# sine wave in a spectrum analyzer

#### Polgi-Wan

Joined Sep 26, 2005
11
can someone explain why a perfect sine wave shows a singular signal viewed on a spectrum analyzer versus a slightly clipped (example: upper peak of sine wave) sine wave which show a signal with too many harmonics on the spectrum analyzer...... ?

i know this is a basic concept but would like to understand. thanks!

#### Papabravo

Joined Feb 24, 2006
14,441
can someone explain why a perfect sine wave shows a singular signal viewed on a spectrum analyzer versus a slightly clipped (example: upper peak of sine wave) sine wave which show a signal with too many harmonics on the spectrum analyzer...... ?

i know this is a basic concept but would like to understand. thanks!
The understanding requires familiarity with Fourier Series. A pure sine wave has a Fourier Series with one term and thus one non-zero coefficient. This is at a frequency of the single peak on the spectrum analyzer.

The central theroem of Fourier Series is that any waveform can be approximateted by an infinite sum of sines and cosines at some fundamental frequency and its harmonics. The most dramatic example is the square wave. With this picture in mind the series of peaks on the spectrum analyzer represents the terms of the Fourier Series that approximates the clipped waveform.

http://mathworld.wolfram.com/FourierSeries.html

#### Polgi-Wan

Joined Sep 26, 2005
11
thanks for pointing me in the right direction.. .. and thanks for the link!

good day. . . .

#### RAH1379

Joined Dec 13, 2005
69
a perfect sinewave has no harmonics, all other waveforms are made of sinewaves with harmonics added .