Agilent Technologies Switch/Measure Manual de usuario descargar pdf (Pagina 9)

Practical measurements

As mentioned, modern test equipment performs the necessary signal processing

automatically, making these measurements straightforward and fast. It is also

useful to view phase error versus time—especially in R&D and when fault

finding. For example, a phase and frequency error test might fail the prescribed

limits at only one point in the burst, for example, at the beginning. This could

indicate a problem with the transmitter power ramp or some undesirable

interaction between the modulator and power amplifier.

Constellation diagrams can also be used to observe some aspects of modulation

accuracy and can reveal certain fault mechanisms such as I/Q amplitude

imbalance or quadrature imbalance.

When to use the measurement

Phase and frequency error measurements can capture a large spread of

fault types and prove that any I/Q calibration process has been successfully

performed. These measurements are typically used at every stage in the BTS

lifecycle. Modern test equipment can make these measurements very rapidly

and with good accuracy (typically the test equipment should be 10x more

accurate than the specification limit so measurement results can be attributed

to the device under test and not the test system).

Figure 5. Quad display of the Agilent E4406A VSA-series transmitter tester with and without frequency error

Figure 6. Constellation diagram on the Agilent E4406A VSA-series transmitter tester

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Agilent Technologies Switch/Measure Manual de usuario Pagina 9