5-8
Optimizing Measurement Results
Making Accurate Measurements of Electrically Long Devices
Decreasing the Sweep Rate
The sweep rate can be decreased by increasing the analyzer's sweep time. To increase the analyzer's sweep
time, press
and use the front panel knob, the and
keys, or the front panel keypad enter in the appropriate sweep time.
Alternatively, the number of points may be increased for the same frequency range, thereby reducing the
sweep rate (in GHz/second).
Selection of the appropriate sweep time depends on the device being measured; the longer the electrical
delay of the device under test, the slower the sweep rate must be. A good way to tell when the sweep rate is
slow enough is to put the vector network analyzer into a stepped list frequency mode of sweeping, and
compare the data. In this mode, the vector network analyzer does not sweep the frequency, but steps to
each listed frequency point, stops, makes a measurement, then goes on to the next point. Because errors do
not occur in the list frequency mode, it can be used to check the data. The disadvantage of the list frequency
mode is that it is slower than sweeping. To select the stepped list mode instead of the swept list mode,
press
and toggle to
.
Alternatively, the analyzer can be forced into stepped sweep mode by:
• Setting the IF bandwidth to either 30 Hz or 10 Hz.
• Setting sweep time to greater than 15 ms/point.
• Activating power meter calibration (even with no calibration).
.
Decreasing the Time Delay
The other way to reduce F is by decreasing the time delay, T. Since T is a property of the device that is
being measured, it cannot literally be decreased. However, what can be decreased is the difference in delay
times between the paths to the R channel and the B channel. These times can be equalized by adding a
length of cable to the R channel which has approximately the same delay as the device under test.
This length of cable can be inserted between the R CHANNEL IN and OUT connectors on the front panel of
the analyzer. The delay of this cable must be less than 5s.
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