Mount 102" between cab and bed

[flip]

Sup guys. This is my first post here so thanks in advance for the help. I've just recently purchased a 959 and a 102" whip. My thoughts are to run it between the cab and the bed and mount from underneath the truck. this will give me a height of around 11' from the ground and keep the antenna centered as well. I've searched the forums and hav'nt found anyone that has done this yet. I'm set on the 102" because I don't think a better antenna can be made, but I'm worried that about 2 feet of the antenna will be closely shrouded by the cab and bed (up to the glass anyways). Has anyone tried to mount their whip in this way and if so what were the results? Any thoughts are appreciated. I'm rdy to get my rig installed and keyed up >:).

[Corn_Bread]

What kind of truck is it?? Do you have a toolbox, if so mirror bracket to the box, ground the box to frame as well as cab and bed and good to go. If no toolbox, Mount to bed and ground the same way!

[Corn_Bread]

mounting it to the frame would cause you some majorly high SWR's. Too Much refection from the cab and bed.

[flip]

Its a 2001 gmc sierra. No tool box but I do have a fiberglass shell on it which is why I wanted to mount it between the cab and bed. I figured swr might be a problem considering its a tight squeeze between the 2 but then again only about 2 feet of it is shrouded the rest of the antenna would basically be in free space. I guess it would be possible to mount on the bed and drill a hole through the top of the camper shell and put a grommet there. Another thing. Is the 102" a 1/4 wave for 11 meters or do I need 108"? Thanks for the reply.

['Doc]

Between the cab and the bed? Don't do that, you'll regret it. The hole and grommet thingy would stand a better chance of working, but I really don't think I'd do that either. Why not just extend a plate from one of the 'stake' holes to the side of the cap and mount it there? Or on the outside of the bed, ball mount?
- 'Doc

[Texas Mobil 219]

Sup flip. I run a 108 on my truck. A 96 Chevy. IMO , use a L mounting style bracket. Mount it to the fiberglass shell as high as you can get it. Let you coax run down between the two. Also run a ground wire for the L bracker to the frame. You should be able to have a low swr. This is were mine is.

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[flip]

Heres the thing though. I do a good bit of trail riding and that antenna sitting that high is sure to take damage >:). Any more antenna suggestions that come close to a full 1/4 waves performance and match? The wanna be Ham in me doesn't like doing things half-@#$ed so I got to figure out a way to use this antenna and still have it somewhat protected and out of the way. Another idea I've had is to mount 2 as low as possible on both sides and the middle of the truck and cophase them but the furthest I could get them apart is a little over 6 feet. Probably no advantage to doing that either?

[Red Warrior]

The first third of antenna radiates 90% of the power. Place the antenna parallel to ground (the cab of the truck) and you will couple 90% of your power directly to ground.

Co-phased 1/4 wave antennas need to be 22 feet away from each other to experience even minimal gain. Otherwise it is just for looks.

You either accept our advise or you don't. Consider exactly why the responders above jumped to alternative solutions. The path you have chosen leads to bad endings.

Mount the antenna in accordance with proven solutions. If it is too tall, get an electrically shortened antenna like a Wilson.

[TheTeZ]

to me it sounds like your gonna have SWR's through the roof because what... 2 feet will be surrounded, than it will have another 2? feet maybe less with the rear window right on it. What i am planning on doing is taking some rod, and coming up on each side of the rear window, then a bar across the top, and mounting the antenna in the center of that.
At first i was thinking about some how connecting it (the riser) between the bed and cab, but its not gonna give me much room, so i think im gonna go all the way down and make an "L" *at the bottom of the riser poles* and bolt *them* to the underside of the bed....


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[flip]

The first third of antenna radiates 90% of the power

Ok that makes sense and I was thinking I had read that somewhere before =/. I may just go the traditional route and mount to the bumper or like you said just get a loaded one. You say the Wilson is comparable to the full 1/4 wave?

make an "L" and bolt it to the underside of the bed....

Yeah that was my intention too. Bolting the actual antenna bracket to the bottom of the bed and running it up between the cab and bed. That would have kept the antenna directly in the center of the ground plane and reduced its height. Foiled by the laws of wave propagation

[Circuit Breaker]

The Wilson won't match the performance of a full 1/4 wave...but it's a good antenna.

I wouldn't go with a magnet mount though if you do trail riding. I'd drill a hole in either the roof of the cab or the camper shell. Now, if you do it on the camper shell, there's no metal to provide a ground plane. But you could get copper adhesive tape and make radials on the inside of the camper shell running in all directions...and even run one down to the bed of the truck and make an electrical connection there.

[sparky17]

Just use a fender mount and be done with it. Or a bed-stake hole mount (Google for "breedlove mounts")

Best thing would be to get a predator 10k and puck mount it on the roof.

I personally use a 102" mounted on my fender, using a hood mount that goes underneath the hood in the small gap between it and the fender.

This allows me to use a tie down on the roof, so I can strap the antenna down when I go through drive-thrus.

[Turbo-T]

Another thing. Is the 102" a 1/4 wave for 11 meters or do I need 108"? Thanks for the reply.

Both are 1/4 wave, but the 102 requires the 6 inch spring with the wire which makes it out to 108. The 108 is a solid 9 foot antenna w/o the spring. Both are 1/4 wave antennas when at 9 feet in total length.

[Bigmic91]

I currently have my 102 mounted on my box and am having some problems with it hitting the box. I am gonna make a mount and put it on the bed rail between the cab and tool box that way it is higher and isnt hitting anything. That should solve my problems but yours is a whole different animal. These guys will give you some good info. They did for me but I didnt listen.

[Springer]

Flip, the information here is dead on. Go to bumper mount if you are opposed to drilling a hole in your cab. You don't want a hole in you topper to get your gear wet.

Springer

['Doc]

Turbo-T,
A 102" whip is a sort of 'standard' size that can be made usable on a number of different frequencies or bands. As a 'standard' size, it assumes that the mount used with it will increase the overall length by some degree. Lot's of possible variations with that, wouldn't you think, different size/shape mounts etc.
A wave length is dependent on what frequency you are talking about, and is different for any frequency. No two frequencies will ever have exactly the same wave length. Real close, but never exact. Same for some fraction of a wave length, 1/8, 1/4, 1/2, 5/8, 26/47, whatever.
Since a 1/4 wave length is a fairly common size, there's a ROT (rule of thumb) formula for finding that particular length. Divide 234 by the frequency in Mhz and you end up with feet. (For inches, just multiply by 12.) That's a 'ball-park' figure, slightly long, but about as close as you can get for all practical purposes for antennas. Why slightly long? Well, would you rather have to cut a little more off, or try to add a little? It's a whole lot easier for me to cut off a bit more than try to add more to an antenna.
Resonance is affected by a lot of things, length is a sort of biggy. But, everything around an antenna is going to affect resonance (or SWR too). That's why you almost always have to do a bit of 'tuning' to get an antenna 'right' in different settings, circumstances. Absolutely right straight out'a the box is more 'miracle' than not. There's almost always at least a little bit of 'fiddling' you gotta do to any antenna. Not much maybe, but some.
That'll get you in to the 'ball-park'. If you want to get a little 'deeper' into it, you can start figuring the diameter of the conductor into that equation, along with the velocity factor of the conducting material. Oh isn't -that- gonna be fun?? Can't wait to get started, can you?? I hope you aren't waiting on me to try explaining all that, cuz I ain't. I'd be happy to tell you where to look for it though. You wanna know?
- 'Doc

[Turbo-T]

A 102" whip is a sort of 'standard' size that can be made usable on a number of different frequencies or bands. As a 'standard' size, it assumes that the mount used with it will increase the overall length by some degree. Lot's of possible variations with that, wouldn't you think, different size/shape mounts etc.

Which is why I said a 102 you want that extra 6 inches in there. I understand there's no such thing as a "perfect antenna for all 40 channels" which is why they tell you to tune for the lowest SWR on the channel you use most, or shoot for the lowest SWR on ch 20 and hope it evens out across the 40.

[Texas Mobil 219]

108'' tunable whip from MFJ. (MFJ-1966) There only 27 bucks. I think i paid 37 and some change after shipping. I picked this antenna because it doesnt have a spring. Just one less thing to break IMO.

[Turbo-T]

Does MFJ have a website to order from? i think I'm going to get me a 108. I hear the SWR's don't change as much as a 102 under windy conditions or when you're going down the road.

[Bigmic91]

You can google them and it should come up.

['Doc]

I don't think I'd put much faith in that 108" whip not changing SWR as much as a 102" whip. If it wiggles around as much as the 102" whip, then it's going to change just as much. That 'wiggling' around is why the thing changes.
- 'Doc

[sparky17]

? My SWR doesn't change with my 102" while i'm driving. It does go up to 3 when I bend it back and put it on its insulated antenna tie down clip.

I think if your SWR is changing on a 102" while driving, then I would blame it on the antenna getting closer to metal on the vehicle.

Even at 70mph however, my SWR's still stays at 1.1 or 1.2.

[Texas Mobil 219]

You all are right about the Swr change between the 108 and 102. My 102 would be at 1.1 when stopped. But driving they would go to 1.5. Now my 108 when sitting still will be at 1.0 and move it will go to 1.2.

The link that Tubo T needs [Please login or register to view this link] This is where you can order the 108.

[Turbo-T]

It's been said the flexing of the barrel spring on a 102 is what causes the SWR changes.