Bouncing a LoRa message off the moon | Hacker News Reader

Bouncing a LoRa message off the moon

electronics360.globalspec.com

147 pointsfortran7768 comments

of all the things to bounce off the moon, why a consumer IoT protocol?

Alien 1: The humans are talking again. Alien 2: What did they say? Alien 1: The front door is locked.

A consumer protocol, but also way over consumer power level (350W). No wonder it's the furthest LoRa message sent. Let's bump it up to 1kW and break the record again...

1kW? Are you crazy??? Let's see 25mW, which is the maximum you are allowed to use in Germany for 868 MHz ...

I agree, if we are doing this, go big. 1MW would be far more exciting and the experiment definitely wouldn't go unnoticed.

To be fair, it can do a few km at 25 mW, which is fairly good for consumer range.

That was the Effective Radiated Power. The actual transmitter was outputting consumer output levels.

I thought most FCC rules are based on effective power and that this wouldn't be legal for terrestrial/consumer use?

Correct.

Because it doubles the range of the PR stunt.

If they had driven the chip with a raspberry pi (or, more importantly, said so enough times to land the keyword in the article), they could have quadrupled the range of the PR stunt.

They could use virtual reality nanotechnology in the blockchain!

Just a guess: given that LoRa operates on line of sight, when trying to update a gateways with sensor status (e.g. GPS position of tracked item) the operator won't be able to get realtime reports if the gateway isn't positioned at a high enough altitude relative to the sensor.

You can mitigate this by having many gateway/collectors at high points on buildings/hills, but bouncing signals off the moon seems like an interesting alternative for connectivity in low coverage locations...

Perhaps this is clear to you I'm just trying to think it through out loud.

Moonbounce isn't practical for any real application nowadays. It's a fun experiment and a PR stunt.

Why isn't it practical? Background noise makes it unreliable?

Because the moon is 238,900 mi away. Nor does it stay locked in position. Nor is it perfectly reflective (albeit quite a high albedo) nor a perfect sphere.

This comment has made me need to go listen to Albedo 0.39 again:

https://www.youtube.com/watch?v=ygcBT87K6BY

The fact they used a 35m radio telescope as the receiver station here, and transmission powers way over legal limits for normal LoRa-like applications is a pretty good hint. You lose a crazy amount of signal with moonbounce, the effort is always easier to put into different methods instead. AFAIK it's only non-experimental use predates human-made satellites (US military, as a further channel to reach far-away war ships even if terrestrial propagation conditions are bad). If you can't use satellites, and can't have a receiver station within a few thousand miles of your transmitter, then it maybe is sort-of an option, but that's not really a situation you have anymore.

Amateur radio operators still do it, and with purpose-made codecs and really slow speeds it's not that out of reach (i.e. at least for those you don't need a radio telescope dish), but that's just because it's an interesting challenge.

Path loss.

Background noise - that's one way to put it! The path loss is around 250 dB, so a practical amateur moonbounce station makes use of a very powerful RF amplifier feeding an array of yagi antennas, all mounted on an altitude/azimuth rotator - in other words, it's a radio telescope, and the receiving side hopefully has something similar. You can do a google image search for "moonbounce," the setups are kind of amazing. A lot of investment mostly to exchange morse and specialized low-bandwidth digital modes.

The upshot is that you can communicate with any station that can also see the moon - somebody on the other side of the planet, 12,000km away. Plus there is the unique experience of hearing your own transmission echo, two seconds after you cease.

This kind of setup is well within reach for a commercial enterprise but will never be practical for IoT owing to the laws of physics. On the other hand, there is SNOTEL, a system that bounces snowpack telemetry off of the ionized trails left by meteors...

This is a cool stunt, but it's not at all practical for IoT communications. For one thing, it requires a big dish and a huge amount of transmission power to get a barely-distinguishable reflected signal.

The other big issue is that it doesn't scale, because there's no directionality: the reflected signal will be scattered off the moon and received everywhere on the hemisphere of earth where the moon is above the horizon. So every single device that tried to use this strategy would have to contend for the same chunk of bandwidth.

it would be interesting to see where else it could've been picked up. like a scatter dispersion map

> given that LoRa operates on line of sight

not exactly, no, one of the most common uses for LoRA is in the US 915 MHz band where it can function in a very much non line of sight environment.

LoRa doesn't have to be LOS, it depends on the carrier frequency you use. 900MHz LoRa is used for building penetration of control signals for racing drones, for example, with the open source ExpressLRS system.

I have a bunch of (low powered, runs for 24+_hrs on a single 18650 cell) 433MHz Lora/Meshtastic nodes - I can get 10km or so range with simple 1/4 wave dipoles indoors in urban environments. Hills kill it a bot, but I've got one shot that gets 3.3km non line of sight with a hill between the nodes.

Amateur radio operators routinely do earth-moon-earth radio communication using specifically designed protocols. So using LoRa here is surely the point: to show what it can do — not that it can be done at all.

I think this is a pretty good thing, certainly promising: IoT protocols are by definition accessible to the general public which gives a lot of potential for future developments. Surely not with LoRa in particular, given the microscopical size of the payloads but the fact that it is possible is really promising. Just a decade ago, this would have been unthinkable for any hobbyist. Hell, even the prices of sdr's a decade ago were off the charts and today a semi-decent one to get you started costs a few bucks.

I think it would be extremely neat to have a fully citizen run global p2p infrastructure that is nearly free, resilient to electrical and internet outages, and able to reach remote and distant places.

I'd crowdfund the maintenance of LoRa repeaters on nearby mountaintops. I'd also do the hiking to maintain them, sounds like as good a premise for adventure as any.

Winlink basically does this. I'm unsure if there's software for other OS, but winlink is email-ish that is p2p on the backend, and can also be used point to point. And don't tell anyone I said this, but if you have a real hardware modem for winlink you can get 3KB/second. It works on any frequency you can tune to.

Also APRS, even though it seems like Google has a huge interest in it, is also a p2p communication network, running on 144mhz and 10mhz.

Check out https://helium.com - it's a blockchain-based LoRA network, where the blockchain is used to reward uptime and certainty of location of the base stations. Transmissions can be received from 10 miles or more away, if the receiver is located high enough.

That would be neat! But before anyone thinks they can build a citizen p2p version of internet this way: LoRa can do bits per minute. Think old time telegraph throghput.

So, something like AX.25 [0][1] on the amateur radio VHF and UHF bands, which is free (once you have an appropriate license) and there is widespread citizen maintained and managed infrastructure, such as repeaters. [2]

0. http://www.ax25.net/

1. https://en.wikipedia.org/wiki/AX.25

2. https://ukrepeater.net/

LoRa isn't really a consumer protocol, more of an industrial one. It's mostly intended for widely distributed sensor networks.

I think Amazon Sidewalk (included w/ every Alexa now) is built on top of LoRa

It looks like they added LoRa to the most recent Ring Bridge[1], but most older Sidewalk devices do their connecting over wifi. Seems likely other new ones will do both.

1: https://fccid.io/2AEUPBHARB001/RF-Exposure-Info/RF-Exposure-...

Wasn't it designed for sending sensor data from oil wells spread out over vast swaths of land or something? I've always though of it as shortwave/vhf for packets

Maybe i'm thinking zigbee?

Zigbee has always (or at least, for a long time) targeted a mixture of consumer and industrial applications and is focused on relatively short range mesh networks. It does have a lot of consumer uses now, it's one of the big protocols used for home automation. Not sure of the exact history of LoRa, but widely distributed oil well sensors would definitely fit the intended use of LoRa. Agriculture is another good use case.

Low power sensors infrequently reporting (mostly one-way) small amounts of data back to a base station over really long distances is what it was originally designed for, though people have done other stuff with it. Zigbee is all about the meshing AFAIU.

Zigbee has a serial bus mode that's identical to RS-485 in practice. There were/are so many industrial applications of RS-485 that they could instantly convert to wireless mesh with a zigbee daughter board or chipset. 'Pro' versions had ~1.5 mile range between nodes.

Started out being used for satellite communication between satellites. It's point to point nature and multiple frequency legs itself to sensor networks over extended distance or in dense areas like cities.

Actually LoRa is not a protocol but physical layer, way of modulating RF. LoRaWAN is probably that consumer protocol which you refer to. There is also Symphony Link protocol (proprietary).

And I wouldn't use LoRaWAN protocol in industrial application, because you have limited way of ACKing every message (more like UDP for sending sensor data rather than TCP), no option for OTA, and Symphony Link claims to have it, so that I would call it more industrial.

So UDP isn't industry-ready yet either then?

Correct, I was hand waving over the distinction but I suppose it's important. LoRa itself is the radio layer. I still think of it as something targeting industrial use cases, though there have been some neat hobbyist projects using it.

Alien 3: We need to find this Alexa person

lora is used for more than just consumer iot control - it's one of the most effective ways to bridge a serial connection across a very low bandwidth/RF difficult or weak link.

The spread spectrum "chirps" that LoRa uses are really effective in allowing you to grab tiny signals from unreasonably large noise floors.

You can see the really obvious signal in the waterfall chart here: https://revspace.nl/DecodingLora

It's way way easier to grab those chirps out of the noise than FSK FM modulated signals or worse AM anything.

LoRa has some ridiculous range with minimal use of power. Being able to bounce it off the moon may allow communication between a whole Earth hemisphere. At the least, this allows beyond-horizon communication.

A personal messaging system for you and all your friends who have a 35m radio telescope dish in their backyards...

They're bouncing them off the retroreflectors on the moon though, right? So that doesn't necessarily translate to being able to send messages to anywhere on the hemisphere.

No, the radio waves bounce off the moon's surface. The retroreflectors are not necessary for that, otherwise stuff like Earth-Venus-Earth bounces[1] would not be possible.

[1]: https://amsat-dl.org/en/earth-venus-earth-experiment-of-amsa...

As others have already pointed out this exercise used a huge dish(a radio telescope[1]) and significant power. This is in no way an economically viable mode of communication. Using satellites in low earth orbit requires less power and a significantly smaller antenna. Putting LoRa on satellites has been done before, see e.g. [2].

[1]: https://en.wikipedia.org/wiki/Dwingeloo_Radio_Observatory

[2]: https://digitalcommons.usu.edu/cgi/viewcontent.cgi?article=4...

Well, here in that case they were using an approach that would be illegal by EU regulations (not sure about US) considering the EIRP limits :)

And if you want real low-power long-range communications with the other side of the earth, you may be interested to have a look at WSPR https://en.wikipedia.org/wiki/WSPR_(amateur_radio_software) !

Hams around the world are already bouncing signals off the moon with a lot less power and gain, using modern signal processing techniques.

I’m having a hard time seeing what’s special about this. This has been a HAM radio thing for a long time.

https://en.m.wikipedia.org/wiki/Earth–Moon–Earth_communicati...

They did it with a data modulation mode (LoRa) which has the following properties:

- it is very resistant to noise

- it is low power

- it is popular

- it is patented/proprietary

It’s basically Wi-Fi to the moon. At very low bandwidth, but still amazing.

ham is not an acronym

Cool! Dwingeloo is like 40km (25 miles) from here. They're doing interesting stuff over there (eg. being a test site for LOFAR [0]).

[0] https://en.wikipedia.org/wiki/Dwingeloo_Radio_Observatory

When it says amplified to 350W, how's that work out of interest, is that done actively with a 'power amplifier' or..?

This. I guess the big deal is supposed to be the single chip transceiver, but that's not a huge step past some small SDR units hams use. Throw 350 watts behind it and most any potato could EME.

Impressed by the headline then I read they amplified it to 350W. Less impressive.

Decoding LoRa: https://revspace.nl/DecodingLora

With a 25 meter dish, moonbounce is not hard. That's a sizable radio telescope. Radio hams have done this with a 3m dish and 150 watts.

As far as i know, Othernet is using LoRa for their geostationary satellite service. Still, moon is much further.

That would be a cool physics lab to replace the Lucite speed of light test

The YoLink products use LoRa for home automation. I am quite happy using their water leak sensors now. You don't need the quarter mile range, but they communicate with low power successfully in situations where higher frequencies might have reflection issues.

I'm also a big fan of YoLink water sensors. I installed them under every sink and have probes going into the sump pumps to detect high water levels. We have a single hub in the basement and it has no issues reaching sensors two floors up at the far corners of the home.

I'm not sure that was the point. Either way, accounting for the doppler effect is possible. We generally know what the offset will be for a given frequency based on the moon's position in the sky. The article itself mentions that the signal behaved predictably with respect to the expected doppler shift.

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