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Making Measurements
Measuring Signal-to-Noise Ratios
Location of noise measurements
Automatic
interpolation
When the signal-to-noise “auto” function is selected, the
Agilent 86120C first determines the proximity of any adjacent signal. If
the next closest signal is ≤200 GHz (approximately 1.6 nm at 1550 nm)
away from the signal of interest, then the noise power is measured
half way between the two channels and an equal distance to the other
side of the signal of interest. See points P
n1
and P
n2
in the following
figure.
If the closest signal is more than 200 GHz from the signal of interest,
or if there is no other signals present, then the noise power is mea-
sured at 100 GHz on either side of the signal of interest. The two mea-
sured noise power levels are then averaged to estimate the noise
power level at the signal wavelength. The noise power measurements
use linear interpolation to estimate the noise power level at the signal
of interest’s wavelength.