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By choosing test frequencies (frequency list mode), you can reduce the effect of spurious
responses on measurements by avoiding frequencies that produce IF signal path distortion.
LO Frequency Accuracy and Stability
The analyzer source is phaselocked to its receiver through a reference loop. In the frequency
offset mode, the mixer under test is inserted in this loop. lb ensure that the analyzer
phaselocks correctly, it is important that you use an LO source that has frequency accuracy
better than
f
1 MHz and residual FM
<
20
kHz
RMS.
Up-Conversion
and
Down-Conversion
Defhition
*
. .
..r
*
men
you
choose
between
~~~:;;,~~~~~~~
and
~~~:~~~~~-i,~~,in
the
frequency
offset
menus,
the
analyzer
.._........
,.,,.,,.,
.;,/
determines which direction the internal source must sweep in order to achieve the requested
IF frequency. For example, to measure the lower sideband of a mixer, where the RF signal
is below the LO (RF
<
Lo),
the internal source must sweep backwards. See the examples in
Figure 6-92.
-
..
Example
of
an
Upconverter
with
RF<LO
Figure 6-92. Examples
of Up Converters and Down Converters
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 upconverter measurement is being performed.
‘Applisation
and Operation Concepts
6-161