From:
Fred Hopengarten K1VR
617/259-0088
Six Willarch Road
Lincoln, MA 01773-5105
permanent e-mail address: fhopengarten@mba1972.hbs.edu
On Wed, 30 Apr 1997 15:53:24 EDT km1h@juno.com writes:
>John, W1FV, has been using ~41 foot tall verticals for many years on
>80M. They use the top set of guys as the loading and are arranged in a
>triangle array with 1/8 wave spacing. John has one of the best 80M
>signals on the East Coast.
>He has also developed a feed method to drive all three verticals as
>one single "fat" vertical on 160M. His signal on 160M is also
>outstanding.
>
>I haven't a clue as to efficiency, feed impedences, radiation
>resistances, ground losses, etc.
>So, while the technical discussion rages on, it is interesting to note
>that another ham has excellent results with short, top loaded antennas
>on Topband.
>
>73....Carl KM1H
K1VR adds: Everything Carl says above is true. I'd like to add to the
discussion.
John (W1FV) also had great concerns about efficiency. He carefully
measured feed impedances, created a matching system, and minimized ground
by installing an extensive ground system (soldered at each intersection)
before seeding the lawn at his newly constructed house. It is not
inconsequential that John is a very smart cookie, holding a BSEE from MIT
and a Ph.D. (EE) from Cornell, and able to use lab equipment from Lincoln
Labs to do his measurements.
As I recall it, Sevick (W2FMI), in a QST article during the 1950's,
"proved" that short verticals can work very well, as long as the ground
system is carefully built (to keep ground losses low) and the 50 ohm coax
is efficiently matched to the very low impedance short antenna
(transitioning 8 ohms, or whatever it may be, back up to 50 ohms).
While Carl, KM1H, is pointing out that short verticals with a top hat can
work very well indeed, he is modestly not mentioning that his own station
performs unusually well because he too has paid attention to creating an
extensive ground system and carefully matching the feedline to the
impedance present at the feed.
Conclusion: He who doesn't waste too much power, by ground losses and/or
with an inefficient feed system, can be happy on topband.
P.S. My own topband antenna still needs improving, both in terms of
ground losses and feedpoint matching.
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