PXI 4464 noise floor instability

[Giustife76]

Hi all,

I'm facing some issue with PXI-4464 used as acquisition card. I'm providing an input signal 1Vp@1kHz and measuring the FFT spectrum using the DSA Soft Panel. The input signal is provided by PXI-4463, but the issue is the same if I use an external waveform generator, so it is not related to the source. The issue is that the spectrum noise floor is not repeatible, that is if I launch the acquisition let's say 10 times, I get  nearly 7 times a "high" noise floor and 3 times a "low" noise floor. Also strange the fact that when the noise is lower at low frequency, it is higher at high frequency and viceversa. I have tried to change the input termination, the input range, the sampling frequency, no way. See attached plots. Another information: it happens only if I stop and restart a new acquisition, while if I continue with the same run the floor tends to be constant.

Looks like some memory or DSP circuit is not well resetted. Any clues?

Thanks in advance.

Federico

[santo_13]

It could as well be a bug in the DSA soft front panel. I would recommend performing the same experiment using the DAQmx drivers.

Stop and restart the acquisition would reset some circuits on-board, that could as well be the case.