Topband: Topband :"T"

[Herbert Schoenbohm]

From: "k4pi"

> my vertical
> portion is 90 ft and the top horizontal of the T is 50 ft. for a total of
> 140 ft.  In practice it would appear that the total amount of wire for the
> vertical and tophat is very to near to a 1/4 wavelength.

To support a Marconi "T" at 90' may be difficult for many of us and a lower
height may be more easily to obtain.  Additionally the wing span of the "T"
of 150' to 180' or longer to obtain a reasonable feed impedance may also be
problematic in normal lot sizes.  So give some consideration to either a
square or delta (triangular) top hat supported by corner supports that drop
the vertical wire.  Two cross wires (on the square wire top hat) with the
vertical drop in the center or three intersecting wires for the triangle top
hat should save space, improve efficiency, and allow for a lower vertical
overall height.  The "T" is simple and easy but does require some real
estate, whereas a smaller profile top hat will do the same thing or better
(cancelling high angle useless radiation) as described.  If someone would be
so kind to model the various shapes you may find the best arrangement that
yeilds the best efficiency for the size.  Early radio 500 Khz and below
antennas were constructed this way and perhaps still are.

Herb Schoenbohm, KV4FZ