Agilent Technologies 8719ES User Manual page 446

Operating Concepts
TRL*/LRM* Calibration (ES Models Only)
The TRM calibration technique is related to TRL with the difference being that it bases the
characteristic impedance of the measurement on a matched Z
transmission line for the third measurement standard. Like the TRL thru standard, the
TRM THRU standard can either be of zero length or non-zero length. The same rules for
thru and reflect standards used for TRL apply for TRM.
TRM has no inherent frequency coverage limitations which makes it more convenient in
some measurement situations. Additionally, because TRL requires a different physical
length for the thru and the line standards, its use becomes impractical for fixtures with
contacts that are at a fixed physical distance from each other.
For information on how to modify calibration constants for TRL*/LRM*, and how to
perform a TRL or TRM calibration, refer to
Analyzers Only)" on page
TRL Options
The
TRL/LRM OPTION
selections under this menu:
• (calibration Z
CAL ZO:
• (set reference)
SET REF:
The characteristic impedance used during the calibration can be referenced to either the
line (or match) standard (
The analyzer defaults to a calibration impedance that is equal to the line (or match)
standard.
When the
CAL ZO: LINE ZO
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
(under menu) and
Cal
CAL ZO: SYSTEM ZO
the impedance of the line standard. This requires a knowledge of the exact value of the Z
of the line. The system reference impedance is set using
menu. The actual impedance of the line is set by entering the real part of the line
impedance as the
OFFSET ZO
was known to have a characteristic impedance of 51 Ω (
be used to calibrate for a 50 Ω measurement (
measurements would be referenced to 50 Ω, instead of 51 Ω. When the line standard is
remeasured, the center of the Smith chart is at the current value of
50 Ω). Since only one value of offset Z
should be a constant value over the frequency range of interest in order to be meaningful.
7-76
"Calibrating for Non-Coaxial Devices (ES
6-50.
softkey accesses the TRL/LRM options menu. There are two
)
0
CAL ZO: LINE ZO
is selected, the impedance of the line (or match) standard is
is selected, the values entered for
CAL ZO: LINE ZO
(within the define standard menu) are ignored.
OFFSET ZO
is selected when the desired measurement impedance differs from
within the define standard menu. For example, if the line
can be selected for the line standard, the value of Z
0
termination instead of a
O
) or to the system (
CAL ZO: SYSTEM ZO
SET ZO
OFFSET ZO
= 50 Ω). After a calibration, all
SET ZO
SET ZO
under the calibration
= 51 Ω), it could still
(in this case,
SET ZO
).
0
0