This PDF link might not work in the future, so for readers reading this far in the future, search Google for “Study of LoRa Performance at 433 MHz and 868 MHz Bands Inside a Multistory Building” or SciHub is your friend
It has been concluded that for nine-story building with concrete floors it is better to deploy 868 MHz LoRa network.
That doesn’t surprise me, higher frequencies usually work better in urban areas; I expect the opposite in open areas.
However, given legal max power is higher at 868, maybe that’s not the case - but be warned, most Meshtastic supported devices declare +20dBm regardless the frequency.
I think this just is one factor; if it was so simple, 10 mW at medium wave frequency (868 kHz) would be equivalent to 10 kW at 868 MHz, and travel thousand of km…
Higher frequencies are more easily scattered and reflected by small obstacles, leading to multiple waves reaching the receiver at slightly different times, summing or canceling each other at random.
This can be partially overcome by continuously changing the frequency - that’s why frequency hopping.
However, the bouncing limits the distance they travel.
Lower frequency tends to be less scattered and more absorbed; so, when there are less obstacles, they tend to go further. On the other end, with many obstacles higher frequency suffer less.
It’s a common path for most bidirectional comm systems: the more people use them, the less the distance mobile-base station, the higher frequency is better, especially in urban areas (think of cellular phones - 0gen 170 MHz, 1gen 470 MHz, 2G 900 MHz, 3G 1800 MHz, 4G 2100+ MHz…)
If I had to design a global LoRa network, I’d start with 433, and move to 868 when it becomes crowded.
Yes, just one - real - factor. Your other thoughts are interesting. The particular factor I mentioned has to do with distance capabilities.
Your theoretical power comparison is interesting.
The physical world needs, as you suggest, to be included, where medium wave typically operates in ground wave, UHF in line of sight - what you describe.
In actual fact adventurous hams do operate at milliwatts power levels in HF.
“with many obstacles higher frequency suffer less.”
Believe you got a little abstract here; consider MF a.m. radio.
And let’s not forget, in your “many reflections” model - every reflection involves power absorption.
But the topic is in UHF and what I mentioned is, as you say, only one factor. I find it a very interesting one.
I have two 433 devices but I’m going to receive two 868 devices soon. I’m going to do a real world range test with these units and see if this research’s results holds true.
@kokroo It’s the best way, let us know…! @csweningsen I’m a radio ham, but by no way an expert - my practical experience is only in V-UHF, and my curse is that I’ve always been living in low houses, except my last one. I know many, with very low power, have covered 100’s to 1000’s of km in 14-30 MHz, but with special conditions. Leaving an unattended repeater operating all the time is another story. Thanks for your good points,
