About signals and systems

[bhuvanesh]

i heard often about sinusoidal signals . But i dont know where it is used and how it is used . How its being used in practical application . Plz explain me basically
i heard often about sinusoidal signals . But i dont know where it is used and how it is used . How its being used in practical application . Plz explain me basically

[eman12]

What you want to know wabout sine waves and sine signals?
The sine signal is one of the most important signals in electronics and physics. It is used in circuits to test them (for instance injecting it to an input and look at the behaviuor of the output via scope and so on). You know, the pure sine wave is the only wave which does not have any harmonic, this is very helpful in electronics most of the times and cause the sine waves even more important in theory and in practice.

[Rerouter]

a sinusoidal wave is also refereed to as a sine wave, it generally consists of only a single frequency, seriously if you want a deeper explanation, then write a more detailed question than something that sounds copied out of the review portion of a textbook...

[MacAttak]

The OP definitely didn't copy and double-paste from somewhere else. Too lazy to even delete the second pasted text block. 

[c4757p]

A sinusoid is the most basic signal in a frequency-domain system, including everything RF. Good enough?

[Skimask]

And the O/P even asked Plz.

That adds credibility right there...

[free_electron]

a sinusoidial signal is just a signal that can neither decide its value nor it polarity... it changes its polarity by the result of the SIN function of a vector rotating at constant speed around the unity circle , scaled by a gain.

there. clear now ?

[c4757p]

And the O/P even asked Plz.

Here is how I interpret that: "I can't be bothered to take the time to type p-l-e-a-s-e, so I can't be bothered to read your response either. Please explain this to me in five words or fewer. And refill my coffee too, slave!"

[IvoS]

I would like to ask you guys something. Is it just a theoretical thinking about that "no THD" in pure sine wave, yes? I don't believe that sine wave without THD is possible to achieve even with the highest quality sine wave generator, there is always a way to measure 0.00000xxxx% of 2nd harmonic THD..??
Anyway, my question is regarding those harmonics, 2nd 3rd  etc. How do those harmonics get created in sine wave generator lets say. I know little about FFT and how to use my sound card with ARTA soft for low frequency audio signals to measure a preamplifier for example, but I don't know how the amplifier adds or creates those harmonics to the fundamental.

[eman12]

And the O/P even asked Plz.

Yea!

[eman12]

I would like to ask you guys something. Is it just a theoretical thinking about that "no THD" in pure sine wave, yes? I don't believe that sine wave without THD is possible to achieve even with the highest quality sine wave generator, there is always a way to measure 0.00000xxxx% of 2nd harmonic THD..??
Anyway, my question is regarding those harmonics, 2nd 3rd  etc. How do those harmonics get created in sine wave generator lets say. I know little about FFT and how to use my sound card with ARTA soft for low frequency audio signals to measure a preamplifier for example, but I don't know how the amplifier adds or creates those harmonics to the fundamental.

Hi,

Well If it is "Really" a "Pure" Sine wave then "No harmonics" appear. But in practice I think most of the times a small fraction of tolerance is acceptable.

Well, the "harmonics" are all related to the frequency. In a pure sine signal you have got just the fundamental frquency, But by changing the waveform or adding/multiplying another signal to it (even a noise or signal or causing/making the pure sine wave itself to change somehow) can simply cause the sine wave to generate other low level signals in in say 2X, 3X and so on called harmonics. Subharmonics can be generated in such situations as well.
 

[IvoS]

Thanks. I think I understand that little bit now, and I also know that an amplifier adds harmonics due to non-linearity etc., but why is it always a multiple of fundamental? Why when I test the amp with 10kHz sine, I can see 2nd 20kHz, 3rd 30kHz etc. Why don't I see a signal lets  say 22,386kHz in FFT for example?

[MacAttak]

My understanding was that you can always detect a harmonic because the measurement process is imperfect. You cannot have infinite resolution in measurement... It is quantized to the sampling rate of the instrument. So a perfect sine wave still looks the same as a drifting step wave.

[IanB]

Thanks. I think I understand that little bit now, and I also know that an amplifier adds harmonics due to non-linearity etc., but why is it always a multiple of fundamental? Why when I test the amp with 10kHz sine, I can see 2nd 20kHz, 3rd 30kHz etc. Why don't I see a signal lets  say 22,386kHz in FFT for example?

Take a look at this and see if it helps:



You may need to watch it a few times to absorb all of it. Vi Hart certainly   d o e s   n o t   s p e a k   s l o w l y . . . . 

[eman12]

Thanks. I think I understand that little bit now, and I also know that an amplifier adds harmonics due to non-linearity etc., but why is it always a multiple of fundamental? Why when I test the amp with 10kHz sine, I can see 2nd 20kHz, 3rd 30kHz etc. Why don't I see a signal lets  say 22,386kHz in FFT for example?

Yes, The "non-linearity" is the main key here. A non-linear medium/circuit does not cause the signals to Simply add in frequency (and even in amplitude), it causes them to MULTIPLE (a pure liner circuit/medium just causes the signals to add in amplitude but yet maintain the original frequency for each). The mathematics says when 2 signals multiple to each other then the second/third and other harmonics would be generated automatically. You can find the math in the net and see how MULTIPLYING 2 or more pure sine signals can lead to "more than" 2 signals with 2X, 3X, and other harmonics...

http://www.learnabout-electronics.org/ac_theory/ac_waves01.php
http://gmanacheril.com/PHY2048/Text%20Materials/Lesson%205.3%20Harmonic%20Waves.pdf