S820E UG PN: 10580-00343 Rev. H 7-3
Calibration, VNA 7-2 Calibration Considerations
When calibration correction is On, the correction is applied to all applicable
S-parameters. For example, if a Full S
11
(1-port) calibration is performed,
then only traces that measure S
11
have a valid calibration. For those traces,
the calibration information data in the Instrument Settings Summary shows
“CAL: OK”. All other traces that do not measure S
11
display “CAL: --” to
indicate that no valid calibration is available for those traces. The calibration
correction can also be turned off manually under the Calibration menu by
toggling the Cal Correction soft key from On to Off. In that case, the display
shows “CAL: OFF” for all traces that have valid correction data available.
Note that “CAL: OFF” means that a calibration correction has been created,
but it is not currently being used. This is different from “CAL: --”, which
means that no valid calibration correction is available for the current setting.
When you have Cal Correction on and Interpolation set to off, you cannot
modify the frequency range or the source power level, or increase the number
of points. You can, however, decrease the number of points without forcing
the calibration to become invalid.
If you reduce only the number of points, then the frequency range is not
changed. The S820E finds a subset of the original points in the sweep that
can be used. You can therefore notice that the instrument may not use the
exact number of points that you have entered. It picks a specific number of
points that allow the calibration correction to continue to be valid. If you use
the rotary knob, then you will more easily find the available number of points
that can be set. For example, if you calibrated with 201 points, then you can
observe that you can reduce the number of points to 101, 68, 51, 41, and so
forth.
If Interpolation is set to on, then you can reduce the frequency range and
modify the number of points without invalidating the calibration. In that
case, the calibration coefficients are regenerated (interpolated) to match the
new settings.
Another status information display that you may see is “CAL: ON (X)”, which
indicates that the instrument temperature has deviated (since the time the
calibration was conducted) by an amount that has more than likely rendered
the calibration invalid. When this occurs, a new calibration is highly
recommended before further measurements are conducted.
Only one calibration is available at one time. Performing a new calibration
overwrites any existing calibration. You can, however, store a measurement
setup, which also stores the calibration. You can therefore have multiple
calibrations available (as long as the calibration settings and conditions
continue to apply).
To Next Page
Loading...
