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Re: dBm plot of frequency spectrum of signal
Posted:
Apr 8, 2013 9:51 PM


"Abhay Kumar" <akumar.elex@dauniv.ac.in> wrote in message <eed0992.0@webx.raydaftYaTP>... > shahida wrote: > > > > > > > > i want to plot frequency spectrum of a signal dBm vs frequency. > > eg. for following signal > > t=(0:1:100)/10e3; > > s=sin(2*pi*t*1e3); > > > > Hi > Thats pretty simple > > s1=fft(s); > w=(0:length(s1)/2)*1/2% generate frequencies > s2=10*log10(s1.*conj(s1)*1e3)%power in dBm > plot(w,s2(1:length(w))) > > hope it helps > Dr. A. Kumar
Thanks for your input, Dr. Kumar. That formula is correct, but I wanted to add that this particular formula is normalized to a system impedance of 1 ohm. A more generalized form would include the system impedance: R=50; s2=10*log10((s1.*conj(s1))/R*1e3);
A good article that goes into depth about plotting a power spectrum can be found here: http://www.bitweenie.com/listings/powerspectrummatlab/
That website also included some interesting information on singlesided and doublesided power spectrums.



