[jtchang]

Correct me if I am wrong but I thought the primary appeal of LoRa was range? Also isn't the primary factor in making long range radio go through things is the frequency? So 2.4ghz is the same frequency as consumer wifi right and thus would propagate about the same right?

It doesn't seem like this would be that useful except that the protocol is LoRa so you can have higher bandwidth between two devices if they happen to be close enough together.

[mikeweiss]

LoRa would go much farther than Wifi on 2.4ghz. Lora uses Chirp Spread Spectrum (CSS) modulation while wifi uses OFDM (Orthogonal Frequency Division Multiplexing). The first being designed for extreme range while the latter for bandwidth. At 2.4ghz you could probably get LoRa connections up to 6 miles with the right antenna height.

[lormayna]

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.

[golem14]

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.

[K0balt]

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.

[po1nt]

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.

[jauntywundrkind]

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.

[KaiserPro]

> 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

[Gibbon1]

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.

[burnt-resistor]

When I worked in the Trimble Navigation radio group, 2.4 GHz was tried but its real world range sucked compared to ~900 MHz and CB ~450 MHz bands of existing solutions. It's simply limitations of physics that lower frequencies propagate farther (at lower bandwidth) than higher frequencies.

[zobzu]

even 900mhz sux vs 433. the lower the better it penetrates matter for the same amplitude.

lower than 430 you start to run into severe bandwidth issues though. and its not allowed to transmit lora/dss on 430 in the us without license hence the 900mhz

at 2.4ghz the real world usage is limited. might as well use wifi. the only advantage is short range bandwidh while keeping lora compat.

[ezwoodland]

What makes OFDM inherently worse at long range? Don't you just lengthen your symbols and use the extra frequency bins until you have tolerable losses?

[dheera]

Just use Unifi Airfiber for 6 miles at gigabit speeds. If you're relying on line of sight then 2.4GHz is nonsense.

And if you don't have line of sight then no you're not getting 6 miles

[mikeweiss]

Is UniFi Air fiber extremely low power and cheap to produce?

[burnt-resistor]

$2000 minimum and closed source.

[drgone]

yes, considering the options.

[mikeweiss]

What are the options?

[e12e]

Something like?:

https://radionor.no/solution/cre-2-series/

[kanbankaren]

> would propagate about the same right?

No. Free space loss increases with frequency.

FSP loss for 915 MHz at 10 kms is ~ -111.67 dB while for 2.4 GHz is -120 dB.

That is a 9 dB loss which is significant. It could mean the difference between a copy or just plain static though the LoRa is supposed to be copyable down to -140 dBm.

The max tx power is around 150 mW (21.76 dBm), so at 10 kms, the RSSI is 21.76-120 = -98.24 dBm which is above the -140 dBm limit.

This calculation is assuming there is no loss due to vegetation or humidity or other barriers.

[bigfatkitten]

LoRa is copyable at -140dBm only at very low effective data rates (under 100bps), which for many applications is too low to be useful.

[jimnotgym]

...or have line of sight at least. But yes higher frequencies have a bigger issue with this. A great mesh network for people who live on hill tops

[derefr]

"Going through things" isn't always necessary / is avoidable in some deployments. And 2.4GHz signals can propagate an okay distance between nodes if there aren't things to go through. (Globalstar's emergency SOS satellite constellation uses the n53 band, which is right above the 2.4GHz "wi-fi" band, and it propagates between handsets and LEO through 1400km of air just fine.)

So you could probably pull off a 2.4GHz mesh outdoors in rural areas? It'd be feasible in the same places a microwave-laser hilltop-to-hilltop link would, but instead of "fast but point-to-point" it's "slow but meshed" (and with much larger tolerance for slop — you don't need to put everything on fixed masts so they have perfect line-of-sight, you can just stick them on the tops of trees or whatever and if they wave in the wind it still works.)

Mind you, the authors' motivating use-case for the hardware seems to be their project (https://github.com/datapartyjs/MeshTNC) to (AFAICT) bridge LoRa (or some specific LoRa L2 protocol — Meshtastic, probably?) to packet radio, i.e. digital packet-switched signalling over amateur (HAM) radio bands.

In that context, the tradeoff of high throughput for low propagation makes sense. Insofar as you're working with LoRa, and want to build and experiment with a bunch of site-local devices that mesh between themselves and interoperate with LoRa data-link protocols, you'd likely be speaking something like LoRA over 2.4GHz (LoRa itself doesn't spec a way to do that, but you could make it happen within the closed ecosystem of your own home/office.)

And in that context, you could use a MeshTNC device as something like "LoRaLAN" router. It'd be something you'd keep somewhere central in your house (like a wi-fi router), plugged into power + an antenna (internal to your house, like a wi-fi router) and plugged into a packet-radio transceiver with its own even-bigger antenna, outside your house. (Like a wi-fi router being plugged into a gateway modem on its upstream WAN port.)

This MeshTNC device would then pick up signals from:

- regular LoRaWAN IoT devices and Meshtastic handsets in your building

- more custom devices in your building†, that you've built yourself, that use another MeshTNC module; where these other devices do their part of the meshing only on the 2.4GHz band, which means they don't need big fiddly external antennas like LoRa devices do, but can be quite compact

- and possibly, a separate bidirectional LoRa repeater (made from any existing "high-gain" LoRa module, i.e. the kind used in mains-powered LoRaWAN base stations) — which brings in LoRa mesh traffic from outside your building, and picks up and carries away "destined for elsewhere in this area" LoRa mesh traffic that your "LoRaLAN" device has emitted (either due to forwarding it from your 2.4GHz-only mesh handsets/devices, or due to forwarding it after receiving it from packet radio.)

Though keep in mind you only need that complexity for the 2.4GHz-only mesh devices, since there isn't an existing mesh to forward those packets. But this whole setup is still also a regular LoRa mesh, and so you can still use regular LoRa (e.g. meshtastic) handsets, and put out packets that make their way through your regional mesh, back to the packet-radio bridge in your building; and from there to who-knows-where.

† To be clear, the 2.4GHz mesh handsets would only work reliably inside your building (if the 2.4GHz antenna is inside your building); but knowing HAMs, half the point would be seeing how far away you could get from your house/office and have your 2.4GHz mesh handsets keep working. (You'd probably want to have a second MeshTNC "base station" with a building-external antenna to try that. Pleasantly, that doesn't complicate the topology; it's all still just mesh, so you can just drop that in.)