

Since you don't say what year it is, it limits the response a bit. BUT since it's a Wrangler? you only need to get the antenna above the top of the tub, NOT the roof line. I've got a 04 LJ and mounted NMO types on the rear edge of the hood. They get an excellent ground plane to work off.
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GRADY
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« Reply #7 on: March 15, 2011, 06:56:40 PM »

Since you don't say what year it is, it limits the response a bit. BUT since it's a Wrangler? you only need to get the antenna above the top of the tub, NOT the roof line. I've got a 04 LJ and mounted NMO types on the rear edge of the hood. They get an excellent ground plane to work off.

Its actually a 2010 Unlimited. Have you found any difference between rear center to rear corner mount? I figured to get it above the tub in order for the tub to act properly as the ground plane. My intent is to get some braided strap and ground the exhaust to the chassis or tub, as well as all 4 doors and the tailgate as well to improve the overall ground. It is a soft top, so no hard top in the way to contend with. Your thoughts?

Thanks
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KF5KZX just the new guy on the block!
WB6BYU
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« Reply #8 on: March 15, 2011, 09:09:07 PM »

Quote from: GRADY
...My intent is to get some braided strap and ground the exhaust to the chassis or tub, as well as all 4 doors and the tailgate as well to improve the overall ground....

That would be useful for an HF ground, but I don't think it will make a lot of difference at VHF/UHF.
The sheet of metal that the antenna is mounted on is the most critical thing.
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KE5PPH
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« Reply #9 on: March 16, 2011, 11:40:09 AM »

Mounting to a tire carrier is a poor choice. In general you won't get a good ground, while moving. The JKs are said to be worse than TJs as far as bad electrical bonding from the factory. Just because a bunch of people claim it's a good spot, in a physical sense. Doesn't make it a good radio spot. A better place would be a well grounded plate that goes behind the license plate. Bonding will help with the noise levels,but it won't make up for sheet metal under the antenna sitting on a tire rack. you might look over on www.jeepforums.com in the radio/electrical section. you'll notice a reoccuring theme, with rack/tire carrier mounted antennas. they work when sitting still MOSTLY, IF you can get the SWRs to a reasonable level. but demonstrate poor broadcast abilities.
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K0BG
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« Reply #10 on: March 16, 2011, 03:25:41 PM »

Lets not confuse a good DC ground, with the need for a good ground plane. It is sort of like comparing grounds for divorce, with camps grounds!
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KJ6MEB
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« Reply #11 on: March 18, 2011, 01:02:52 PM »

Grady,

Please keep us posted on your decisions.  I have a 2008 JK Unlimited soft top and am in the same situation as you.  I only have an HT right now, but want to start with and antenna, then get the mobile unit.

Jeff
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KE7VUX
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« Reply #12 on: March 18, 2011, 02:20:01 PM »

"L" bracket at the top center of the windshield, to the front, would be one of the better choices.

You would have a good ground plane left-to-right thanks to the windshield top, and you would certainly get it up "in the clear" above the rest of the metal.

I've often considered the same location for my Scout II, but wound up going back to a steel top and just stuck an NMO in the middle of the steel sheet roof.
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W7CLC
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« Reply #13 on: March 21, 2011, 10:51:23 AM »

Before I bought my WK Grand Cherokee, I looked at a few Wranglers.  My plan, after bringing the discussion here for review, was to fabricate a riser with a sheet metal shelf above the spare tire, and mount a proper NMO in the middle of that.  It was going to sit just above the tire and slightly below the roof line.

My question for the group here (had I gotten the Wrangler) is how big of a shelf would I need to get a proper ground plane? 
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WB6BYU
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« Reply #14 on: March 21, 2011, 11:53:14 AM »

For 2m something like 3' square would be about ideal for a quarter wave whip.

To get the full advertised gain out of a 5/8 wave whip the ground plane needs to extend out
50 wavelengths or more, but that isn't convenient for most mobile applications.
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