On 02/21/2016 09:47 PM, Justin Bennett wrote:
The solution used in tunnels, caves, mines etc. is to use a
radiating cable instead of a normal antenna. This is a coax
cable that is designed to 'leak' part of the energy that
passes through it, usually by having some holes in the
shield (a standard coax won't work).
yes, that’s what I meant. There was for a long time a sound art piece
on the Afsluitdijk in the Netherlands by Moniek Toebosch that used
a leaky coax cable all along the dijk. Drivers could tune into the frequency
and listen to Angels.
very local and linear coverage!
thanks for pointing this out. i had heard about this technique before,
but i was assuming that it works because the cable is like a line
radiator and it's straight.
i'm no radio guy, so i'm applying acoustic principles here and may be
totally wrong, but my reasoning is that at uhf, say 600 MHz, you end up
with a wavelength of about half a meter. that means the distance between
the leaks would have to be small compared to that. fine. should give you
a uniform cylindrical field. but what if you follow a u-shaped or zig
zag path because that's what the building is like, with a distance
between the legs of the u that are a lot longer than the wavelength?
i would expect pretty fancy interference patters with loads of complete
nulls all over the place. or is there some sort of near-field effect
that makes the effect of parallel lengths of wire negligible?
--
Jörn Nettingsmeier
Lortzingstr. 11, 45128 Essen, Tel. +49 177 7937487
Meister für Veranstaltungstechnik (Bühne/Studio)
Tonmeister VDT
http://stackingdwarves.net
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