R3131 Spectrum Analyzer Operation Manual
APPENDIX 2 GLOSSARY
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(a)
Figure A2-4 Noise Sidebands
20 kHz
(b)
Bandwidth Selectivity
The bandpass filter normally attenuates using a Gaussian distribution instead of the so-called rectangular
characteristic. Consequently, if two adjacent signals of different sizes are mixed, the smaller signal hides at
the tail of the larger signal (Figure A2-5).
Therefore, the bandwidth at a certain attenuation range (60 dB) should also be defined. The ratio between the
3 dB width and 60 dB width is expressed as the bandwidth selectivity (BW60 dB/BW3 dB).
(a) Separation of signal at different levels (b) IF filter selectivity
Figure A2-5 Bandwidth Selectivity
Bandwidth Accuracy
The bandwidth accuracy of the IF filter is expressed by the deviation from the nominal value of the 3 dB
lowered point. This deficiency has almost no effect on measurement of normal signals at a continuous level,
but it should be taken into consideration when measuring the level of a noise signal.
A2-4
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