ex-KV4FZ:
>When you travel around the countryside take notice of the
>locations of AM radio stations antennas. They are seldom if ever placed on
>hilltops but you will find plenty down in the flood planes and river valleys.
The reason why Broadcast AM radio antennas are on flat terrain instead on
hilltops is because elevating a vertically polarized antenna from ground the
low angle radiation is decreased and mainly the ground wave radiation is
badly affected.
Another reason to place an AM aerials on a flat area is generally the better
soil conductivity but also the absence of ground discontinuities (cliffs,
hills and valleys) that attenuate ground wave when comparable in dimensions
with wavelenght.
The AM Broadcast antennas are generally designed and installed to maximize
the ground wave and to target an area.
In the other hand I respectfully but fully disagree that angles below 20°
aren't useful for 160m long range traffic because they are instaed quite
important, althoug a vertical on a hilltop doesn't help to obtain a low
angle radiation and ground wave is also unimportant for amateur purposes.
73,
Mauri I4JMY
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