High frequency noise originating in BNC-2090A with PXIe-8135

[efmkoene]

Dear NI forum,

I'm dealing with a case of high frequency noise originating from the DAQ board. With the DAQ simply turned on, not triggering, a constant ±10 mV signal is output through the output channel, with occasional 'blips' of ±100 mV. In the current set-up, this DAQ output is connected to an 100x voltage amplifier and used to control an acoustic projector. The noise level strongly interferes with measurements. I think that the high frequency blips cause an impulse response at the side of the projector, causing it to resonate constantly.

The image below gives an example of the encountered noise, with the system on standby.

(TOP: recorded signals, BOTTOM: FFT spectrum of signals // red: recorded (acoustic) signal, yellow: output voltage signal from PXIe-8135, blue: feedback voltage from TREK amplifier). The 'blip' is clearly visible in the top frame in the yellow signal.

The encountered frequencies are a 'low frequent' noise of 60 kHz, 200 kHz, 400 kHz (the three visible peaks on the above image), while the 'blip' has a wavelength of around 1.6 MHz (see image below for a zoomed view of the blip).

Does anyone have an idea of how to resolve this issue / familiarity with noise in this frequency range?

[mattsnow]

Hi efmkoene, 

I understand you're experiencing some high frequency noise from (presumably) your DAQ board. Your system consists of a PXIe-8135 controller connected to a DAQ board, which interfaces with a BNC-2090A connector block. On the output there is a 100x Trek amplifier which is controlling an acoustic projector. 

May I ask some questions to gain a better understanding of the setup you have running;

What model DAQ board are you using? 
What is an accoustic projector in the context of your system (some searching only returned home cinema products)?
At what point in the system are you measuring this noise?
What sort of noise level would be acceptable for your system? 

I'll admit I'm not too familiar with high-frequency noise relating to this product but I'll do my best to help find a solution.

Kind regards