Mobil Antenna Fiberglass Roof

[JD]

I have a install for a Kenworth truck that has a fiberglass roof. Any suggestions on an antenna that works well for this in VHF ?

I can also install on side mirror mount if no other options. In VHF, would this mirror need a metal plate mounted under it ?

Motorola has the 4 or 5" circular aluminum disc.

[kf4sqb]

You have two options (that immediately come to mind):

1. Use a "no ground plane" antenna. I don't have a part number handy, but I know several antenna manufacturers make them. Them are designed to work without a ground plane.

2. Install a metal sheet under the bottom of the roof to "make" a ground plane. Needs to be app. 19" square or round, thickness isn't an issue. Gluing a piece of aluminum foil to the bottom of the roof would work just fine, provided you could get a reliable electrical connection to it. You'd probably be better off trying to find a piece of thin-gauge sheet steel. Try checking with your local HVAC contractor. They may even have an old piece of duct laying around that they'll let you hack up for free.

[tvsjr]

Been there done that, on our tanker (2005 T300 chassis). Make sure you have an NMO designed for thick mounting surfaces. I used a chunk of thin sheet metal that someone had - drilled the roof and the sheet, slathered the sheet liberally with RTV silicon, then stuck it up to the roof. You could do just as well with some copper foil tape - construct a "disc" underneath the NMO base, then lay down several radials. Make sure the NMO mount gets a good bite on whatever metal you use.

A no-ground-plane antenna for VHF would be a 5/8 wave, 40-something inches tall. If you're going on top of the cab, you'll tear the antenna off in no time. I went with a Larsen NMOWBQB VHF wideband quarter-wave.

Mirror mounts? Meh. Too trucker-ish for me.

I hope you have a different model. You need to pull the headliner to do all of this, and it's a giant pain in the arse on our T300.

[JD]

Thanks guys. It is a T800 Kenworth. A no ground plane is too tall, I need to go with the unity vhf antenna.

I will try the plate under the roof if I can get the headliner down.

Merry Christmas !!!!!

[wx4cbh]

If there's insufficient access to get a sheet metal ground plane in place on the roof's underside and you have a thick mount that can handle the necessary thickness, try a proper sized piece of copper (preferable) or aluminum screen wire. It will roll up or flex into place, and then you can temporarily tape it in place. Then place a few small blobs of silicone adhesive/sealer through the screen in strategic places for the permanent side of the installation. Use a metal fender washer the same size of the mounting hole (probably 3/4 inch) on the underside which will encompass a good surface contact of the screen around the hole. Done quite a few of the more difficult ones like that.

[JD]

Thanks, appears I will have to do something like that.