  When deploying a spectrometer in an adverse environment, such as during a
typical ODNP experiment or experiments that require low-volume low-field
measurements, a clear and modern protocol for characterizing and quantifying
the absolute signal and noise levels proves essential. This paper provides such
a protocol. It also highlights the clarity and insight that comes from (1)
discussing NMR signal intensities in (conserved) units of square root
instantaneous power that are derived from a theory and notation developed
initially for ESR spectroscopy; as well as (2) characterizing the spectral
distribution of the noise.
  Crucially, the strategy introduced here applies not only to ODNP
measurements, but to all low-field NMR. Low-field NMR offers immense
flexibility: it enables integration with other instrumentation and deploys in
practical applications not accessible to higher-field instrumentation. More
generally, the protocol introduced here should apply to a wide range of
instruments, and should prove especially useful in cases subject to design
constraints that requires integration with multiple other modules that are not
dedicated to NMR but that control other forms of spectroscopy or other crucial
aspects of the measurement. However, in the specific case of ODNP, this
protocol demonstrates that the absolute signal and noise level can be estimated
from the clarified theory presented here, and uses that theory to identify the
inefficient distribution of fields in the hairpin loop probe as the main
remaining bottleneck for the improvement of low-field low-volume ODNP SNR.
