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use your Rigol DS1052E to measure distortion?

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I'm working on calibrating a newly repaired WaveTek 275 function generator.
Internally, it produces triangle waves and shapes them into sine waves, using
a variety of circuits to make the sine waves "clean".

The calibration procedure calls for a distortion analyzer and in spite of my
predilection for getting odd test equipment off of Ebay, this is something I
don't have.

Since the procedure requires looking at sine waves to 100Khz, I was thinking
I could just feed it to my Rigol scope and turn on the FFT.  Then do the
adjustments looking for the best display with the fewest spurs. 
Crackpot idea? 

Does the 1502E have enough resolution to make a half-way decent
distortion analyzer?

Failing that, I may just skip that part of calibration and hope that it's
good enough.


Not really half-way decent (which would be something like .01% distortion), but most function generators don't produce sines with half-way decent distortion either, so it might just work, not sure what the distortion specs are? I believe I verified something for harmonics below -55dB, but it was on a different scope. Hook it up, set the scope to FFT and check if the harmonics are significantly above the noise floor. If they are, you can adjust for lowest harmonic amplitude. If it's hard to see, I would just leave it, if it's reasonably close, no point in risking making it worse. Note that THD is based on the sum of squares of the amplitudes of the harmonics.

Looking at the manual:

Sine Distortion (THD at 5Vp-p)
< 0.5% 10mHz to 99.9kHz (yes, that's millihertz)
No harmonics above
- 40 dBc 100Khz to 999kHz
- 30 dBc 1Mhz to 12Mhz


There's a discussion on this on a thread on spectrum analyzers

Since the Rigol has an 8 bit ADC, the maximum resolution is 1/256.  That likewise is the maximum the FFT can measure.  It should detect the amplitude of harmonics >= 0.4% but it wouldn't be able to measure values lower than that.

-40dBc should be detectable I think, <0.5% probably not. Noise is likely to limit dynamic range even more than the vertical resolution would suggest, the effective number of bits of the system is likely significantly less than 8.


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