Agilent Technologies 4395A - Page 397

Spectrum
Measurement
Basics
Selectivity
of
the
RB
W
The
selectivity
of
the
RBW
is
the
ratio
of
the
60 dB
bandwidth to
3dB
bandwidth (RBW)
of the
lter
.
The
selectivity
denes
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
dierence 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