RN2483 - How do you eliminate a "no_free_ch" error?

I'm getting a no_free_ch response from the module. How can I eliminate it?

This is entirely a duty cycle issue, which is regulatory. Generally, the duty cycle limit is 1% (but it does vary sometimes by frequency band and region) and RN2483 keeps "on air" and "off air" timers for each channel to help ensure that you don't violate the regulations. By default, there are three channels enabled, each with 0.33% duty cycle allocation. When pseudo-randomly hopping around the channels, the algorithm looks at the next channel and decides if the timers have enough remaining duty cycle allocation for the transmission. If not, then it skips that channel and moves to the next. If you've used all the allocation for all channels, you get the no_free_ch response. This is quite a common problem during development/learning/debugging, where you tend to send messages far more frequently than normal. In real "sleepy" applications it is rarely an issue.

You can cheat the safeguards just by raising the duty cycle limit for each channel using the command mac set ch dcycle (from the "RN2483 LoRa® Technology Module Command Reference User’s Guide", which could be found on the RN2483 product page under the "Documents" section).

The value that needs to be configured can be obtained from the actual duty cycle X (in percentage) using the following formula: = (100/X) - 1

  • mac set ch dcycle 0 9 sets channel 0 to 10% (= 90% off)
  • mac set ch dcycle 1 99 sets channel 1 to 1% (= 99% off)
  • mac set ch dcycle 2 999 sets channel 2 to 0.1% (= 99.9% off).

The no_free_ch means that all channels are busy transmitting and you have to wait until you can transmit again. You can try to enable more than the three default channels so you have more channels to use at the moment of transmission.

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