JP frequency - 20mW limit, change freqs to avoid duty cycle

[fifieldt]

Thanks to user Goyath on Discord, we discovered that in Japan the 250mW radio level requires licensing, and 20mW is the practical limit. We also discovered that a duty cycle of 10% is needed on most frequencies:

• CH 24-38 920.5-923.5 20mW no airtime restrictions
• CH 39-61 923.5-928.1 20mW 10% airtime

This patch limits the power and restricts the frequency to those with no airtime restrictions.

[Talie5in]

May need to account for remapping channel slots.

JPN Slot 20 been default for Public LongFast and been above 923Mhz

[fifieldt]

Conclusion from discord discussion is:

• CH 24-38 920.5-923.5 20mW no airtime restrictions
• CH 39-61 923.5-928.1 20mW 10% airtime

[fifieldt]

It looks like we discovered this some time ago:

#346
https://meshtastic.discourse.group/t/about-the-japanese-version/1171/4

but it got left off the task list somehow

[numpad0]

Just passing by & just FYI, 920MHz low-power in JP is indeed license free but modems need to be type certified and 〶[R]xxx-xxxx marked for full legal conformance, similar to Wi-Fi cards

[truedat101]

〶

Thanks for this post ... we are trying to figure out the list of compliant devices so we can maintain them for Japan. Esp since there are like 7 public nodes in Japan and only in Tokyo , we would like to improve this situation. Still trying to figure out why this is the case....