Electronics World Cover,TOC,and list of posted Popular Electronics articles QST Radio & TV News Radio-Craft Radio-Electronics Short Wave Craft Wireless World About RF Cafe RF Cafe Homepage RF Cafe in Morse Code Google Search of RF Cafe website Sitemap Electronics Equations Mathematics Equations Equations physics Manufacturers & distributors Engineer Jobs Twitter LinkedIn Crosswords Engineering Humor Kirt's Cogitations Engineering Event Calendar RF Engineering Quizzes AN/MPN-14 Radar 5CCG Notable Quotes App Notes Calculators Education Magazines Software,T-Shirts,Coffee Mugs Articles - submitted by RF Cafe visitors Simulators Technical Writings RF Cafe Archives Test Notes Wireless System Designer RF Stencils for Visio Shapes for Word Search RF Cafe Sitemap Advertising Facebook RF Cafe Forums Thank you for visiting RF Cafe!

Why Harmonic Appear in Output of Amplifier When Pure Sine Wa - RF Cafe Forums

The original RF Cafe Forums were shut down in late 2012 due to maintenance issues. Original posts:

Amateur Radio | Antennas | Circuits & Components | Systems | Test & Measurement

Post subject: Why harmonic appear in output of amplifier when pure sine wa
Unread postPosted: Tue Mar 22, 2005 5:34 pm

Joined: Tue Mar 22, 2005 5:29 pm
Posts: 3
Pure sine wave does not have harmonics. If this pure sine wave is input to a power amplifier, why does harmonic start to appear on the output. The reason behind my question is if a pure sine wave go into the power Amplifier, the output should still be a pure sine wave with higher amplitude. Hope someone can help to shed some light on this.


Post subject: Harmonics
Unread postPosted: Tue Mar 22, 2005 9:59 pm

The output of the power amplifier is not exactly a constant times the input. As the output departs from strict linearity, other frequencies are generated. If there is only a single sine wave present at the input, only harmonics are generated. The other signals are generated in and by the amplifier.

For example, suppose the actual output of the amplifier is
5Vin + 0.01 Vin^2. If the input is sin(wt), then the output is
5 sin(wt) + .01 sin^2(wt). But sin^2(x) = 1/2[cos(0)+cos(2x)], so we now have a 2x or 2wt or second harmonic present, where none was present at the input.

I hope this helps.

Good luck!


Post subject:
Unread postPosted: Wed Mar 23, 2005 5:27 am


I agree with the posting from another fellow. I'd like to add regarding this harmonics signals. One of the main reason is because active devices in power amplifier design pratically is non-linear. As we know the active devices such as BJT, MESFET, HBT,etc all are non-linear devices.

That's why it produces output signals with frequency different with input signal frequency, which are known as harmonic signals.

Hope it helps..



Post subject:
Unread postPosted: Wed Mar 23, 2005 3:09 pm

The other two posts are correct , that what you are seeing is the non-linear behavior of the amplifier. If you look at the the output in the time domain the sahpe of the signal will not be a perfect sine wave, but slightly distorted. Simple test for you, back the input power of the sine wave into the amplifier off, you will see that the lower in power the lower the harmonics , until they dissapear. This is because you are away from the compression poin tof the amplifier and are operating in the linear region.


Post subject:
Unread postPosted: Thu Mar 24, 2005 5:39 pm

Joined: Tue Mar 22, 2005 5:29 pm
Posts: 3
Thankyou to both of you for your input to help me to see the light.

Posted  11/12/2012

RF Cafe Software

   Wireless System Designer - RF Cafe
Wireless System Designer

RF & EE Symbols Word
RF Stencils for Visio
Calculator Workbook
RF Workbench
Smith Chartâ„¢ for Visio
Smith Chartâ„¢ for Excel

About RF Cafe

Kirt Blattenberger - RF Cafe WebmasterCopyright
1996 - 2022
Kirt Blattenberger,

RF Cafe began life in 1996 as "RF Tools" in an AOL screen name web space totaling 2 MB. Its primary purpose was to provide me with ready access to commonly needed formulas and reference material while performing my work as an RF system and circuit design engineer. The Internet was still largely an unknown entity at the time and not much was available in the form of WYSIWYG ...

All trademarks, copyrights, patents, and other rights of ownership to images and text used on the RF Cafe website are hereby acknowledged.

My Hobby Website:

Try Using SEARCH
to Find What You Need. 
There are 1,000s of Pages Indexed on RF Cafe !