Agilent Technologies PSA Series Manual page 365

Linearity Verification
Definition
The spectrum analyzer which is part of the N5531S measuring receiver uses an
ADC and digital signal processing to determine the level of a signal. Because
traditional analog logarithmic amplifiers are not used, the accuracy of detection
and linearity when measuring different signal levels is extremely good. Besides
ADC linearity, spectrum analyzer stability and signal source stability are major
contributors to meeting specification.
The following linearity test verifies the linearity specification in the Tuned RF
Level section of the Measuring Receiver Specifications.
Specification
Linearity ± (0.009 dB + 0.005 dB/10 dB step)
Specs apply to following conditions:
Frequency must be set manually. (Do not use the measuring receiver Frequency
Count measurement).
Accuracy mode must be set to High.
Description
A highly calibrated step attenuator is used in conjunction with a highly stable
signal source to provide signal levels to the measuring receiver.
The spectrum analyzer is placed in the Measuring Receiver mode, and the TRFL
level measurement is selected.
The step attenuator is set to 0 dB and a reference measurement is taken.
The step attenuator is stepped from 0 to 50 dB and the amplitude at each step
recorded.
The difference between the expected attenuation value as recorded on the step
attenuator calibration report, and the measured value, is the linearity accuracy.
Chapter 8
N5531S Measuring Receiver Performance Verification
Performance Verification Tests
365