[AT] Garden tractor???/Now RF hazard

[Ken Knierim]

On Tue, Jan 26, 2010 at 5:28 AM, charliehill <charliehill at embarqmail.com>wrote:

> He's certainly doing something he shouldn't unless he's staying clear of
> the
> area while the wood is cooking.
>
> I've got a question for those that might know.  I used to mow the guy wire
> lanes for some transmission towers for a local broadcast company.  There
> were three towers.  One was a 100,000 Watt FM and the other two were 50,000
> watt.   The two smaller ones had a chain link fence around the base of the
> tower and the transmitter building with warning signs about RF danger and I
> never went inside them.   The area was covered in rock and there was no
> need
> to mow.  The big 100,000 watt station had a larger chain link and a much
> larger transmitter building.  On that one I mowed inside and right up
> within
> 4 feet of the base of the transmitter.   I've always wondered how much RF
> load I was getting and how much danger I was in while I was right around
> the
> base of that tower.   Anyone got thoughts on that?
>
>
Charlie,
    A couple thoughts come to mind. From the description you're dealing with
one FM tower and possibly a couple possibly AM towers. The FM tower would
have a higher frequency and may have the elements mounted up the tower a lot
further. FM does not require such large elements for the same antenna;
frequency and wavelength are inverse numbers. So it's quite possible that
the radiating element was actually mounted way up the tower to get a better
"line of sight" picture.
   AM is lower frequency and you need a lot larger element to do the same
job. A lot of AM antennae use a ground plane and a "hot" element which comes
down next to the ground (I think it's a pretty standard dipole
configuration). You would actually have a live radiating element closer to
you with that configuration than the FM element up in the air a ways.

The only way to be able to really tell how much power you were absorbing
would be to get a field strength meter since near field antenna theory is
such a black art (OK, not an art but the math is way past what I know and
most of the RF folks I know feel the same).

Another thing about it.. different frequencies absorb and/or penetrate your
body differently. I'm sure there is a chart for this along with an
"acceptable" level for the various bands. Certain bands are absorbed readily
(like the water absorption band at 2.2-2.4 Ghz used for microwave ovens)
while others are not easily absorbed. I believe that in 1965 the government
noted that even minute levels of microwave radiation changes the chemical
composition in the human brain but it never affected me in all the years
I've been (twitch) at it (twitch twitch).

I'm not one for the tinfoil hats but I'm sure there are those too. Maybe I
SHOULD have though... some of the stuff I play with has some real watts to
it. :)

Ken in AZ