Rohde & Schwarz R&S FSP Series, Operating Manual

Page: 47 / 796

Operating Manual 1164.4556.12 - 06 2.23
R&S FSP Getting Started
Measurements on Modulated Signals
6. Stabilize the measurement result by activating trace averaging.
➢
Press the TRACE key.
➢
Press the AVERAGE softkey.
Fig. 2-1 Measuring phase noise with the phase-noise marker function
The frequency offset can be varied by moving the marker with the spinwheel
or by entering a new frequency offset as a number.
2.5 Measurements on Modulated Signals
If RF signals are used to transmit information, an RF carrier is modulated. Analog
modulation methods such as amplitude modulation, frequency modulation and
phase modulation have a long history and digital modulation methods are now used
for modern systems. Measuring the power and the spectrum of modulated signals is
an important task to assure transmission quality and to ensure the integrity of other
radio services. This task can be performed easily with a Spectrum Analyzer. Modern
Spectrum Analyzers also provide the test routines that are essential to simplify com-
plex measurements.
2.5.1 Measurements on AM signals
The R&S FSP detects the RF input signal and displays the magnitudes of its compo-
nents as a spectrum. AM modulated signals are also demodulated by this process.
The AF voltage can be displayed in the time domain if the modulation sidebands are
within the resolution bandwidth. In the frequency domain, the AM sidebands can be
resolved with a small bandwidth and can be measured separately. This means that
the modulation depth of a carrier modulated with a sinewave signal can be mea-
sured. Since the dynamic range of a Spectrum Analyzer is very wide, even
extremely small modulation depths can be measured accurately. The R&S FSP has
a test routine which measures the modulation depth in %.