AMATEUR RADIO
BY GARRY CRATT, VK2YBX
Radiation hazards in amateur
radio -:-- some simple precautions
Concerned about the possible adverse health
effects of long-term exposure to RF energy? If you
operate amateur radio equipment, there are a
few simple precautions that you should follow.
Electromagnetic radiation is part of
every day life. For the most part, such
background radiation is of little or no
consequence to the general public. In
fact, energy resulting from RF radiation is deliberately used, under closely
controlled conditions, by members of
the medical profession to treat a variety of ailments. The heating effect of
exposure to RF on human tissue is
often used by physiotherapists to great
During World War II, considerable
concern was expressed over the
number of radar operators suffering
internal burns and cataracts. Such radar installations ran high levels of
power and safety precautions were
inferior by today's standards. Exposure to power densities of 1 OrnWI cm 2
was considered safe but today some
scientists believe that exposure to levels of just 1mW/cm2 can cause tern-
"Without conclusive evidence regarding
minimum safe exposure levels, it is certainly
good advice to keep as far away as possible
from strong electromagnetic fields."
advantage and the effects under such
conditions are well documented.
Most households operate a microwave oven, most have electric blankets, and most have TV and VDU
screens. The use of electric razors and
hairdryers is almost universal, so that
some exposure to electromagnetic
fields is unavoidable.
Amateur radio operators, and particularly those working in the electronic industry, also face frequent exposure to a variety of other types of
electromagnetic radiation and should
be aware of the possible hazards such
exposure presents.
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SILICON CHIP
porary ailments such as minor headaches.
The research studies necessary to
determine such "safety" levels can
last for many years but, even after
such lengthy periods, can be inconclusive, as the test subjects are normally animals which may be affected
in different ways to humans. Nevertheless, it is prudent to exercise caution when periods of exposure are
lengthy.
Without conclusive evidence regarding minimum safe exposure levels, it is certainly good advice to keep
as far away as possible from strong
electromagnetic fields, including
fields at low frequencies. Identifying
such fields may be difficult without
suitable instrumentation but there are
certain commonsense guidelines
which do apply.
It is considered unwise to operate a
hand-held UHF (in particular) transceiver over a long period of time in
close proximity to the face . A far more
sensible approach is to use a speaker
microphone, allowing the operator to
place the transceiver some distance
away. As the intensity of an electromagnetic field is inversely proportional to the distance squared, removing the source of radiation by a relatively small amount lowers the field
intensity dramatically.
Hand-held cellular phones may
pose a similar hazard, although the
field intensity is much lower than
from a typical amateur transceiver due
to the lower output power level (typically 400mW). A study in the US some
years ago identified the use of 5W
800MHz hand-held transceivers as a
definite hazard.
Similarly, it is hazardous to stand
in front of a high-gain antenna, such
as a multi-element Yagi, while it is
operational. The EIRP (effective isotropic radiated power) of such antennas can reach levels of several kilowatts. Phased arrays of multi-element
Yagis pose a very significant hazard.
Hence, antenna testing should be approached with caution.
Also, the human body absorbs more
energy at lower frequencies than at
higher frequencies and safety standards reflect this. Hence, there may
exist more significant hazards when
operating high powered HF equipment, compared to the relatively lower
that strong sources of electromagnetic radiation are located away from the operating area.
Antennas and transmitters should be located away
from the area where most
time is spent, and high voltage power supplies should
be located on the other side
of the room rather than under the operating desk. Linear amplifiers, particularly
those capable of operating
at high power levels, should
always be operated with the
RF shielding intact.
Minimum standards
powered VHF and UHF amateur
equipment in general use today. It
therefore makes good sense not to
stand close to an HF transmitting antenna when it is in use.
No doubt, those working in the
broadcast industry are particularly
aware of this point.
Mains fields
Numerous studies have been made
to determine if there is any link between exposure to 50Hz (mains) electromagnetic fields and various medical ailments, such as leukaemia and
cancerous tumours. Although none
has proven conclusively that such a
link exists, many have shown a higher
incidence of such problems in groups
of people having the same vocation.
According to the IEEE journal "Spectrum", twelve US studies to date have
all shown that an increased risk of
leukaemia exists when workers are
exposed to high field intensities of
60Hz. electromagnetic radiation for
long periods.
Due to the use of 240V domestic
power distribution in Australia, Australians would appear to be at less
risk than those in countries with 1 lOV
power distribution. The average field
intensities are lower in a 240V system
due to the lower currents involved.
Although it can be argued that such
problems are as yet unproven, it would
seem that action based on "prudent
avoidance" is the safest solution. This
may mean rearranging the "shack" so
There are standards set
in Australia which specifically spell out the maximum
safe exposure to RF and lowfrequency magnetic fields.
Australian Standard AS-2772, Part 1
& 2, precisely sets out the limits applying to handheld transceivers and
other RF sources, and the methods
used to measure these limits.
These specifications are based on
very carefully controlled scientific
research carried out by a number of
organisations within Australia.
Finally, the National Health and
Medical Research Council, based in
Canberra, has produced a paper entitled "Interim Guidelines On Limits of
Exposure to 50/60Hz Electric & Magnetic Fields (1989)". It details safe
field intensity levels for low-frequency
electromagnetic radiation. Both parts
of this paper are recommended reading for amateurs wishing to familiarise themselves with radiation hazards.
Further reading
(1). "IEEE Spectrum", August 1990.
(2). "Practical Wireless", May 1990.
(3). "Reference Data for Radio Engineers" - published by Howard Sams.
(4). "Australian Standard AS 2772".
Parts 1 & 2.
(5). "Interim Guidelines On Limits of
Exposure to 50/60Hz Electric & Magnetic Fields (1989)" - produced by
the National Health & Medical Research Council, Canberra.
Further information is also available from the NSW Environmental
Protection Authority, Radiation Control, PO Box 136, Regents Park, 2143,
or contact the environmental protection agency in your state
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JULY 1992
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