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jgromes / RadioLib

Universal wireless communication library for embedded devices
https://jgromes.github.io/RadioLib/
MIT License
1.59k stars 399 forks source link

RTTY DECODER #70

Closed lucapgt closed 5 years ago

lucapgt commented 5 years ago

Hi, is it possible to decode RTTY directly? I have a module with sx1276, esp32 and oled display. I would like to receive and decode itty directly on board and show messages on display. Can you explain how to make it with your library? rtty.read() is not implemented.

Thanks

jgromes commented 5 years ago

RTTY decoding is not implemented and most likely won't be on any of the modules that currently support RTTY (SX127x, SX126x, RFM9x, RF69, CC1101 and nRF24).

The reason for that is the following: RTTY is implemented by directly manipulating the output frequency of the radio module while transmitting. Receiving RTTY would require to either:

  1. Measure RSSI in extremely narrow band - cannot be achieved by none of the above listed modules.
  2. Somehow exploit continuous transmission mode - don't know how.
  3. Setting frequency shift of the RTTY transmitter so high the RSSI measurement is influenced only by one of the transmitted frequencies (either mark or space). This requires shift of 20 kHz or more and very low RTTY speed (10 baud or less). Result here is a signal that no other RTTY decoder will recognize.

Furthermore, frequency drift and error of these cheap radio modules would make tuning very hard. I suggest to stick with SDR to decode RTTY.

Side note: None of these modules were ever design to transmit RTTY in the first place. Just getting them to transmit it is a massive hack and probably outside the specification.