Even with context!
A itch I really wouldnt suggest you start to scratch! As noted you quickly disappear down rabbit holes…
It is a nice round number that is easily articulated and measured and as that is a simple small percentage of other much higher powered transmitters that were common in other use cases (and in other territories - and depending on bands with limits like 10mW, 25mW, 100mW etc.) at the time when they proposed (100W, 250W, 1KW, etc.) - ones where a licence would certainly have been required for legal operation. Calling out a limit of 1%, 0.25%, 0.1% even 0.01% as being insignificant for ‘unlicensed use’ would be an easy win irrespective of any underlying physics, electrical/electronic engineering or metrology solutions (remember that RF attenuates over distance and free space losses quickly limit the effective range - and potential interferer distances - for such low power Tx’ers, quickly falling below classical noise and detection limits helping mitigate impact as they proliferate). You quickly start to ask, on similar basis, why have e.g. duty cycles at 10%, 1%, 0.1% etc. where applicable etc. Why is US dwell time limit 400ms - why not 333ms or 500ms etc. Why 125khz channels vs 100khz, 150khz? As I say a rabbit hole you may get lost in. Mostly these were pragmatic ‘reasonable’ and workable solutions that seem to have been proven manageable over the decades. Remember many limits were set early on in the days before technical implementations like LoRa were even the figment of some innovative folks imaginations.
If you really want to know suggest you refer back to the discussions and outputs of early working groups and standards bodies like ETSI, ITU, IEE(IET) & IEEE etc. from 25, 50years & even longer ago. Not many Forumites would be into the weeds on this stuff I’m afraid…
Climbing out of the rabbit hole…bye! Image may be NSFW.
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