Re: Faraday Cage

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Harold Weiss by way of Terry Fritz <twftesla-at-qwest-dot-net>" <hweiss-at-new.rr-dot-com>

 > >I forgot about the floor, but I have enough chicken wire
 > >T/G 3/4" plywood to put a floor in.  The concrete floor
 > >does have reinforcing mesh in it though.
 >          Irrelevant, since it can't be tied to the cage wall.

I did not originaly think of the floor, due to the effects of a spark cage I
built to protect myself when I first started coiling.  The cage fit over the
top half of the coil. Flourescent and neon lamps would only come to light at
a 45 degree outward angle from the bottom of the cage.  At 2 1/2" to the
mesh and 6" to the water table, I didn't think it would be a problem for
this cage.  Tying it into the water table is the main reason for the ground
rod.

 > >I chose to use a separate ground rod for the cage,
 >
 >          Can't hurt, but irrelevant.
 >
 > >(too many weird things happen on power ground) power ground
 > >  will only run up to the variac in my controller and from
 > >that point everything else is on RF ground.
 >
 >          The RF ground is the inside of the cage.
 >          (this is not negotiable....)

The only things running thru the hole are power leads from the filter after
the variac.  Xfmrs, SRSGs, and RF ground is on the coil.

 >          IF the wire to the external ground pipe is
 >          tied to the cage wall, well tied, then it
 >          does no harm.

It will be soldered to the copper cage supports at 3 points. All wall frames
will have jumpers soldered to them in three points.

 >          If the wire to the external ground pipe is
 >          run 'through' (insulated) from the cage wall,
 >          then the cage is useless, pointless and
 >          defeated.  (except as a sparks box).
 >          Been There, Done That.
 >          This is physics, not subject to negotiation.
 >
 > >I don't think the cable passthru will be much of a
 >
 > >problem
 >
 >          It Will.
 >          Period.
 >          Been there, Done That.
 >          Any Insulated, Unshielded, Unfiltered Conductor
 >          Going Thru Will Carry Stuff Out.
 >          (Any given installation may luck out.  Or
 >          May not.)
 >
 > >as the controller will be sitting only 1" away from the
 > >cage with the connectors protruding into the hole.
 >
 >          Must be a metallic, bonded, filtered join.
 >          The RF wavelengths of the power sparks are long
 >          they may be contained:
 >          There is SUBSTANTIAL energy All Over The Place,
 >          including VHF.  This WILL ride out on the any
 >          unfiltered, insulated lines.
 >          Been there, Done that.
 >
 >          (it was 'work'.  We had a spectrum analyzer & could
 >          'see'.)
 >
 > >The variac output and SRSG outputs will both be filtered.
 >
 >          THAT's Better.  Filter MUST be 'in' the cage wall
 >          (to work well).  Old EMI Engineer taught me this:
 >          Picture the rf trash as flowing down the wire.
 >          It comes to a 'wall'.  Unless the filter is bonded
 >          IN the wall, the trash radiates AROUND the filter.
 >          (He learnt his trade controlling SCRs on 3kvdc,
 >          3000 amp Railway circuits...  WE weren't working up
 >          there, but he had.)
 >
 > --
 >          best
 >          dwp

Looks like I'll have to add another set of filters at the passthru.  A
little sheet copper work in order to keep the then filtered lines from
getting recontaminated.  It will also be a good place to tie the coils RF
ground cable.

David E Weiss