I am new to LoRa and I would like to get some confusion on chirp-based modulation process clarified. I was reading the very good thread Understanding the relationship between LoRa chips, chirps, symbols and bits

My additional question is: up or down chirps change frequency from Fmin to Fmax. Now, clearly all chirps in a spectrometer diagrams look the same since they (mostly) all have same frequency change (again Fmin to Fmax or viceversa). But am i correct that although is not visible in those type of diagrams, during that frequency change process is where the magic happens? Because if we'd look in detail there we would see per-symbol phase changes in order to modulate a specific code or sequence of raw-bits (e.f. 7 bits symbol)? In other terms the phase-change pattern is specific to a symbol whereas the frequency change is the same for all possible symbols?


1 Answer 1


Reading some of your links, the Lora rate-of-change of frequency is a constant, and the minimum and maximum frequencies are well defined, but the duration of the frequency-change-ramp is the variable that encodes the information.

Thus the amount of frequency change is the encoding.

  • \$\begingroup\$ what do you mean for frequency-change-ramp? As i understand, what makes the encoding is the phase change in every frequency ramp. \$\endgroup\$
    – toto'
    Sep 23, 2018 at 12:33
  • \$\begingroup\$ In some of the links, a diagram showed the upper and the lower frequencies, and the modulated frequency. All the frequency changes were at the same linear up-ramp of dFreq/dTime. From what I remember. Read the links info. \$\endgroup\$ Sep 23, 2018 at 16:25
  • \$\begingroup\$ But again the frequency change's rate Fmin to Fmax should be the same in every chirp (so no magic here). Hence my question was: how the raw data are encoded? I assume this is happening anytime a chip (not chirp!) is changing phase within a chirp.. (sorry for the words game) \$\endgroup\$
    – toto'
    Sep 23, 2018 at 17:05
  • \$\begingroup\$ Did you examine the plots of frequency sweeps? The more change in frequency, the more phase-change. \$\endgroup\$ Sep 29, 2018 at 16:54

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