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The 60 Hz waveband.
The spectra are summarized consistent with the methodology of the
original researchers, as follows. The waveforms of the three axes were
used to independently compute magnetic field intensity at 5 Hz
intervals using standard Fast Fourier Transform techniques. The
resultant magnetic field intensity for each 5 Hz waveband was computed
as the square root of the sum of the squares of the corresponding
waveband of the three axes. The magnitude of each waveband component
is divided by the square root of two in order to convert to a
root-mean-square (rather than a peak-to-peak) value.
The original researchers noted that this procedure results in some
inappropriate leakage of spectral energy from the 60 Hz band into
adjacent bands. Following the example of the original researchers, a
correction is applied by diverting some energy found in adjacent
wavebands back into the 60 Hz band. A factor for each nearby waveband
was established by the original researchers. The square of the
product of this factor and the observed 60 Hz component are subtracted
from the square of the nearby waveband component and added back to the
square of the 60Hz component. The factors (and corresponding
waveband) used for the correction are as follows: 0.040 (40Hz); 0.052
(45Hz); 0.076 (50Hz); 0.141 (55Hz); 0.197 (65Hz); 0.090 (70Hz); 0.058
(75Hz); and 0.043 (80Hz).
The power frequency resultant magnetic field is the
corrected 60 Hz waveband component.
Approximately 3%, but no better than about 0.1 milligauss.
A positive real number, in units of milligauss.