[Premium-Rx] Farady Shielded Room

[Michael O'Beirne]

    A propos the many solutions, I suggest a different approach.  Many armies have mobile radio stations or command posts, comprising a truck chassis onto which is fitted a communications shelter.  
    These shelters have a high degree of EMC protection with appropriate filters for the incoming power supply, internal air conditioning (often with nuclear/biological/chemical filters), internal power distribution and suppressed lighting, and if you get the right shelter, it will have aerial bases on the roof with feeds through to the room below.  Some also have N type coax connectors on a panel on the side and internal coax switching.  There are fixing points on the walls and floor for bolting down cabinets, tables etc.  Mine often carried a small fridge as well for the beers, wine and fois gras, essential items on a long exercise, and the Bollinger if we were feeling extravagent.
    We Brits use these a lot fitted to a Bedford 4 tonne chassis.  The size is 16 feet long x 8 feet wide and about 6.5 feet high and can be reasonably comfortable, virtually an office in the field.  Brand new these shelters cost a fortune but often they can be picked up at fairly affordable prices at the government surplus auctions or from the surplus dealers, and would make an excellent instant radio shack.  The hassle is transporting them home, usually involving a crane.  
    I would guess that similar shelters could be obtained in many other countries.
    However, if local computer gunge and/or TV timebase QRM are the problem it would be vastly cheaper to use a decent balanced loop aerial.  The Welbrooke Loop for example (about £140 in UK) is far better at suppressing local computer QRM than an active whip or dipole such as the Datong AD370. It works on the magnetic component of the wave which is far less affected by such QRM. It can be easily rotated to give a 30dB null, which could be useful in some conditions.  I use one inside the shack fitted to an old B&O record turntable.  If anyone is interested I can dig out the comparative tests done by John Wilson for Short Wave Magazine a few years ago.  John is an EMC expert and was mightily impressed with this loop.
73s
Michael
G8MOB
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