# Electronics - Visualizing the effect of a low pass filter on harmonics.

Discussion in 'Amateur Radio News' started by KB7TBT, Dec 30, 2021.

1. ### KB7TBTXML SubscriberQRZ Page

Electronics - Visualizing the effect of a low pass filter on harmonics.

KB1YM, N2MDA, K8XG and 9 others like this.
2. ### W1YWHam MemberQRZ Page

Nice demo. Good example for Fourier decomposition with harmonics, also.

Last edited: Jan 1, 2022
N0NEV and KC7ZXY like this.

Very interesting and informative. Thanks for sharing that, the visual aspect makes for easier understanding.

KC7ZXY likes this.
4. ### KB1YMXML SubscriberQRZ Page

This is a perfect visualization of what took me two semesters of Transmission and Radiation in my EE courses (thanks to Dr Wm Teso, W1AI, at Univ of Hartford). After grinding thru a bunch of higher math the statement was made that a square wave is the sum of all odd and even harmonics.

The lightbulb went on in my head when I looked at that statement from the opposite direction - when you generate a square wave you generate harmonics. Therefore overdriving an amplifier causes clipping of the peaks of your sine wave signal and starts to make that signal look more like a square wave - i.e. with all those nasty harmonics.

The visualization also shows that the odd harmonics are more significant than the even harmonics, especially the lower order ones.

Thanks for video.

5. ### KJ7QQGHam MemberQRZ Page

If you were to use an oscilloscope to view the harmonics of an amplified RF signal, there would come a point where the fundamental can't get any higher in amplitude, but if you keep cranking the drive up, the amp is trying to shove more power into the signal but since that can't go into the fundamental, the average power is raised through the creation of harmonics; and as the 2nd order and 3rd order harmonics come to this power threshold that the fundamental came upon (when you're REALLY overdriving) then the other harmonics come up higher and higher behind it to keep increasing the average power, squishing as much as it can into the 50% duty cycle of the sine-turned-square wave.

You gave the top-down view with amplifier harmonics, I think this is pretty close to the bottom-up view... but I'm not sure. I guess the second part of what I said isn't really true because as you were saying, there's a lot more complicated higher math involved than individual harmonics reaching power thresholds.

6. ### W1YWHam MemberQRZ Page

Its LEGO's friends:

A sine wave and harmonics 'compose' into a... XXXX wave.

XXX = .....

The objectives of audio synthesis are somewhat different than RF visualization, but given the limitations, this is a a pretty good example of how an RF filter works. Not intended as a lecture on the different types of filters... not a signals and systems course;-)

AF--what used to take a roomfull of modules for audio synthesizers now can be had in a pocket size (big pocket) with audio synths such as the OP-1. Great 'audio' visualization of 'composing' waveforms to taste BTW. FYI--older ears lose high end dramatically past 8 KHZ so HPF is typical, often past 11 KHz. When present, digital distortion in A/D, D/A is more apparent above 8 KHz and thus filtering is typical. IOW KB7TBT's demo reveals that filtering is very common in our daily lives; we just don't think about it.

73
Chip W1YW

Last edited: Jan 13, 2022