RFM95 datasheet(82/121 Pages) HOPERF

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Page 82

RFM95/96/97/98(W)

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WIRELESS & SENSING

PRELIMINARY

DATASHEET

Table 83 RssiSmoothing Options

RssiSmoothing

Number of Samples

Estimated Accuracy

Response Time

‘000’

± 6 dB

‘001’

± 5 dB

‘010’

± 4 dB

‘011’

± 3 dB

‘100’

± 2 dB

‘101’

± 1.5 dB

‘110’

128

± 1.2 dB

‘111’

256

± 1.1 dB

2(RssiSmoothing+1)

· RxBw

[kHz] [ms]

The RSSI is calibrated when the image and RSSI calibration process is launched.

5.5.5. RSSI in

LoRaTM Mode

The RSSI values reported by the LoRaTM modem differ from those expressed by the FSK/OOK modem. The following

formula shows the method used to interpret the LoRaTM RSSI values.

RSSI

[dBm] = –137 + RSSI

5.5.6. Channel Filter

The role of the channel filter is to reject noise and interference outside of the wanted channel. The RFM95/96/97/98(W)

channel filtering is implemented with a 16-tap finite impulse response (FIR) filter. Rejection of the filter is high enough that

the filter stop-band performance is not the dominant influence on adjacent channel rejection performance. This is instead

limited by the RFM95/96/97/98(W) PLL phase noise.

Note

To respect sampling criterion in the decimation chain of the receiver, the communication bit rate cannot be set at a

higher than twice the single side receiver bandwidth (BitRate < 2 x RxBw)

The programmed single side bandwidth RxBw of the channel filter is determined by the parameters RxBwMant and

RxBwExp

in RegRxBw:

RxBw = ------------------------

----X----O

----S----C-------------------------

RxBwMant

× 2RxBwExp

+ 2

The following channel filter bandwidths are hence accessible in the case of a 32 MHz reference oscillator.

Table 84 Available RxBw Settings

RxBw (kHz)

RxBwMant

(binary/value)

RxBwExp

(decimal)

FSK / OOK

10b / 24

2.6

01b / 20

3.1

00b / 16

3.9

10b / 24

5.2

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