Agilent Technologies Printer Accessories 85671A Manuale Utente
4
If
Y
ou
Have
A
Problem
Signal
disappears
during
measurement
If
the
output
frequency
of
the
device
under
test
is
sensitive
to
changes
in
match,
such
as
an
unbu ered
oscillator
,
the
signal
may
disappear
during
the
measurement
process
.
The
input
attenuation,
and
therefore
the
input
match,
of
the
spectrum
analyzer
is
varied
during
the
measurement
process
.
A
bu er
(attenuation
and/or
ampli cation)
between
the
device
and
the
spectrum
analyzer
may
be
required.
Repeated
measurements
have
di erent
results
If
you
make
the
same
phase
noise
measurement
several
times
and
the
results
keep
changing,
either
getting
better
or
getting
worse
,
it
may
be
because
the
signal
is
drifting
and
the
rate
of
drift
is
changing.
It
may
be
possible
to
measure
a
drifting
signal,
but
the
phase
noise
can
appear
either
higher
or
lower
than
it
actually
is
,
depending
on
the
direction
of
the
drift.
This
e ect
is
usually
more
noticeable
when
the
device
is
rst
turned
on.
A
signal
with
a
constant
drift
rate
will
have
a
repeatable
,
but
incorrect,
phase
noise
plot.
Drift
can
easily
be
veri ed
by
making
a
spot
frequency
measurement
which
does
not
track
drift.
Measured
value
or
noise
oor
is
not
correct
The
system
noise
oor
is
a ecting
the
measurement.
It
must
be
checked
with
a
clean
source
for
the
frequency
o sets
being
examined
(such
as
an
8662).
Set
the
source
frequency
the
same
as
the
signal
to
be
tested,
since
the
system
phase
noise
is
a
function
of
the
spectrum
analyzer
center
frequency
.
Do
NOT
use
the
internal
calibrator
to
nd
the
noise
oor
because
phase
noise
cancellation
will
occur
.
This
will
make
the
noise
oor
appear
to
be
lower
than
it
actually
is
.
Phase
noise
measurements
made
in
the
bottom
division
of
the
display
will
not
be
as
accurate
as
the
remainder
of
the
display
.
If
measurements
are
occurring
in
the
bottom
division,
the
reference
level
(under
the
NNNNNNNNNNNNNNNNNNNN
CONFIG
key)
should
be
decreased
(made
more
negative).
The
phase
noise
can
appear
to
be
either
higher
or
lower
than
it
actually
is
.
When
signal
tracking
is
on,
a
slowly
drifting
signal
will
be
tracked
during
If
Y
ou
Have
A
Problem
4-1