Changing Signal Path After Calibration; Set The Attenuators; Store Trace Memories - HP 8510 User Manual

Changing Signal Path After Calibration

If any attenuator or other external equipment is changed after calibration, the measurement
results cannot be speci ed except by your own estimation of the error contribution of
the change. For example, when the port attenuation is changed with correction On, the
CAUTION: CORRECTION MAY BE INVALID is displayed. The operator must judge
whether the error is tolerable in the particular application and how to compensate for the
change.
The only reason to change the internal attenuators or external equipment between calibration
and measurement is to maximize the levels under both conditions, thus minimizing
uncertainty due to noise. Many factors will enter into the decision of whether it is more
accurate to calibrate at a low signal level without changing the setup, or change the setup
to optimize levels for both calibration and measurement. Changing the Port 1 or the
Port 2 attenuator does not seriously change the test set mismatch, directivity, or isolation
characteristics, but will change the frequency response magnitude and phase. This di erence
in the frequency response between calibration and measurement can be normalized using the
HP 8510 trace memories.
The application question is: Does increasing the signal levels during calibration improve the
calibration enough to risk greater error contributions possible by changing the setup?

Set the Attenuators

If only the Port 1 or Port 2 attenuators are changed, the following procedure can minimize the
errors.
1. Connect a short or a thru and set the Port 1 and Port 2 attenuators for best IF signal
levels during calibration.
2. Perform the appropriate measurement calibration.
3. With an appropriate standard connected, set the Port 1 and Port 2 attenuators to the
setting required for operating the test device.
If you view the response of a short circuit, notice that changing the Port 1 attenuators
has negligible e ect on the S
negligible e ect on the S
paired. Both the reference and the test signal are changed an approximately equal amount.
However, when viewing S
marker reading by the di erence in the Port 1 and Port 2 values.

Store Trace Memories

The main frequency response e ects of changing the attenuators can be compensated for by
using the HP 8510 trace memories and trace mathematics as follows.
1. Connect the thru used for calibration. Set the port attenuators to the value used for
measurement of the device. Recheck the user parameter levels then press
2. Press
NNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNN
DATA
4 DISPLAY 5
trace is the frequency response di erence of the S
measurement.
10-6 High Power Measurements
marker reading, and that changing Port 2 attenuators has
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marker reading. This is due to the way that the attenuators are
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or S , changing the Port 1 or Port 2 attenuators o sets the
21 12
!
to store the S
MEMORY
trace in default trace memory 1. This
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signal path between calibration and
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.
4 S 21 5