Revision 2.0 – July 2010
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SX1231-31SKB
USER GUIDE
For operation with low modulation index signals, it is recommended that the user follows the
recommendations for setting the correct DCC bandwidth for optimized low modulation index systems that
can be found in the SX1231 datasheet.
5.3.2 LNA Gain Window
The LNA gain window provides the status of the configured LNA gain. The gain can be configured
automatically or manually. In automatic mode the LNA gain is set based upon the RSSI value. In manual
mode, the gain should be set according to the expected signal power.
Note that the AGC reference threshold is set according to:
dBm
]
in
FadingMarg
DemodSNR
)
RxBw
*
2
log(
*
10
NF
174
[
AgcRef
+
+
+
+
−
=
Figure 19: LNA Gain Window
5.3.3 AFC / FEI
The AFC / FEI (Frequency Error Indicator) window is illustrated below. Note that when AFC is activated
(either AFC auto “ON” or manually), the RF frequency in the General window of the Common
Configuration Register Tab does not update, although a measure of frequency error can be obtained by
clicking on the FEI Read button to verify correct AFC operation.
Enabling AFC low beta implements a double AFC function to offset the local oscillator of the SX1231 to
ensure that the central tone at f
0
associated with low modulation index signals is not unduly attenuated by
the cut-off frequency of the DCC.
Please refer to the optimized set up for low modulation index systems section of the SX1231 datasheet
for further details.
Figure 20: AFC / FEI Window
5.3.4 RSSI
The RSSI window provides access to the RSSI timeout and timeout threshold functions and enable either
automatic or manual RSSI detection threshold values to be programmed. Note that the RSSI threshold
