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Re: RF-exposure safety (was: microwave absorption)



The USA is actually ahead of Aus in this - the ACA (equiv of FCC) has just
released the guidelines for the proposed exposure limits and they are soon
to become law.

In any well designed amateur station the limits should not pose a problem as
I interpret them, I have also had to evaluate all of our sites (digital
radio trunked system) for work to ensure that they also comply with the
limits where they are located on public buildings.

There weren't any problems there unless you walked up to the antenna on the
top of the roof - have had to erect safety exposure warning signs etc

Rex


----- Original Message -----
From: "Estes Wayne-W10191" <W10191@motorola.com>
To: "Rex's mail" <perisonr@dingoblue.net.au>; <amsat-bb@AMSAT.Org>
Sent: 23 January 2001 08:38
Subject: RF-exposure safety (was: microwave absorption)


> Rex VK8RH wrote:
>
> And twenty years ago cigarettes didn't cause cancer - we know where that
> stands now.
>
> I think caution is warranted until the facts are proven - and they are a
> long way from that.
>
> We as amateurs, some running high power should also be careful with
exposure
> limits not only from antenna's but from the equipment within the shack.
(eg
> a 1000 watt plus amplifier on 400Mhz not properly shielded)
>
>
> Wayne W9AE replies:
>
> The U.S. does have RF exposure safety regulations for amateur stations.  I
imagine that Australia does, too, considering that the Australian government
is a world leader in RF safety regulations.  U.S. Amateur operators are
required to keep their stations safe for themselves and others, within the
guidelines specified by the FCC.  That is, the antennas must be located in a
manner that humans can't accidentally get in the path of the RF energy
within a certain safe distance (determined by the frequency and ERP).  For
instance, it's not legal to run a kilowatt into a 15 dB-gain Yagi aimed
directly at your neighbor's house 20 feet away.  There are many links to
more information on this subject on the ARRL WWW site (regulations,
articles, RF-exposure calculator programs, etc.)
>
> http://www.arrl.org/tis/info/rfexpose.html
<http://www.arrl.org/tis/info/rfexpose.html>
>
> Here are "Some Sensible Guidelines" from the ARRL safety committee:
>
> 1.      Although antennas on towers (well away from people) pose no
exposure problem, make certain that the RF radiation is confined to the
antennas' radiating elements themselves. Provide a single, good station
ground (earth), and eliminate radiation from transmission lines. Use good
coaxial cable, not open-wire lines or end-fed antennas that come directly
into the transmitter area.
>
> 2.      No person should ever be near any transmitting antenna while it is
in use. This is especially true for mobile or ground-mounted vertical
antennas. Avoid transmitting with more than 25 W in a VHF mobile
installation unless it is possible to first measure the RF fields inside the
vehicle. At the 1-kW level, both HF and VHF directional antennas should be
at least 35 ft above inhabited areas. Avoid using indoor and attic-mounted
antennas if at all possible.
>
> 3.      Don't operate high-power amplifiers with the covers removed,
especially at VHF/UHF.
>
> 4.      In the UHF/SHF region, never look into the open end of an
activated length of waveguide or point it toward anyone. Never point a
high-gain, narrow-bandwidth antenna (a paraboloid, for instance) toward
people. Use caution in aiming an EME (moonbounce) array toward the horizon;
EME arrays may deliver an effective radiated power of 250,000 W or more.
>
> 5.      With hand-held transceivers, keep the antenna away from your head
and use the lowest power possible to maintain communications. Use a separate
microphone and hold the rig as far away from you as possible.
>
> 6.      Don't work on antennas that have RF power applied.
>
> 7.      Don't stand or sit close to a power supply or linear amplifier
when the ac power is turned on. Stay at least 24 inches away from power
transformers, electrical fans and other sources of high-level 60-Hz magnetic
fields.
>
> Wayne Estes W9AE
> Mundelein, IL, USA
>

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