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92
Figure 5-20 Measuring a Small Signal Using a Preamplifier
IV. Noise Signal Measurement
1
Concept
In communication system, the signal-to-noise ratio is usually used to characterize the noise. If the
noise level added to the system is much larger, the signal-to-noise ratio will be worse, resulting in more
difficult in demodulating the modulated signal. In a communication system, the signal to noise ratio
measurement also normally refers to the ratio measurement of carrier to noise.
The S5105D/E/F microwave analyzer has a noise marker function that can be used to measure signal-
to-noise ratio and noise. The following illustrates the measurement steps of the noise signal by taking
the measurement of the signal-to-noise ratio of a single-frequency signal as an example.
2
Measure Signal-to-noise
a)
Reset the microwave analyzer:
Press
【
Reset
】
, [Factory State] .
b)
Set the signal generator and connect the microwave analyzer with a cable:
Set the frequency of the signal generator to 300MHz and the amplitude to -60dBm. Connect the RF
output of the signal generator to the spectrum input of the microwave analyzer and turn on the RF output
of the signal generator.
c)
Set the center frequency, span and reference level of the microwave analyzer:
Press
【
Frep
】
, [Center Freq] , 300 [MHz];
Press [Span], 1 [MHz];
Press
【
Amplitude
】
, [Ref Level], -20 [dBm]
d)
Place the marker at the peak position of the signal, then place the difference marker at the noise
position with a frequency offset of 200 kHz:
Press [peak];
Press
【
Mkr
】
, [Delta Mkr], 200 [kHz] .
e)
Turn on the noise marker function to view the signal to noise ratio:
Press
【
Mkr
】
-> [Noise Mk Off On] -> [Peak] -> [Max] , as shown in Figure 5-21.
