Agilent Technologies 8753ET User Manual page 270

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
SWEEP TIME [MANUAL]
Sweep Setup
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
SWEEP TYPE MENU EDIT LIST
Sweep Setup
to .
LIST TYPE [ ] LIST TYPE [STEPPED]
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).
Cal PWRMTR CAL
.
ONE SWEEP
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 5µs.
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