GMRS Antenna help for Wrangler JL soft top

snowfiend

Member
I am picking up a used Midland MXT275 that needs an antenna. I have a 2 door soft top wrangler JL which is causing me (a GMRS noob) some confusion as to what antenna I can use and how it should be mounted, especially as it relates to ground planes/related issues. The JL has limited steel on the body, really just the roll cage structure and the rear tub. The hood, front fenders, cowling, doors are all aluminium or composite. Tailgate is magnesium.

Looking at the Midland antenna offerings, I see two maybe three potential options. I like #1 the best since it's probably the cleanest, but I would like to hear opinions and how to ensure the best functionality of the radio. I don't have a SWR meter (or know anyone with one) and read conflicting information if you need one using the GRMS specific Midland antennas.

1) the super small 3.5" Ghost antenna on the roll bar under the soft top. I think there will be enough room with the mount if I can use one of the existing holes on the roll bar to keep the mount flush. 3.5" plus mount, the steel surface is 7" wide front to back.

IMG_20200312_092807.jpgIMG_20200312_092946.jpgIMG_20200312_093024.jpg

2) the big whip antenna, 32" plus mount on the rear tailgate hinge bolt. Will this big antenna radiate my kids when they are in the backseat? :ROFLMAO:

IMG_20200312_093246.jpgIMG_20200312_093140.jpg

3) The Ghost antenna on top of the spare where the 3rd brake light is.

Thanks for reading
 

dreadlocks

Well-known member
All metals make a good groundplane, dont matter if its aluminum or not, just needs to be conductive... all your passengers will be fine.

What are your range expectations? Ive got a big giant whip on mine but its also hooked to a HAM radio, for only GMRS one of the nice things about it is a small antenna works just fine for most needs.. If your talking with handhelds then small antenna is fine, if you have others in your caravan with big whips on mobile radios then you might wanna match them for keeping in touch over long distances.

What about your hood?
 

mep1811

Gentleman Adventurer
Is your hood made of metal ? If so you could use a mag mount. Your kids will be fine.
You want your antenna as high as possible in the air. If you mount the ghost antenna on the spare tire it will radiate mostly through the vehicle. limiting the range.

The whip would work great on the tire carrier. There are all sorts of vendors that make antenna mounts.
 

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snowfiend

Member
I don't have range expectations or requirements, I had a previous post about the area a GMRS radio would get most frequent use and the consensus was that the terrain is always going to hinder reception. I have 4 Midland GXT1000 handhelds to communication with them is important vs. car to car.

Not a huge fan of hood/front fender mounts, just as a personal preference. Hood does not hold a magnet but is aluminum.
 

Billoftt

Active member
Try looking into a 1/2 wave antenna meant to be used without ground planes. GMRS is high enough of a frequency that they are not very tall.

I have a “stealth” or “ghost” antenna on my wife’s van because it was the only one she would go for. Usually those style of antennas require larger ground planes than a normal whip to function properly. I installed a Pulse Larson that looked like a hockey puck at 1.5 inches tall and 4.5 inches in diameter. It required 24 inches of ground plane. They also radiate a little differently, as in their RF lobes are at a 30 degree angle which works well for the repeater systems used by the police/fire/EMS that use that style a lot.




Sent by electrons or some crap like that.
 

snowfiend

Member
If
Try looking into a 1/2 wave antenna meant to be used without ground planes. GMRS is high enough of a frequency that they are not very tall.

I have a “stealth” or “ghost” antenna on my wife’s van because it was the only one she would go for. Usually those style of antennas require larger ground planes than a normal whip to function properly. I installed a Pulse Larson that looked like a hockey puck at 1.5 inches tall and 4.5 inches in diameter. It required 24 inches of ground plane. They also radiate a little differently, as in their RF lobes are at a 30 degree angle which works well for the repeater systems used by the police/fire/EMS that use that style a lot.




Sent by electrons or some crap like that.
If I go with option 1, is the 7" wide roll bar enough ground plane for the Midland Ghost or is a no ground plane antenna such as this one better? The soft top fabric and plastic support ribs won't block anything, right?

 
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Billoftt

Active member
You cannot go wrong with Laird antennas. Laird, PCTel and Pulse Larson are universally known for their high levels of quality and performance.

I do not know exactly who manufactures the Midland antenna, I just know they don’t build it in house.


Sent by electrons or some crap like that.
 

gatorgrizz27

Active member
I recently installed the same radio with their ghost antenna. I haven’t done extensive testing on it yet, but so far I’m not thrilled with the range/reception. I talked to two different people at Midland who claimed the ghost antenna didn’t need a ground plane, which was a significant factor in purchasing it. However, I called them due to having a shorter range than I feel is acceptable, and their tech emailed saying my aluminum roof bar should work as a ground plane, implying it does in fact need one.

I mounted it using their NMO cable and a bracket I made out of mild steel flat bar to test it. I’m sure I may be losing some range due to being right behind the roof crossbar, but the trails we run are extremely tight with tree limbs. It’s not uncommon to go through “tunnels” of them where they are dragging all over the vehicle for short distances, so it’s the only place that will be protected, my spare tire is under the vehicle.

A5A8EFB5-DBF1-45F5-97A7-FEB833DF680D.jpeg

My primary uses are just trail riding with other vehicles, right now using handhelds, but they will eventually add the MXT275’s as well. I was expecting a 2-3 mile range from mine to a handheld, and 5-6 between the vehicle mounted ones in flat wooded terrain.

One car was about 100 yards being me and crystal clear, the one about 200 yards behind me was crackling and breaking up. At one point he took a wrong turn and I was able to stay in contact with him, even though we were far enough away to not hear each other’s horns.

When driving through town and using the scan function, I pick up transmissions for 2-3 seconds before they drop off, which also makes me think the range isn’t good n my setup. There have only been two times where I’ve been able to overhear multiple transmissions while driving.

The main reason I want as much range as possible, is I also picked up one of their XT511 base camp radios. While camping, my plan was to leave that at the tent/trailer for whoever might be there, and be able to communicate from my vehicle that’s running trails nearby.

Can anyone confirm what I was told about that antenna not needing a ground plane, or see an obvious issue with my setup? I was half convinced their ghost antenna might be the same as the Laird one since the appearance and dimensions are identical. From my research, if it does need a ground plane it doesn’t necessarily need to be what would work as a good electrical ground, meaning paint scraped off at attachment points, etc?

I need to do a test with a friend standing there using a handheld, and me driving away using the 275 and another handheld. If the 275 doesn’t have more range, something’s obviously wrong.
 

Billoftt

Active member
On Midland's web site it states it is a 5/8 wave antenna, and a 5/8 wave by its nature will require a ground plane. Also, a 1/2 wave antenna (one not requiring a ground plane) will still have its RF lobes flatten out at a lower angle with a ground plane under it. A 5/8 wave antenna's wave pattern, although having higher gain, has an RF pattern that is flatter and straighter. A 1/4 wave antenna, although having a "shorter reaching" pattern, its patter is more full with no "empty" spots. This is why I usually recommend ignoring gain figures on mobile applications and just use a 1/4 wave antenna.

I doubt that it is a re-branded Laird on account of it somehow being less expensive than the Laird model linked above.
 

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prerunner1982

Adventurer
1) the super small 3.5" Ghost antenna on the roll bar under the soft top. I think there will be enough room with the mount if I can use one of the existing holes on the roll bar to keep the mount flush.

View attachment 573025View attachment 573026View attachment 573027
Can you get inside the roll bar to run the coax and secure the NMO mount?

Here is another option for a 1/2 wave antenna (no ground plane): https://www.amazon.com/gp/product/B00IDTJ2KE/ref=ppx_yo_dt_b_asin_title_o01_s00?ie=UTF8&psc=1
A front fender mount would work well also. https://www.rightchannelradios.com/products/jeep-jl-cb-antenna-fender-mount-2018
With the mount I linked above you would need coax with a NMO connector that has a 3/8" center, such as this: https://www.amazon.com/C213SNMO-Antenna-mount-cable-asm/dp/B00AR095HC
 

snowfiend

Member
Can you get inside the roll bar to run the coax and secure the NMO mount?

Here is another option for a 1/2 wave antenna (no ground plane): https://www.amazon.com/gp/product/B00IDTJ2KE/ref=ppx_yo_dt_b_asin_title_o01_s00?ie=UTF8&psc=1
A front fender mount would work well also. https://www.rightchannelradios.com/products/jeep-jl-cb-antenna-fender-mount-2018
With the mount I linked above you would need coax with a NMO connector that has a 3/8" center, such as this: https://www.amazon.com/C213SNMO-Antenna-mount-cable-asm/dp/B00AR095HC
Yes I can get in the roll bar, but that antenna would only work when the roof is down.

https://www.arcantenna.com/blog/antenna-ground-plane-calculation/ said:
"For example, if the ideal radial length is calculated at 4 inches, that means that the ground plane must extend out at least 4” in each direction from the antenna in the center, for a ground plane size of 8x8 inches (64 square inches.) Keep in mind that the ground plane does NOT need to be perfectly shaped, the antenna simply needs to be in contact with a total of 64 square inches of metallic surface area."
Is this accurate regarding ground planes in mobile applications not needing to be perfectly shaped? Radial length of ~6" would be a ground plane of 12"x12" or 144 square in. But if it doesn't need to be perfectly shaped, my roll bar being 7"x24" meets the minimum requirement. This Larsen Mirage puck antenna actually specifies a 20" diameter ground plane, which would be 10"x10" or 100 square inches.
 
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Billoftt

Active member
That Larsen puck is the one I was referencing earlier. I was a bit mistaken as it “only” requires a 20 inch circle, not a 24 as I earlier stated.


Sent by electrons or some crap like that.
 

prerunner1982

Adventurer
An oddly shaped ground plane can distort the signal as it is pulled in the direction with the most metal.
1584114440965.png
With the roll bar being tied to the rest of the body it may not effect it too much, I also wouldn't worry about it too much.
Also with the soft top, if the antenna fit with the top up it may work ok. I have friends who have run mag mount antennas on the top of the rear fenders inside of their Jeeps and it worked well enough for them, not great but well enough to fit their needs/expectations.
 

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snowfiend

Member
Thanks everyone for your help. I ordered a Larson LP450NMO puck antenna and 3/8" thru-hole NMO mount with PL-259 connector to mount on the roll bar. I'll update next week once everything arrives and I get it installed.
 
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