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Old 18th Feb 2009, 11:52 am   #10
John M0GLN
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Join Date: Jan 2004
Location: Southport, Merseyside, UK.
Posts: 1,156
Default Re: Measuring Resonant Frequency

Thank you all for your very helpful suggestions, I've quickly re-run the experiment, I wasn't too far out initially, but as a number of you pointed out I needed a resistor in there somewhere, the output of the signal gen' is now connected across the LC via a 82K resistor, the only one lying on the bench at the time, this as suggested will stop damping the signal gen', and the scope is connected across the resistor which damps the 'scope's input, I've attached another crude sketch showing this, this seems to work very well, with the variable cap' either fully open or fully closed the 'scope reads 2V peak to peak, and with the variable cap' about halfway the 'scope reads 10mV peak to peak, by varying the input frequency I can find resonance at different positions for the variable cap', its quite easy to find this resonant point, I might rig up something more permanent in the future, either a more elaborate version of what I've done or like jim_jobe or oldtimer74 have suggested. Yes Sean, I've used similar sites to the links you posted, there excellent, I always used to get lost with all those 10 to the -12's at tech'.

John
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