#622 Square Wave Harmonic Tricks

Episode 622
Use harmonics to get higher frequencies or turn a square wave into a sine wave
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[oldblokeh]

Don't forget that if you start with a sine wave you can always stuff it through a schmitt trigger to get a square wave and hence all those lovely harmonics.

[ChrisSmith-tcdf]

That frequency multiplication technique is often used in Rb and Cs references to create microwave frequencies by feeding their (usually 5 or 10MHz) low phase noise crystal reference oscillator into a series of multiplier stages. Some stages might use a step recovery diode to create a rainbow of harmonics that they can then filter out a much higher order harmonic. Different manufacturers use slightly different designs, but they generally follow that architecture.

[herbertsusmann]

Yea, odd harmonics are not supposed to be all the same. Falls off as 1/n I believe. Can easily check by looking up the Fourier Series for a square wave.

[WistrelChianti]

Cannot like this hard enough! Thanks! Really interesting. Total bonus unexpected learning there!

[VeryMuchBlessed]

Very interesting good information. Was good to see the process refined down to the sine wave. Thanks much.

[gudgejm]

this video enlightened me. you explained exactly what i was curious about, thank you SO MUCH!!!

[vidasvv]

Nice demo ! I think the "counter" function is standard on that series of HP SA's

[nfachannel]

awesome, i want to understand more about harmonic signal and how to solve it, can you detail the filter circuit sir?

[azavraa]

Questions: 1) which option in the 8591E includes the frequency counter? That is rather cool! 2) Can the 8591E be attached to a 10Mhz external reference like an GPSDO. Looking at a couple HP8591s on on e-bay.

[Master_zzz]

It's a nice trick to extract a harmonic from a square wave but also an expensive one. You are stuck with expensive LPF or BPF. I did it once building an 87.5MHz...108MHz FM DDS with a DDS only capable of outputting 12.5MHz max. Good luck building a BPF with steep rolloff.

[____________________________.x]

I’m never going to do this, but I like knowing that I could, thanks

[mikaelkalki]

It is impossible to create an audible square wave as a perfectly vertical line in a wave form is physically impossible due to the continuous passage of time unless you can teleport air itself from point a to point B and back and forth

[charlessmith]

So if I wanted a calibration source for my shortwave receiver across the band using harmonics it looks like I should generate a square wave from my crystal instead of a sine. Right? In other words a 100KC crystal changed to a square wave output would give me better harmonics for calibration across the dial? Please correct my thinking if I am wrong.

[perdidoanonimo]

very nice, I really enjoy your videos!

[eetech_fix]

You’re dealing with a square wave, an assortment of harmonics from its very nature. Your amplification and your capacitor arrangement just aggravate the system. If you look at the output on a spectrum analyzer, it’ll be obvious what you’re dealing with. Input a sine wave that’ll give you better results. Your scope is just triggering the predominant foreground harmonics. You’re missing what is there.

[lightbulbgonewild]

The harmonics: for example 100hz sine wave
300hz
500hz
700hz
900hz and so on...

[amirb]

if the odd harmonics all had equal amplitude you would never get a square wave, in fact it would not be any physical wave at all (Fourier series will not even converge). So please study the basics before making educational video. The odd harmonics fall off as 1/n (n=1, 3, 5, 7, ...). The even harmonics appear if the duty cycle is not perfectly 50%. Also linear rising, falling edges also contribute to even harmonics a little