Digital Demodulation
R&S
®
FPC
164User Manual 1178.4130.02 ─ 07
Modulator
with Tx filter
Lowpass
filter of I/Q
capture HW
RX
filter
Demodulation &
symbol decision
Modulator
with Tx + Rx
filter
ASK / FSK
demodulator
Signal
processing,
correction of
estimated errors
Set by user
Auto
fct(CaptureOV,
symbol rate)
Auto
(function of
Tx filter)
Display evaluation
+
Error
signal
Auto
(function of
Tx filter)
Correction
parameters
DUT
(transmitter)
Analyzer
Ref signalMeas signal
Figure 17-8: Block diagram of measurement filter
Selecting the filter type
The R&S FPC provides several filters that have to match the DUT transmit filter.
1. Press the "Meas" key to open the measurement menu.
2. Select the "Demod Parameters" menu item to open the demodulation menu.
3. Select the "Filter Type" menu item to open the filter type menu.
4. Select an appropriate filter for your signal. The filter type should be the same as
that used by the transmitter; for example, if the transmitter uses a Gaussian filter,
you should analyze the signal with a Gaussian filter, too. Otherwise, measurement
results are not valid.
The R&S FPC provides the following filter types.
● "Root Raised Cosine" (RRC)
● "Raised Cosine"
● "Gaussian"
● "Unfiltered"
You can define the roll-off factor for all filters.
Defining the roll-off factor of the measurement filter
The roll-off factor defines the slope or bandwidth of the filter. Most radio transmissions
use a roll-off factor of about 0.3 to 1.0. Increasing the roll-off factor increases the filter
bandwidth.
For the raised cosine or RRC filter, the filter bandwidth is defined in terms the alpha
value. For the Gaussian filter, the filter bandwidth is defined in terms of the BT value.
1. Press the "Meas" key to open the measurement menu.
2. Select the "Demod Parameters" menu item to open the demodulation menu.
3. Select the "Alpha/BT" menu item.
4. Enter the roll-off factor you want (a value between 0 and 1).
Measurement Configuration
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