User`s guide

6-5
Calibrating for Increased Measurement Accuracy
Calibration Considerations
• Greater than 100 dB: Same as 90 to 100 dB, but alternate mode should be used. See "To
View a Single Measurement Channel" on page 5-13.
Saving Calibration Data
You should save the calibration data, either in the internal non-volatile memory or on a
disk. If you do not save it, it will be lost if you select another calibration procedure for the
same channel, or if you change stimulus values. Instrument preset, power on, and
instrument state recall will also clear the calibration data.
Restarting a Calibration
If you interrupt a calibration to go to another menu, such as averaging, you can continue
the calibration by pressing the softkey in the correction
menu.
The Calibration Standards
During measurement calibration, the analyzer measures actual, well-defined standards
and mathematically compares the results with ideal "models" of those standards. The
differences are separated into error terms which are later removed during error correction.
Most of the differences are due to systematic errors—repeatable errors introduced by the
analyzer, test set, and cables—which are correctable.
The standard devices required for system calibration are available in compatible
calibration kits with different connector types. Each kit contains at least one short circuit,
one open circuit, and an impedance-matched load. In kits that require adapters for
interface to the test set ports, the adapters are phase-matched for calibration prior to
measurement of non-insertable and non-reversible devices. Other standard devices can be
used by specifying their characteristics in a user-defined kit, as described in "Modifying
Calibration Kits" on page 7-56.
The accuracy improvement of the correction is limited by the quality of the standard
devices, and by the connection techniques used. For maximum accuracy, ensure that the
connectors are clean and use a torque wrench for final connections.
Frequency Response of Calibration Standards
In order for the response of a reference standard to show as a dot on the smith chart
display format, it must have no phase shift with respect to frequency. Standards that
exhibit such "perfect" response are the following:
• 7-mm short (with no offset)
• type-N male short (with no offset)
There are two reasons why other types of reference standards show phase shift after
calibration:
• The reference plane of the standard is electrically offset from the mating plane of the
test port. Such devices exhibit the properties of a small length of transmission line,
including a certain amount of phase shift.
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