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muhammad asad
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Phase Spectrum

02/19/2017 5:42 AM

Why a simple positive frequency sine wave shows a phase angle of -90 degrees or π/2 radians in the phase

spectrum?
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Rixter
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#1

Re: phase spectrum

02/19/2017 7:18 AM

Because the sine wave is pi/2 or 90 degrees out of phase with the cosine wave, which is zero phase.
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redfred
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#2
In reply to #1

Re: phase spectrum

02/19/2017 8:40 AM

True but you didn't mention why the cosine function is preferred to the sine function in discrete time base to discrete frequency base conversion.

Obviously the sum of sinusoidal equations could use all sine or all cosine functions with just different values for phase. However the derivation of the Discrete Fourier Transform is less cluttered using the cosine function since the unitary maximum occurs when the phase angle equals zero instead of having to always carrying a transcendental, pi/2 coefficient through all of the equations.

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Usbport
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#3
In reply to #2

Re: phase spectrum

02/19/2017 9:28 AM

But... would the OP have understood that explanation? From the questions he's asking, I doubt it.

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redfred
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#4
In reply to #3

Re: phase spectrum

02/19/2017 10:20 AM

You may be right, my explanation maybe beyond the OP. My explanation might be like explaining the mechanics of rayleigh light scattering to a child is the reason why the sky is blue. Then again who knows which answer will solve, inspire, baffle or continue the curiosity to know more.

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Rixter
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#5
In reply to #3

Re: phase spectrum

02/19/2017 11:08 AM

That's why I tried to make it simple.

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Phys
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#6
In reply to #5

Re: phase spectrum

02/20/2017 10:05 AM

We need a "rating" page where OP's can click into and select the correct answer:

1. answer helped

2. answered did not help

3. answer left me so baffled I maybe should quit engineering

We almost never get a response on posts like this and are left wondering if any of the answers helped.

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Flash_In_The_Pan
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#7
In reply to #6

Re: phase spectrum

02/20/2017 10:12 AM

I think this is a great suggestion. I 2'nd it!
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Rixter
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#8
In reply to #6

Re: phase spectrum

02/20/2017 11:31 AM

That sounds like a good idea.

I try to judge how much understanding the questioner has and match the answer to that level of understanding.

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Brave Sir Robin
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#9
In reply to #6

Re: phase spectrum

02/20/2017 12:03 PM

4. gave me a good chuckle for the day
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Rixter
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#10

Re: Phase Spectrum

02/20/2017 6:23 PM

https://www.mathsisfun.com/algebra/trig-sin-cos-tan-graphs.html
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Brave Sir Robin (1); Flash_In_The_Pan (1); Phys (1); redfred (2); Rixter (4); Usbport (1)

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