RFM69 Bandwidth investigations part 1

Usually there are several 433MHz devices around the house. Remote controls and various sensors. Normally the exact operating frequency is notknown. A lot of work described on the internet is done with wide-band receivers. The following graphs show the relation between the receiver bandwidth and the bandwidth of the received signal.

Frequency sweeps of continuous OOK transmission with different receiver bandwidth settings. The graphs show the variance on the sampled RSSI signal.

A rule of thumb is that the sweep is performed with the RFM69 receiver OOK-bandwidth being equal to the frequency step size of the sweep. This gives about 3 datapoints with elevated variance, providing good view to estimate the the peak frequency (433.81MHz for the KAKU remote)First a coarse sweep with steps of 100kHz can be perfoemd, followed by a narrow sweep with step size of 5 or 10kHz.

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