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81
I.
Apply resolution bandwidth to resolve signals with very close frequencies
1
Description of resolution bandwidth
The signal resolution is subject to the resolution bandwidth (RBW) of the microwave analyzer. When a
signal passes through the IF filter, the microwave analyzer uses the signal to sweep the bandpass shape
of the IF filter. Therefore, when the microwave analyzer receives two signals of equal amplitude and
close frequency, it appears that the top of the bandpass filter waveform swept by one of the signals
covers almost the other signal, so that the two signals look like a signal. If the two signals are not equal
in amplitude but their frequencies are still close, there is a possibility that the small signal is
overwhelmed by the response of the large signal.
2
Resolve Two Equal Amplitude Signals
If two equal amplitude signals are to be resolved, the resolution bandwidth must be less than or equal to
the frequency spacing of the two signals. For example, to resolve two equal-amplitude signals differing
by 100 kHz, the resolution bandwidth of the microwave analyzer should be set to be less than or equal
to 100 kHz. The following is the step of measuring the equal amplitude signal with two frequencies
differing by 100 kHz:
a) Use the T-connector to connect the outputs of the two signal generators to the RF input port of the
microwave analyzer as shown in Figure 5-7.
Signal Generator 1
Power
Microwave analyzer
Signal Generator 2
Figure 5-7 Connection Diagram for Instrument for Obtaining Two Input Signals
b) Set one of the signal generators to have a frequency of 300 MHz and the other signal generator to
have a frequency of 300.1 MHz. The output amplitudes of the two signal generators are both set to
-20 dBm, and the signal output amplitude of two signal generators are respectively adjusted. Then
observe the display signal of the microwave analyzer, so that the two signals displayed by the
microwave analyzer are equal in amplitude.
c) Set up Analyzer to observe the signal:
Press
【
Reset
】
, [Default State] ;
Press
【
Frep
】
, [Center Freq] , 300 [MHz] , [Span] , 2 [MHz] ;
Press
【
BW
】
, [RBW Auto Man] , and enter 300 [kHz] .
At this point, user can see that there is only one signal peak in the display screen of Analyzer, as shown
in Figure 5-8.
