"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?

"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!

and that proves? ... nothing


Now put that
power inches from your head and how more concentrated is that power?



why not look it up?

you will find that a 5 watt transmitter operating on 450 MHz with a 1/4 wave
antenna might produce enough heating to damage the cornea of the eye IF the
tip is placed within one CM of the eye.

On 18 Aug 2004 21:25:13 GMT, "Frank Dresser"
wrote:


"lsmyer" wrote in message
...
This is a link to an article investigating leukemia rates in areas near AM
transmitters.

http://www.wired.com/news/medtech/0,1286,64579,00.html

I don't doubt that high levels of RF can be dangerous. The first two chief
engineers I worked with both died of cancer in their 50s.

Maybe they got cancer from some other cause (both smoked), but I still
feel
like I'm inside a microwave oven anytime I'm around an AM transmitter
site.




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.

Anyway, there's been over 80 years of kW+ levels of AM broadcasting, and it
seems strange this leukemia concern has gone unnoticed until now.

Frank Dresser

It is another one of these cases where there may indeed be a link, but
there is no assurance at all that the link is causative. For example
you can find a link between smoking and cirrosis of the liver. Many
smokers are also significant drinkers. It wasn't the smoking that
caused the problem, but the smoking and other behaviours that are
causative are often seen together. I.E. most high power AM
transmitters are in major cities, and there are significant other
hazards from things like air pollution that exist independent of the
AM broadcast facilities.

As far as those working around the equipment, I'd be more interested
in the potential X-ray exposure. The voltages used in high power
transmitter tubes produce significant X-ray hazards, and these weren't
recognized for a long time.

It is another one of these cases where there may indeed be a link, but
there is no assurance at all that the link is causative. For example
you can find a link between smoking and cirrosis of the liver. Many
smokers are also significant drinkers. It wasn't the smoking that
caused the problem, but the smoking and other behaviours that are
causative are often seen together. I.E. most high power AM
transmitters are in major cities, and there are significant other
hazards from things like air pollution that exist independent of the
AM broadcast facilities.

Therefore, smoke as many cigarettes as you want to, and if you get lung cancer,
just blame it on the air pollution.

Perhaps when I walk into a fire, the blistering burns all over my skin are caused
from the chemicals in the sun tan lotion I used the day before.

Voting for Nader or Badnarik is somehow taking a vote away from Kerry, but no one
ever suggests Bush and Kerry drop out of the race because they are taking votes
away from the other two. Ridiculous.

The RF energy could conceivably have an effect on cell membranes and the
potentials that develop across cell membranes. Perhaps some cells are more
sensitive to such changes in membrane potentials and lead to higher incidences
of certain diseases which in this case is leukemia.

As for not noticing the correlation for over 80 years that isn't so unusual. It
really is contingent on many factors including the increase in the number of
stations over the years, the increase in power over the years, the proximity of
the population to RF over the years (ie. the shift from a rural to an urban
population), the extent of the exposure, lifestyle and dietary changes and so on
and so on. It such a case it may take quite awhile to isolate a potential
causative agent and even then it wouldn't be overwhelmingly conclusive proof.
Too many variables to take into account.

Regards

John Barnard

Frank Dresser wrote:

"lsmyer" wrote in message
...
This is a link to an article investigating leukemia rates in areas near AM
transmitters.

http://www.wired.com/news/medtech/0,1286,64579,00.html

I don't doubt that high levels of RF can be dangerous. The first two chief
engineers I worked with both died of cancer in their 50s.

Maybe they got cancer from some other cause (both smoked), but I still
feel
like I'm inside a microwave oven anytime I'm around an AM transmitter
site.




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.

Anyway, there's been over 80 years of kW+ levels of AM broadcasting, and it
seems strange this leukemia concern has gone unnoticed until now.

Frank Dresser