Re: Coupling Experiments

Hi all,
        Mark asked...

> ><snip>>
> >Load R ->    o/c    220k     22k    2.2k     220     0    Ohms
> >------------------------------------------------------------------
> >50nF,25uH
> >k=0.2         5     266      334    391      394     -  (no change)
> <snip>

> I am not clear on the experimental set-up for this set of
> measurements. Was this under sparking conditions (damped
> oscillations), or were you driving the coil system with a low
> impedance sine wave generator? I assume the load resistance is the
> resistance value placed across the secondary coil.  Is this
> correct?  Also, how did you measure the primary impedance?  Did you
> retune each experiment for maximum secondary voltage, or was this
> fixed as R was varied? Most interesting!

The setup : The load resistors were connected between the top of the 
secondary and ground. I had strong reason to think the system must
be considered coupled under sparking conditions from previous 
experiments, so I set out to determine what the primary circuit
was seeing under those conditions.
    The spark gap was shorted (since it is effectively a voltage 
source, it can be represented by a short piece of wire), and a signal
generator was connected in series with a pot across the primary L-C 
circuit. One beam of the scope monitored the sig gen directly, and
the other measured the voltage across the primary circuit. All 
measurements were taken with the generator tuned to the secondary fr.
I adjusted the pot until the voltage across the L-C circuit was 50%
of that coming out of the generator. Since the L-C circuit was 
resonant at the generator frequency, I was effectively measuring the 
drop across a resistive divider comprising the pot and the dynamic
(shunt) resistance appearing across the primary circuit. Having 
adjusted the pot to meet the V/2 requirement, I was then able to
measure the dynamic resistance by simply measuring the pot.
(Sounds awfully jumbled - I hope it's clear :(