Data Sheet

Page 32
RFM69HCW
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SX1239
signed result is loaded in FeiValue in RegFei, in 2’s complement format. The time required for an FEI evaluation is 4 times
the bit period.
To ensure a proper behavior of the FEI:

The operation must be done during the reception of preamble

The sum of the frequency offset and the 20 dB signal bandwidth must be lower than the base band filter bandwidth
The 20 dB bandwidth of the signal can be evaluated as follows (double-side bandwidth):
= ⋅
The frequency error, in Hz, can be calculated with the following formula:
RFM69HCW in Rx
mode
Preamble-modulated input s ignal
Signal level > Sensitivity
Set FeiStart
= 1
FeiDone
No
= 1
Yes
Read
FeiValue
Figure 13. FEI Process
3.4.15. Automatic Frequency Correction
The AFC is based on the FEI block, and therefore the same input signal and receiver setting conditions apply. When the
AFC procedure is done, AfcValue is directly subtracted to the register that defines the frequency of operation of the
module, F
RF
. The AFC can be launched:

Each time the receiver is enabled, if AfcAutoOn = 1

Upon user request, by setting bit AfcStart in RegAfcFei, if AfcAutoOn = 0