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RE: Shorted turns, primary proximity - Add a sheild???

Subject:  RE: Shorted turns, primary proximity - Add a sheild???
  Date:   Sat, 10 May 97 06:43:32 UT
  From:   "William Noble" <William_B_Noble-at-msn-dot-com>
    To:   "Tesla List" <tesla-at-pupman-dot-com>


now this got me thinking, probably incorrectly, along the following
lines:
if I have a quarter wave AM antenna at some high frequency, and I want
to 
elevate it above the ground, I put a little star burst like assembly on
the 
mast at the quarter wave point to provide a mini ground plane.  It would
seem 
to me that the tesla secondary would very much like to have a nice sheet
of 
metal right at it's base to make a nice close ground plane.  Yet that
same 
thing would also look like a shorted turn to the primary, right.  Well, 
perhaps, unless you put a cut half way through it, like the ASCII art
below
note use courrier font so it looks ok if your reader uses a proportional
font:


|--------------------------------|
|                                |
|               O ---------------|  cut here, O is sec coil  
|                                | 
|                                |
|--------------------------------|

Now, if you were to do this (put a properly cut piece of metal under the
coil) 
you wouldn't have a shorted turn "on axis", but there is still plenty of
metal 
"off axis" that could act as a shorted turn.  On the other hand, the
thing 
will shield anything below it pretty well, and it will act as a E field 
reflector as well.  An interesting question of course is what would
happen if 
it were iron/steel versus aluminum because it would increase the primary 
inductance.

Someone has probably already tried this and can say what the truth is,
but 
it's intersting thinking

-----Original Message-----
From:   Tesla List 
Sent:   Friday, May 09, 1997 9:46 PM
To:     tesla-at-poodle.pupman-dot-com
Subject:        Shorted turns, primary proximity

Subject: Shorted turns, primary proximity
  Date:  Fri, 9 May 97 09:31:53 EDT
  From:  Gary Lau 09-May-1997 0916 <lau-at-hdecad.ENET.dec-dot-com>
    To:  tesla-at-pupman-dot-com
    CC:  lau-at-hdecad.ENET.dec-dot-com


The recent discussion about metallic toroid supports acting as a
shorted turn got me to thinking about the other end.  While the
toroid may be far enough away from the primary so as to have no
real shorted turn effects, there is potentially a lot of stuff
below the primary that may be affected - caps, gaps, motors,
fans, and big metal transformer cases.  I'm still in the earliest
stages of building my first coil and was hoping to make the
primary and stuff below it as compact as possible, for the sake
of esthetics and ease of storage.  Now I'm wondering if
compactness will work against me in creating eddy currents.

I do realize that all of the tank wiring must be viewed as
extensions of the primary.  Do people typically mount this stuff
just below the primary, or is there some deliberate distance
kept?

Gary Lau
Waltham, MA