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Frequency vs temperature
Original poster: "Jim Lux by way of Terry Fritz <twftesla-at-qwest-dot-net>" <jimlux-at-earthlink-dot-net>
Looking over your extensive F, R, and Q data...
How much would you expect the Fres to change over temperature... You're
looking at tiny fractions of a % for frequency, and it seems to me that
dimensional changes in your coil and topload will be on that order...
Resistance changes over temperature are going to be significant too.. and
that slightly changes the apparent resonant frequency (i.e. it's really not
=sqrt(1/LC) but a function of LC and R.. although.. your Q of 200 is high
enough that this effect might be small...
A quick and dirty Wheeler calculation, while not accurate in absolute terms
to hundredths of a percent, could probably give you a sensitivity... that
is, L goes as some function (x/(x+1)?) of Length.... and so
forth...obviously N isn't changing...but length and diameter certainly are...
Likewise, C of topload will also change as a function of temperature (CTE
of aluminum is what? 23 ppm/degree... so a 30C change will be a
dimensional change of about 700 ppm, and, to a first order, capacitance
will change the same (that is, about 0.07%), resulting in a 0.03%
frequency change, which is of the same magnitude as you are seeing...
The elliptical F vs T curves seem to indicate a thermal/mechanical time lag
between parts of the system, that is, some things get bigger and smaller at
different rates than other things...
This is pretty nifty, in that you can actually make reasonably precise
measurements (assuming that the error bars are reasonably sized!)