# Harmonic distortion

#### ronybhai

Joined Sep 18, 2012
97
what method could be used to estimate the harmonic distortion in the output of an oscillator?

#### vk6zgo

Joined Jul 21, 2012
677
what method could be used to estimate the harmonic distortion in the output of an oscillator?
If you want to simply estimate the harmonic distortion,you could compare the waveshape to an ideal sinewave,but there are a number of ways in which you can test for it:

(1) Examine the signal with a Spectrum Analyser,or perhaps the FFT function of a DSO.

(2) Use a Band Stop (notch) filter centred on the fundamental frequency.
Everything at the output will be either distortion or noise,so you will read Distortion +Noise--if the noise is very low level it may be neglected.(this is the classic method used in the Noise & Distortion test set).

(3) Use a Selective Millivoltmeter.
First,tune to the fundamental,then to each harmonic in turn.

#### t_n_k

Joined Mar 6, 2009
5,448
This is homework forum. Normally one expects the OP to show some effort before some form of answer is furnished.

Why not simply look at Wikipedia for a start? Or Google THD meter ....

#### vk6zgo

Joined Jul 21, 2012
677
This is homework forum. Normally one expects the OP to show some effort before some form of answer is furnished.

Why not simply look at Wikipedia for a start? Or Google THD meter ....
True,but if he doesn't know anything,my answers won't make any sense to him!

#### WBahn

Joined Mar 31, 2012
24,572
True,but if he doesn't know anything,my answers won't make any sense to him!
And he may not care if all he wants is the answers to copy onto his homework and turn in.

I don't think that is the case with this OP, if I'm recalling from prior experience. But who knows?

Actually -- with this OP that may well be all he cares about. I just went and looked at a couple of prior threads of his, such as this one:

and getting him to do anything other than want the answer spoon fed to him was like pulling teeth.

#### bountyhunter

Joined Sep 7, 2009
2,498
There are waveform analyzers that are designed to specifically read THD. They are the easiest to use.

#### t_n_k

Joined Mar 6, 2009
5,448
True,but if he doesn't know anything,my answers won't make any sense to him!
Presumably that reasoning would apply to anyone who posts in the homework forum. They don't know so they ask for help.

#### ronybhai

Joined Sep 18, 2012
97
If you want to simply estimate the harmonic distortion,you could compare the waveshape to an ideal sinewave,but there are a number of ways in which you can test for it:

(1) Examine the signal with a Spectrum Analyser,or perhaps the FFT function of a DSO.

(2) Use a Band Stop (notch) filter centred on the fundamental frequency.
Everything at the output will be either distortion or noise,so you will read Distortion +Noise--if the noise is very low level it may be neglected.(this is the classic method used in the Noise & Distortion test set).

(3) Use a Selective Millivoltmeter.
First,tune to the fundamental,then to each harmonic in turn.
I was kind of thinkig about the 1st answer you gave. Thanks