HP 8753D - Page 419

Filtering
Harmonics
, linearity
,
and
spurious
signals
also
introduce
errors
that
are
not
removed
by
frequency
response calibration.
These
errors
are
smaller
with
a
narrowband
detection
scheme
,
but
they may
still
interfere
with
your
measurements
.
Y
ou
should
lter
the
IF
signal
to reduce
these
errors as
much
as
possible
.
Correct
ltering
between
the
mixer's
IF
port
and
the
receiver's
input
port
can
eliminate
unwanted
mixing
and
leakage
signals
from
entering
the
analyzer's
receiver
.
Figure
6-89
shows
a
plot
of
mixer
conversion
loss
when
proper
IF
ltering
was
neglected.
Figure
6-89.
Example
of
Conversion
Loss
versus
Output
Frequency
Without
Correct
IF
Signal
P
ath
Filtering
Figure
6-90
shows
the
same
mixer's
conversion
loss
with
the
addition
of
a
low
pass
lter
at the
mixer's
IF
port.
Figure 6-90.
Example of Conversion Loss versus Output Frequency With Correct IF
Signal P
ath Filtering and Attenuation at all Mixer P
orts
Filtering is required in both xed and broadband measurements, but you can implement it more
easily in the xed situation. Therefore, when conguring broad-band (swept) measurements,
you may need to trade some measurement bandwidth for the ability to more selectively lter
signals entering the analyzer's receiver.
6-152 Application and Operation Concepts