The top hat consists of eight 20 foot 1.25
inch diameter aluminum tubing mounted on two plywood disks. I have tested this
antenna an it works very well. This antenna cost me about $1000.00 to build
That's very expensive plywood!
Seriously, this type of antenna would be very efficient for its physical size as
the coil is high up and the capacity hat is very low loss. However, being small,
the ground losses will be high, so it is unlikely to outperform anything that has
a higher radiation resistance, such as a T or L with 40m or more of top wires.
Mike, G3XDV (IO91VT)