Agilent Technologies Switch/Measure Uživatelský manuál stáhnout pdf (Strana 13)

Transmitted RF carrier power versus time

Purpose of measurement—what it proves

This measurement assesses the envelope of carrier power in the time domain

against a prescribed mask. In GSM systems transmitters must ramp power

up and down within the time division multiple access (TDMA) structure to

prevent adjacent timeslot interference. If transmitters turn on too slowly,

data at the beginning of the burst might be lost, degrading link quality, and if

they turn off too slowly the user of the next timeslot in the TDMA frame will

experience interference. This measurement also checks that the transmitters’

turn off is complete.

If a transmitter fails the “transmitted RF carrier power versus time”

measurement, this usually indicates a problem with the unit’s output amplifier

or leveling loop.

This measurement does not test to see if the transmitter ramps power too

quickly, which has the effect of spreading energy across the spectrum and

causing interference. The “spectrum due to switching” measurement can be

used to test for this effect.

Theory in pictures

The measurement of transmitted RF carrier power versus time is made using

an analyzer in zero-span mode. The pass/fail mask is placed over the measured

trace and referenced in two ways. Horizontally (time axis), the measurement is

referenced from the transition between bits 13 and 14 of the training sequence.

Therefore, as with mean transmitted RF carrier power, it is necessary for the

test equipment to demodulate to make this measurement correctly. Vertically

(power axis), the measurement is referenced against the measurement of mean

transmitted RF carrier power.

Time (µs)

not to scale

Timing referenced to transition between

bit 13 and 14 in training sequence

Power

(dBc)

Power

referenced

to mean

tansmitted

RF carrier

power

Prescribed mask

Figure 9. Theory of transmitted RF carrier power versus time

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Agilent Technologies Switch/Measure Uživatelský manuál Strana 13