Hi,
I couldn't gauge your level of LabView expertise from the email, but
here's a few things to try to get you started.
I think you have a two part problem: the first is to properly extract
the (I,Q) pairs, then next is to perform the complex FFT.
To start - you'll need to figure out the precision of the numbers that
are encoded into Hex - basically - how many bytes per I and how many
bytes per Q. There must be some sort of documentation that accompanied
the I,Q data. You'll also need to know if the file it binary hex or
ASCII hex. If you open the file in a text editor (Notepad (PC), or
TextEdit (Mac)) do you see gobbledy gook, or numbers and letters
running from 0 to 9 and A-F?
Lets say (for example only) that you have 32 bit values (4 bytes) - I
would write a VI that reads through the entire file as a binary file or
text file (not a datalog file) in 4 byte chunks, pass each of the 4
bytes through the "Hexadecimal String to Number". Continue reading, 4
bytes for I, 4 bytes for Q, I,Q,I,Q,I,Q,I,Q,I,Q,I,Q,...
You should familiarize yourself with the Complex Numerics pallet - only
5 VIs. They let you go from I,Q (Real, Imaginary) to Z complex to and
from R,Theta.
Once you've got the IQ reading in you should convert them to what's
called Complex(z). You'll want to use the Complex Numeric VI called
"Re/Im to Complex". Send I into the "re", and Q into the "im". Once
you're in Z space, send the Z into the "Complex FFT.vi" what comes out
will be Z in the frequency domain. Using another complex vi - "Complex
to Polar" will give you R and Theta - you'll want R.
As far as the signal processing from there, you're on your own. I
should mention that you'll almost always want to add a windowing
function to the data before it's FFT'ed. For starters try a Hanning or
Hamming window (both available in the Windowing palette). You'll need
to apply the window to I and to Q before the complex FFT. I know that I
typically use a Hanning window, FFT, get R, square R (to get power) and
put into dB space (log b10 times 10).
So:
Read in hex -> hex to number (I,Q) -> window I,window Q, -> I,Q to Z
complex -> Complex FFT -> Z to R Theta...
Good Luck,
Jason
[EMAIL PROTECTED]
_____________________________________
Jason C. Dickinson
Terahertz Scientist
Submillimeter-Wave Technology Laboratory
University of Massachusetts Lowell
Lowell, Massachusetts
______________________________________
> Subject: FFT a set of I & Q signals
> From: "Mohamed Ezzat" <[EMAIL PROTECTED]>
> Date: Wed, 3 Mar 2004 08:58:55 -0800 (PST)
>
> Hi All,
>
> I have a hex file that contain a set of I & Q signals
> and I would like to plot them in the frequency domain.
> I know that I have to use FFT to do so but the file
> saved them in number next to each other. what should I
> do in order to display the signal in the frequency
> domain.
>
> Thanks.
>
> Mohamed
>
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