At 07:22 AM 9/17/99 +0800, Steve, VK6VZ wrote:
>My concern is that
>there is lots of cancellation of radiation with the skirt wire hanging down
>so far.
Steve, I played around with computer models and then built some 30 meter
scale models for verification when faced with the same problem. My
experiments proved, to me at least, that drooping top hat wires more than
about 30 degrees from horizontal was a waste of time.
>
>What I am wondering about trying instead is a 50 - 55' top loaded vertical
>with a large square section coil wound on a big 3 litre soft drink bottle
>or plastic bucket with 3mm or so diameter wire, working against a small top
>hat consisting of two wires about 10 - 15' long. The loading wires and
>vertical radiator would be in a tee configuration.
>
Field strength measurements and on-the-air performance indicated to me that
the best place for the loading coil was at the center or just above center.
Any higher and the additional inductance required causes the coil losses to
skyrocket. Last 80 mtr loaded vertical I built used 1/4" (6MM) copper tube
for the coil. If you can, use three or four wires for the hat and connect
the ends. It's surprising how much you gain with that method.
73,
Larry - W7IUV
w7iuv@arrl.net
http://www.axtek.com/w7iuv
Amp pix at http://207.108.137.61
--
FAQ on WWW: http://www.contesting.com/ampsfaq.html
Submissions: amps@contesting.com
Administrative requests: amps-REQUEST@contesting.com
Problems: owner-amps@contesting.com
Search: http://www.contesting.com/km9p/search.htm
|