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STM32WL55 FSK receive bandwith setting, SubGHz_Phy_Per example

Erlkoenig
Associate III

Hi,

the STM32WL55's reference manual states:

> BW[DSB] > BR + 2 x frequency deviation + frequency error

However, in the SubGHz_Phy_Per example, FSK is configured as follows:

 

 

 

#define FSK_FDEV                                    25000     /* Hz */
#define FSK_DATARATE                                50000     /* bps */
#define FSK_BANDWIDTH                               50000     /* Hz */

 

 

 

Therefore, "BR + 2 x frequency deviation" would be equal to 100000Hz. But the bandwidth is set to just 50000Hz. But the example still works. Why? The gaussian filter (BT=0.5) reduces the bandwith, but not that much.

The reference manual also states:

> In receive mode, the bandwidth is automatically adjusted to match the selected data rate

Does this mean I don't have to specify the bandwidth?

 

Is the following interpretation of the FSK frequency parameters correct?

FSK.png

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