Anritsu MS8608A, Operation Manual, Page: 129 / 338

Section 6 Performance Tests
6-17
Resolution bandwidth (RBW) and selectivity
If there are two input signals with the frequency difference corresponding to 3 dB
bandwidth (of IF final stage), these signals can be resolved as two spectrum waveforms.
This is called the resolution bandwidth.
Selectivity can be improved by narrowing the 60 dB bandwidth. The selectivity is
defined by the ratio of the filter width, in Hz, at the –60 dB point, to the filter width, in
Hz, at the –3 dB point, as shown in the formula below.
Center frequency
3 dB
bandwidth
60 dB
bandwidth
3 dB
60 dB
Frequency
60 dB bandwidth (Hz)
3 dB bandwidth (Hz)
Selectivity =
To test the resolution bandwidth and selectivity, first measure the resolution bandwidth
(3 dB bandwidth), then the 60 dB bandwidth and calculate the 60 dB/3 dB bandwidth
ratio.
(1) Specifications
• Resolution bandwidth accuracy:
±
20% (RBW=300 Hz to 10 MHz)
±
40% (RBW=20 MHz)
• Selectivity (60 dB/3 dB bandwidth):
≤
15:1
(2) Test instrument
• Synthesized signal generator: MG3633A
Amplitude