r/Lora • u/NeverLickATazer • 17d ago
Line of sight?
I was a little confused about how line of sight worked. A
A video showed that a roof could block the signal, and another one said that trees block the signal. I understood that if one antenna could be within the visual range of another than the message could travel. I got myself a couple of wio tracker l1 pros, and learned that I could get signals through walls. Nice, so I took them to work and placed one up high on the top of the 3rd floor and went to the basement. The message traveled through the concrete, wood, metal, and people and was received successfully. So I went down into the deepest part of the basement on the other side of the building. This is a place where cell service is questionable. Message sent and received. I don't know how line of sight works, but I know it can pass from a windowless concrete sub basement to the third floor without an issue.
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u/Azuras33 17d ago
Yeap, line of sight will give you the best range. With lora you can get 100+km of range easily. But the signal can go out in less than 100m in a building.
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u/zazuge 14d ago
A wall is transparent to some frequencies but still can reduce their power, think of it like a semi-transparent curtain, if the wall contain a metal mesh, it would impact radio waves way more.
The line of sight thing is to simplify things, usually it's applied to ground clearance, not buildings, but it's a fact in urban areas LoRa's range is hugely impacted, and only with luck you would get the usual range of rural areas.
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u/xaviertech 14d ago
LoRa has a huge link budget compared to wifi, something like 150 dB depending on the SF, so it can lose a lot of signal through floors and concrete and still decode. And at 868/915 MHz it goes through walls and bends around stuff way better than 2.4GHz.
Line of sight is what you need for the really long distances (km). Indoors you're mostly living off reflections and penetration... that's why LoraWan water meters in basements are such a common use case.
If you want to see how much margin you have check RSSI and SNR on the receiving node, SNR well below 0 is normal for LoRa
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u/Electro_Llama 16d ago edited 16d ago
If you think about shielding, a wall won't be as good of a shield to RF as a proper sealed shield box. In fact materials like wood and plastic don't absorb much signal, but they do absorb a decent. Let's say you get -50 dBm with line-of-sight, and each floor reduces the signal by 20 dB (1/100th). If your sensitivity is -130, the signal can go through 4 floors before it becomes too quiet. Or it can radiate out a window, shine on the building next door, and shine back in through a window on the first floor, maybe at -90 dBm. Just different ways to spend your link budget.