miso@sushi.com wrote:

Do you mean the tower being like an AM radio type radiator? You need
to isolate the tower from the ground with ceramic insulators...

Not really. You can shunt feed a grounded tower.
It's exactly the same principle as a Jpole antenna
or a gamma match on a yagi. Feed the grounded
element a given distance from the ground point
and you create the desired 50 ohms impedance.

Anyway,
there is usually a transmitter shack nearby.

That's what I wondered about the heft and size
of the tower. The transmitter guts could be
located inside the tower. With extremly high
frequencies, there is no "feedline". The output
of the transmitter finals is connected directly
to the horn or whatever is doing the radiating.
Radar and even the 1200MHz hams do that.

I suppose it's possible that the internal structure
of the thing is more traditionally "tower shaped",
that is larger at the base, tapering to the top.
And the outside is a fascia. But again, it seems
kind of weird to involve all the secrecy just for
some kind of antenna tower.

In terms of engineering tower buildings, is there a
point where the thing can be the same size at the
base as it is at the top? There are multi story
buildings that certainly exist in that manner.
They probably aren't as tall as our tower, but
they are several stories high and the same size
at the base as they are at the top. There are,
of course, some that are built opposite. ATC
towers, those "golf ball on a T" looking water
towers, some dedicated "crows nest" style
observation towers are built on a straight "pole".


Craig 'Lumpy' Lemke

www.n0eq.com