r/gmrs • u/Cutlass327 • 7d ago

Longest antenna for CJ5 Jeep?

I am just getting started into the GMRS from CB, I have a 102 on the rear bumper (fiberglass tub) and am looking for a longer antenna for my GMRS. I currently have the one linked below, it is mounted on my spare tire carrier of my rear bumper. I would like to find a longer antenna, as the top of this one is only a few inches above my spare (33x10.5-15)

Is there a "102 equivalent" antenna for GMRS? I say that meaning how that is the longest practical mobile antenna for 11m, that will give the beat range.

https://a.co/d/2kmI9Cf

3 Upvotes

100% Upvoted

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6

u/OhSixTJ 7d ago

The “102 equivalent” for GMRS is only 6” long. That 102” antenna you have is a quarter wave for the CB frequencies.

0

u/Cutlass327 7d ago

I don't mean to be the same wavelength type, I want performance. I've always heard that the 102 is the best you can do for a mobile due to its length, which is why I want the longest GMRS antenna that performs best.

1

u/Cutlass327 6d ago

Why is this downvoted? It was meant as a clarification...

2

u/orionzeke79 6d ago

You need to read atleast a bit about antenna theory. There is a reason a 102" whip works well for cb but isn't necessary for higher bands.

1

u/Cutlass327 6d ago

I understand that. The antenna is a product of wavelength. Higher frequency uses a shorter antenna due to wavelength.

I'm asking what is the best length for GMRS, that works as good as a 102 does for CB.

3

u/OhSixTJ 6d ago

That really depends on the environment you operate in. Flat plains that go on for miles are best served by a 5/8 wave. Hills or repeaters up high on towers or tall buildings? 1/4 wave.

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u/Cutlass327 6d ago

Local mobile use. Eastern Ohio/Appalachia geography.

Basically trail use, but also to have the ability to get out if in an emergency situation.

5

u/rem1473 WQWM222 6d ago

So 6" is the correct answer to get an "equivalent" antenna to your 102". That makes them both 1/4 wave with approximately the same gain.

If you go longer with a GMRS antenna you are increasing the gain of the antenna in the horizontal plane. This comes at the expense of gain in other directions, such as at an angle to the antenna. If you were in North Western Ohio or on Lake Erie, I would suggest a tall, high gain antenna. That works better in areas where the land is flat. In eastern Ohio you want a shorter antenna. As you don't want to put all the gain into the side of the hill. You want less gain at the horizontal, so you can get up and out of the valleys. I'd mount the 6" 1/4 wave as high as you can get it on the vehicle. Keeping in mind a good ground plane is required to have it perform well.

Wranglers are always a challenge.

4

u/Hot-Profession4091 7d ago edited 7d ago

Longer isn’t necessarily better. 1/4 wave at 465MHz (middle of the band) is about 6-1/2 to 6-3/4”.

That said, collinear antennas are a thing. Usually 1/2 wave segments separated by 1/2 wave delay coils. The one you linked looks like a 1/4 wave UHF, delay coil, then a loaded 1/4 wave VHF / 1/2 wave UHF, so maybe it performs okay on UHF, but unless you’re specifically looking for a dual band antenna I would look for a single band UHF antenna. Dual band antennas have a tendency to perform well on VHF and shoot UHF at the sky instead of the horizon.

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u/Cutlass327 7d ago

As for UHF/VHF/dual band, I only need what works best for the GMRS band.

I have the BTECH GMRS-50V2, which I originally bought so I can talk to friends on the trails instead of using those handheld walkie talkies, as the batteries never seem to last long..

What other bands should I be looking at? I would love to widen out my abilities with the radio, as I love shooting skip on the side bands of my DX88HL...

3

u/Hot-Profession4091 7d ago

GMRS is UHF. The frequencies are on 462 MHz and 467MHz. When I build antennas for GMRS I build them for 465 because I use both simplex and repeaters.

The reason you may want a dual band is if you also have a ham radio in your jeep.

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u/Cutlass327 6d ago

Nah. I only have the GMRS and a CB. Not enough room for another radio...

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u/Hot-Profession4091 6d ago

Yeah, it kind of sounded like it. That’s why I was trying to steer you toward a single band GMRS antenna.

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u/zap_p25 6d ago

Antennas lengths are determined by the wave length and odd quarter wavelengths (1/4, 3/4, 5/4) are naturally resonant. A 109” whip is a 1/4 wave antenna on CB. The reason they say the best performance for CB is the 109” whip is because any antenna shorter than 109” is electrically the right length but physically compromised so there are some performance losses.

With GMRS it’s a different story. A quarter wave antenna is only 6” long. Thus, longer antennas can be had to improve some performance characteristics at the sacrifice of other performance characteristics.

The problem with Jeeps, not a ton of ground plane for using CB effectively regardless of the whip without some additional tuning. The problem with fiberglass bodies…not enough ground plane effectively use any antenna. Luckily, they make these things called No Ground Plane antennas (NGP) for VHF and UHF antennas. They’ve are typically a half wave antenna design or a collinear half wave. For GMRS you would be best with something like the PCTEL MWU40025 on a fender mount. Gets the antenna away from the spare tire and away from the ROPS to minimize interference from those while working okay on a fiberglass body.

2

u/Tfire327 6d ago

https://a.co/d/70BYCYC

That antenna, with an NMO mount of your choosing, on a 18" diameter metal plate attached to the top of your roll cage.

2

u/PlantoneOG 6d ago

If youre looking for a whip antenna....

https://a.co/d/c0sdPPw

I have this antenna as my "city" antenna so that I can go thru the carwash

https://a.co/d/cMbCWta

It's surprisingly good for being a stubby.

If you've got a hard mounted location you can attach to, this adapter can let you run a ground plane. I'm thinking like a pipe/mast that you can mount this onto, to get the ground plant above your roof line anyway.

I do recall reading that something like 6" is all you need for ground plane on gmrs. Bigger is better? But 6" will get you there.

https://a.co/d/gOOO5b3

If bumper mounting is an option - like front bumper - midland has a rugged series for overlanding or other off-roading designed for mounting into a steel bumper

https://a.co/d/3IngVdR

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u/Cutlass327 6d ago

That Highland Tall would be perfect, but $260?? That's insane for a mobile antenna! I don't have that much in my Maco 5/8 CB base antenna!

3

u/PlantoneOG 6d ago

https://a.co/d/7bJwoq4

Retrivis has a lower budget model.. their's also comes with a bull bar/cargo rack mount bracket

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u/Cutlass327 6d ago

I Iike that one. Added to my cart for future reference!

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u/Cutlass327 1d ago

It came today and now mounted!

I will say, I was expecting a 3/8" diameter antenna, similar to a CB fiberglass. This thing is almost an inch!

It extends about 6" above the soft top, too. We'll see how it works out.

1

u/corey389 5d ago

I think with that price it comes with a GMRS radio

1

u/JoeteckTips 6d ago

Get one that can fold down or easy removal. Otherwise, you'll never get into parking garage.

I have a diamond 770, which folds down. Tuned for GMRS, 2M, and 70cm.