# Safety precautions in the amateur station

## RF and microwave hazards

A great deal of research has been done on the effects of exposure to radio frequencies. It is generally agreed by Western scientists that the only biologically significant property of RF energy is heating; and that this is only a hazard if the heat is not removed quickly by the body's temperature regulating mechanisms. This is the principle of the microwave oven and medical diathermy. RF radiation is therefore totally different in its properties to ionising radiations such as gamma rays and X-rays. The maximum continuous exposure to RF was set at a power density of 10mW/cm2 over 30 years ago. This level is still accepted in the UK and the Western world. It has been suggested in Russia and some Eastern countries that there are effects other than thermal ones and that the maximum power density should be 10µW/cm2. Evidence of this is regarded with suspicion in the West.

Close proximity to a source of RF energy must therefore be avoided. Measurements of power density made in the vicinity of various 300-400W output amateur stations operating on 28MHz and 144MHz and their antennas have given values of less than 1mW/cm2. Calculation shows that standing 20cm from a vertical λ/4 antenna fed with 140W at 28MHz is equivalent to being in a 10mW/cm2 field. This is not, however, a normal situation to be in!

Microwave radiation is not itself more hazardous, but the smaller area over which microwaves are likely to radiate results in a greater power density. Any exposure to RF which results in a sensation of heat is far in excess of 10mW/cm2 and is therefore very dangerous. The eyes are particularly susceptible to damage in this way.

### Situations to be avoided

1. Do not look down a wave-guide unless you know that there is no RF at the other end.
2. Do not work on high-power RF equipment with the covers off. (There is probably high voltage present as well!)
3. Do not use an unscreened dummy load or a small antenna in the shack for test purposes.
4. Do not adjust antennas using full power; use low power only.
5. Do not use a hand-held set without a thick insulating cap on the end of the antenna.
6. Hold a hand-held set so that the antenna is as far as possible from the face.

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