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Making Measurements
Measuring Signal-to-Noise Ratios
Measuring Signal- to- Noise Ratios
Signal-to-noise measurements provide a direct indication of system
performance. Signal-to-noise measurements are especially important in
WDM systems because there is a direct relation between signal-to-
noise and bit error rate. The Agilent 86120C displays signal-to-noise
measurements in the third column. For example, the selected signal in
the following figure has a signal- to-noise ratio of 30.0 dB.
Signal-to-noise display.
During a signal-to-noise measurement, the absolute power of the car-
rier, in dBm, is compared to the absolute power of the noise at the
carrier wavelength. See the following figure. The noise power at the
carrier must be determined by interpolation because the carrier, in
most cases, can not or should not be turned off.
You can select one of two methods used to determine the wavelength
where the noise is measured: automatic interpolation or a user-entered
wavelength. In the figure above, notice that “S/N AUTO” is displayed
to indicate that automatic interpolation is selected.