HP 8753D - Page 416

Mixer T
esting
Mixers
or
frequency
converters
,by
denition, exhibit
the characteristic
of having
dierent
input
and
output
frequencies
.
Mixer
tests can
be performed
using the
frequency oset
operation
of
the
analyzer
(with
an
external LO
source) or
using the
tuned receiver
operation of
the
analyzer
(with
an
external
RF
and LO
source). The
most common
and convenient
method
used
is
frequency
oset.
Frequency
Oset
F
or
a
single-sideband
mixer
measurement,
the
RF
source
can
be
oset
in
frequency
from
the
input
receiver
frequency
,
allowing
for
a
swept
RF
stimulus
over
one
frequency
range
and
measurement
of
the
IF
response
over
another
(in
this
case
the
output
IF).
T
o
use
the
frequency
oset
guided
setup
for
conguring
a
mixer
measurement:
1.
Enter
the
IF
and
LO
frequencies
.
2.
Set
the
LO
source
to
the
entered
LO
frequencies
.
3.
Specify
up
conversion
or
down
conversion.
4.
Select
an
RF
that
is
higher
or
lower
in
frequency
than
the
LO
.
(The RF
frequencies needed
are
calculated
by
the
analyzer
.)
Tuned
Receiver
The
analyzer's tuned
receiver
mode
allows
you
to
tune
its
receiver
to
an
arbitrary
frequency
and
measure signal
power
.
This
is
only
possible
if
the
signal
you
want
to
analyze
is
at
an
exact
known
frequency
. Therefore
,
the
RF
and
LO
sources
must
be
synthesized
and
synchronized
with
the
analyzer
time base
.
Since
the
analyzer
is
not
phaselocking
in
this
conguration,
you
can
use
it to
measure
conversion
loss
of
a
microwave
mixer
with
an
RF
frequency
range
output.
Note
Y
ou
must
take
care
to
lter
the
output
of
the
mixer
because
some
of
the
intermodulation and
leakage
products
may
be
very
close
in
frequency
to
the
desired
IF
.
If
these
components
are
not
ltered
o,
the
analyzer may
have
diculty
selecting
the
correct
signal
to
measure
.
Tuned
receiver
mode
also
increases
dynamic
range
.
Broadband
techniques
like
diode
detection
have
a
high
noise
oor
,
while
narrowband
techniques
like
tuned
receivers
are much
less
susceptible
to
noise
.
Application and Operation Concepts 6-149