Environment and Site Survey Measurement
56 H157655_1_008
7.3.4.2 Most Commonly Studied Nuclei
Nuclei NMR Frequency (MHz)
Magnets 400 500 600 700
1H 400.000 500.000 600.000 700.000
2H 61.422 76.773 92.124 107.474
11B 128.378 160.462 192.546 224.630
13C 100.613 125.758 150.903 176.048
15N 40.560 50.697 60.834 70.971
19F 376.498 470.592 564.686 658.780
27AI 104.261 130.318 156.375 182.432
29Si 79.495 99.362 119.229 139.096
31P 161.976 202.456 242.937 283.418
Table7.7: List of Most Commonly Studied Nuclei and Corresponding Resonance Frequencies
7.3.4.3 Guidelines for HF Interference
As a general guideline the level of any HF interference should be less than an electrical field
strength (detection: max. peak) of 80 dBuV/m with a minimum Resolution Band Width (RBW)
of 300 kHz at the side of the magnet.
7.3.4.4 Reducing HF Interference
Screening a site for possible HF Interference is complicated and expensive. Shielding of the
laboratory with a Faraday cage is a possible solution, though having to take such measures
is quite rare.
When designing and manufacturing the Bruker spectrometers, care is taken to provide
adequate shielding and the instruments rarely suffer from interference in normal HF
environments. Furthermore, the advanced BSMS digital lock system - included with all Bruker
AVANCE spectrometers - allows a shift in the 2H lock frequency with certain limits. This may
allow enough variation in the absolute magnet field strength to shift the NMR signal away
from that of local broadcasting frequencies.
HF interference may occur between two or more spectrometers located in close proximity
and operating at the same nominal 1H resonance frequency. These problems can be avoided
by energizing the different magnets at slightly different fields, such that their operational
frequencies are separated by ~ 200 kHz at the nominal 1H resonance frequency.
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