Keysight Technologies FieldFox A Series User Manual page 586

Noise Figure Mode (Option 356 – CPU2 Only)
Calibration Wizard
receiver calibration has virtually no influence on the noise figure measurement,
either with or without a user calibration. The receiver calibration only effects
the gain measurement, and only when there is no user calibration.
As already stated, the receiver calibration measures the measurement
bandwidth of the receiver. In most cases, this is set primarily by the digital
processing of the receiver. The receiver calibration is needed, because it is
influenced by the IF analog circuitry of the FieldFox. Additionally, the
bandwidth is extremely stable, and does not vary significantly with time or
temperature. So, once the receiver calibration has been successfully performed
there is no need to repeat the receiver calibration.
Exceptions: Re-do the receiver calibration when the FieldFox receiver
hardware is changed (factory repair) or in the rare case where a filter is added
to the measurement system which has a narrower bandwidth than the receiver
(i.e., the external bandwidth is less than the lowest resolution bandwidth (Res
BW) setting of 300 kHz).
User Calibration (User Cal):
Performing a user calibration is recommended only when the
measurement setup includes a preamplifier. The user calibration is
unnecessary for accurate measurements when no preamplifier is used.
In general, a user calibration should be performed whenever a preamplifier is
used in the noise figure measurement. If there is no preamplifier, the user
calibration is not necessary.
Although it will be interpolated if other frequencies are used, when a user
calibration is performed, it should be made at the same frequencies as the
measurement. The user calibration also needs to be performed with the same
resolution bandwidth as is used in the measurement. The user calibration
determines the noise contribution of the preamplifier, so that it can be removed
from the measurement when computing the noise figure of the DUT. Also, the
user calibration establishes the power gain of the receiver—preamplifier system
so that the reported gain of the DUT will be the gain between input of the DUT
(where the noise source is connected during the measurement) and the
calibration plane (which is the point where the noise source is connected
during the user calibration). Therefore, for the best gain accuracy, the noise
source used in the calibration, should be connected at the same point as the
DUT will be during the measurement.
Optimizing Measurement Accuracy:
— Both gain and noise figure measurement accuracy will be enhanced by
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using a noise source with as low a reflection coefficient as possible for the
user calibration.
Keysight N9927-90001 User's Guide