Ronde & Schwarz 1304.0004.03, User Manual

Page: 127 / 1076

The Spectrum Application (RF Measurements)
R&S
®
FPL1000
127 User Manual 1178.3370.02 ─ 09
7.2.4 Channel Power and Adjacent-Channel Power (ACLR) Measurement
Measuring the power in channels adjacent to the carrier or transmission channel is
useful to detect interference. The results are displayed as a bar chart for the individual
channels.
● About Channel Power Measurements .................................................................. 127
● Channel Power Results .........................................................................................128
● Channel Power Basics ..........................................................................................129
● Channel Power Configuration ............................................................................... 133
● How to Perform Channel Power Measurements ...................................................141
● Measurement Examples ....................................................................................... 144
● Optimizing and Troubleshooting the Measurement .............................................. 147
● Reference: Predefined CP/ACLR Standards ........................................................ 148
7.2.4.1 About Channel Power Measurements
Measuring channel power and adjacent channel power is one of the most important
tasks during signal analysis with the necessary test routines in the field of digital trans-
mission. Theoretically, a power meter could be used to measure channel power at
highest accuracy. However, its low selectivity means that it is not suitable for measur-
ing adjacent channel power as an absolute value or relative to the transmit channel
power. Only a selective power meter can measure the power in the adjacent channels.
A signal analyzer cannot be classified as a true power meter, because it displays the IF
envelope voltage. However, it is calibrated such as to display the power of a pure sine
wave signal correctly, irrespective of the selected detector. This calibration cannot be
applied for non-sinusoidal signals. Assuming that the digitally modulated signal has a
Gaussian amplitude distribution, the signal power within the selected resolution band-
width can be obtained using correction factors. The internal power measurement rou-
tines in a signal analyzer normally use these correction factors to determine the signal
power from IF envelope measurements. These factors apply if and only if the assump-
tion of a Gaussian amplitude distribution is correct.
Apart from this common method, the R&S FPL1000 also has a true power detector, i.e.
an RMS detector. It displays the power of the test signal within the selected resolution
bandwidth correctly, irrespective of the amplitude distribution, without additional correc-
tion factors being required.
The R&S FPL1000 software allows you to perform ACLR measurements on input con-
taining multiple signals for different communication standards. A measurement stan-
dard is provided that allows you to define multiple discontiguous transmit channels at
specified frequencies, independent from the selected center frequency. The ACLR
measurement determines the power levels of the individual transmit, adjacent, and gap
channels, as well as the total power for each sub block of transmit channels.
A detailed measurement example is provided in Chapter 7.2.4.6, "Measurement Exam-
ples" , on page 144.
Measurements and Results