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Comment by lormayna | Hacker News Reader

6 miles seems a very optimistic estimation: 2.4Ghz propagation is very reduced by obstacles like buildings or trees and at that frequency the atmospheric water (fog, rain, humidity) have a big impact on propagation. And you need also to consider that 2.4Ghz is a very polluted band, then the noise floor is significatevly higher than in the 865/915 Mhz. Moreover at 2.4Ghz the Fresnel window is smaller and the risk of multipath fading is higher.

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The record seems to be 830 miles (with antennas at sea level, no less)

https://www.thethingsnetwork.org/article/new-lora-world-reco...

But, that's receiving 3 of maybe thousands of packets.

There's work on bouncing of LoRA signals off the moon:

https://engprojects.tcnj.edu/lora-eme/

Yes, but Joe Shmoe won't see this on their home setup trying to talk to a buddy 2 miles away behind a hill.

LORA uses a sub noise-floor link budget. It allows some pretty crazy performance, at the expense of massive speed losses. Like 203kbps for LoRa vs 1,376,000kbps for WiFi lol.(max phy speeds, ymmmv).

WiFi sensitivity is about -90dB, while LoRa sensitivity is around-150dB…. So that’s about a million times more sensitive. So you need about a million times more signal strength to use low bandwidth WiFi (still impossibly fast by LoRa standards) than to use low bandwidth LoRa.

Those are radio specifications. Real links require about 10db more to get any kind of reliability, but the comparison stands.

I did a test with my long range drone on ELRS and managed to get 6km (not miles) so it might be reachable with higher TX elevation.

I have skepticism too. But also, from a recent LoRa thread, and talking about 900MHz here, but someone said:

> Wifi HaLow 802.11ah. LoRa is another level. It works down to -146dBm. 802.11ah dies around -100dBm.

https://news.ycombinator.com/item?id=47890598

LoRa looks like someone is dropping a saw wave on the spectrum. It so clearly looks like such a blunt force user of spectrum. Just wild.

> 2.4Ghz propagation is very reduced by obstacles like buildings

I never did much 2.4ghz stuff because that was what rich people did, or people mad enough to modify microwave oven magnetrons. However I was always under the impression that freespace loss on 2.4 was terrible. but it turns out its "only" ~9db more than 865

Worth mentioning that 2.4GHz has a lot more attenuation due to clutter than 900MHz. Your problem is usually buildings and non line of site transmission paths. When the signal has to pass through and bounce off things your link budget takes a big hit.

There is the idea of the path loss exponent. In a vacuum it's 2.0. 900Mhz with clutter it's -2.5 At 2.4 MHz it's -3 and -5.8 it's -3.5.

Other downside for higher spreading factor spectrum is data rate drops which results in longer packets. Longer packets means more energy per packet and a higher chance someone else will blow your packet out of the water.

You've been able to buy 900 and 2.4GHz transceivers for the last 20 years.

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