SECTION 6 PERFORMANCE TESTS
6-18
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 (3dB bandwidth), then
the 60 dB bandwidth and calculate the 60 dB/3 dB bandwidth ratio.
(1) Specifications
• Resolution bandwidth accuracy:
±20 % (RBW=1 kHz to 1 MHz)
±30 % (RBW=3 MHz)
• Selectivity ( 60 dB/3 dB bandwidth ):
≤ 15:1 (RBW=1 kHz to 3 MHz)
(2) Test instrument
• Synthesized signal generator: MG3633A
Amplitude
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