Bruker BioSpin NMR Fourier 300, Site Planning Manual

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B127527_00_03
Lab Requirements
4.7.2.2 Reducing 16-2/3 Hz and 50/60 Hz Interference
The general goal of reducing 16-2/3 and 50/60 Hz interference is to shield the source of
the interference from the magnet system. Soft iron has been found to be effective in
reflecting this interference, and thus providing an effective shield for the magnet. Bruker
provides planning for shielding using various metals and shielding techniques, please
contact your Bruker office for further information.
4.7.2.3 Guidelines: 16-2/3 Hz and 50/60 Hz Interference
The amplitude threshold for causing interference is approx. 200 nT (2 mG RMS) for
unshielded magnets and 500 nT for shielded magnets, based on laboratory tests. Thus,
acceptable limits must be well below this whenever possible.
The magnet must not be placed within a 6.1 m (20’) radius of a normally-sized
transformer. If there is a large transformer adjacent to the proposed magnet location,
measurements will be required to determine if the transformer will adversely affect NMR
spectra.
The magnet must also not be placed directly under fluorescent lights, which may cause
some 50/60 Hz EMF, and more importantly may switch off temporarily during a quench.
4.7.3 RF Interference
The NMR instrument is effectively a very sensitive radio frequency receiver. Possible
sources of interference are local radio or television broadcasts, low Earth orbit satellite
systems, and signals emitted by personal paging systems. Of particular concern will be
interference at frequencies at which NMR experiments are carried out. Although the
interference effects will depend greatly on the strength of the transmitter, as a rule of
thumb only broadcasting transmitters located within a radius of approximately

5 kilometers (3 miles) are likely sources of interference.
RF interference may also occur between two or more spectrometers located in close
proximity and operating at the same nominal 1H resonance frequency.
4.7.3.1 Measuring RF Fluctuating Fields
Radio Frequency interference measurements should be conducted using a spectrum
analyzer . The analysis should be done for the resonance frequency of each of the nuclei
of interest (proportional to the 1H resonance frequency of the spectrometer). The
minimum frequency sweep is 400 kHz. Any peaks with RF fields above -80 dBm should
be recorded, as well as any broad frequency ranges with any level of RF signals.
Table 4.3 contains a list of the most common studied nuclei at the corresponding
frequencies for 300 MHz NMR systems.