Sevick showed in the 1970s that if proper attention is paid to radials,
loading and feedpoint impedance, shortened verticals can work very closely
in performance to their full-size counterparts.
One of the best illustrations of that was a 40 meter vertical about six feet
tall. It had a top hat with about a six-foot diameter above a loading coil
and over a model radial bed. I think he theorized the difference in
performance was less than the resolution of his test equipment at the time.
Anyone with QSTs that old will probably remember the photo of his wife
sitting on a lawn chair under the top hat.
I think shortened antennas get a bad rap when people don't take the time to
understand and resolve the various issues involved.
----- Original Message -----
From: "Jim Brown" <email@example.com>
To: "Tower Talk List" <firstname.lastname@example.org>
Sent: Wednesday, September 27, 2006 11:36 AM
Subject: Re: [TowerTalk] 160 meter vertical
> On Wed, 27 Sep 2006 09:50:17 -0500, K4SAV wrote:
> >A 45 ft vertical for 160 is a little problematic.
> Yes, but it can be made to work with a lot of top loading in the
> form of a capacity hat, and an effective counterpoise or radials.
> Will it be as good as a quarter wave? Of course not. But it will
> work. In general, the shorter the antenna, the more important the
> radials. The more top loading the better, but it will load fine if
> you have enough loading to get it within range of your antenna
> Very effective top loading can be obtained as simply as suspending
> a vertical wire from a horizontal wire hung between two trees or a
> tree and a house or a house and a tower, connecting the vertical
> wire to the horizontal wire. Or it can be an inverted L. The
> vertical wire will do most of the radiating, the transmitter sees
> the length of vertical wire plus the length/capacitance of the
> horizontal wire.
> There are good discussions of antennas like this in Kraus (W8JK),
> and ON4UN's book (Low Band DXing), which is an excellent resource
> for 160/80/40 antennas. The vertical I described in an earlier
> post in this thread works as the "T" form -- I tie both sides of
> the feedline together and load it against 25 radials (and will add
> more). In Chicago, I had a few short radials and a big wrought
> iron fence. I wasn't the strongest signal on the band, but over
> about two years, I had a lot of fun in contests and worked the
> lower 48 and 20 countries.
> Jim Brown K9YC
> TowerTalk mailing list
TowerTalk mailing list