Skrevet av Emne: Cave-Link - underground message system  (Lest 1415 ganger)

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Utlogget Rolf

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Cave-Link - underground message system
« på: 10.11.2013 13:32 »
"Cave-Link is a data communication and measurement system for cave research and mining.
It allows safe data transmission thru several hundreds of meters of solid rock.

Beside measurement data it is also possible to transmit short text messages. If one of the surface stations is equipped with a GSM modem,
short messages (SMS) can be sent from and into the cave.

Due to the possibility of automatic forwarding thru several Cave-Link stations, even very great distances can be covered.

For communication VLF (Very Low Frequencies) frequencies were used. Coverage is up to 1300m and more from cave to cave.

Because all transmissions are secured by checksums and automatic query, no transmission errors are possible.
A bad link (great distance, atmospheric noise, interferences) just lengthens the communication time, but did not cause transmission errors."

More:

http://www.cavelink.com/joomla1/index.php?lang=en
"When I try to imagine a faultless love
Or the life to come, what I hear is the murmur
Of underground streams, what I see is a limestone landscape."
W.H. Auden, "In Praise of Limestone"

Utlogget Rolf

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Sv: Cave-Link - underground message system
« Svar #1 på: 02.12.2015 18:54 »
"APRS Cave-Link uses the amateur radio’s Automatic Packet Reporting System (APRS) inside caves to get their position data (and other messages) out.

Imagine that you’re coordinating a large scale search-and-rescue mission in a cave. You need to know where all your groups are, and whether or not they’ve found anything. But how do they all communicate to the command center?

You’d guess radio, but you’d guess wrong. Radio doesn’t propagate well at all in a maze of twisty passages, all alike; rocks absorb radio waves, especially in the VHF/UHF range that’s best suited for most small radios. In the past, you’d run wire and transmit along it. This article runs through the options in detail. But adding miles of wire to your already heavy caving and climbing gear is a nuisance or worse.

Some experiments by groups of amateur radio operators, and cavers, with APRS repeaters aim to change that. Digipeaters, as they’re known in the APRS world, take an incoming message and forward it on again. On each successive hop, the station that received the signal appends its name to a list of paths that are sent along with the message, which assures that the message propagates but doesn’t get repeated around forever in a loop.

Digipeaters and battery packs are dropped, in Hänsel and Gretel fashion, as the cavers work their way through the cave. The trick is to make sure to place one repeater before you’ve entirely lost the radio signal from the previous one, of course. But the APRS Cave-Link project got one mile’s worth of transmission in Mammoth Cave without using wires at all. That’s not bad!"

More:

http://hackaday.com/2015/11/25/aprs-repeaters-get-the-signal-out-of-mammoth-cave/?utm_source=feedburner&utm_medium=feed&utm_campaign=Feed%3A+hackaday%2FLgoM+%28Hack+a+Day%29
"When I try to imagine a faultless love
Or the life to come, what I hear is the murmur
Of underground streams, what I see is a limestone landscape."
W.H. Auden, "In Praise of Limestone"