I guess I can take a shot at this. I worked as an engineer for PCS
companies for 8 years doing system design. As the lead engineer of
many markets I did RF strength calculations on hundreds and hundreds of
cell sites. I can tell you that if the site antennas are 65 feet or
more off the ground the RF exposure directly under the antennas is
typically less than 1% of the FCC limits for long term RF exposure. The
same RF exposure rules apply to amateur operations as well although
there are slightly different limits based on frequency. If you are
even 1/10 of a mile from cell site you will receive thousands of times
less exposure to RF field strength than you would get using your own
cellular or cordless telephone in your own home. Without running the
calculations I would expect more than 10,000 times less signal from the
cell site at a half mile than the exposure from your own cordless
phone. The worry is not even a reasonable consideration. The 1 over R
square rule really gets huge at those distances. A few times I had the
expensive test equipment to measure the actual field strength from a PCS
system and the only place I could get a signal to exceed the limits for
long term exposure was typically less than a foot from the antenna
directly in the beam pattern with the transmitter running at maximum
output.. No.... that equipment to make those measurements is not cheap
or simple to do. I also was able to exceed the limit with my mobile
ham antenna on my car running 100 watts on HF but only inches from the
antenna, even a few feet from the antenna was safe.
There are quite a few documents out there that show that in a typical
city the RF field strength in your neighborhood from all other RF souces
such as pager, broadcast, two-way, police services, TV etc..all add up
to hundreds to thousands of times more RF already than a cell site would
ever contribuite to a neighborhood even if you lived right next door to
it. I used to tell people that suppose 100 cars per hour drive down
your street.....if a cell site is added it might add one more car per
DAY to the traffic already present in the neighborhood.
In short, a cell site 1/2 mile away is not even worth the effort to be
concerned about it. Still there are people out there who hate cell
towers just like ham towers and they like to bring up the RF radiation
issue to generate anti tower support, even though simple physics shows
that there is clearly little additional exposure in our communities due
to the addition of cell sites that blanket our communities.
The cell/PCS systems are the ultimate in QRP application of radio and
using the minimum power levels to accomplish the communication goals at
every instant.. The systems all must work on the minumum power for
each call to be served and there are elaborate software schemes that do
closed loop power control to ensure that the minimum power is used at
every instant on every call to maintain your phone call. You can see
simple evidence of this when you compare the battery life of the old
analog cell phones to the new digital cellular or PCS phone. If your
new small PCS/Cellular phone ever roams on an old analog network you
find out quickly about the closed loop power control systems (or lack
of). Analog cellular is quickly on it's way out and all the new
systems are safer and more reliable than ever.
-Dave WD7Z
lcomden@comcast.net wrote:
>Can any one on TT answer Todd's questions?
>
>73
>
>Larry K3VX
>
>
>---------------------- Forwarded Message: ---------------------
>From: Todd Wade <twadepgh@yahoo.com>
>To: n3sh@yahoogroups.com
>Subject: [N3SH] Cell tower questions
>Date: Wed, 10 Aug 2005 17:29:49 +0000
>
>I have a co-worker who is considering a move to a new
>home. The house he's looking at is within a 1/2 mile
>of a cell tower that is approx. 75-100 ft. His wife
>is raising concerns over RF exposure.
>
>Since I'm no expert in microwave (or any other RF
>subject for that matter!), I told him that I would ask
>a few questions of the group.
>
>1. What sort of exposure would someone have at that
>distance? What are typical power numbers from cell
>sites? Would there really be any significant RF at
>the house's location?
>
>2. Is there some kind of cheap way that they could
>take field strength readings around the house that
>would give them a feel for their exposure? I realize
>that some kind of receiver would work, but they want a
>simple scheme, be it something they borrow or buy, or
>be it from someone doing the survey using their own
>equipment.
>
>Thanks for any help. He wants to put his wife's
>worries to rest fairly soon.
>
>Thanks,
>
>Todd - W8LEV
>
>
>------------------------ Yahoo! Groups Sponsor --------------------~-->
><font face=arial size=-1><a
>href="http://us.ard.yahoo.com/SIG=12hbjsm1a/M=364397.6958316.7892810.4764722/D=g
>roups/S=1705063108:TM/Y=YAHOO/EXP=1123702123/A=2915264/R=0/SIG=11t7isiiv/*http:/
>/us.rd.yahoo.com/evt=34443/*http://www.yahoo.com/r/hs";>Get fast access to your
>favorite Yahoo! Groups. Make Yahoo! your home page</a></font>
>--------------------------------------------------------------------~->
>
>This is the club email reflector for the Wireless Association of South Hills,
>Inc. N3SH / WA3SH / NP2SH/B, located in Pittsburgh, PA
>Yahoo! Groups Links
>
><*> To visit your group on the web, go to:
> http://groups.yahoo.com/group/n3sh/
>
><*> To unsubscribe from this group, send an email to:
> n3sh-unsubscribe@yahoogroups.com
>
><*> Your use of Yahoo! Groups is subject to:
> http://docs.yahoo.com/info/terms/
>
>
>
>_______________________________________________
>
>See: http://www.mscomputer.com for "Self Supporting Towers", "Wireless
>Weather Stations", and lot's more. Call Toll Free, 1-800-333-9041 with any
>questions and ask for Sherman, W2FLA.
>
>_______________________________________________
>TowerTalk mailing list
>TowerTalk@contesting.com
>http://lists.contesting.com/mailman/listinfo/towertalk
>
>
>
>
_______________________________________________
See: http://www.mscomputer.com for "Self Supporting Towers", "Wireless Weather
Stations", and lot's more. Call Toll Free, 1-800-333-9041 with any questions
and ask for Sherman, W2FLA.
_______________________________________________
TowerTalk mailing list
TowerTalk@contesting.com
http://lists.contesting.com/mailman/listinfo/towertalk
|