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4.1.2 Peak Threshold Method
When the “Demod Method” is set to “Peak TH”, the demodulator dynamically detects the peak value of the RSSI. The
comparison threshold (Demod TH) is then obtained by reducing N dB from the peak. The magnitude of N is internally calculated
according to the different bandwidths, symbol rates and filtering settings.
0
255
Detected Signal Peak
Time
RSSI
Demodulated
Data
Reduced by N dB
Demod TH
Figure 20. OOK Demodulation Using Peak-N Threshold
When the signal disappears, the peak is detected on the noise floor (see more descriptions in the next section).
To compare the two different modes, the Peak TH mode is used by default on the RFPDK, due to its high adaptability to the
different environments and it is carefree for the user. The Fixed TH mode allows the system to only receive the signals whose
strength is above a preset value, which is helpful for the user to control the communication distance between the Tx and the Rx.
4.2 Fixed Demod TH
This parameter defines the value of the fixed threshold. It is only available when the Demod Method is set to Fixed TH.
4.3 Peak Drop Step, Peak Drop Rate
When using the Peak TH mode, the Peak Drop function is very useful to deal with the long string of logical “0” on the received
data.
When the Peak Drop function is turned off, the dynamically detected peak remains 8 symbols. This means within a moving
8-symbol time window the peak value of the RSSI will be recorded to calculate the demodulation threshold. This might have
problem when a string longer than 8 symbols of logical “0” appears, as shown in the below figure.
0
255
Time
RSSI
Demodulated
Data
Reduced by N dB
8 Symbols
24 Symbols
Signal Peak
Demod TH
Peak
Suddenly Drops
Peak
Suddenly Rises
Figure 21. OOK Demodulation Using Peak-N Threshold, with Peak Drop Off
