Posted by
N2EY on
Oct 27, 2006; 9:27pm
URL: http://elecraft.85.s1.nabble.com/Attic-Antenna-tp394788p394820.html
-----Original Message-----
From:
[hidden email]
It reminds me of the verticals Gotham made in the 1950s.
----
But it's very different.
The Gotham verticals were just 22 feet of tubing, some mounting straps,
and a big custom-made coil of B& W miniductor. The only difference
between the various models was how big a coil they sent.
You supplied the feedline, mounting, some hardware, a ground or
counterpoise, and a weatherproof cover for the coil.
The way the Gotham verticals worked was that you connected the coil
between the bottom of the 22 foot radiator and ground/counterpoise.
Then you connected the coax braid to ground.
You also needed to tap the coax center conductor onto the coil, and to
short out turns at the top of the coil.
The trick was that with the right number of turns shorted out at the
top of the coil, and the center conductor tapped on at the right spot,
you'd get a low SWR on the frequency of your choice. Of course if you
QSYd, you had to go change the taps and shorting jumper. Since the coil
was at the base of the antenna, that could be convenient - maybe.
Depending on how good the ground connection was, and what band you were
using, performance could range from great to awful. 22 feet is about
5/8 wave on 10 meters, too.
The BB7W doesn't work like that. There's some sort of magic,
nonadjustable network inside the feedpoint device. I suspect it has a
near-unity power factor.....
73 de Jim, N2EY
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