CR4® - The Engineer's Place for News and Discussion®


Previous in Forum: Minimum and Maximum Reference VLT HVAC Basic Drive FC 101 (Danfoss)   Next in Forum: 3 Phase Motor Starter Won't Stay Engaged. Details Inside.
Close
Close
Close
10 comments
Active Contributor

Join Date: Jan 2017
Posts: 14

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?

Register to Reply
Interested in this topic? By joining CR4 you can "subscribe" to
this discussion and receive notification when new comments are added.

Comments rated to be Good Answers:

These comments received enough positive ratings to make them "good answers".
Guru

Join Date: Apr 2010
Posts: 5618
Good Answers: 558
#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.

Register to Reply
3
Guru
Engineering Fields - Electrical Engineering - Been there, done that, still doing it. Engineering Fields - Control Engineering - New Member

Join Date: Dec 2008
Location: Long Island NY
Posts: 12153
Good Answers: 770
#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.

__________________
"Don't disturb my circles." translation of Archimedes last words
Register to Reply Good Answer (Score 3)
Guru
Engineering Fields - Optical Engineering - Member Engineering Fields - Engineering Physics - Member Engineering Fields - Systems Engineering - Member

Join Date: Apr 2010
Location: Trantor
Posts: 5176
Good Answers: 616
#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.

__________________
Whiskey, women -- and astrophysics. Because sometimes a problem can't be solved with just whiskey and women.
Register to Reply
Guru
Engineering Fields - Electrical Engineering - Been there, done that, still doing it. Engineering Fields - Control Engineering - New Member

Join Date: Dec 2008
Location: Long Island NY
Posts: 12153
Good Answers: 770
#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.

__________________
"Don't disturb my circles." translation of Archimedes last words
Register to Reply
Guru

Join Date: Apr 2010
Posts: 5618
Good Answers: 558
#5
In reply to #3

Re: phase spectrum

02/19/2017 11:08 AM

That's why I tried to make it simple.

Register to Reply
3
Guru
Engineering Fields - Instrumentation Engineering - EE from the the Wilds of Pa.

Join Date: Feb 2006
Location: middle of nowhere, Pennsylvania
Posts: 2491
Good Answers: 58
#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.

__________________
Remember when reading my post: (-1)^½ m (2)^½
Register to Reply Good Answer (Score 3)
Member

Join Date: Oct 2012
Posts: 7
#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!

Register to Reply
Guru

Join Date: Apr 2010
Posts: 5618
Good Answers: 558
#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.

Register to Reply
Guru
Hobbies - DIY Welding - Wannabeabettawelda

Join Date: May 2007
Location: Annapolis, Maryland
Posts: 4121
Good Answers: 230
#9
In reply to #6

Re: phase spectrum

02/20/2017 12:03 PM

4. gave me a good chuckle for the day

Register to Reply
Guru

Join Date: Apr 2010
Posts: 5618
Good Answers: 558
#10

Re: Phase Spectrum

02/20/2017 6:23 PM
Register to Reply
Register to Reply 10 comments
Interested in this topic? By joining CR4 you can "subscribe" to
this discussion and receive notification when new comments are added.

Comments rated to be Good Answers:

These comments received enough positive ratings to make them "good answers".
Copy to Clipboard

Users who posted comments:

Brave Sir Robin (1); Flash_In_The_Pan (1); Phys (1); redfred (2); Rixter (4); Usbport (1)

Previous in Forum: Minimum and Maximum Reference VLT HVAC Basic Drive FC 101 (Danfoss)   Next in Forum: 3 Phase Motor Starter Won't Stay Engaged. Details Inside.

Advertisement