Topband: T Top Verticals and yagis

[Charles Moizeau]

I would prefer to have the horizontal radiation canceled by using an inverted T, but I haven't discovered a workable configuration to achieve that.  Therefore I use an inverted L with a vertical leg of 86', the most I can get.  I have no serious limitations on the length of the horizontal leg and I chose 68'.  I  did that in order to place the current maximum (always a quarter wavelength, 128' assumed, back from the open end of any antenna) at the midpoint of the vertical leg, thus getting as much rf current as I can into the vertical leg.  This also gives me the convenience of only using a vacuum capacitor the bring the feedpoint impedance down to 50 Ohms.

I must say that I have a lingering doubt about this arrangement.  That is because my in-ground radial system has no radials longer than 150'.  By raising the maximum current point to 43' above ground level the rf that bounces off the ground and needs to be returned to the feedpoint will occur farther out from the feedpoint than would be the case of an antenna with a vertical leg still at 86' but now with a horizontal leg of just 42'.  That would put the current maximum at ground level where the existing radial field would have its best effect.  It would also reduce the radiation from the horizontal leg.  Of course a different matching network would be needed.

I would welcome any comments on this reasoning.

73,

Charles, W2SH
________________________________
From: Topband <topband-bounces+w2sh=msn.com at contesting.com> on behalf of Ed Sawyer <sawyered at earthlink.net>
Sent: Saturday, February 29, 2020 12:37
To: topband at contesting.com <topband at contesting.com>
Subject: Re: Topband: T Top Verticals and yagis

Mike, I am not sure where you find your information, but  ALL of the
radiation of a T top vertical is vertically polarized assuming the T section
is balanced.  The whole point of the T is that the horizontal portions of
the radiation cancel themselves out because they are 180 degs out of phase.
Providing loading but not distorting the vertical pattern and not using that
wasted horizontal energy.



An inverted L, while simple, is exactly the opposite. A portion of the
energy is in the vertical section and a portion in the horizontal section.
On 160M, whatever the length is of the horizontal section, its not desired
energy for DX work.  Although it may actually be helpful as a more
all-around antenna for local and DX work for this reason.



The smaller the ratio of horizontal to vertical, the less this compromise
exists.  However very few stations that say they are using an inverted L on
160 have 100ft plus of it vertical.  Much more typical is 50 - 75 ft.  And
the horizontal portion is usually longer, sometime a lot longer, than the
vertical portion.



Ed  N1UR





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