Agilent Technologies 4395A - Page 398

Spectrum
Measurement
Basics
Noise
measurement
Noise
Format
and Marker
Noise F
orm
When
a spectrum
analyzer
measures
noise
,
the
power
shown
by
an
analyzer
is
in proportion
to
RBW (because
spectrum
analyzers
measure
total
power
coming
thorough
RBW).
F
or
noise
measurement,
the
measurement
value
is
usually
normalized
by
an
equivalent
noise
bandwidth
of
an
RBW
lter
(frequency).
The
noise
format
automatically
normalizes
noise
power
by
the
equivalent
noise
bandwidth
and
displays
the
trace
on
the
screen.
The
marker
noise
form
also
reads
out
the
noise
level
normalized,
even
if
the
format
is
the
spectrum.
Sample
Detection
Mode
for
Noise
Measurement
F
or
noise
measurement,
the
sample
detection
mode
is
best.
Because
the
power
of
noise
is
uniformly
distributed
over
frequency
,
it
is
not
necessary
to
measure
all
the
frequencies
between
the
display
points
.
It
is
sucient
to
measure
only
the
display points
. This
is why
the
sample
detection
mode
is
used
for
noise
measurement.
VB
W
for
Noise
Measurement
Y
ou
should
specify
a
smaller
VBW
when
using
the
4395A
to
measure
noise
levels
.
T
o
obtain
accurate
noise
level
measurements
,
it
is essential
to determine
the average
value
over
a
relatively
long
period.
With
a
smaller
VBW
,the
4395A can
determine the
average time
domain
at
each
measurement
point.
A-22 Basic Measurement Theory