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Calibrating for Increased Measurement Accuracy
Power Meter Measurement Calibration
Power Meter Measurement Calibration
A GPIB-compatible power meter can monitor and correct RF source power to achieve leveled power at the
test port. During a power meter calibration, the power meter samples the power at each measurement point
across the frequency band of interest. The analyzer then constructs a correction data table to correct the
power output of the internal source. The correction table may be saved in an instrument state register with
the SAVE key.
The correction table may be updated on each sweep (in a leveling application) or during an initial single
sweep. In the sample-and-sweep mode the power meter is not needed for subsequent sweeps. The
correction table may be read or modified through GPIB.
Power meter calibration is useful for the following applications:
• when you are testing a system with significant frequency response errors (for example, a coupler with
significant roll-off, or a long cable with a significant amount of loss)
• when you are measuring devices that are very sensitive to actual input power for proper operation
• when you require a reference for receiver power calibration
The power meter can measure and correct power in two ways:
• continuous correction—each sweep mode
• sample-and-sweep correction—single sweep mode
The time required to perform a power meter calibration depends on the source power, number of points
tested, and number of readings taken. Refer to the “Specifications and Characteristics” chapter of the
reference guide for characteristic power meter calibration sweep speeds and accuracy.
Regardless of the measurement application, the analyzer's source can only supply corrected power within
the selected power range. If power outside this range is requested, the annotation will change to PC?.
Loss of Power Meter Calibration Data
The power meter calibration data will be lost by committing any of the following actions:
Turning power off. Turning off the instrument erases the power meter calibration table.
Changing sweep type. If the sweep type is changed (linear, log, list, CW, power) while power meter
calibration is on, the calibration data will be lost. However, calibration data is retained if you change the
sweep type while power meter calibration is off.
Changing frequency. Power meter calibration data will also be lost if the frequency is changed in log or
list mode, but it is retained in linear sweep mode.
Pressing . Presetting the instrument will erase power meter calibration data. If the instrument
state has been saved in a register using the key, you may recall the instrument state and
the data will be restored. Saving the instrument state will not protect the data if the instrument is turned
off.
Interpolation in Power Meter Calibration
If the frequency is changed in linear sweep, or the start/stop power is changed in power sweep, then the
calibration data is interpolated for the new range.
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