Modulation Analysis
R&S
®
Cable Rider ZPH
286
User Manual 1321.0950.02 ─ 07
The measurements are performed in two digital demodulation domains:
● "ASK": Demodulates 2ASK signals.
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 case of 2ASK signal, the binary values of 1 and 0 are trans-
mitted with a certain fixed amplitude and reduced amplitude respectively.
Often the amplitude of the "1" and "0" signal is respectively at 100 % and close
to 0 % of the nominal carrier amplitude (OOK = on-off-keying).
The R&S Cable Rider ZPH detects the different amplitudes, demodulates the
signal and retrieves the original sequences of the digital symbols. For proper
demodulation, you have to match the center frequency of the R&S Cable Rider
ZPH to the ASK carrier frequency.
● "FSK": Demodulates 2FSK signals.
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 case of 2FSK signal, the binary values of 0 and 1 are trans-
mitted with a certain frequency f
1
and f
2
respectively. For proper demodulation,
you have to set a center frequency that is the arithmetic mean of f
1
and f
2
.
4. Select the modulation domain of the signal you want to demodulate ("ASK" or
"FSK" softkey).
5. Select the "Display Mode" softkey to view the measurement readings.
The R&S Cable Rider ZPH opens a submenu to select the display mode. See
Table 12-5
.
6. The R&S Cable Rider ZPH demodulates the signal and displays the measurement
results in the selected display mode. See
Table 12-5
and
Table 12-4
.
Table 12-5: Display mode for ASK and FSK demodulation
Display mode
Description
Eye diagram shows the modulation accuracy, it
analyzes the transitions from one modulation
state to the other.
An open "eye" indicates little distortion in the sig-
nal transmission. A closed "eye" indicates poor
signal quality with signal due to clock jitter, inter-
ference, poorly synchronized of the phase-locking
circuitry or reflection due to imperfect termination.
With bit rate increases, timing error also increa-
ses, reducing the size of the eye opening which
increases the potential of data error.
Symbol diagram shows the streams of symbols of
binary digits transmitted in the signal.
Digital Demodulation
