Frank Dresser wrote:
Wouldn't FM broadcast antennas be an even greater concern? The height of
most adults would make them resonant somewhere near, or in, the FM broadcast
band. I'd expect energy transfer to be more effiecnt from the FM broadcast
antenna to the human body than it is in the AM broadcast band.

I'd sure think so.

On the other hand, the FM signal is radiated from an antenna atop the
tower. Stand at the base of a 300' FM tower, and you're 300' from the
thing that radiates.

At an AM station, the entire tower radiates.
--
Doug Smith W9WI
Pleasant View (Nashville), TN EM66
http://www.w9wi.com

"Doug Smith W9WI" wrote
On the other hand, the FM signal is radiated from an antenna atop the
tower. Stand at the base of a 300' FM tower, and you're 300' from the
thing that radiates.

At an AM station, the entire tower radiates.
___________

Also - most FM broadcast transmit antennas are arrays of several elements in
a vertical stack to concentrate radiation in the horizontal plane. As a
result the radiation directed around the tower base is much lower than the
station's licensed power.

RF

Visit http://rfry.org for FM broadcast RF system papers.

"Doug Smith W9WI" wrote in message
...
Frank Dresser wrote:
Wouldn't FM broadcast antennas be an even greater concern? The height of
most adults would make them resonant somewhere near, or in, the FM broadcast
band. I'd expect energy transfer to be more effiecnt from the FM broadcast
antenna to the human body than it is in the AM broadcast band.

I'd sure think so.

On the other hand, the FM signal is radiated from an antenna atop the
tower. Stand at the base of a 300' FM tower, and you're 300' from the
thing that radiates.

At an AM station, the entire tower radiates.

One of the issues with most FM arrays with gain is that, for many, the spacing which
results in the array having gain also results in a fairly pronounced hot-spot
directly above the antenna, where few people would be expected to be, as well as
directly below, where technical personnel might spend a substantial amount of time.
Personally, I think that the AM radiation hazards are overstated in this study, and
that the issue comes more from environmental circumstances by virtue of the fact that
many AM transmitter installations share the same area as other industrial concerns.
--
-----------------------------------------------------------------------------
If there's nothing that offends you in your community, then you know you're not
living in a free society.
Kim Campbell - ex-Canadian Prime Minister - 2004
-----------------------------------------------------------------------------
For direct replies, take out the contents between the hyphens. -Really!-

"Bob Haberkost" wrote
One of the issues with most FM arrays with gain is that, for many,
the spacing which results in the array having gain also results
in a fairly pronounced hot-spot directly above the antenna,
where few people would be expected to be, as well as
directly below...
_________________

This is true only when each element in the array has high relative field at
+/-90 degree elevation, and the elements are vertically spaced about one
wavelength apart. Shorter vertical spacings reduce such radiation from
these arrays. Using 1/2 wave spacing reduces it to a theoretical zero at
+/-90 degrees elevation (the zenith and nadir).

BUT, the great majority of FM broadcast transmit elements used today have
elevation patterns with very low relative field at +/90 degrees. An array
of such elements also has low relative field at +/-90 degrees -- even with
elements spaced at one wavelength intervals. IOW, no hot-spots above and
below the array.

Patterns of four element types in common use today, and an elevation pattern
for a 6-element, 1-wave-spaced array of one type are included in the PDF
slide show listed as Paper 10 at http://rfry.org.

RF

"Doug Smith W9WI" wrote
On the other hand, the FM signal is radiated from an antenna atop the
tower. Stand at the base of a 300' FM tower, and you're 300' from the
thing that radiates.

At an AM station, the entire tower radiates.
___________

Also - most FM broadcast transmit antennas are arrays of several elements in
a vertical stack to concentrate radiation in the horizontal plane. As a
result the radiation directed around the tower base is much lower than the
station's licensed power.

RF

Visit http://rfry.org for FM broadcast RF system papers.

"Richard Fry" wrote in message
...
___________

Also - most FM broadcast transmit antennas are arrays of several elements
in
a vertical stack to concentrate radiation in the horizontal plane. As a
result the radiation directed around the tower base is much lower than the
station's licensed power.

RF


Right, but often times there are a large number of people living in high
rise buildings near the FM antenna. It's conceivable there are more people
living in a high power FM radiation area than a high power AM radiation
area.

Frank Dresser

"Frank Dresser" wrote
... often times there are a large number of people
living in high rise buildings near the FM antenna. It's
conceivable there are more people living in a high power
FM radiation area than a high power AM radiation.
________________

Could happen in the odd case, but not usually. FM broadcast transmit
antennas located on building tops normally have radiation center heights
that easily clear the tops of nearby buildings. If they didn't, the
station's signal would be affected by shadowing (blockage) beyond the nearby
buildings, and have widespread multipath problems from reflections off the
building sides. Competitive issues make this situation unlikely.

RF

"Frank Dresser" wrote
... often times there are a large number of people
living in high rise buildings near the FM antenna. It's
conceivable there are more people living in a high power
FM radiation area than a high power AM radiation.
________________

Could happen in the odd case, but not usually. FM broadcast transmit
antennas located on building tops normally have radiation center heights
that easily clear the tops of nearby buildings. If they didn't, the
station's signal would be affected by shadowing (blockage) beyond the nearby
buildings, and have widespread multipath problems from reflections off the
building sides. Competitive issues make this situation unlikely.

RF

On the other hand, the FM signal is radiated from an antenna atop the
tower. Stand at the base of a 300' FM tower, and you're 300' from the
thing that radiates.

This is the same theory in which people claim using their cell phones are safe,
because the power they put out is so low.

They are powerful enough to transmit to cell towers miles away! Now put that
power inches from your head and how more concentrated is that power?

"Truth" wrote in message ...
On the other hand, the FM signal is radiated from an antenna atop the
tower. Stand at the base of a 300' FM tower, and you're 300' from the
thing that radiates.

This is the same theory in which people claim using their cell phones are
safe,
because the power they put out is so low.

They are powerful enough to transmit to cell towers miles away! Now
put that
power inches from your head and how more concentrated is that power?