Topband: T loaded vertical

[Tod - Idaho]

Jeez, I am just reacting to the thought of 260 feet of top loading on a
vertical. It almost seems as though one is using a single wire feed line to
feed an horizontal antenna. I may have to get out my ON4UN book and see what
the equations tell me the feed point resistance would be -- I have never
thought of doing something like this and maybe I have missed something that
would work better than what I am using.

Maybe this is just an oddly proportioned DDDR antenna.

Herb, what is the reasoning behind the statement, ""Try to get the current
loop to appear at the connection to the flat top
T.  This can be done by modeling or in the old days we would just tape a
small 6 volt bulb on a loop at the T." I suppose that by doing so one will
maximize the current at the highest point above ground and thereby get
maximum radiation from that point. Using Earl's rule of '1/4 wave from its
open end' would suggest that an L that has a flat top of 130 feet or so will
achieve that. A T loaded top should not be necessary (to get the current
maximum at the top of the vertical segment). The T load will, however,
produce a balanced pattern when modeled, the L will not. What happens to the
pattern in real life is probably not the same as either of the models.

A interesting special case would be when the vertical segment is 130 feet.
Now when one adds 130 foot legs for a T or L you are challenged with a feed
point that should be rather high impedance. Presumably one would not need
radials in this case.

Rich, I would not expect the T to be quieter than the L.

As usual, the comments of other folks on this reflector stimulate thought.

Tod, KOTO




-----Original Message-----
From: topband-bounces at contesting.com
[mailto:topband-bounces at contesting.com]On Behalf Of Earl W Cunningham
Sent: Monday, September 22, 2003 7:05 PM
To: herbs at vitelcom.net; rmf01 at comcast.net; topband at contesting.com
Subject: Re: Topband: T loaded vertical


Herb, KV4FZ wrote:

"Try to get the current loop to appear at the connection to the flat top
T.  This can be done by modeling or in the old days we would just tape a
small 6 volt bulb on a loop at the T."
==========
The highest current point on any antenna is always 1/4 wave from its open
end, regardless of how long the vertical section is.  In the case of an
L, this means the horizontal portion would have to be about 130 feet long
to achieve maximum current at the bend in the L.

If the top portion is a T, make sure each of the two sides are equal and
are each about 130 feet long.

73, de Earl, K6SE
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