16 ms·
Cave-Link: Underground text communication system
- deleted 5y ago[deleted]
- c_o_n_v_e_x 5y agoSimilar tech was used during the rescue of the boys out of a cave in Thailand back in 2018 https://bcra.org.uk/creg/heyphone/ https://bcra.org.uk/creg/heyphone/ https://hackaday.com/tag/heyphone/ https://hackaday.com/tag/heyphone/
- rendall 5y agoHow do the Mole People feel about this?
- ChrisMarshallNY 5y agoThat's pretty cool! [V|E]LF stuff is used for many things. For example, the Navy uses it to communicate with subs.
- Ellipsis753 5y agoThis site is a bit scarce on details. There's more details and some photos here: https://de.wikipedia.org/wiki/Cave-Link https://de.wikipedia.org/wiki/Cave-Link http://www.hoehlenverein-blaubeuren.de/index.php/cavelink-telemetriesystem http://www.hoehlenverein-blaubeuren.de/index.php/cavelink-te... (Use Google Translate)
- dll 5y agoI wonder how the licensing issue referenced in the Wikipedia article is handled in the UK. I imagine Ofcom will have had to approve and license these installations, or will they have made these exempt (I can't find any evidence of this)?
- detaro 5y agoas far as I know similar general licensing exists for such purposes. Lots of inductive applications need it.
- gnfargbl 5y agoI can't see these devices specifically mentioned in https://www.ofcom.org.uk/__data/assets/pdf_file/0028/84970/ir-2030.pdf https://www.ofcom.org.uk/__data/assets/pdf_file/0028/84970/i..., though the frequency range they operate in (20-140kHz) is allowed to be used by induction loop type applications, at a suitably low power.
- goodpoint 5y agoI'm really surprised ELF are not commonly used for this. Even a simple single-frequency CW transmitter for emergencies. I wonder if audio frequencies below 20KHz can be used to make a cheaper system.
- ttyprintk 5y agoAt the extremity of that band, fewer nations have constructed transmitters than have nuclear weaponry. You can combine acoustic with radio in TARF (yes, really).
- meibo 5y agoSomething that is mentioned here and not on the main page: the devices form a mesh network and can relay messages between each other. Seems strange, feels like a pretty big selling point.
- dll 5y agoThis was used in the recent rescue in Wales [0]. I seem to recall a colleague telling me years ago (in about 2000) that he got stuck in a cave once (somewhere in South Wales I think) due to unexpected rain causing flooding and there was a phone available that could be used to request rescue (or to tell people you were going to sit it out). [0] https://www.bbc.co.uk/news/uk-wales-59219380 https://www.bbc.co.uk/news/uk-wales-59219380
- jlturner 5y agoExtremely / Very Low frequency radio is fascinating and is surprisingly not used that often. Radio propagation characteristics include being able to pass through water and ground, and continually bounce across the ionosphere / circle the globe. The navy experimented with this for some time to talk to submarines but seems to have ended the experiment. Additionally I learned that lightning strikes generate a high burst of low frequency radio and commercial lightning detectors (which I use while hiking) actually is just a radio receiver on a harmonic of the lightning signal.
- _def 5y agoI'm a noob regarding radio: do I understand it correctly that low frequency radio signals can more easily be used with more solid carriers while higher frequencies allow more/faster bandwidth? (I'm totally oversimplifying here)
- williamtwild 5y agoYes
- ajsnigrutin 5y agoYou need bandwidth to transfer more data (there is a theoretical limit of how much data you can transfer at a given bandwidth with a given signal to noise ratio). The lower you go with frequencies, the larger antennas you need (quarter wavelength is usually the minimum... for FM radio (around 100MHz) it's 75cm which is very realistic length for a car or a house radio... at 14mhz (ham radio freq), it's 5.3 meters, which is still doable if you live in a house, and at 1.8MHz (another ham band) is ~40 meters, which is hard.. going lower is even harder, and special "tricks" are needed. The second problem is the bandwith itself... some wifi equipment supports bands up to 100MHz of width (to simplify, you use all the frequences from eg. 5.1GHz to 5.2GHz), and if you want to stay at low frequencies, it's impossible to create such a wide band, because the antenna sizes are so different at 1MHz and 101MHz, the propagation is different, etc., so usually you're stuck with narrower bandwiths at lower frequencies (and of course, many of the low frequencies are already in use.. eg for fm radio). But generally yes, higher the frequency, more directly (in a straight line) it goes, and you get more losses in stuff between the transmitter and receiver.
- sideshowb 5y agoAlso in caving news this week https://www.bbc.co.uk/news/uk-wales-59203695 https://www.bbc.co.uk/news/uk-wales-59203695
- binbag 5y agoYeh, this is the system they used to communicate during the rescue.
- baq 5y agoSee also https://en.wikipedia.org/wiki/Communication_with_submarines https://en.wikipedia.org/wiki/Communication_with_submarines
- Isamu 5y ago> Because all transmissions are secured by checksums and automatic query, no transmission errors are possible. Just a reminder to people implementing systems with error detection: undetected errors are always possible. Checksums may be just fine for this application but if you need to achieve some target error rate you may have to consider error detecting or correcting codes that fit with the interference you find in your transmission channel. [edit] Error detecting checks work not by making errors impossible but by making them unlikely. It is part of the work to quantify your design to show that probability is low enough for your goal.
- egberts1 5y agoGo-lay is arguably the best forward error correction for up to 24-bit. https://en.wikipedia.org/wiki/Binary_Golay_code https://en.wikipedia.org/wiki/Binary_Golay_code
- WithinReason 5y agoIf you hashed every 1000 symbols with a 512 bit hash to check message integrity and retransmit, a hash collision would be practically impossible, so "no transmission errors are possible" is perfectly fair to say under some circumstances.
- malik9 5y agoIf you're concerned about one or two bits being toggled, a 512-bit hash will merely increase the chance of bit errors; on a noisy medium, using such a big "checksum" will BOTH detect and cause a high number of packet faults.
- lazide 5y agoAlso possible they are using a 1 byte CRC heh
- kabdib 5y agoA piece of communications gadgetry even mentioning checksums is like a car salesman proudly claiming "... and this baby comes with working brakes!" The very pronouncement leads to worry, and additional questions (like this very thread, QED :-) ). My inexpert digging came up with: They use APRS packets, which use AX.25, whose framing includes a 16-bit Frame Check Sequence, which looks like it came from HDLC, and is a 16-bit CRC-CCITT. Phew.
- SamuelAdams 5y agoCould see this being used in the Mammoth Caves National Park. A lot of the cave is undiscovered and having reliable comms might make that work a bit safer.
- marcodiego 5y agoSuppose you're lost inside a cave... In a great feat of luck, you find a cave-link base unit. Nice let's ask for help! You then discover the system is in German and you can't understand how to use it: https://www.cavelink.com/cl3x_neu/index.php/en/component-overview/base-unit https://www.cavelink.com/cl3x_neu/index.php/en/component-ove... Ok, I know it supports other languages, but there's no reason for the main site not to use English to illustrate it. Or better: make the interface intuitive enough that you can use even without reading instructions. We did it with smartphones.
- pmyteh 5y agoThese are highly specialised pieces of technical equipment with a tiny potential market. The use case isn't fixed unattended public installations to be used by untrained randoms, but ad-hoc use by trained users like cave rescue teams and speleologists. As for the UI, production (like much in the caving world) is semi-commercial at best; an iPhone it isn't and frankly it doesn't need to be.
- graderjs 5y agoA quantum entangled communication system wouldn't have any 'transmission' issues (through mediums, etc), correct?
- colechristensen 5y agoYou can’t transmit information with quantum entanglement.
- graderjs 5y agoReally? But can't you influence 1 side of an entangled pair, then measure the other side, and you can pass information through the correlation? I thought quantum-entangled FTL communication devices were a legitimate thing.
- colechristensen 5y agoNope. You can’t change the outcome, you can only make an observation on one and then and only then know the state of the other. What is being observed is entirely random.
- genewitch 5y agoInformation cannot be transceived faster than light. The thought experiments and whatabouts and whatifs are fun to discuss, especially after drinks - but seeing which spin or collapse or whatever isn't information in the actual definition of information. Information involves entropy and all that stuff is bound by the speed limit.
- seiferteric 5y agoThis uses VLF RF, but there was another interesting thing I have read about long ago called "earth mode" or "conduction mode" maybe. You put two conductors in the ground some distance apart (10s or hundreds of feet) and inject the signal into the ground. The signal causes a current in the ground which will cause voltage differentials that can be picked up miles away with a similar receiver. I believe it is also low bandwidth, but I often wonder if you could create a mesh network of these. Also would the FCC actually be able to regulate this since it is not actually a radio wave?
- TedDoesntTalk 5y agoI think it is still a radio wave, but propagated through soil and moisture rather than air.
- seiferteric 5y agoMaybe, but I thought it was different since it uses conduction. For example I am pretty sure you could detect a DC signal, whereas with radio you cannot.
- twic 5y agoSee also the HeyPhone and Nicola systems built by underground boffins in the UK and France: https://www.shropshirecmc.org.uk/radio.html https://www.shropshirecmc.org.uk/radio.html http://www.scavalon.be/avalonuk/technical/radio1.htm http://www.scavalon.be/avalonuk/technical/radio1.htm https://www.electronicsweekly.com/blogs/engineer-in-wonderland/british-electronics-thai-cave-rescue-2018-07/ https://www.electronicsweekly.com/blogs/engineer-in-wonderla... https://www.caverescue.org.uk/nicolaradio/ https://www.caverescue.org.uk/nicolaradio/ http://site2.caves.org.uk/radio/comms_in_caves.html http://site2.caves.org.uk/radio/comms_in_caves.html
- foobarbecue 5y agoIf you liked this you should check out the British Cave Research Association's Cave Radio and Electronics Group at https://bcra.org.uk/creg/ https://bcra.org.uk/creg/
- tdeck 5y agoReminds me of an interesting Great War technology. During WW1 the British used a system called the "power buzzer" which used two spaced electrodes and sent an alternating current through the earth. Apparently this could be picked up and amplified by another ground electrode at some distance, and was used to send morse code communications. I'm struggling to find a good modern explanation but here is a scan of the original military manual: https://cgsc.contentdm.oclc.org/digital/collection/p4013coll9/id/255 https://cgsc.contentdm.oclc.org/digital/collection/p4013coll...