Hi Daniele,
It is not OT!
Am 13.09.2011 17:07, schrieb Daniele Tincani:
I'm
looking for a (reasonably) reliable method for measuring Q of a
parallel LC resonator at LF frequencies (ferrite-cored coil + variable
air cap).
I
have a spectrum analyser (without tracking capability), oscilloscope
with 10x probes, RF generator with built-in attenuator and sweep
function, frequency counter. I'm doubtful in particular about how to
avoid loading the LC with either the output Z of the generator or the
input Z of the meter (or both). Any tips?
Just make a small turn of wire and connect it to the VFO, say 30 cm
diameter. Then couple a signal into the ferrite core, by adjusting the
distance. Take the 1:10 probe (10 MOhm input resistance and some 10 pF)
and measure the voltage across the LF circuit with the scope.
For example adjust the distance to measure +- 4 div at resonance. Then
increase and decrease the frequency until you get 2.83 div.
(4/sqrt(2)). Note these values.
If fres is 137 kHz, flow=136.7 kHz and fhigh is137.4 kHz, your Q is
137/(137,4-136,7)= 196.
73, Stefan/DK7FC
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