*** RF Radiation from Radios ***

Date: Fri, 28 Nov 1997 22:05:48 -0800
From: mlynch@impulse.net (Mike Lynch)
To: sar-l@islandnet.com
Subject: RF Radiation Limits

A recent thread on the SAR-Dogs e-mail list has been handheld radio use and
speaker/mics. One of the thread participants requested that I provide them
with information on RF radiation limits. Some members of this list may also
be interested in the recommended RF radiation limits. (My apology to
SAR-Dog list members for the duplicate post.)

Most of the studies have been done on whole body heating and the
recommendations are based on whole body heating effects (and date back to
about 1990). Recent studies have indicated that the head and eyes are more
sensative to RF radiation than the whole body studies indicate. There is
also a  concern of radiation damage to the lens of the eye, which does not
have blood vessels or nerves and, therefore, can not repair damaged tissue
or feel pain.

The National Council for Radiation Protection and Measurement (NCRPM - a
U.S. FCC/EPA group) has recommended a limit of 0.2 mW/(square cm) for RF
radiation in the 30 to 300 MHz range. 
The standards setting organization ANSI also recommends a limit of 0.2
mW/(square cm), but their studies only involved transmission power down to
7 watts (draw your own conclusions about 5 watts).

For a typical transmitting scenario of a five watt transmission with 50%
radiating efficiency perpendicular to a six inch rubber duck antenna held
three inches from the eyes, the power density is 3.34 mw/(square cm)
- about 16 times the upper limit recommended by the NCRPM and ANSI.

These studies have prompted the amateur radio group ARRL to commission a
Biological Effects Committee which established guidelines for safe radio
use. This group developed the ARRL's RF Awareness Guidelines, which, in
part, states:  

 "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."

Studies indicate a long term health risk in the use of hand held antennas
transmitting in close proximity to the face. There is also a correlation
between the frequency of occurance of such transmitting situations and the
associated health risks.
The use of a speaker/mic with a handheld would reduce the health risks
discussed above. The only situation that I can think of where a
speaker/mic should not be used with a handheld would be in a
swiftwater/flood rescue when the radio is in a sealed bag to prevent it
from drowning if it and the user go for a swim.
The intention of this post is to provide communications safety information.
The issue of using speaker/mics with handhelds generated a heated
discussion on the SAR-Dogs list, which, hopefully, will not be duplicated
on this list. 

Mike Lynch, mlynch@impulse.net

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