The following describes the method I used to determine the optimum tuning point for my coil. This
method is described in detail by Malcolm Watts in a magazine article detailing the construction of a
small TC. If you want a copy please email me.
Above is the setup I used to determine the Fres of the Tank circuit
The photo above shows the exact tank circuit frequency at the given tap point
Compare the photos above and below. Note the CRO response above when the
generator is set to the Fres of the secondary as opposed to below when the generator
is not at the Fres of the secondary. The 'peaking' response is very rapid. It is possible to
determine the 'Q' of the secondary by comparing the frequency range at the 70% peak frequency
both above and below the Fres peak.
The photos above and below show the Fres being taken again but now with the secondary
installed in it's final position. Note that the frequency for Fres is now different than
for the standalone secondary - thanks to Finn for this observation.
In practise, the primary tap point is set at 6% below the Secondary Fres to allow for
arc loading. Thanks to Robert Stephens for this observation.
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