At 10:15 AM 6/22/03 -0400, Chuck Counselman wrote:
>At 1:50 PM -0700 6/21/03, K wrote:
>>...been thinking about mounting another Screwdriver
>>antenna on top of my 10x20 foot and 9 ft high metal
>>top garage in the middle. I was wondering how well it
>>might work 80-10m without any other radials?
>1. Make a short, fat, low-inductance connection between the shield of the
>coaxial feedline and the metal of the garage roof at the feedpoint of the
>antenna. (Otherwise too much current will flow on the outside of your
>coax. This happens in automobile/van/truck installations, too.)
>2. Bond, electrically, well, all the seams of the metal of the garage
>roof. (Otherwise, nonlinear conduction will generate harmonics and
>3. Mainly for 80 m, and if your soil conductivity is good, maybe drop some
>fat conductors from the corners or edges of the roof to 8-ft. ground rods.
>If you do #1 and #2, it should work very well.
As an alternative to the bonding process, I laid 3 125-foot radials right
on the galvanized 30 x 40 foot garage roof under my Butternut HF9V. I'm
not sure whether this is theoretically enough coupling to bring the whole
roof into play as a counterpoise, or to avoid harmonic and intermod
generation, though I have not experienced any additional level of either
one. But I've used the antenna on my second radio in a number of contests
and it seems to work surprisingly well with 100 watts.
73, Pete N4ZR
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