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VHF antenna for tractor

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ford_shooter

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Hi, I'm new to this VHF radio stuff. I"m setting up a kenwood tk-762 in a couple of our tractors on our business band freqs. I'm looking at no ground plane antennas so I can mount them to the mirror bracket. All the whips that I find are around the 48+inch height range. Are there shorter options out there so I can have some more clearance for pulling into my shop.

THanks
 
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What kind of tractor. Last 4 years or so john Deere has been installing NMO mounts on the roof (w/ground plane) at the factory.


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n0nhp

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You are going to find it difficult to find a no ground plane antenna that is much shorter because you have to have both sides of the dipole represented in the length of the antenna. these will usually be advertised as 1/2 wave antennas in the catalogs. The best bet if you don't want to drill holes in the cab and fish the headliner will be a 1/4 wave (18 inches or so depending on freq) on a "L" bracket mounted to one side of the cab. This will give you a directional preference that may or may not be a problem depending on how far away the other stations are and what kind of power is being used.

I did a lot of antennas both ways on heavy machinery and in most cases the L bracket mounts worked adequately. The other problem, if the cab is fiberglass (some of the older tractors were) then you need a ground plane under the antenna. The local metal fab shop would cut us a square of Stainless Steel, poke the 3/4 hole in the center and give the piece a slight crimp for stability for a pretty reasonable price. 4 zinc plated self tapper screws and a good dollop of silicone would fasten these to the roof of the equipment and last forever.

Bruce
 
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How big are your mirror brackets? They might have enough ground plane in them to suffice for VHF 1/4 wave antennas. If you know someone with and antenna analyzer or VHF SWR meter you could test it out using a VHF mag mount sitting on the mirror bracket.

Most modern tractor roofs are fiberglass. I've seen some guys adhere aluminum tape (about a 1/4 wave radius) to the roof before mounting a NMO mount through the roof (of course it requires you completely pull the headliner).
 

ford_shooter

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What kind of tractor. Last 4 years or so john Deere has been installing NMO mounts on the roof (w/ground plane) at the factory.


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its a 2012 New Holland T8-330

THe owner manual states that some tractors are equipped with a power cable and an NMO type antenna. I found a spare power cable where they said it should be but can't find the NMO.
 

ford_shooter

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the bracket is extends from the cab to about 3 feet out from the tractor. Its an all metal bracket too.
 
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its a 2012 New Holland T8-330

THe owner manual states that some tractors are equipped with a power cable and an NMO type antenna. I found a spare power cable where they said it should be but can't find the NMO.
Deere puts them on the roof (closer to the door side) with a little black cap that unscrews off them. That's where I'd look or dead center on the roof. See if the mount is up there before trying to find the feed line in the cab.
 

LtDoc

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For what it's worth.
We needed to put several antennas on a high-top fiberglass van. One already there with a built-in 'groundplane'. Just happened to have a stop sign... drilled a couple of holes in it, then in the fiberglass roof, and 'attached' that stop sign to the van. Works just dandy. Find your own stop signs.

It really doesn't take much to make that 'groundplane' or 'other half' of an antenna. A few wires/metal strips will work just fine. Attaching it to fiberglass isn't impossible, just not easy, sort of. In the case of that tractor, if those mirror brackets are metal and if they attach to the metal parts of the tractor, they will certainly work.
So, what'cha gonna do?
- 'Doc
 

cmdrwill

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It really doesn't take much to make that 'groundplane' or 'other half' of an antenna.
- 'Doc
The groundplane/counterpoise, which IS the other half of the antenna, must be at least 1/4 wave long in all directions from the base of the antenna.
 

BirkenVogt

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The groundplane/counterpoise, which IS the other half of the antenna, must be at least 1/4 wave long in all directions from the base of the antenna.
It might not be idea, but a mirror bracket usually is sufficient to comprise the other half of the antenna. One way to look at it is as a stretched out (straight) dipole with the lower half of the bracket being one part and the whip itself being the other half. 75 ohms, resonant to length, and the impedance bump will be 1.5:1 SWR. Maybe a little worse in the real world but anything under 2:1 is good enough in my book.
 

RodStrong

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Personally, if I was in your situation, I would not worry initially about finding a no ground plane antenna, and rather buy a basic 10 dollar quarter wave antenna and try it out before spending significantly more on a "better" antenna. Depending on what your coverage area is and some other factors, you might just find out it works adequately for you. Worse case scenario, you are out 10 bucks. You can throw truckloads of money at antennas, and sometimes unexplicably, the simplest ones work as good or better than the best.

Good luck.
 

teufler

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larsen and others make no ground plane antennas. https://www.tessco.com/products/displayProducts.do?groupId=90269&subgroupId=90435
I have one here someplace. It was made for installing on a boat. Check with marine dealers as they have antennas that mount on fiberglass boats.http://www.theantennafarm.com/catalog/antennas-191/mobile-antennas-192/108-174-mhz-vhf-195/commercial-vhf-antennas-457/no-ground-vhf-antennas-209/
http://www.scoden.com/pdf/mobile.pdf
you might consider a glass mount antenna. Several people I know, have had success with these.
 
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larsen and others make no ground plane antennas. https://www.tessco.com/products/displayProducts.do?groupId=90269&subgroupId=90435
I have one here someplace. It was made for installing on a boat. Check with marine dealers as they have antennas that mount on fiberglass boats.http://www.theantennafarm.com/catalog/antennas-191/mobile-antennas-192/108-174-mhz-vhf-195/commercial-vhf-antennas-457/no-ground-vhf-antennas-209/
http://www.scoden.com/pdf/mobile.pdf
you might consider a glass mount antenna. Several people I know, have had success with these.
OP has looked at NGP and decided they are too long for his purposes.

One thing I've noticed, VHF antennas are very impractical on tractors. Especially in rural areas with underpasses as most newer tractors/sprayers/combines/strippers/etc only clear by 6" or so.
 

teufler

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NZ0J

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FOUND EXACTLY WHAT YOU WANT. NMO STYLE MIRROR MOUNTS.
https://www.theantennafarm.com/catalog/mobile-antenna-mounts-264/mirror-bracket-mounts-269/nmo-mirror-mount-kits-1041/
I KNOW THEN YOU CAN ADD A 18" STINGER THAT IS NMO MOUNT. I HAVE ONE HERE ON MY DESK TOP. aNTENNA fARM HAS SEVERAL MODELS THAT ARE 18" AND TUNEABLE. NOW THE SHORTER ANTENNAS, YOU TRADE RADIATED POWER FOR FUNCTIONALITY BUT I HAVE SEEN MANY CARS WITH 18" STINGERS THAT WORK FINE.
The 18" quarter wave should have a ground plane under it, something a mirror mount won't provide.
 
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FOUND EXACTLY WHAT YOU WANT. NMO STYLE MIRROR MOUNTS.
https://www.theantennafarm.com/catalog/mobile-antenna-mounts-264/mirror-bracket-mounts-269/nmo-mirror-mount-kits-1041/
I KNOW THEN YOU CAN ADD A 18" STINGER THAT IS NMO MOUNT. I HAVE ONE HERE ON MY DESK TOP. aNTENNA fARM HAS SEVERAL MODELS THAT ARE 18" AND TUNEABLE. NOW THE SHORTER ANTENNAS, YOU TRADE RADIATED POWER FOR FUNCTIONALITY BUT I HAVE SEEN MANY CARS WITH 18" STINGERS THAT WORK FINE.
That's debatable. In theory yes. In practice, I've seen very little difference between a 1/4 wave VHF antenna and a 5/8 wave. Especially when using repeaters and while mobile. I think where you really begin to notice a difference however is where the antennas are mounted on a hood or trunk.
 

VernM

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You make it sound hard. Unless you need several miles range, just mount the quarter wave on what ever cheapest mount (or NMO for durability, if you want to spend that much) and know that the signal will seek its way back down either mount or coax shield and give you a workable signal in almost all insances. Find a ham who's been around and has mobile experience on VHF, show him or her what you want to do and do what he or she shows you.

I have seven antennas outside on my conversion van and it ain't that big a deal!!!!

W0JOG
 
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