How to measure crystal ESR

I have used a simple setup to do this. It uses the same principle as crystal resistance meters.

Take a signal generator and pad it down to give about a 1 ohm source resistance. From this source, put the signal thru a crystal in

series and then a 20 ohm resistor to ground. Tune the generator freq for MAXIMUM voltage on the 20 ohm resistor. This will be very very very sharp. Then substitute a resistor for the crystal to give the same voltage reading. The resistor value that gives the same reading as the crystal did is equal to the crystal esr.

You really need a tuneable generator with a good vernier to do this, but it works.

The reason I chose a 20 ohm resistor was because this was a ball park value of what I expect a 20Mhz crystal esr to be.

The reason I padded the generator down to 1 ohm was becaues I didn't want any interaction with the generator output impedance, and I had a lot of signal to work with just seemed like a good idea at the time.

I used a spectrum analyzer across the 20 ohm resistor as a detector, cause it was handy, and plenty sensitive for the padded down generator signal. A Booton RF meter would work well with good sensitivity, also. Actually, since I was using a substitution method, almost anything would work..

Since I used the substitution method, all of the extraneous variables and impedance mismatches cancel out.......

Good Luck,


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I want to sort a bunch of 20MHz crystals by ESR. Is there a lab setup someone can suggest that will work?



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I suggest a series resonant oscillator such as a butler tuned to the crystal frequency with a AC coupled resistor of say 50 ohms in place of the crystal. You will observe that as the supply is reduced the transistor current reduces and the gain reduces. Replace the resistor with a crystal reduce the supply till the oscillation stops Find the resistor value that gives the same starting voltage as the crystal. Note that the technique will show up crystals with high start up resistance and low running resistance (second level)

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doug dwyer

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