Topband: Topband :"T"

[w2pm at aol.com]

> 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



Pete W2PM Replies:

But how can a top hat device be supported with a vertical wire?  Ive 
seen some on 60 foot vertical masts but I don't think you can do this 
with a wire or a small gauge tapered 60 ft mast.   This is why I wonder 
if under these circumstances a top load coil with a shortened (100 ft 
top wire) would be more feasible as you can hang the coil from the rope 
which holds up the vertical wire...