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20
Fig. 3.8 Small Signals when pre-amplifier On
CAUTION
After finishing the test, please remember to increase the attenuation of the Spectrum
Analyzer to protect the RF input port of the Spectrum Analyzer.
3.3.2 Reduce resolution bandwidth to measure small signals
The resolution bandwidth affects the internal noise base of the Spectrum Analyzer but will not affect the level of
measured continuous wave signal. The relation between noise reduction and resolution bandwidth can be
expressed with the following formula:
L
10log BW
1
BW
2
Where, ∆L is the change of the noise amplitude, expressed in dB.
BW
1
, BW
2
are different resolution bandwidths, expressed in Hz.
Therefore, when the frequency bandwidth is reduced by 10 times, the noise floor will be reduced by 10 dB.
a)
Reset the spectrum analyzer
Press
【
Preset
】
key to restart the spectrum analyzer.
b)
Set the center frequency, the span, and the reference level
Set the frequency of the external signal generator to 300MHz and set the amplitude to -80dBm, and connect the
radio frequency output end of the signal generator to the radio frequency input end of the spectrum analyzer. Set
the center frequency of the spectrum analyzer. Press
【
Freq
】
and select [Center Freq] to set the center
frequency to 300MHz, and then select
【
Span
】
to set the span to 5MHz. Press
【
Ampt
】
and select [Ref Level]
to set the reference level to -40dBm.
