Agilent Technologies 4395A, Manual Change

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Spectrum Measurement Basics
Selectivity of the RB W
The selectivity of the RBW is the ratio of the 60 dB bandwidth to 3 dB bandwidth (RBW) of the
lter . The selectivity denes the shape of the lter . This factor is important when resolving
small signal that is adjacent to a large signal. The small adjacent signal is hidden by the large
signal even when the resolution bandwidth is set to smaller than the dierence of frequency
between the signals . T o resolve small adjacent signals , the resolution bandwidth must be set so
that the small signal is not hidden by the large signals as shown in Figure A -13.
Figure A -13. Resolving Small A djacent Signal
Because the 4395A uses a digital lter technique , the selectivity of the analyzer is better
(smaller) than a conventional spectrum analyzer (which uses analog lter technique). This
means the 4395A can detect a small signal that could not be detected by a conventional
spectrum analyzer .
Basic Measurement Theory A-21