Frequency Settings for EU 868 MHz, Plus Duty Cycle and Avoiding "no_free_ch" Messages

@JDP
The RN2483 is set up with 3 channels by default (868.1, 868.3, 868.5 MHz) each with data rates 0-to-5 and 0.33% duty cycle.
 
All EU gateways are capable of supporting 8 channels, and some support 16. The RN2483 can manage a list of 16 channels. 
 
The additional channels can be added using these commands:
> mac set ch freq 3 868850000   // Sets ch3 to 868.850 MHz
> mac set ch dcycle 3 999       // Sets the duty cycle to 0.1% (= 99.9% off)
> mac set ch drrange 3 0 5      // Allows data rates 0 to 5 on this channel
> mac set ch status 3 on        // Enables the channel
Note that the default channels are numbers 0, 1 & 2. This group of commands sets up channel 3, and should be repeated for 4, 5, etc
 
Generally the overall duty cycle limit for an EU device is 1% (but it does vary some times by frequency band and region) and RN2483 keeps "on air" & "off air" timers for each channel to help ensure you don't violate the regs. By adding new channels, the overall duty cycle limit has increased above 1% and so you should correct the 3 default channels to a lower value and make sure that everything adds up to 1% (or whatever local limit you are targeting):
> mac set ch dcycle 0 999       // Sets the duty cycle to 0.1% (= 99.9% off)
> mac set ch dcycle 1 999       // Sets the duty cycle to 0.1% (= 99.9% off)
> mac set ch dcycle 2 999       // Sets the duty cycle to 0.1% (= 99.9% off)

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 no, 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. 

During testing you can cheat the safeguards just by raising the duty cycle limit for each channel using the same commands:
(From the cmd ref guide: The <dutyCycle> value that needs to be configured can be obtained from the actual duty
cycle X (in percentage) using the following formula: <dutyCycle>  = (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)
 
All of these frequency & duty cycle settings can be stored in EEPROM using the "mac save" command.