"Sam Goldwasser" bravely wrote to "All" (12 Nov 04 16:04:32)
--- on the heady topic of " electron gun(s) and magnetic fields"

SG From: Sam Goldwasser

SG (Gary DeWitt) writes:

I have a 54" RCA rear projection. I had a new hardwood floor installed
with an electric heating grid underneath. The grid consists of heavy
screen mesh, similar to window screen but 2-3 times heavier wire, laid
in one continuous circuit back and forth across the room. There is a
high voltage, low amperage current running through it. Here's the
problem - when the heater is on, the guns in my tv misalign, looks
like 3-d image viewed without the correct glasses. Soon as I turn off
the heat, the tv returns to normal. How can I shield the tv from the
floor induced field? Faraday cage? (I don't really want to view thru
wire mesh!) Grounded sheet of steel under the set? Raise the set a
foot or two off the floor? Both? Any suggestions, particularly from
those who have solved this problem or engineers, would be greatly
appreciated!

SG A Faraday cage won't help. It's magnetic interference and magnetic
SG fields are difficult to block.

A magnetic field is impossible to block, however it can be readily
redirected. If the tv were completely enclosed in an iron box the
interfering AC field would flow around the tv and through the iron
instead. This may not be very practical however, after all the screen
needs to be seen to be of use. Perhaps a metal shelf could work but
this is often a cause of colour purity problems in itself.

There are other strategies, for example we all know magnetic field
intensity decreases as the square of the distance. Therefore raising
the tv away from the floor enough may be all that is needed. Perhaps
leaving a sheet of iron on the floor below the tv's stand would
further decrease the field even more in the vicinity of the tv.

Another idea would be to induce a small field under the tv with the
opposite phase in the hope that the second field would cancel the
first enough to allow the tv to operate properly. Maybe just a few
loops of wire wound under the base of the tv would be enough for the
same effect. Of course phasing the small cancellation field would be
trial and error or how for example it should be oriented.

However, as a side issue, one concern I might have would be of living
in a space with such a significant magnetic environment that it
noticably affects the tv. I've heard of people living over transformer
rooms having a myriad of problems from infertility on through to
childhood leukemia. Then again people have been using electric
blankets for ages and I don't think any co-relation has been shown
there. It's a concern I really don't feel qualified to comment about.

A*s*i*m*o*v

.... Inductor designers do it in the gap.