[Gllug] Lightning - was Evolution won't fetch my mail (Help)

[Chris Bell]

On Sat 10 Aug, Mark Preston wrote:
> 

> 
>    Surprisingly, the way that people die in a lightning strike is not a 
> result of severe burns, as most people think, but because the electrical 
> force shocks the heart into cardiac arrest and cuts off breathing by 
> paralyzing the chest muscles.
> 
   There are different problems with very high power radio frequencies,
which are much more difficult to contain. BBC external services (World
Service) transmitters have to be retuned every few minutes and re-directed
to another part of the world. The old valve transmitters used to be switched
off while tuning components were wheeled around on mini railway tracks, and
someone had to cycle out to transfer the aerial feeders to different aerial
arrays. The aerials covered a vast area of fields, so it was not unusual to
get lost in the dark or fog, or fall into a stream on the way.
   The standard method of deciding when to move the feeder was to move an
earthed pole near enough to the feeder to draw an arc, and wait for the arc
to go out. You then had a short time to move the feeder and get clear before
it was switched back on. There was so much RF power around that everything
started arcing in fog or rain, and you could even hear a mix of all the
programmes being transmitted coming from the trees, the cattle, and anything
else. One light weight aerial insulator system made of plastic was tested,
but surface arcing set fire to the insulators as soon as they got damp.
   All the windows in the transmitter building were opened by cranked
winders, and each one was labelled with the transmitter frequencies which
would cause RF burns if you went near it.
   They now have aerial routing relays, so you just need to push a button.
It is nominally non-ionising radiation, so is only supposed to be a hazard
through its heating effect, and I have not heard of anyone suffering
anything else. Even microwave ovens use similar technology, except that they
are tuned to the resonant frequency of water molecules. The only arguments
seem to be about any possibility of microscopic spot ionisation, creating
short lived but possibly hazardous free radicals.

-- 
Chris Bell


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