Batboard

is there a good way to mount an antenna in a fiberglass roof? the roof of the van i'm installing in is 100% fiberglass with just a few metal braces going across for support. there is definately no flat panel for a ground plane. can i just ground the mount to the support or is there anything special i need to do?

Well, you didn't say what band it's for, but...

What I've seen one person do with an Oldsmobile minivan who's roof is fibreglass... Cut out a circular piece of metal with a radius equal to slightly larger than 1/4 wave at the operating frequency. He glued this to the inside of the roof, and mounted the NMO mount in the middle. This gives the radio a proper 1/4wave groundplane. Not a perfect solution, but it works pretty well.

-Mike

sorry, it's UHF. that's the answer that i figured, but not the one i was hoping for. lol. looks like i got alot more work than i expected if i gotta bond a piece of sheet metal in there. thanks.

Back when I worked for the Private ambulance biz.. I did pretty much the same thing . I had a sheet metal shop make a dozen 16" circluar plates. I would drop the center headliner drill a 1 1/4 hole in the roof through the fiberglass then mount the plate to the roof with short sheet metal screws and silicone then dril the NMO hole up from the bottom . Worked like a charm

would sheet aluminum work? i have some stuff laying around here i think it's about 16 ga.

oh, and does this sheet have to be grounded to the chassis of the vehicle or can i just float it in the middle of a fiberglass panel?

thanks again guys

Not really necessary. The sheet is only acting as an RF groundplane for the antenna system.

On the underside of the fiberglass, install a section of metal door screen. The diameter of the screen shall be 1/4 wave X 1.25

Attach the screen with uphousltry adhesive to the fiberglass and make sure it is solidly grounded to the NMO mount.

It looks clean and there's nothing on the roof. Works great too!

ok in order to keep it simple, i opted to use sheet aluminum and some may consider this ugly, but i mounted it to the outside of the fiberglass roof. since it's a large van (like a ups truck) you're not gonna see it unless you're in a helicopter or perhaps a suicidal jumper. the reason i didn't mount the aluminum to the inside is because there was literally about 100 rivets holding up a cardboard type of headliner panel. i didn't feel like drilling them all out and re-riveting. even standing on the roof (i don't weigh much) and looking down at the antenna install, it doesn't look bad at all. the roughtly 2' square aluminum neslted in between the raised ribs of the roofline looks like it belongs there. i'm happy with it and more importantly so is the boss.

thanks again for all the help. i love this site.

just use a 1/2 wave antenna -- no counterpoise (ground) necessary.

You can also use hardware cloth, either the 1/4" or 1/2" mesh (found at Home Depot), and then apply a fiberglass repair kit to the bottom side to make it physically part of the roof.

I did this in a fire truck........if its a UHF 1/4 wave take 4 pices of wire that are the same length of the antenna and put ring terminals on them that are big enough to put on the NMO mount and evenly tape them to the roof surface between the head liner and fiber.. to create a ground plane for the antenna to have something swing againest . Then check you SWR... IT should be atleast less than 10% of you forward power Iknow this really doesnt explain very well but it works... if you need to talk to me shop number is 910-276-9693 ask for Joe

A friend of mine had a fiberglas camper shell, with 8-10 NMO mounts on it.. he used copper foil tape on the underside of the shell as radials..