Author Topic: 'Cave Link' Text-Only Cave Radio  (Read 2574 times)

Offline jarvist

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'Cave Link' Text-Only Cave Radio
« on: November 09, 2013, 12:02:52 am »
During the summer 2013 Expedition to Tolminski Migovec, Slovenia, Imperial College CC very kindly had the loan of a 'Cave Link' radio system from the manufacturers. This is a text only system, and was found to be extremely useful for exploration logistics.

I've collated a few reports on the use of the system, and include it below as I thought it would be of interest to expedition organisers. There doesn't appear to be much written in English at all about the cave link system -- which is a pity as it's seems an almost perfect technical solution for deep expeditions.

A text only 'Cave Link' cave radio system was used to communicate between underground camp and the surface. The radio functioned extremely well (through 600 m of rock) and allowed cavers to send their new findings, equipment requests and weather reports to and from the surface.

The system is easy and comfortable to use, and the build quality is very nice (swiss made : ) You type in text messages using a full keyboard. The units also synchronize time with each other regularly. Transmitting messages is absolutely reliable, since the system re-sends the information until the whole message is correctly transmitted. At the end of the received messages, also the information about the transmitted bits and number of repetitions can be read. The design is basically fool-proof, not harder then to send a text with a mobile phone; yet, you can go into details and you can re-program many things if you wish.

Generally the text approach has serious plus points for routine camp use - low power, silent operation, likely greater range, no need for regular radio checks, ability to just send and forget for non-urgent messages ('bring more chocolate', etc), automatic keeping of logs of messages, no sensitivity to a particular person's voice quality. Particularly for small teams, not needing regular radio checks is a big plus.

Obviously, for important stuff a confirmation needs to be waited for to make sure the message arrived.

Battery-wise (using the provided dedicated lithium ion packs), the underground set seemed to get reasonably low after two weeks, but possibly it was doing more work to get a signal above the surface noise - I think the surface set only dropped to ~90% in the last week. That was with the message check interval set fairly frequent (2 minutes) - it could have been set longer and presumably the battery would have lasted longer.

The energy needed for the transmission of a message can change drastically depending on the weather and some other factors (e.g. you need much more energy during the night than during the day, and about 1000 times less energy when it was raining...)

The Cave-Link system can have multiple stations (which should act as relays for each other; here we used just one surface station and one subsurface station). Each station is equipped with an antenna, which is a circa 70 meters long wire; the ends of the wire must be properly grounded using a grounding plate (this proved to be the hardest task of the setup on the surface). The antennas of the stations should be more or less parallel to each other, with as close vertical projections as possible; in our case, the conditions were ideal, since Friendship Gallery is almost directly below the Bivvy. The through-rock distance distance is about 650 m.  A station plus its antenna fits in a SRT bag, so it is easy to transport in the cave.

The surface station also contains a GSM unit, with which you can directly send and receive text messages from the GSM network (so one can text your girlfriend from underground camp and she can reply back to you from home : ) Alas, there is no mobile phone reception at the Bivvy and we did not bother moving the base station to a spot with signal, so we did not try this feature.

I prefer it over speech transmission, since messages can be read back, direct communication is also possible, and there is no screw-up because of misunderstading speech.

In a rescue situation, advantages/disadvantages compared to voice might alter, but still not all in favour of voice - voice is quicker when it works, but text is maybe more likely to work, with messages getting through correctly or not at all.
Many thanks to Gergely Ambrus and Dave Wilson for writing the above text, and to Oliver Myerscough for verbal explanation. Any errors are almost certainly due to my editing!

Offline Goydenman

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Re: 'Cave Link' Text-Only Cave Radio
« Reply #1 on: November 09, 2013, 11:53:10 am »
Very interesting. I can see this being a real advantage for our rescue team. I like the fact that if the message gets through you know accurately what was said no ambiguity especially with technical details like request for gear or recordings of the injured patient.

Offline JJ

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Re: 'Cave Link' Text-Only Cave Radio
« Reply #2 on: November 10, 2013, 12:45:43 pm »

You have a PM