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Original Message

RE: Power supply ripple???

Posted by 6AS7_6SN7 on March 21, 2017 at 10:05:37:

Great!

The FFT will show you all the line harmonics and other CW components (if any).

I personally prefer the 'flat top' window (that gives the best measurement of continuous wave components).

By the way, the standard Hanning or Hamming windows works fine as well.

Scopes with built in FFT (and time averaging in the case) are very powerful measuring instruments and as soon as you learn to use it you will see.

Hint - If you select some CH2 low voltage signal (synchronous with mains) as the trigger source (for example the filament 6.3 or 12.6 VAC) you can easily average the noise on CH1 and THEN apply the FFT (to the averaged noise signal): this allows to see a new universe of previously unseen signals that were buried in the noise.

For example, if there is an even minimal magnetic coupling of the current pulses of the HT transformer/rectifier into the HT they emerge from the noise with even moderate averaging.

And by the FFT of the averaged signal you can see the CW spectrum much more clearly and fully exploit the maximum dynamic range of the instrument.