Radio Free DAQ?

[jasonhill]

After installing a lowpass filter on the SCB-68 for my PXI-6133, I still get 850kHz noise.  I realize that it is unreasonable to exclude all noise, but this one is ~15% of my full scale voltage and will therefore have a significant impact on all of my measurements.  Any ideas?

Message Edited by jasonhill on 04-20-2006 03:25 PM

[AnalogKid2DigitalMan]

Strange, that's right in AM broadcast band as you stated, is there a local station around with that frequency?

What is your sampling rate and BW of signals you are interested in?

Does it show up on an oscilloscope with the DAQ hardware disconnected, if a scope is available? To figure out if it is noise external to the DAQ HW or being generated within it somehow.

Notch filter at 850kHz???

[jasonhill]

There is a local station that broadcasts at 850kHz.  Oddly, there are closer stations that do not show up.  The noise is apperent even at the highest sampling rates (2.5M/s).  Thankfully, the signal I am interested in is at a much lower frequency.  I am just confused as to how the noise made it through my lowpass filter.  It should be KILLING everything over ~10Hz. 

Yes, I know it is crazy to be using this equipment to measure such a low signal, but this is the only equipment I have availible.  I cranked up the sampling rate to limit the anti-aliasing.  And I put in the brutal lowpass to try to get rid of the noise.  It got rid of the 60Hz from my power supply, but not the stupid 850kHz.