ground plane for 2m/440

[arz]

my van has 3 holes in the roof from the previous owner's installations. They're about NMO size, which is good, but it's a fiberglass hightop roof, which is bad.

How large a ground plane do I need to put underneath the antenna to help get my signal out? I'm thinking of just using a round pizza pan underneath the roof, maybe a 16" round one if I can find one easily enough.


I know someone is going to ask, but I forgot exactly which antenna it is. IIRC it's a 1/4 wave on 2m and 1/2 wave on 440. Think it is the Comet SBB-1.

 

[Clark White]

I'm no antenna genius, but I'm pretty sure that antenna works the same as the Diamond antenna I have, which does not require any ground plane. I called Diamond and they said nothing is to be gained by giving it a ground plane.

Clark White

 

[xtatik]

my van has 3 holes in the roof from the previous owner's installations. They're about NMO size, which is good, but it's a fiberglass hightop roof, which is bad.

How large a ground plane do I need to put underneath the antenna to help get my signal out? I'm thinking of just using a round pizza pan underneath the roof, maybe a 16" round one if I can find one easily enough.


I know someone is going to ask, but I forgot exactly which antenna it is. IIRC it's a 1/4 wave on 2m and 1/2 wave on 440. Think it is the Comet SBB-1.

For an FM antenna just run three or four discrete wires off the shield (mount ground) side of the coax. Hide them in the headliner or tape them off with 3M VHB tape. Cut them to approx. the same length as the antenna. This will approximate the "image" side of your dualbander. It's not that fussy with FM....mag mounts and pizza pans are field day standards.

 

[SunTzuNephew]

Or get as big a piece of light sheet metal (roof flashing works well, as do pizza pans) and put them underneath the roof. Lots of fire engines (especially the old roofless models) used pizza pans as ground planes...

 

[gary in ohio]

my van has 3 holes in the roof from the previous owner's installations. They're about NMO size, which is good, but it's a fiberglass hightop roof, which is bad.

How large a ground plane do I need to put underneath the antenna to help get my signal out? I'm thinking of just using a round pizza pan underneath the roof, maybe a 16" round one if I can find one easily enough.


I know someone is going to ask, but I forgot exactly which antenna it is. IIRC it's a 1/4 wave on 2m and 1/2 wave on 440. Think it is the Comet SBB-1.

The answer is make it as big as practical. 19" will do fine.. If you have a marine store nearby you can get ground sheet. They are used in fiberglass boats. Its a sticky back then copper sheet 6 inches or so wide. A couple of sheets of that under the hole will work. The pizza pan might be a little small and I think would be noisy.

 

[gary in ohio]

I'm no antenna genius, but I'm pretty sure that antenna works the same as the Diamond antenna I have, which does not require any ground plane. I called Diamond and they said nothing is to be gained by giving it a ground plane.

Clark White

Most mobile antennas require a ground plane. There are a few that dont but the SBB-1 does.

 

[matt s]

I often hear 19" as the magic number.

 

[SunTzuNephew]

It depends on the frequency. The ground plane should have a diameter equal to 1/4 wave....which works out to around 19" for 2 meter:elkgrin:

 

[Clark White]

Most mobile antennas require a ground plane. There are a few that dont but the SBB-1 does.

Huh, learn something new every day. Duly noted, thanks!

Clark