[Test-Equipment] Q measurement

[Brian Burns]

Hello All,

 

Thanks for all the good information on Q meters!

Anything that resonates has a Q, and I measure the Q's of my wooden Spanish
guitar parts to determine their acoustic loss properties. I used to do it by
exciting them with a sine wave audio source, coil, and rare earth magnet,
and then tuning the audio source above and below the resonant frequency
until a microphone registered a 3db drop in volume. 

That half-power bandwidth divided into the resonant frequency gave me the Q.
Now I use an audio analysis program, Spectra Plus, that calculates the Q of
any resonance it looks at. But the old slow way is certainly repeatably
accurate.

Though it might be a bit labor intensive, I would think that it would be
possible to measure the Q of a tuned circuit with an accurate signal
generator and a VTVM by essentially the same method. Is the convention in RF
measurements to use the bandwidth at the 6db down points, divided into the
center frequency, for Q's? In audio we use the bandwidth at the 3db down
points divided into the center frequency.

Cheers,

Brian

 

 

 



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