Hi there fellow spinlanders,
Hope everyone is doing well and enjoying the last bits of summer. I am
writing to this group to see if any of you might have suggestions in
things to try to remove a radio station's noise from a NMR spectrum.
One of the researchers here at UVM is interested in doing 77Se NMR, and
we've been running spectra most of the year, since I calibrated pw's
back in February. As soon as I started acquiring these 77Se spectra, I
also noticed significant noise in the baseline, later to be determined
that it is coming from a radio station's transmitting tower, located
about a mile as the crow flies. Unfortunately both our NMR
spectrometers are 500MHz spectrometers, putting the 77Se signal at about
95.4 HMz (500ppm), depending on where you center the spectrum. The 77Se
spectrum spans a very wide ppm, from -1000ppm to +2000ppm. The
compounds we are looking at resonate at about 270ppm and as far up as
1200ppm.
To test whether this is a radio signal noise, I changed the BSMS field
value by about 5000 units. The 77Se peak from the sample changed
position, while the radio noise stayed in the same place. I later also
determined that the noise spans 150kHz or 1600ppm in the 77Se scale, and
it is centered at 95.50 MHz, which is the frequency of WXXX FM (triple
X) ...and I'll leave it up to your imagination as to what kind of music
they broadcast! I'm attaching a spectrum of what this noise looks like,
although this particular spectrum doesn't encompass the entire noise
range, just might give you an idea as to how difficult it is to pick up
sample signals in this range.
Upon Bruker's suggestions, I have tried a few things, to no avail. I
have tried disconnecting the thermocouple and heater cables to the
probe, to see if they are acting as antennae. I've tried disconnecting
the receiver cable from the back of the preamp, to see if signal is
getting in thru there. And yep, radio signal is still there whether
receiver cable is connected or not. I've also tried disconnecting the
yellow cable that leads to the top of the BST, I think it is the spin
regulation monitoring cable, and still saw the radio noise.
Please let me know if you might have some simple suggestions that would
help eliminate this noise. I also don't want to pour tons of my time
into this, and not willing to build a whole Faraday cage around my
spectrometer. If we only had a 400 or a 600... but then likely some
other radio station would interfere with one of the nuclei we're
interested in... The other NMR in town is a 300 with a quad probe,
there are other NMRs across the lake, just too hard to get to.
If you have any ideas, please let me know!
Cheers,
Monika
--
Monika Ivancic, PhD
NMR Facility Manager (A-212)
Department of Chemistry
82 University Pl.
University of Vermont
Burlington, VT 05405
(802) 656-0285 office
(802) 656-0279 NMR lab
Monika.Ivancic_at_uvm.edu
Received on Mon Aug 17 2015 - 10:38:18 MST