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On Thursday, November 6, 2014 3:15:23 PM UTC-5,
wrote:
I'm planning on building a 10 meter ground plane antenna out of PVC pipe
and #12 wire radials drooping about 40 degrees. This will be mounted on my
roof on a tripod and mast, with the radials also serving as guy wires. The
ARRL antenna book mentions that a ground plane antenna should be mounted
at least one half wavelength above "ground". I know that this sounds like
a stupid question but I have to ask: for this example do I consider the
roof, which is more than 5 meters above ground level as "ground" or do I
need to be at least 5 meters above the roof. I would like to secure the
radials, (guy wires) to my roof, but with the antenna at 5 meters high my
droop angle will be off and then I can't guarantee a 50 ohm match. The
house is wood frame, no foil backed insulation and a non metallic roof.
Thanks for any advice. Lenny

To build this antenna I plan on using an SO239 inside a length of 1.50 or 2
inch PVC pipe, and bringing the 4 radials, which are cut to 1.05
wavelength,(as per the ARRL Antenna book) out through four drilled holes up
toward the top of it. Then I'll use an adapter to convert to half inch pipe,
cap the top end of the half inch and run the # 12 wire radiator straight up
into that. I'll bring my 213 up inside the pipe, connect to the SO 239 and
seal the whole thing up with silicone. The thing will be mounted on a tripod
and the radials will have insulators on them so that they'll double as guy
wires as well.

I built another ground plane years ago and it's still up there and in use
using this method for my business band radio. That unit operates in the 40
MHZ band and I recall that I came up with a very good SWR on that one. I'm
nowhere near half wavelength above the roof with that one either but I had
to ask.

So now I have to ask another stupid question. I'm stripping old Romex for
the wire and I mentioned this to a local friend the other day. He asked me
if I was using bare wire for the radiator. I said that I didn't think that
it mattered. He assured me that it did. I would think that either in free
space or inside a plastic pipe that it wouldn't matter. Am I correct or is
he? Lenny



Any material around the wire will make some differance. At 10 meters it
will only make an inch or two worth of differance. The PVC pipe you put it
in will make about the same ammount of differance. The angle of the radials
will make more differance than the insulation in your case.

If this was at two meters and above then you will notice a larger ammount of
differance. The higher the frequency the more th differance will be noticed
in any material around the bare wire.

The insulation tends to make the antenna look longer so you can cut some off
the ends if it is too low in frequency.








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