Ground plane and mounting Ghost antenna to van roof

[JimK]

Question about ground plane and mounting my MXTA25 Midland Ghost antenna to my Ford Transit high roof Van.

Aluminum angle with 2-inch legs is mounted to the length of the van roof with mounting brackets in a roof rail configuration. 
Three solar panels are secured to the aluminum angle roof rails to the rear of the preferred antenna mounting location with an LED Light Bar spanning between the two roof rails to the front of the preferred antenna mounting location. 

For optimal performance the antenna should be mounted directly to the roof of the van, however, when mounting the antenna directly to the roof, the rest of the structure on the roof will effectively block transmitting or receiving signals from the antenna. 

Raising the antenna (on a stalk or mast) up about 8 inches would position the antenna clear of the roof structure obstructions. Although mounting the antenna 8 inches above the roof, the antenna will likely still function, but it may not perform as well as if it was mounted directly to the roof. 

In your opinion, would I need to mount a 19 inch ground plane, 8 inches above the roof on the stalk or mast that the antenna is connected to ? 
Do you have any suggestions to consider when raising the antenna clear of the obstructions and still get optimal performance from the Ghost antenna ?

Thanks
 

[BoxCar]

I take it the aluminum angle work is bolted to the van roof so mounting the antenna to the center aluminum piece running crosswise would work. Virtually any metallic surface will act as a ground plane for an antenna.

[JimK]

Yes, the aluminum angle work is bolted to the van roof.

Yes, I would use another peice of aluminum running crosswise to raise and mount the antenna off the surface of the roof by about 8 inches.

Should I be concerned with an 8 inch gap between the surface of the van roof and the base of the antenna ?

[SteveShannon]

3 minutes ago, JimK said:

Yes, the aluminum angle work is bolted to the van roof.

Yes, I would use another peice of aluminum running crosswise to raise and mount the antenna off the surface of the roof by about 8 inches.

Should I be concerned with an 8 inch gap between the surface of the van roof and the base of the antenna ?

Why not just use a piece of steel running crosswise and stick the antenna base to it?

The metal will serve as your ground plane. 

[JimK]

Yes, I would use a piece of steel (or aluminum) running crosswise and stick the antenna base to it to raise the antenna 8 inches off the roof.

I was wondering if you thought that an 8 inch gap between the surface of the van roof and the base of the antenna would reduce the performance of the antenna signifiantly. Or if the 1.5 inch peice of steel (or aluminum) running crosswise with the antenna attached to that would be enough of a ground plane.

 

[gortex2]

You can use aluminum. The antenna isn't that good of a unit to worry about the 8" difference in height. Just mount it and enjoy. Personally I'd swap on a uhf 1/4 wave but thats me. 

[PACNWComms]

If a small steel baking sheet can work, it is worth a try. That gap is not going to make much difference for UHF......you get up into SHF and then it will. Just mount the antenna with some steel under it and go on with life. More sheet metal and more uniform shape under the antenna will be better. 

I had an older Antennex "Phantom" antenna (probably where they get the "ghost" name from) the same size and shape mounted to the corner of a 2004 Pontiac Grand Prix trunk for about 14 years, everyone said that it would never work for GMRS because it was not in the center of the roof, center of the trunk, and the car fender sloped down to one side. I was able to get 10-12 miles easily with that small antenna, and often times more if I was on top of a hill. Even being on the trunk lip rather than the roof did not impact very much. 

The advantage of this type of antenna is that they do not get ripped off by car washes (no coil to grab), they look discrete and a lot like some vehicle antennas now, and many are sensitive to the electric and magnetic field that gives you a little gain (just stay away from the soup can VHF version of these antennas that are very narrow band and must be tuned). 

Ideal would be in the center of the steel roof, but barring that, just being on top of the roof will be fine. A good test would be a steel baking sheet mounted as you want, 8" off the roof to see how it works. Testing is always a good thing before mounting something more permanent. 

When finished show pictures and results here too, might help someone else.

[PACNWComms]

I went back into the gallery and found one of my pictures, showing antennas on my old Pontiac. I had a Sirius satellite radio antenna, a UHF Antennex Phantom antenna, and then a whisker style VHF antenna mounted on the right side of the trunk lip. Original configuration was spaced out, but too many people thought it was a cop car (local PD's bought Pontiac's for their detective vehicles), and I was even pulled over a few times to find out how they could get the shorter antennas like mine. The local radio shop put larger antennas on those detective vehicles and they were not very discrete. Once I put all the antennas next to one another, people just thought it was the factory configuration and I never had anyone wonder (at least to me) after that. 

Worked well with a VHF and a UHF Vertex VX-3200 stack mounted in the console. It was nice having enough room to mount mobile radios in the dash, making them look like part of the dash. I miss that car.

[JimK]

Thank y'all very much !

The MXT275 Midland radio is the first radio that I have ever mounted into a vehical. The small magnet antenna is already up on the roof with the wire simply going through the door just so I could get started. I have one more set of LED lights to go up onto the roof rails and when that install happens I will be running the antenna cord through the roof at the same time. I will be running the DC Power cables up to the lights on the passenger side, while antenna cable will be run up through the roof on the driver side. I really apprecate the comments and insights.

I will be mounting the antenna in the center of the aluminum flat bar, spanning crosswise between the roof rails with a gap of 8 inches between the roof and the base of the antenna. 

Again, thank you for your comments and insights. I will grab and post a pic after the install.