Specifications

48 Chapter 7
Measuring Noise
Measuring Signal-to-Noise
Measuring 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. Preset the analyzer:
Press
Preset, Factory Preset (if present).
Step 2. Enable the internal 50 MHz amplitude reference signal as follows:
(PSA)
Press
Input/Output, Input Port, Amptd Ref.
(ESA E4401B and E4411B)
Press
Input/Output, Amptd Ref (On).
(ESA E4402B, E4403B, E4404B, E4405B, E4407B and E4408B)
Connect a cable from the front panel AMPTD REF OUT to the analyzer
RF input:
Press
Input/Output, Amptd Ref Out (On).
Step 3. Set the center frequency, span, reference level and attenuation:
Press
FREQUENCY Channel, Center Freq, 50, MHz.
Press
SPAN X Scale, Span, 1, MHz.
Press
AMPLITUDE Y Scale, Ref Level, −10, dBm.
Press
AMPLITUDE Y Scale, Attenuation, 40, dB.
Step 4. Place a marker on the peak of the signal and then place a delta marker
in the noise at a 200 kHz offset:
Press
Peak Search.
Press
Marker, Delta, 200, kHz.
Step 5. Turn on the marker noise function to view the signal-to-noise