Keysight Technologies 86120B, User Manual

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70
Measurements Applications
Measuring Signal-to-Noise Ratios
Location of noise measurements
Automatic
interpolation When the signal-to-noise “auto” function is selected, the Keysight 86120B 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 fig-
ure.
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 measured at 100 GHz on either side of
the signal of interest. The two measured noise power levels are then averaged to
estimate the noise power level at the signal wavelength. The noise power measure-
ments use linear interpolation to estimate the noise power level at the signal of inter-
est’s wavelength.
Automatic interpolation