Understanding Harmonic Distortion Measurements

[@zynthos9]

4:40 the width of the harmonics increase with order. Is this equivalent to saying the phase noise of the harmonics ‘decrease’ with order, the harmonics are less spectrally pure than the fundamental?

[@pauldenisowski]

Phase noise usually *increases* with harmonic order - i.e. the 2nd harmonic has worse (that is, more) phase noise than the fundamental, the 3rd harmonic has worse phase noise than the 2nd, etc. Generally speaking, frequency multiplication always increases phase noise as well.

[@MacsLounge_]

Nice presentation. If you could include real time measurements of Harmonics at zero span, with additional settings of RBW, it would have provided more clarity.

[@pauldenisowski]

Thanks! Actually, I've already completed another video "Measuring Harmonic Distortion with the FSW" which shows exactly this :) It should be live on KZbin in the next few days.

[@pauldenisowski]

Here's the video showing measurements using a spec an: kzbin.info/www/bejne/r6OskoKtlMmLnbM

[@MacsLounge_]

@@pauldenisowski Followed that! Thanks a lot!

[@fotispagonis6071]

Nice presentation

[@pauldenisowski]

Thank you!

[@kristianstepancic3440]

Shouldn't the THD(dB) formula be 10*log if the reference unit is watts?

[@Berk-lf6ge]

No, because the sqare root of a power ratio is equivalent to a voltage ratio. So you need to account for that with the factor of 20

[@Jakobiez]

What does it mean when the 3rd harmonic is larger than the 2nd harmonic in power?

[@pauldenisowski]

It's actually not uncommon in some applications for the amplitudes of odd order harmonics to be greater than even order harmonics. If a signal is pulsed or square wave shaped, then it usually will have higher odd than even order harmonics (the old "square wave is the sum of odd harmonics"). For example, a switch mode power supply draws current in "bursts" or "pulses" and thus the current waveform will have higher odd than even harmonic content, and thus the power (voltage * current) waveform will also have higher odd than even harmonics. I'm actually just finishing up a video on current harmonics that talks about exactly this topic :) Thanks for the question!