From: Paul
Date: Wed, 20 Dec 2000 23:45:36 +0000
Subject: Re: [TSSP] Measurement Techniques
Metlicka Marc wrote: > as per your guidelines for areas and setups, i would like to > say that i have an upstairs bedroom that measures 18' by 16' > with a seven foot ceiling. > 1. it has rock lathe and chicken wire plaster coated walls, > will this be a problem? The chicken wire sounds like a plus to me - ready made Faraday cage? > 2. as a ground plane, it has a linoleum flooring but i have > several 4' by 8' sheets of sheet steel that i can cover it > with. The ground plane doesn't have to be thick. Foil will do quite ok and it means you can easily put in slits, radiating out from the center beneath the coil, so that you end with a circle of foil segments, joined only in the center where the incoming feed coax screen also connects. The splits in the ground plane are intended to minimise the size of eddy current loops induced in the foil by the B field of the secondary. Marco Denicolai operates Thor over a steel floor and his coil inductance shows strong evidence of the influency of eddy currents. Lay out the foil and maybe cover with a poly sheet to keep it all together. Ideally extend the foil out for a couple of coil heights away from the base. You'll need something in the center to support the coil a little above the foil, say 2 or 3 inches. > if i dedicate a ground connection through the wall and to a few > ground rods, will this be a good ground plane? It's probably a good idea simply to nominate the screen of the feed coax as the single path to earth from the ground plane. No need for ground rods or anything like that. The coax screen earths through the instrument ground. > the good news is that it only caries two duplex outlets in it, > both of these can be disconnected for a no grid frequency > interference. No need to disconnect them, the 60Hz won't interfere with any measurements I can think of. You'll need the outlets and more! > it also has a doorway into a sub closet that could be used as > a control room for the test equipment. > all setups can be left in place for as long as needed. > if this room sounds good to all, i will begin cleaning it out > and getting ready, this may take a little time but i will work > as steady as possible. Well, before rearranging the house, why not try the base drive from the sig gen in your regular shop and pick out the resonant frequencies. You'll soon get a feel for how far away things need to be. An assistant is useful - a mobile E-field target, see how close in you can move a person before the Fres changes by one percent - say. We can see from your web page http://www.fortunecity.com/meltingpot/syria/1210/id19.htm that you have an interesting room to work in. You might find an adequate spot in there - it doesn't have to be perfect, the important thing is the repeatability. Cheers, -- Paul Nicholson, Manchester, UK. --
Maintainer Paul Nicholson, paul@abelian.demon.co.uk.