FSK bandwidth selection documentation error?

[JKo]

In 5.5.3 FSK modem

BR = 32 x HSE32_freq / BitRate where HSE32_freq = 32 MHz

Fdev = Fdev[Hz] / FreqStep where FreqStep = HSE32_freq / 2^25

The document then states that to ensure correct modulation the following limit applies:

(Fdev + BR/2) < BW

In the Semtech document the limit is given as:

(2*Fdev + BR)  < BW

What is the correct limit?

Does BW above actually refer to the values in the BW[DSB] column of Table 28 (also Semtech SX126x DS Table 6-4)?

The bandwidth must be chose so that:

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

Should the BR here be BitRate , and not the BR parameter which is referenced to the HSE32 frequency?

[DTomi.1]

Any updates on this?

[DTomi.1 · Accepted solution]

@JKo​ do you mean the expression on the Page 72. of DS13105 Rev 11 in the Table 30. Sub-GHz radio general specifications in "FDA Frequency deviation, FSK" row?

That is actually the same expression as in the Semtech document, multiply both sides by 2.

BW given in ST's expression (250 kHz) is SSB (single-sideband bandwidth) and in the Semtech it is DSB (double-sideband bandwidth) which is going to be 500 kHz.