Electrical signal analisis

[Jaime Alberto Silva]

I'm new in the use of this tools (octave, mathlab, etc.) and since I'm a 
full time Linux user I am using octave.

Currently, I'm trying to do some electrical signal analysis and I will 
like to know if there are predefined functions for some calculations or 
how can I do them with octave:

1. Frecuency: I have founded in the "Signal Processing" section the fft 
function, OK it is great but how do I find the frecuencies from the 
returned vector. I know that using the max function I can find the 
fundamental frecuency like this:

# Create the signal:
octave:190> t= [0: 1/2000: 5 - 1/2000];
octave:191> sint= sin(2*pi*60*t);
# Transform the signal:
octave:192> ft= abs(fft(sint));
# Find the position of the max value of the transformation:
octave:193> [val, idx]= max(ft);
# Use the sampling rate to obtain the fundamental frecuency:
octave:194> fund_frec= 2000 * idx/ length(ft)
fund_frec = 60.200
octave:195>

But how can I find the other frecuencies in case it has more components 
like in
f= sin x + 0.5 sin 3x + 2 sin 10x ?

2. Phasors: If I have 2 signals like v1 an v2 how do I find the angle of 
v2 with respect of v1. I mean if v1= sin (t) and v2= sin (t + 15°) and I 
have sampled those signals in time, how do I find that v2 is delayed 15 
degrees with respect to v1? taking in account that v2 samples where 
taken in different times to v1 samples like this: v1(1) was taken at T0, 
v2(1) was taken at T0 + dT. And, of course, you know the value of dT.

3. Electric Power: If I have sampled the signals of voltage (V) and 
current (I) are there any tools that l can use to obtain the active (P) 
and reactive (Q) power, the S vector angle, etc. ? I know that I can 
multiply the signals but, you know if there are tools for that why do it 
again.

Thanks in advance for any help you can bring me.

--
--
Jaime Alberto Silva Colorado



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