Hello Monika,
I recently had a similar problem with seeing a radio station. The problem
was caused by a broken cable. Once we replaced that cable, the radio
station signal was removed. In the past, I have added extra shielding
around cables and extra grounding connections. Also, in my case with the
broken cable, we noticed that the signal was actually folding in by opening
up the sw. If that is the case for you, you may be able to move the signal
into a region, where it is outside your signal. Of course finding the
origin of the leakage of it would be better, but that might be a trick to
avoid the signal.
Good luck,
Ulli
On Mon, Aug 17, 2015 at 5:38 PM, Monika Ivancic <mivanci1_at_uvm.edu> wrote:
> 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
>
>
--
Dr. Ulrike Werner-Zwanziger
Adjunct Professor
Department of Chemistry, IRM, NMR-3,
Dalhousie University
6274 Coburg Road
PO BOX 15000
Halifax, NS B3H 4R2
e-mail: Ulli.Zwanziger_at_Dal.ca
Tel. 902 494 8085
Received on Tue Aug 18 2015 - 14:23:18 MST