HP 8753D - Page 127

Measurement Considerations
T
o
ensure
successful
mixer measurements
,the
following measurement
challenges must
be taken
into
consideration:
Mixer
Considerations
Minimizing
Source
and
Load
Mismatches
Reducing
the
Eect
of
Spurious Responses
Eliminating
Unwanted
Mixing
and
Leakage
Signals
Analyzer
Operation
How
RF
and
IF
Are
Dened
Frequency
Oset
Mode
Operation
Dierences
Between
Internal and
External R-Channel
Inputs
P
ower
Meter Calibration
Minimizing
Source
and
Load
Mismatches
When
characterizing
linear
devices
,
you
can
use
vector
accuracy
enhancement
to
mathematically
remove
all
systematic
errors
,
including
source
and
load
mismatches
,
from
your
measurement.
This
is
not
possible
when
the
device
you
are
characterizing
is
a
mixer
operating
over
multiple
frequency
ranges
.
Therefore
,
source
and
load mismatches
are not
corrected for
and
will
add
to
overall
measurement
uncertainty
.
Y
ou
should
place
attenuators
at
all
of
the
test
ports
to reduce
the measurement
errors
associated
with
the
interaction
between
mixer
port
matches
and
system
port
matches.
To
avoid
overdriving
the
receiver
,
you
should
give
extra
care
to
selecting
the attenuator
located at
the
mixer's
IF
port.
F
or
best results
,
you
should
choose
the
attenuator
value
so
that
the
power
incident
on
the
analyzer
R-channel
input is
less
than
0
10
dBm
and
greater
than
0
35
dBm.
Reducing
the
Eect
of
Spurious
Responses
By
choosing
test
frequencies
(frequency
list
mode), you
can reduce
the
eect
of
spurious
responses
on
measurements
by
avoiding
frequencies
that produce
IF signal
path
distortion.
Eliminating
Unwanted
Mixing
and Leakage
Signals
By
placing
lters
between
the
mixer's IF
port and
the receiver's
input
port,
you
can
eliminate
unwanted
mixing
and
leakage
signals
from entering
the analyzer's
receiver.
Filtering is
required
in both
xed and
broadband
measurements
.
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
receiver.
How RF and IF Are Dened
In standard mixer measurements
, the input of the mixer
is always connected to the analyzer's
RF source
, and the output of the mixer always produces
the IF frequencies that are received by
the analyzer's receiver
.
However, the ports labeled RF and IF on most mixers are not consistently connected to the
analyzer's source and receiver ports, respectively. These mixer ports are switched, depending
on whether a down converter or an up converter measurement is being performed.
It is important to keep in mind that in the setup diagrams of the frequency oset mode, the
analyzer's source and receiver ports are labeled according to the mixer port that they are
connected to.
3-2 Making Mixer Measurements