IFFT using complex numbers

[kengkc]

Hi,

    I am trying to use IFFT to compute my impulse response for my channel. I have some problems in converting my data to complex numbers. I have some questions in mind.

1) The IFFT.vi allows me to choose dor 1D complex numbers. I wonder what is the orientation of the input array. Is it (x+yi)? By the way, I have extracted two sets of numbers (One is real (x) and another is imgainary(y)).

2) Currently, I have two sets of numbers. one is the real and another is imaginary numbers. I have tried to convert both of them to a rectangular form, using re/img to complex.vi. However, my displayed results are only in real numbers ( I cannot see the form x+yi after saving the data in .dat file but only x value). I wonder the said re/img to complex.vi allows to convert into x+yi? If possible, how can I acheived in getting the x+yi, rectangular form to input to IFFT.vi for further conversion for impulse response.

Thanks for help.

Rdgs

Keng Boon

[GerdW]

Hi Keng,

for point 2:
Instead of saving to a .dat file (How did you do that? A file extension doesn't say anything about how you created that file...) create an indicator on the output of the "re/img to cmplx" function. Here you can see your complex numbers...

[kengkc]

Hi Gerd,

              Thanks for advice. I have tried your method. However,  my output seems to show only my real value. I wonder the complex numbers are refering to rectangular form of x+yi? For x+yi, is it a 2 dimension form? Thanks for advice.

Regards

Keng Boon

[GerdW]

Hi Keng,

I don't know what your doing with your complex numbers, but I get "x+yi" representation:

(I made an array of ComplexDBL numbers to show flexibility of Labview programming)
 


Message Edited by GerdW on 06-23-2008 04:05 PM

[kengkc]

Hi Gerd,

             Thanks. I think I have set the wrong indicator. Thanks. Currently, I have to wonder is the input for IFFT.vi, be complex numbers in rectangular form (x+yi)?

Rdgs

Keng Boon

[MathGuy]

LabVIEW stores complex scalars in Cartesian form (i.e. rectangular form). Polar form of complex data requires separate storage for the magnitude and phase components. In the case of arrays of complex data (e.g. CDB, etc), the particular storage is abstracted away by indexing and vector operations but you should still think of each array element as a complex value stored in Cartesian form.

When using the functions on the Complex palette, the Polar To Complex and Complex To Polar functions will convert the complex value to and from the internal form (aka Cartesian). That means that the function Polar To Complex is numerically equivalent to the function Polar To Re/Im followed by the function Re/Im to Complex.