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
>intermod products.)
>
>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
The World HF Contest Station Database was updated 17 June 03.
Are you current? www.pvrc.org/wcsd/wcsdsearch.htm
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