Addition of Noise NI 6211

[RAMOLEMISS]

I was using N16211 card to record the FM modulated signal with 100kHz sampling rate. The data which I have taken 2 months ago was less noisy than recent data, the FFT data attached it is clearly visible. Why the noise increases almost 100 times 

[MRicefield]

What I understood from the images is that the noise was up over a wide range of frequency. Nothing such as an environment was changed between two measurements?

[RAMOLEMISS]

Yes, experimental condition is just the same, but how the noise increases, NI card used to generate a TTL to record the FM modulation? Is it because of grounding issue ? The modulation frequency is 200Hz, but in  the demodulation I have observed a addition harmonic frequencies of 60Hz, 120 Hz, etc

[GerdW]

Hi Ramolemiss,

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@RAMOLEMISS wrote:

Yes, experimental condition is just the same, but how the noise increases, … The modulation frequency is 200Hz, but in  the demodulation I have observed a addition harmonic frequencies of 60Hz, 120 Hz, etc

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Do you live in a country where the main supply uses 60Hz AC (in contrast to Central Europe with 50Hz)?

Did something change inside/outside the test chamber about main supply wiring or larger devices (regarding power consumption)?

[RAMOLEMISS]

Yes, I am working in the United States, 2 months back the demodulation doesn't contain these frequencies. Now, noise and these frequencies get added.  This 6211 NI card which also used for generating a TTL output with clock frequency 100kHz to trigger the camera when the camera needs external triggering.