On Sat, 08 May 2004 17:34:06 GMT, "Dave Pitzer"
wrote:

First of all, I'm a novice where taransmitting antennas are concerned.

It seems to me that many AM "broadcast band" antennas are four-footed
towers. Do these towers merely serve to hold the actual antenna (a "wire")
off the ground vertically. The "wire" runs up the center of the tower?

Hi Dave,

No, the physical structure, in this case, is also the radiating
structure. Some are isolated from ground (they sit on glass mounts)
or are grounded and fed by other means.

FM and TV (and some AM) towers tend to be slim "guyed" towers with some sort
of antenna element(s) at the top. Is this correct? Is the actual tower ever
a radiating element?

Depends on the wavelength and the physical dimension and if the
structure is constructed with isolated elements (glass barriers along
its length to become a stacked, phased system). But by-and-large,
those that you see are holding up antennas for the height advantage.

This is not to say that BOTH could not be achieved. Here in Seattle,
we have phased AM towers holding up hundreds of VHF/UHF/SHF antennas.

Also... Some tower structures (AM, FM & TV) tend to be cited on hight
ground -- mountains or atop high buildings. Other antenna structures tend to
be intentionally located on "low" flat ground. Why the difference?

Those same phased AM towers are in fact atop two of the city's largest
hills, Queen Anne and what we call Pill Hill (lots of hospitals
located there). We also have lots of lake country and estuaries
filled with AM stations. Economics of Real Estate and coverage drives
such things far, far more than engineering.

73's
Richard Clark, KB7QHC