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Digital Demodulation
R&S
®
FPC
159
User Manual 1178.4130.02 ─ 07
Analyzer
Extraction of
ideal signal
Comparison
Result display
Device under
test (DUT)
Figure 17-1: Demodulation principle
The R&S
FPC provides several measurements and numerical and graphical result dis-
plays. These result displays show various aspects and characteristics of the demodula-
ted signal.
Selecting the measurement
The measurement type selects the modulation scheme that the signal is modulated
with. The signal processing is different, depending on the selected modulation.
1. Press the "Meas" key to open the measurement menu.
2. Select the modulation of the signal you want to measure.
● "ASK": Demodulates 2ASK signals.
Amplitude-shift keying (ASK) is a digital modulation scheme that changes the
amplitude of the carrier to transmit different values (or symbols). Each value
corresponds to a different amplitude. In the most basic form (2ASK), there are
two (binary) values: 0 and 1. When a value of 1 occurs, the signal is transmit-
ted with a certain, fixed amplitude. On a value of 0, the signal is transmitted
with a reduced amplitude.
Often the amplitude of the "1" signal is 100
% and the amplitude of the "0" sig-
nal is close to 0
% of the nominal carrier amplitude (OOK = on-off-keying). The
R&S
FPC detects the different amplitudes, demodulates the signal and
retrieves the original sequences of the digital symbols.
For proper demodulation, you have to match the
to the ASK
carrier frequency.
● "FSK": Demodulates 2FSK signals.
Frequency-shift keying (FSK) is a digital modulation scheme that changes the
frequency of the carrier to transmit different values (or symbols). Each value
corresponds to a different frequency. In the most basic form (2FSK), there are
two (binary) values: 0 and 1. When a value of 0 occurs, the signal is transmit-
ted with a certain frequency f
1
. On a value of 1, the signal is transmitted with a
frequency f
2
.
For proper demodulation, you have to set a
metic mean of f
1
and f
2
.
Make sure to apply a signal with the correct modulation scheme. If you apply a sig-
nal with a different modulation than the selected one, the results are not valid.
Measurements and Result Displays