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Radio Concepts

Warning

SX1262 Modem (LoRa/FSK Modem)

This is a modem that is capable of TX/RX of LoRa signals. I have learned a lot by looking at the datasheet and trying to understand how it works.

This is the block diagram for the modem. Acronyms are as follows:

  • Matching: provides matching for a poorly mismatched antenna to prevent damage to the rest of the transciever
  • LPF: low pass filter. This means frequencies higher than the cutoff get attenuated. Low frequencies can pass the filter.
  • LNA: low noise amplifier. Takes the weak signal and boosts the power level to make it perceptible for later stages without adding much of its own noise.
  • ⊗ is a mixer. Takes the frequency generated by the PLL and mixes it with the incoming signal to reduce from the many MHz to around the bandwidth of the signal. On outbound TX this is not needed.
  • ADC: analogue to digital converter. At this stage, further parts of the transciever can recover the signals digitally using e.g., the Fourier transform.
  • Block to the right of the ADC: bandpass filter. Allows a specific band to go through to the modem, supressing all other frequencies.
  • Block below that: lowpass filter. Blocks high frequency noise from the rest of the circuit on the output.
  • PLL: phase locked loop. Responsible for generating a stable frequency from the given crystal oscillator frequency.
  • PA: power amplifier. Allows output to the antenna.
  • DC-DC: power supply coming directly from a correctly matched power supply.
  • LDO: low-dropout regulator. Creates a stable voltage from a battery or other fluctuating power source.
  • SPI: serial peripheral interface. How the microcontroller interfaces with this peripheral.