Measuring Signal-To-Noise - Keysight X Series Measurement Manual

Measuring Noise

Measuring Signal-to-Noise

Measuring Signal-to-Noise
Signal-to-noise is a ratio used in many communication systems as an indication of
noise in a system. Typically the more signals added to a system adds to the noise
level, reducing the signal-to-noise ratio making it more difficult for modulated
signals to be demodulated. This measurement is also referred to as carrier-to-noise in
some communication systems.
The signal-to-noise measurement procedure below may be adapted to measure any
signal in a system if the signal (carrier) is a discrete tone. If the signal in your system
is modulated, it is necessary to modify the procedure to correctly measure the
modulated signal level.
In this example the 50 MHz amplitude reference signal is used as the fundamental
signal. The amplitude reference signal is assumed to be the signal of interest and the
internal noise of the analyzer is measured as the system noise. To do this, you need to
set the input attenuator such that both the signal and the noise are well within the
calibrated region of the display.
Step
1 Set the analyzer to the
Spectrum Analyzer
mode.
2 Preset the analyzer.
3 Enable the internal
reference signal.
4 Set the center frequency,
span, reference level and
attenuation.
5 Place a marker on the
peak of the signal and
place a delta marker in
the noise.
6 Turn on the marker noise
function.
Action
• Press Mode, Spectrum Analyzer.
• Press Mode Preset.
• Press Input/Output, RF
Calibrator, 50, MHz.
a. Press FREQ Channel, Center
Freq, 50, MHz.
b. Press SPAN X Scale, Span, 1,
MHz.
c. Press AMPTD Y Scale, Ref Level,
−10, dBm.
d. Press AMPTD Y Scale,
Attenuation, 40, dB.
• Press Peak Search, Marker Delta,
200, kHz.
• Press Marker Function, Marker
Noise.
72
Notes
This enables the spectrum
analyzer measurements.
This enables you to view the
signal-to-noise measurement
results.