LoRa to the Moon and back: Messages bounced off lunar surface using off-the-shelf hardware A team of scientists has managed to bounce a LoRa message off the Moon, setting an impressive record of 730,360km for the furthest distance such a data message has travelled. While much of the technology was off-the-shelf (Semtech's LR1110 RF transceiver chip was used) the signal was amplified to 350w using the 25-metre dish …
Possibly unique in the world. The dish they're using was originally built for scientific research (and was the largest in the world for a bit). In 2007 it was given to a group of amateur radio astronomers and they've spent a lot of time rebuilding the dish and making the whole thing operational again. Since iirc 2016 the radiotelescope is now available for amateur radioastronomers and other people interested in doing something with large dish like that who can convince the people running it that what they want to do makes sense and won't break the thing (barring apparently some internal kerfuffles within the organisation running the scope and the whole global virus stuff).
See also: www.camras.nl and the wiki page on the Dwingeloo radio telescope
The stuff doesn't even have to fit in a garden. I witnessed 10 GHz moonbounce between Queensland and Texas at a ham radio conference. VERY shallow angles, but a 30cm antenna has good gain, and when driven with a 50W amplifier put out a big signal.
Lora over that distance is impressive. Getting up there with Joe Taylor (K1JT) work using Arecibo. 61dBi gain at 433 MHz is massive, and that allowed one other party to use a handheld radio with a rubber ducky (or so is claimed). Believable since the spot size of the beam was 1/2 the diameter of the moon. https://physics.princeton.edu/pulsar/k1jt/Moonbounce_at_Arecibo.pdf
Darn you... You said "radio" and "rubber duck(y)" in the same sentence and my mind immediately went to "CB radio" and the song "Convoy".
(The music of which -- as I've said long ago -- was written by Chip Davis, leader/arranger/composer for Mannheim Steamroller; given the season, it's time to warm up the Steamroller's Christmas playlist.)
I happen to have a friend in the broadcast business.
When his station was converting from analog to DTV, he was managing the project to strengthen the existing tower and another project to design the new DTV antenna, to be shared by a number of broadcasters using the tower.
He also happens to be a radio ham. His plan was, during the weekend after the antenna was mounted, but before all the users powered up, to attach a 440MHz ham radio to the feedline and see who he could work.
Sadly, the schedule didn't work out. I can see much the same thing going on here. I wonder how many of those involved were (or had been at one time) hams
I admire the investigators who managed to write a project proposal and succeeded in getting time on the dish for this experiment.
"Does this help?" - not really but all your down votes demonstrate that the majority of El Reg readers have decent brains and want to find out the technical information about everything ... that's why we are all here and not on social media. LOL so you have made a good point.
Reasonable question -- deserves an answer.
LoRa is a proprietary spread spectrum technology that is used in license free bands. It presumably allows multiple user pairs to communicate over the same band simultaneously without requiring them to find a free frequency slot. The Wikipedia article is at https://en.wikipedia.org/wiki/LoRa
There's also a Wikipedia article on EME (Earth Moon Earth) communications in general at https://en.wikipedia.org/wiki/Earth%E2%80%93Moon%E2%80%93Earth_communication
Not that complicated if you've ever had to look at radar return waveforms. A bit puzzling if not.
If the moon were a glassy smooth sphere, you'd only get one return signal -- from the center of the moon. Any other reflections would go off to your sides. But the moon is bumpy. Craters and such. So in addition to the return from the center point, you'll get some signal bounced back from other lunar features. Those are further away from you than the center of the moon. It takes a tiny bit longer for your signal to get to them and a bit longer for the signal reflected from them to get back. Result: instead of one tidy set of pulses that is mirror image of your outgoing signal, you'll get a reflected signal that's smeared out over (I'd guess) 20 or so milliseconds.
I may have some of the details wrong. It's not like I spend my spare time bouncing radio signals off the moon. But I think the above is the general idea.
You also get information from the different frequency shifts due to the (slight) rotation of the moon. So you get radial information from the center because of the delay and "left to right" information from the frequency shifts. Doing this several times allows one to disambiguate various areas and get a radar picture of the whole moon.
As worded this isn't really anything special. Ham radio operators have been doing this for decades and with smaller antennas. Some just by leaning a Yagi against the garden fence.
I suspect ignorance on the reporters part, though. A signal is not "amplified to 350w using the 25-metre dish of the Dwingeloo Radio Observatory in the Netherlands" just by changing the antenna. A more likely case is that a couple of milliwatts sent through the dish had an ERP (effective radiated power) equivalent to a 350 watt sent to a dipole. A pretty good accomplishment but hardly headline worthy.
Come back to us when you are doing it through a a handheld Yagi.
Yep, first read of the story didn't say anything spectacular. In the HAM world, we have done this for quite a while with some cheap gear.
I don't see a mention on the Frequency used by Lora and considering the modules are available in 433Mhz, 868Mhz and 915Mhz, it may make a difference. Certainly 433Mhz would be quickest to get working with a borrowed ham yagi and suitable amp.
Might be harder with 915Mhz but i've not read up on the propagation properties of this frequency at distance. Normally higher frequency = less penetration.
What I find more of an achievement is the use of Meteor Scatter for communications. Bouncing your radio signal off of the ionised trail of a meteor passing through the upper atmosphere when that trail may only last from a few seconds to 30 seconds.
I've been doing lots of mucking around with LoRa - the things that most people seem to use it for when testing are either the current temperature, or paxcounter.
If the latter I trust we can presume the number of persons detected was zero...
Bought two LoRa modules from the Pihut - one plugged into my Pi4, the other via my mobile running a terminal app. Wrote a bash script to send a message every second with timestamp, and set the mobile to receive. Walked about five miles away from home.
What I should have done is checked the ground profile first, as my route after a quarter of a mile blocked the signal due to terrain. Haven't bothered since but intend to plan the next route. As I have a relative perched on a hill in Ryde, Isle of Wight, I'd like to see if it would work over on the ferry to Portsmouth. Don't see why not?
Now what would be really scary is if the message that bounced back from the moon responded with 'hello we're fine up here how's the weather on earth?'
The Register 
Biting the hand that feeds IT
Copyright. All rights reserved © 1998–2024
