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93
Figure 5-21 Measurement Signal to Noise Ratio
The reading of signal-to-noise ratio is expressed in dBc/Hz because the noise value is a value noise
bandwidth that is normalized to 1 Hz. If it is desired to obtain noise values at different channel
bandwidths, the ratio is reduced by 10 x log (RBW). For example, if the data read by the microwave
analyzer is -77.45dBc/Hz, and the channel bandwidth is 1MHz at this time, the signal-to-noise ratio is:
S/N=77.45dBc/Hz - 10×log(1MHz)=17.45dBc/(1MHz)
At this time, if the difference marker is less than a quarter of the signal peak-to-response edge distance,
there is a potential error in the noise measurement.
3
Measure Noise with Noise Marker Function
This example will use the noise marker function to measure noise in the 1 Hz bandwidth.
a)
Reset the microwave analyzer:
Press
【
Reset
】
, [Default 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 Analyzer:
Press
【
Frep
】
, [Center Freq] , 299.98 [MHz] ;
Press [Span] , 1 [MHz] ;
Press
【
Amplitude
】
, [Ref Level] , -20 [dBm]
d)
Activate the noise marker: Press
【
Mkr
】
, [Noise Mkr On Off] .
Note that the detection mode at this time will be automatically set to sample detection. If you want to get
the noise power value under different bandwidths, the value will decrease by 10×log(BW). For example,
if you want to get the noise power in the 1 kHz band, please add 10 × log (1000) or 30 dB to the read
data.
e)
Move the marker to 300MHz:
Press
【
Mkr
】
and turn the rotary knob in the front panel to make the noise frequency readout 300MHz.
