Agilent Technologies Switch/Measure Uživatelský manuál stáhnout pdf (Strana 12)

Practical measurements

In practice, many types of test equipment can be used to make power

measurements in GSM systems. Accuracy, linearity and repeatability are

key here and the perfomance required from test equipment depends on the

application.

It is possible to make power measurements in GSM systems by triggering off

the rising edge of the signal instead of the bit 13/bit 14 transition, although this

method will result in increased levels of uncertainty.

It is also possible to use either a peak or thermal power sensor with a

conventional meter. Both sensor types should be used with care. Peak power

sensors will capture the overshoot at the top of the burst’s ramp up and give

incorrect readings, and thermal sensors will give results that are largely affected

by the burst shape differences from one transmitter to the next.

Some modern test equipment, suitable for GSM R&D, manufacturing and

installation and maintenance can make this measurement as defined in the

ETSI and ANSI specifications by demodulating and gating.

Note: power measurements are extremely vulnerable to mismatch. If the

transmitter output to test equipment input is not matched properly, and some

energy is reflected back into the transmitter, the test equipment will give a low

power reading.

When to use the measurement

Power measurements are normally performed in every phase of the BTS

lifecycle. Accuracy, linearity and repeatability requirements typically are more

stringent in R&D than in installation and maintenance.

In manufacturing where power calibration is required, measurement speed

is a significant factor. To fully calibrate and characterize, for example, a GSM

BTS transceiver in manufacturing might require hundreds of measurements.

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Agilent Technologies Switch/Measure Uživatelský manuál Strana 12