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Open-source communications by bouncing signals off the Moon
- gus_massa 1y agoI started reading thinking it was impossible but it has been done with other devices https://en.wikipedia.org/wiki/Earth%E2%80%93Moon%E2%80%93Earth_communication https://en.wikipedia.org/wiki/Earth%E2%80%93Moon%E2%80%93Ear...
- cactacea 1y agoNot impossible, just extremely difficult. I'm a ham and getting some contacts over moonbounce is a personal goal of mine. Historically this kind of thing has required some pretty large antenna arrays and very high power though: https://hamradio.engineering/eme-moonbounce-bouncing-signals-off-the-moon/ https://hamradio.engineering/eme-moonbounce-bouncing-signals... http://www.g4ztr.co.uk/app/download/13284489/RaCcom_Feb14+EME+part+1.pdf http://www.g4ztr.co.uk/app/download/13284489/RaCcom_Feb14+EM... http://www.g4ztr.co.uk/app/download/13300096/Radcom_Mar144+EME+part+2.pdf http://www.g4ztr.co.uk/app/download/13300096/Radcom_Mar144+E...
- dbcurtis 1y agoIsn't there a moon bounce mode in WSJT (or one of those digital modes) that provides enough coding gain that 100W and a single large Yagi is enough? I seem to recall hearing something like that... but, yeah, on CW a monster antenna and the legal limit of 1500W seems to be the median system. A long time ago I started collecting parts for a 432MHz EME system. Life got in the way and I never built it out. Good luck with your endeavor!
- ErroneousBosh 1y ago> but, yeah, on CW a monster antenna and the legal limit of 1500W seems to be the median system. A good ten years ago or more, they used Arecibo to transmit CW moonbounce on 70cm. I was able to receive it in my back garden with a handheld and an 11-element Yagi balanced on my clothesline ;-)
- ErroneousBosh 1y agoIt's been being done for 70 years or so. You just need to be able to generate quite a lot of power on VHF upwards, and have a very low-noise antenna preamp, and a large array of directional aerials to focus the signal. If you're reasonably handy with simple hand tools you can build a moonbounce array for a couple of thousand and a month or so of evenings.
- Polizeiposaune 1y agoThe big dish antenna at Stanford University (visible from I-280) was, among many other things, used to monitor Soviet radar signals from Sary Shagan in Kazakhstan, that bounced off the moon some of the time. The wikipedia article: https://en.wikipedia.org/wiki/Stanford_Dish https://en.wikipedia.org/wiki/Stanford_Dish links to: https://web.archive.org/web/20201108114110/https://www.cia.gov/library/center-for-the-study-of-intelligence/kent-csi/vol11no2/html/v11i2a05p_0001.htm https://web.archive.org/web/20201108114110/https://www.cia.g... which has this tidbit which explains why it works as well as it does when it works: "Fortunately for us, the moon appears only slightly rough to radio waves; most of the reflected energy comes back from an area at the near point just a few miles in diameter. The bulk of the energy striking farther around on the side is reflected out into space and never returns to earth."
- cactacea 1y agoExpected array gain: ~39.3 dBi / EIRP: ~63.1 dBW Tx power: 1 W per antenna Yeah... so free space path loss at legal frequencies for hams this thing can transmit on is ~283dB. Neat idea but consider me skeptical. Having said that I can see some interesting applications for this kind of gear, EME seems overly optimistic though.
- jacquesm 1y agoA few hundred Watt at a minimum would be my first guess.
- cactacea 1y agoYeah that is what is used for moonbounce today (if not full legal power - 1500W for US amateurs) but these little panels won't put out anything remotely close to that. Hence my skepticism.
- deleted 1y ago[deleted]
- mschuster91 1y agoY'all can run at 1500W? Here in Germany the legal limit (depending on band of course) is 750W.
- dbcurtis 1y agoAt those power levels they would have to use some kind of highly error-corrected modulation and coding scheme to provide enough coding gain to overcome the path loss. I agree they are pretty optimistic, but until they detail their modulation scheme, it's hard to tell. A few years ago I was experimenting with 900 MHz LoRa for a work project -- we had need to communicate a very small data payload from inside elevator cabs, with forgiving latency requirements. So we took a LoRa board to a hotel building 2 city blocks away from our lab and cranked the coding gain up to the max, which gave us about a 1 byte payload every second. Perfectly sufficient for our application. Astoundingly, we had great copy in our lab even when the doors of the elevator cab were closed, inside a building 2 blocks away. I can't remember the power level, 500mW I think, but I may be wrong.
- amelius 1y agoLatency?
- _bernd 1y ago1 sec up and 1 sec down... more or less. Speed of light and distance to the moon, two times.... roughly.
- whatsupdog 1y agoI'm more interested in bitrate.
- radiorickky 1y ago300bps
- wslh 1y agoIs that right? Only 300bps? It is easy to infer that having a bigger antenna you can scale that.
- firesteelrain 1y agoKA1GT recently found a $100 “solar cooker” dish on AliExpress. Also available on Amazon. It was tested back in August. Announced on the EME Facebook Group: https://www.facebook.com/share/p/19zLsGZiE7/?mibextid=wwXIfr https://www.facebook.com/share/p/19zLsGZiE7/?mibextid=wwXIfr Output power was 500w
- NoiseBert69 1y agoThere's nothing that can't be modulated. Lol.
- zerosummer 1y agoThe open.space phased array is a similar power, but an electronically steerable all-digital beamformer. Was covered on zr: https://www.zeroretries.org/p/zero-retries-0224?#%C2%A7openspace https://www.zeroretries.org/p/zero-retries-0224?#%C2%A7opens... Looks beautiful on a tripod.
- skeptrune 1y agoI'm skeptical, but how can you not cheer for this? Sounds so awesome.
- NewJazz 1y agoHave you read Three Body Problem?
- kieranl 1y agoI got to see this in person at pacificon a few weeks ago. Also the creator is my friend from UIUC who I consider a brilliant rf/DSP engineer. The demo was able to show and end to end tx chain from gnuradio to a receiver. Really excited to see this! As there are a myriad of other things that this hardware can be used for as well.
- mrtnmcc 1y agoGreat seeing you at Pacificon! We’re starting with the “Quad” tile — a 4 Tx × 4 Rx SDR designed for arraying — and expect to ship the first units toward the end of this year. They're actually quite capable as a standalone SDR. A Quad can interface directly with a Raspberry Pi 5, and we’ve built a combined enclosure for the SDR + Pi setup. You can run SDR software locally on the Pi or stream IQ samples over gigabit Ethernet to a remote PC. Software support includes GNU Radio, Pothos SDR, and just about any tool compatible with SoapySDR. We’re also doing some fun demos, like visualizing Wi-Fi signal sources in real time ("Wi-Fi camera") and performing mm-scale 3D localization—a prerequisite for the automatic array calibration. Larger arrays are assembled by simply tiling these Quads into an aluminum/PCB lattice framework, enabling anything from compact 4-antenna MIMO nodes up to 240-element lunar-bounce arrays. The goal is to have full phased-array capability by March 2026. The broader vision behind open.space is to make advanced RF and space-communications hardware open and accessible—so anyone can experiment with technologies once limited to national labs: moon-bounce (EME) links, satellite reception, terrestrial RF imaging. Happy to answer questions here. One thing I'm excited about getting working is mobile moon bounce!
- drmpeg 1y agoWill you have arrays with the opposite antenna polarity for point to point links? That is, LHCP (Tx), RHCP (Rx) instead of RHCP (Tx), LHCP (Rx).
- mrtnmcc2 1y agoGreat question, the latest version has Tx RHCP, and then Rx either LHCP or RHCP controlled with RF switches (in each antenna). This allows point to point links (where the Tx pol and Rx pol should be the same), or "bounce links" where the circular polarization flips with the bounce. I should note RHCP Rx has a bit worse noise figure (LNA is different) but good enough for any line of sight.
- dreamcompiler 1y agoIf the goal is only to communicate with people on the other side of the world, HF ionosphere skip can do that with cheap 100-year-old technology (although transistors make it easier). I assume the goal is to do something cooler than that.
- lll-o-lll 1y ago> I assume the goal is to do something cooler than that. Yes. Bounce the signal off the moon. The moon.
- cwillu 1y agoWhat if we tried more power?
- topspin 1y agoHams bounce signals off of everything. Aircraft scatter, for example. Probably the coolest is using the ion trails of meteorites. When meteors punch through the atmosphere, they create ionized trails. These trails can reflect RF signals. Some of these happen to be optimal at low VFH frequencies, and hams make contacts using frequencies that ordinarily don't work beyond line of sight.
- ErroneousBosh 1y agoWe've bounced 2.4GHz signals off Venus. Venus.
- deleted 1y ago[deleted]
- topspin 1y agoVHF frequencies, that is.
- kragen 1y agoThe entire HF band, including the parts already used for something, is only 27 MHz of bandwidth, it's full of noise, and at any given time only a fraction of it can propagate to the other side of the world, dependent on time of day and, literally, sunspots. This antenna has 1100 MHz of bandwidth, the analog front end has 40 MHz for any given conversation, and noise levels are much lower. It could conceivably deliver Shannon bit rates one or more orders of magnitude higher. But it only works when the moon is visible to both sides of the connection. I discussed these possibilities and some more challenging ones in 02013 in https://dercuano.github.io/notes/ultraslow-radio.html https://dercuano.github.io/notes/ultraslow-radio.html, although I was considering laser moonbounce rather than phased-array microwave moonbounce because of the higher antenna gain available.
- euroderf 1y agoThis was a Cold War thing to surveil Soviet air defense radars.
- whatsupdog 1y agoFor someone not well versed with the terminology, can someone please tell what kind of bitrate this can provide? In bytes per second.
- shakna 1y agoIt's not even a byte per second. The latency of the distances involved mean you're looking at around two seconds per round trip, plus a little extra because of the fuzziness of radio in space and absolutely everything that can distort it. There's a lot of math that goes into selecting the right bit-width for the signal, which I ain't doing here and now [0], but most 24dB things tend to be 32bit for reasons. The arrays here are a bit more, but probably fit that kind of channel. Assuming 32bit and 30dBi, you'd be sending at roughly 20-30MHz, and receiving at about 1kHz. (Less if you hit bad weather.) So... 1 bit per second. Not byte. Bit. [0] https://www.spaceacademy.net.au/spacelink/spcomcalc.htm https://www.spaceacademy.net.au/spacelink/spcomcalc.htm
- whatsupdog 1y agoThank you so much. Are these rough calculations based on the smallest (quad), mini or the large array?
- shakna 1y agoThat was for the large array, assuming you were bouncing from you to moon and back again. Point-to-point on the Earth would actually be semi-decent, as another comment pointed out.
- radiorickky 1y agoNo, if you do the math it's about 40 bytes per second (300bps) for Earth-Moon-Earth using their 240-antenna array.
- shakna 1y agoCare to share the math, if you've done it? It's 1.3 to 1.6 seconds each way to the moon, by radio link. JPL's much, much, much bigger arrays can only achieve 64kbps.
- shevy-java 1y agoThe moon is so useful.
- fourthark 1y agoWe probably wouldn’t be here without it!
- baq 1y ago12 V DC (≈1.5 kW peak) How thick is the cable powering this holy amps Batman.
- HPsquared 1y agoCar starter motors and alternators are on a similar power level.
- tonyarkles 1y agoDefinitely. The alternator on a small aviation engine (~100 HP) that I work with is rated for 24V/150A ~= 3.6kW and it’s not really that big in the whole scheme of things. The cables are about the thickness of my thumb.
- mikestew 1y agoI’ve wired a 3000W inverter into an RV, and the cables were a bit thicker than my thumbs. Use welding cable, it’s much more flexible.
- fouronnes3 1y agoTomorrow on HN: Polishing the moon surface
- henrikf 1y agoThat's very impressive and I'm even more impressed if you can manage to sell tiles at that low price. PA looks suspiciously similar to SE5004L. I just needed some for my own projects but every distributor is out of stock. I wonder if this is where all of them went?
- tatjam 1y agoHaha love this "Not intended for radar applications. Core functionality needed for radar not included due to export control restrictions". Wonder how they prevent usage as radar as this thing could pretty much be a drop-in missile seeker.
- giantg2 1y agoThe wavelength is suboptimal for that type of tracking/intercept.
- jmpman 1y agoI’d wondered about using moon bouncing in order to distribute video streaming keys (piracy) in a way which would make it impossible to locate the sender. Unlikely to be viable at scale, as the moon isn’t always visible, but it’s an intriguing covert broadcast mechanism.
- npsomaratna 1y agoI have no understanding of the physics involved, but could the broadcast location be reverse engineered? (With triangulation and clever math?)
- Redster 1y agoYour location is very very visible to any plane or satellite passing overhead.
- freedomben 1y agoIndeed, though it would take some coordination to actually narrow it down precisely. You'd need a few different planes/satellites to detect the signal and share their reading to allow triangulation. With only a single plane or a single satellite that is not in geosynchronous orbit, you could take multiple readings and get a rough idea of location, but the inability to turn from a straight line (not impossible for a plane of course, but it would require intentionality and willingness for the crew/commanders and typically not cheap as it disrupts whatever flight plan they previously had) would be a hindrance. That said, with how many satellites are up there I doubt it would take much extra effort to do that coordination if the satellite operators have motivation to do so.
- giantg2 1y agoHighly directional antennas on a moving platform can perform effectively radio direction finding independently.
- hdjrnevehhe 1y ago
- giantg2 1y agoReally cool phased array. However, I don't think this will really make EME more accessible when their EME version is $2499+. Maybe the 4 element version would be fun to play around with.
- retrac 1y agoWhile it isn't exactly communication, the Moon is not the only planetary body of which signals have been bounced off. Radar is workable within the solar system, including the moons and rings of the outer planets. https://www.jpl.nasa.gov/news/radar-astronomy-used-to-research-titan/ https://www.jpl.nasa.gov/news/radar-astronomy-used-to-resear... (1991)