Re: ferrites on lines?

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

Original poster: Harvey Norris <harvich-at-yahoo-dot-com> 


--- Tesla list <tesla-at-pupman-dot-com> wrote:
 > Original poster: "Shaun Epp" <scepp-at-mts-dot-net>
 >
 > I just aquired some ferrite beads.  They are 1 1/8
 > inch long x 1 inch OD x
 > 1/2 inch ID.  I was thinking of putting them on the
 > hv wires between the NST
 > and the Terry filter.
  I'm at a total loss here to understand what these
ferrite beads are, or what is going on? Just looked at
Terry's pic of the rotary gap, and I couldnt identify
where these were, or how they are applied. Is the idea
just to surround the ferrite pieces with turns of the
arc gap supply wire connections?
    I have many cylinders of unmagnetised ceramic 8
SrFe. These however are a hard ferrite that can be
magnetised, or it is a magnetic grade ferrite, and
inclusion in the core of an air core coil only doubles
its inductance at best.
     I am told that soft ferrites are used for cores
that have a high magnetic permeability. Is it these
soft ferrites with windings made across cylindrical
pieces that would be suitable as rf chokes? Are rf
chokes a must option for the TC coiler, and where
would they go schematically???
     I am also wondering whether the ceramic 8
cylinders would be useful as rf choke cores? When
reading about ferrite, I saw that it was classified as
a semiconductor? But it does have a totally nonlinear
effect as far as its resistivity compared to the
impressed voltage, where demonstration from DC
rectified 3 phase AC from alternator resonant
components can show 8000 ohms across a 3/8 inch block
at the start of a Ohms law trial to ascertain the
pieces DC resistance. Increasing the voltage to about
160 volts will show that the piece then readily looses
resistance, until a corner of the piece is glowing red
hot, and the ohms law measurement at finish shows that
it has gone from 8000 ohms to only 8 ohms! (The
outside AC resonant alternator components regulate the
input voltage down according to the resistance of the
load, so that typically we may end up with 24 volts
passing 3 amps through the ferrite, or an 8 ohm value
by ohms law.) I have also noted that this magnetic
grade ferrite subjected to AC electrical currents
emits rf, so I am surmising here that the heating is
do to some kind of self induced induction heating
effect, even though this particular end process is DC.
    But back to the question here, would the magnetic
grade ferrite be useful for rf choke application? We
can hypothesize that it may also act nonlinearly if it
sees a high frequency vibration, one that we are
trying to isolate from the transformer secondary.
HDN