Revision 1.0 STD – February 2010
Page 19 of 31
www.semtech.com
© Semtech 2011
SX1233SKA
USER GUIDE
dBm
]
in
FadingMarg
DemodSNR
)
RxBw
*
2
log(
*
10
NF
174
[
AgcRef
+
+
+
+
−
=
Figure 20: 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 SX1233 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 SX1233 datasheet
for further details.
Figure 21: 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
(which should not be confused with the LNA or AGC threshold) can be calculated from and equates to the
effective noise floor of the receiver for a given filter bandwidth.
dBm
]
DemodSNR
)
RxBw
*
2
log(
*
10
NF
174
[
RSSIthres
+
+
+
−
=
