Cross power spectrum and problems with number of averages.

[rjerez]

"I am using Labview 5.1 on Windows 95 and the AT-MIO-16XE-50 board.
I have been trying to get the Cross Power Spectral Density (CPSD) of two signals in the frequency range from 2.0mHz to 10 Hz with a reazonable resolution. I am not seeking for any peaks, but for the shape of the CPSD. When I acquire many sets of two-averages-CPSD, and make the final average, I get wrong result. But, when I acquire many sets of five-averages-CPSD, the final result is correct.
My question is: Why the final result (say, 100 averages), is wrong when the sets are formed by two-averages, but is correct when it is formed by a number larger than 2?

Thanks in advance.
Ricardo."

[Jeremy Braden]

I am no expert, and I am guessing here. By averaging the signals, you reduce the signal to noise ratio to a point lower than that of the unaveraged signals. This reduction in noise is why you are getting the better readings.

Jeremy