2m/440 dual band tonneau cover installation

[KD5ITM]

I’v mounted a Comet SBB-7 dual band antenna to the top of my trucks Leer fiberglass tonneau cover on the right side right behind the passenger side back glass using a custom made stainless steel mounting bracket. I fully understand that this installation doesn’t have the most efficient ground plane. Sticking with this antenna installation, what can I do to maximize what ground plane there is?

Should I run a copper ground strap from one of the mounting bracket bolts (bottom side of the tonneau cover) to the inside top lip of the bed rail using something similar to a star washer to insure that the ground strap has a solid bond connection to the bed rail lip? I’v also thought about lining the compleat underside of the tonneau cover with aluminum window screen, making sure that it has a good solid bond to the antenna mounting bracket, which will act as a ground plane.

As the curre dual band antenna installation is, I can hit a local club repeater from located on the south side of Houston, Tx from my QTH drive way 45 miles south of me. The issue I have is that where the antenna is located on the truck, when talking on this repeater located 45 miles south of me, my RX/TX signal is somewhat directional depending on where the truck is pointing, but when talking on repeaters located with in 15 - 20 miles from me, the issue with the RX/TX signals being somewhat directional is not a very noticeable issue, or not an issue at all. It’s only an a bit of an issue when talking to stations/repeaters located at further distances . Which is caused by not having the most efficient of a ground plane. For almost 25 years, my 2m/440 dual band antenna has been mounted in the same location on 2 prior trucks with no issues with the RX/TX signals being somewhat directional. Both of those trucks, the antenna was mounted with the same stainless steel bracket to the side of a drop in bed diamond tool box. The antenna mount did not have any metal directly under the base of the antenna so therefore what ground plane that was below the antenna was not the most efficient. The first pictures below is how my Comet SBB-7 dual band was mounted to the side of the tool box on both prior trucks. The second picture was taken when I was installing the antenna which is how it’s currently mounted now.
Thanks
Tim - KD5ITM

 

[mmckenna]

A strap from the mount to the bed isn't likely to help. There's a difference between an RF ground plane and DC ground. The strap is really only going to give you that DC ground, which you probably already have with the current mount.

Really the only way to improve that would be to have a 1/4 wave of conductive material in all directions under the very base of the antenna. That's not going to be possible off to the right side of the truck. Adding it in other directions is still going to result in a lopsided radiation pattern.

Even if you went with a 1/2 wave 'ground independent' antenna, the lopsided ground plane is still going to be an issue.

One of the reasons why we mount antennas dead center on the cab roof.

 

[KF0NYL]

I would do like @mmckenna suggested. Get a sheet of metal that is at least a 1/4 wave all around and install the NMO mount in the center of the sheet. You can epoxy the sheet to the underside of the tonneau cover. In the center of the cove will be best. I know a lot of people do this with camper shells/toppers for their trucks.

You will want a sheet of metal that is 3 ft by 3 ft for the 2m band and place the NMO mount dead center of the sheet.