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Operating Concepts
TRL*/LRM* Calibration (ES Models Only)
TRL Options
The softkey accesses the TRL/LRM options menu. There are two selections under
this menu:
• (calibration Z
0
)
• (set reference)
The characteristic impedance used during the calibration can be referenced to either the line (or match)
standard (
) or to the system ( ). The analyzer defaults to a
calibration impedance that is equal to the line (or match) standard.
When the is selected, the impedance of the line (or match) standard is assumed to
match the system impedance exactly (the line standard is reflectionless). After a calibration, all
measurements are referenced to the impedance of the line standard. For example, when the line standard is
remeasured, the response will appear at the center of the Smith chart. When
is
selected, the values entered for (under menu) and (within the define
standard menu) are ignored.
is selected when the desired measurement impedance differs from the
impedance of the line standard. This requires a knowledge of the exact value of the Z
0
of the line. The
system reference impedance is set using
under the calibration menu. The actual impedance of
the line is set by entering the real part of the line impedance as the within the define
standard menu. For example, if the line was known to have a characteristic impedance of 51
(
= 51 ) , it could still be used to calibrate for a 50 measurement ( = 50 ) .
After a calibration, all measurements would be referenced to 50 , instead of 51 . When the line standard
is remeasured, the center of the Smith chart is at the current value of
(in this case, 50 ). Since
only one value of offset Z
0
can be selected for the line standard, the value of Z
0
should be a constant value
over the frequency range of interest in order to be meaningful.
The location of the reference plane is determined by the selection of and
. By default, the reference plane is set with the thru standard which must have a
known insertion phase or electrical length. If a non-zero length thru is specified to have zero delay, the
reference plane will be established in the middle of the thru. The reflect standard may be used to set the
reference plane instead of the thru provided the phase response (offset delay, reactance values and
standard type) of the reflect standard is known and is specified in the calibration kit definition.
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