Hello, I am trying to get the phase difference of two signals. They are at the same frequency. The phase value of each signal is calculated by the angle function of a signal's FFT. One thing I could not understand is that the absolute phase value of each signal changes with the sample size of the FFT but the phase difference between the two signals keeps the same. I am not so sure whether the unwrap function makes any difference here. Also,do I need use window for the FFT processing? Thanks, Jade %%%sampling freq clear all fo=10.23*10^6; %%%sampling_resolution(s) %res=100; fs=100.5*10^6; %%%duration=10048/fs duration=0.9999*10^(-4); %duration=10*10^(-4); t = 0:1/fs:duration-1/fs; tp=1*10^(-8); theta0=0; x1 = sin(2*pi*fo*t+theta0); x2 = sin(2*pi*fo*(t+tp)+theta0); s1=x1; s2=x2; s11=s1; y1 =fft(s11); N=length(y1); y = y1*2/N; m = abs(y); m(1)=m(1)/2; TTT=round(mod(fo,fs)*N/fs+1); y(TTT) theta11=unwrap(angle(y(TTT))); theta12=(angle(y(TTT))); s12=s2; y2 =fft(s12); N=length(y2); y = y2*2/N; m = abs(y); m(1)=m(1)/2; TTT=round(mod(fo,fs)*N/fs+1); y(TTT) theta21=unwrap(angle(y(TTT))); theta22=(angle(y(TTT))); (theta21-theta11)/2/pi/fo
Help! Phase difference of two signals
Started by ●October 11, 2007
Reply by ●October 12, 20072007-10-12
On 12 Okt, 04:58, "jade" <yunqiyun...@gmail.com> wrote:> Hello, > > I am trying to get the phase difference of two signals. > They are at the same frequency.... Why do you re-post the same question you asked two days ago? Rune
Reply by ●October 12, 20072007-10-12
Since you're only interested in one frequency, you can multiply the signal with a complex rotating phasor of the same frequency, and integrate/sum over a number of periods. -mn
Reply by ●October 12, 20072007-10-12
Reply by ●October 12, 20072007-10-12
Rune Allnor wrote:> On 12 Okt, 04:58, "jade" <yunqiyun...@gmail.com> wrote: >> Hello, >> >> I am trying to get the phase difference of two signals. >> They are at the same frequency. > ... > > Why do you re-post the same question you asked two > days ago? > > Rune > >Its a phase shift thing. You compare the answers to two similar questions asked out of phase, then correlate for consistency in the answers. :-) Steve
Reply by ●October 12, 20072007-10-12
Steve Underwood <steveu@dis.org> writes:> Rune Allnor wrote: >> On 12 Okt, 04:58, "jade" <yunqiyun...@gmail.com> wrote: >>> Hello, >>> >>> I am trying to get the phase difference of two signals. >>> They are at the same frequency. >> ... >> Why do you re-post the same question you asked two >> days ago? >> Rune >> > Its a phase shift thing. You compare the answers to two similar > questions asked out of phase, then correlate for consistency in the > answers. :-)You can also reduce the noise by averaging... -- % Randy Yates % "She's sweet on Wagner-I think she'd die for Beethoven. %% Fuquay-Varina, NC % She love the way Puccini lays down a tune, and %%% 919-577-9882 % Verdi's always creepin' from her room." %%%% <yates@ieee.org> % "Rockaria", *A New World Record*, ELO http://www.digitalsignallabs.com
Reply by ●October 12, 20072007-10-12
Steve Underwood wrote:> Rune Allnor wrote: >> On 12 Okt, 04:58, "jade" <yunqiyun...@gmail.com> wrote: >>> Hello, >>> >>> I am trying to get the phase difference of two signals. >>> They are at the same frequency. >> ... >> >> Why do you re-post the same question you asked two >> days ago? >> >> Rune >> >> > Its a phase shift thing. You compare the answers to two similar > questions asked out of phase, then correlate for consistency in the > answers. :-)Maybe the phase shift is to make sure there's no dead center. Consider a two-cylinder steam engine. One problem, though. It's hard to ask questions in quadrature without knowing the period. Jerry -- Engineering is the art of making what you want from things you can get. ¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯
Reply by ●October 12, 20072007-10-12
On Oct 12, 2:30 pm, Jerry Avins <j...@ieee.org> wrote:> Steve Underwood wrote: > > Rune Allnor wrote: > >> On 12 Okt, 04:58, "jade" <yunqiyun...@gmail.com> wrote: > >>> Hello, > > >>> I am trying to get the phase difference of two signals. > >>> They are at the same frequency. > >> ... > > >> Why do you re-post the same question you asked two > >> days ago? > > >> Rune > > > Its a phase shift thing. You compare the answers to two similar > > questions asked out of phase, then correlate for consistency in the > > answers. :-) > > Maybe the phase shift is to make sure there's no dead center. Consider a > two-cylinder steam engine. One problem, though. It's hard to ask > questions in quadrature without knowing the period.Maybe the OP is still trying to collect enough reply samples to estimate the period? There's also a decay parameter to be estimated: how long on average will a particular Q&A thread stay on topic? Or perhaps two universities are teaching the same course, but with offset semester start dates, so the automated DSP-homework-question-asking bot net got two initiate commands instead of one?
Reply by ●October 13, 20072007-10-13
Sorry. I am new to this website. I thought this website and the google discussion group are different... Jade>On 12 Okt, 04:58, "jade" <yunqiyun...@gmail.com> wrote: >> Hello, >> >> I am trying to get the phase difference of two signals. >> They are at the same frequency. >... > >Why do you re-post the same question you asked two >days ago? > >Rune > > >
Reply by ●October 13, 20072007-10-13
: ) Really apologize. Did not mean to correlate for consistency in the answers. Just one post got delayed. It seems that the post through google discussion group is faster. Thanks for the help from all your guys... Jade>Steve Underwood <steveu@dis.org> writes: > >> Rune Allnor wrote: >>> On 12 Okt, 04:58, "jade" <yunqiyun...@gmail.com> wrote: >>>> Hello, >>>> >>>> I am trying to get the phase difference of two signals. >>>> They are at the same frequency. >>> ... >>> Why do you re-post the same question you asked two >>> days ago? >>> Rune >>> >> Its a phase shift thing. You compare the answers to two similar >> questions asked out of phase, then correlate for consistency in the >> answers. :-) > >You can also reduce the noise by averaging... >-- >% Randy Yates % "She's sweet on Wagner-I think she'ddie for Beethoven.>%% Fuquay-Varina, NC % She love the way Puccini lays down atune, and>%%% 919-577-9882 % Verdi's always creepin' from herroom.">%%%% <yates@ieee.org> % "Rockaria", *A New World Record*, ELO>http://www.digitalsignallabs.com >
