HP 8753D - Page 158

Isolation Example
Measurements
Isolation
is
the
measure
of signal
leakage in
a mixer
.F
eedthrough is
specically the
forward
signal
leakage
to
the
IF
port.
High isolation
means that
the amount
of leakage
or feedthrough
between
the
mixer's
ports
is
very
small. Isolation
measurements do
not use
the frequency
oset
mode
.
Figure
3-24
illustrates
the signal
ow in
a mixer
.
Figure
3-24. Signal
Flow in
a
Mixer
Example
The
RF
and
LO
feedthrough
signals may
appear at
the
mixer
IF
output,
together
with
the
desired
IF
signal.
The
LO
to
RF
isolation
and
the
LO
feedthrough
are
typically
measured
with
the
third
port
terminated
in
50
ohms
.
Measurement
of
the
RF
feedthrough
is
made
as
the
LO
signal
is
being
applied to
the
mixer
.
LO to
RF
Isolation
1.
Initialize
the
analyzer
by
pressing
4
PRESET
5
.
2.
T
o
select
the
analyzer
frequency
range and
source power
,
press:
4
ST
ART
5
4
10
5
4
M/

5
4
STOP
5
4
3000
5
4
M/

5
4
MENU
5
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
POWER
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
NN
NN
NN
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
PWR
RANGE
MAN
4
0
5
4
x1
5
This
source
stimulates
the
mixer's
LO
port.
3. T
o
select
a
ratio
B/R
measurement,
press:
4
MEAS
5
NNNNNNN
NNNNNNNNNNNNNNNNNNNNNNNNN
NNN
INPUT PORTS
NNNNNNN
NNNN
B/R
4. Make the connections as shown in Figure 3-25.
Making Mixer Measurements 3-33