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Variation of secondary Q
Original poster: "Paul Nicholson by way of Terry Fritz <twftesla-at-qwest-dot-net>" <paul-at-abelian.demon.co.uk>
It occured to me that if someone has one of those nice digital
scopes that can be remote controlled over a serial RS232 connection,
then they would be able to carry out an interesting experiment.
A TC secondary is set up and driven by a low frequency, sharp
edged square wave into the base, so that the coil rings down at
its 1/4 wave Fres at each edge.
The scope captures the base current waveform and downloads to the
A PC program analyses the trace to determine both Q and Fres by
matching the ringdown waveform to a function
A * cos(w*t+theta) * exp(-rt)
and finding the parameters A, theta, w, and r which give the
closest (least squares) match to the waveform.
A 2048 point trace would give around 0.1% accuracy on the Fres
measurement, and an 8 bit vertical resolution would give about
0.4% accuracy on Q.
The program could be left running for a week or two, recording the
values of Fres and Q into a data file which could then be compared
with environmental factors.