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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. 72 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 SC MASSIVE TEST EQUIPMENT SALE The following equipment is surplus to requirements and is now offered for sale. Most prices are negotiable. SIEMENS LEVEL TRACER K2202 digital storage, new $500.00 HEWLETT PACKARD HP 8064A realtime audio spectrum analyser. 50Hz-1 0kHz. As new condition $2000.00. AWA TEST OSCILLATOR G250-2 10Hz-61 0kHz $200.00 RACAL DANA 9008 automatic modulation meter, 1GHz, as new $600.00 HEWLETT PACKARD HP 141 T spectrum analyser (8554B + 8552B) $5700.00 ** HEWLETT PACKARD 1640B serial data analyser, new $1800.00 HEWLETT PACKARD HP432A power meter with cable & HP47BA thermistor mount power head $750.00 AWA MTS-A220 audio test set 100Hz-650kHz, nicads incl $250.00 Other items available, too many to list. See our advert on page 34 of the June 1992 issue of SILICON CHIP. We also buy used equipment, even if not operational. Turn your surplus equipment into cash. Please call write or fax: AV-COMM PTY LTD PO BOX 225 BALGOWLAH 2093 Tel: (02) 949 7417 Fax: (02) 949 7095 **Delivery within 30 days of order JULY 1992 73