Ground Plane

[java]

Since you guys seem pretty knowledgeable i figured id ask. i have a most;y fiberg;*** roof, so i plan on mounting my antenna on my roof rack. i was thinking of putting a piece of copper on the floor of the roof rack to use as a ground plane, however the antenna wouldnt be mounted in the middle of it. would thisd help any or make any difference or should i just stick with a larsen mounted on a tab?
TIA:sombrero:

 

[gary in ohio]

what kind of antenna, what model antenna?

 

[4RunAmok]

Comet makes a great number of ground independent antennas, you should look into these, they're the best ones for the roof racks.

 

[java]

what kind of antenna, what model antenna?

NMO larsen is waht i was thining, havent ordered one yet because i dont know how im gonna mount it. heard good things about the comet

 

[gary in ohio]

Since you guys seem pretty knowledgeable i figured id ask. i have a most;y fiberg;*** roof, so i plan on mounting my antenna on my roof rack. i was thinking of putting a piece of copper on the floor of the roof rack to use as a ground plane, however the antenna wouldnt be mounted in the middle of it. would thisd help any or make any difference or should i just stick with a larsen mounted on a tab?
TIA:sombrero:

You can get copper adhesive backed foil at many boating supply houses. This can be put on the underside of a fiberglass roof to form a ground plane. For VHF and UHF the groundplane size is pretty small, center is best but most antennas are a compromise so put it were you can..

 

[java]

well i have a section of sheet metal roof about 8"wide between the sunroof and fiberglass would that be enough i *might* be able to get an antenna in there cant get tape of the back of the fiberglass its all one piece, the inside trim part too, and it has a sun roof too.

 

[rusty_tlc]

The size of ground plane required will be dependent on the frequency of operation. The optimum size of ground plane is about 1/4λ away from the base. Less isn't effective and more has little improvment.

Ground "plane" is a little misleading, four 1/4λ radials will work just as well as a solid plane.

 

[ScoutII]

Edit.. Ground "plane" is a little misleading, four 1/4λ radials will work just as well as a solid plane.

Correct and it does not need to be copper either. But it should be grounded to the frame of the truck.

Larson is a good anntena, and I would make some sort of 1/4 wave ground plane. 2 meters divided by 4 is 1/2 meter. So you need something around 20 inches across or at least 10" out from the antenna mount if not centered. This should give you some gain over no ground plane. Which allows better simplex operation.

 

[java]

thnaks guys its a 144/440 but it wouldnt be able to be in the center. is it worth the extra trouble or should i just get a comet?