RIGOL Technologies (test equipment) - RF Cafe
LadyBug Technologies LB479A RF Power Sensor - RF Cafe

About RF Cafe

Kirt Blattenberger - RF Cafe Webmaster

Copyright: 1996 - 2024
    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 World Wide Web (Internet) was largely an unknown entity at the time and bandwidth was a scarce commodity. Dial-up modems blazed along at 14.4 kbps while tying up your telephone line, and a nice lady's voice announced "You've Got Mail" when a new message arrived...

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:


Electronics World articles Popular Electronics articles QST articles Radio & TV News articles Radio-Craft articles Radio-Electronics articles Short Wave Craft articles Wireless World articles Google Search of RF Cafe website Sitemap Electronics Equations Mathematics Equations Equations physics Manufacturers & distributors Engineer Jobs LinkedIn Crosswords Engineering Humor Kirt's Cogitations RF Engineering Quizzes Notable Quotes App Notes Calculators Education Engineering magazine articles Engineering software Engineering smorgasbord RF Cafe Archives RF Cascade Workbook 2018 RF Symbols for Visio - Word Advertising RF Cafe Homepage Thank you for visiting RF Cafe!
everythingRF RF & Microwave Parts Database (h2) - RF Cafe

Why harmonic appear in output of amplifier when pure sine wa - RF Cafe Forums

RF Cafe Forums closed its virtual doors in 2012 mainly due to other social media platforms dominating public commenting venues. RF Cafe Forums began sometime around August of 2003 and was quite well-attended for many years. By 2010, Facebook and Twitter were overwhelmingly dominating online personal interaction, and RF Cafe Forums activity dropped off precipitously. If the folks at phpBB would release a version with integrated sign-in from the major social media platforms, I would resurrect the RF Cafe Forums, but until then it is probably not worth the effort. Regardless, there are still lots of great posts in the archive that ware worth looking at.

Below are the old forum threads, including responses to the original posts.

-- Amateur Radio
-- Anecdotes, Gripes & Humor
-- Antennas
-- CAE, CAD, & Software
-- Circuits & Components
-- Employment & Interviews
-- Miscellany
-- Swap Shop
-- Systems
-- Test & Measurement
-- Webmaster

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
high frequency PCB of PCBONLINE
Werbel Microwave - RF Cafe
Amplifier Solutions Corporation (ASC) - RF Cafe

Please Support RF Cafe by purchasing my  ridiculously low−priced products, all of which I created.

These Are Available for Free