[Prev][Next][Index][Thread]

Re: Tesla and Measurements.

Hi everyone,
            I'd like to add a further note to all this. The Zo of
the secondary coil can be viewed as a "pivot" about which the 
impedance at each end swings. This reflects what Mark said about
the coil being a kind of lever. Since the open circuit impedance
of the coil at the top end can vary from near infinity (and this
IS Q limited by the non-spark circuit resistances) to quite low
values, it follows that a low Zo secondary (low L/C ratio) is going 
to produce far less wild swings at the primary end under different 
loading conditions since the secondary termination (spark) is never 
going to be stunningly low. I would expect a better wide range match 
to be effected by such a coil.
     This may explain why a large top capacitance on the secondary
has been found to work well with high inductance coils.  You can 
implement a low Zo secondary with large L by using a large terminal 
capacitance and enjoy the advantages of low fr at the same time.
This approach (as opposed to low-L moderate top C) allows a much
greater degree of latitude in the choice of primary L/C's as well.
A high frequency secondary is always going to be limiting in this
regard.
     There is anecdotal and experimental evidence that the optimum 
secondary is arrived at when the secondary fr causes the wire in
the secondary to be 1/4 wavelength long at fr also. I showed last
year in an analysis that as coil diameter increaes, so does the
amount of terminal capacitance to reach this condition. I also showed
that for a given diameter former, any coil wound on that former with
the same top-C is going to meet this condition.

A few more things to factor in perhaps.
Malcolm