The British Caving Association

Following negotiations between local authorities and a private hydroelectric powerhouse operator, at mid-August, throughput will be augmented in order to lower the water level in the artificial reservoir that happens to feed a glacio-tectonic cave that runs under city houses. The drying out of this underground river will let us explore beyond the current sump. In case the weather or some problem causes the water to rise again, authorities require that we have a means of getting informed by surface personel. The limestone layer is at most 20m, often less, but we'd be about 500m from the entrance. I thought of using a pair of waterproof FRS/GMRS Motorola radios that operate in the 462-467MHz range, but I fear they won't go through very well. Since we need to move forward and map a stooping passage, I figured a cave radio with its long antennas would not be very convenient. So I searched for voice-powered telephones, thinking I could build a wire spooler with rotating contacts and thus stretch a line as we go. I found such phones on the Internet. The Vietnam-era US types (sold on eBay from Austria!) are of the half-duplex type, featuring a side handle acting as a PTT switch. The French full duplex "genephones" sold used in the UK seem more interesting. I recall using a pair of these in the 1980's; the sound was so good you just had to whistle in one to call for attention at the other end, even a few meters away. The UK supply I found is:

http://www.armyradio.com/arsc/customer/ ... =88&page=1

but the guy doesn't reply. That's too bad because he also has very tough wire too.

Does someone know this UK supplier? Is he still in business? Or do you know of a better equipment supplier? Or can you suggest another technology? Ideas are most welcome!


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Luc Le Blanc
http://www.speleo.qc.ca/Auriga

Hi Luc,

Stuart France (member of CREG, contact details at http://www.chelseaspelaeo.org.uk/contacts.htm) designed and built a cave telephone for the South Wales Cave Rescue teams. I recall watching an interesting talk on the subject from Stuart himself. The article describing it is available from http://bcra.org.uk/pub/cregj/index.html?j=82.

The clever bit is that it only uses a single wire, halving the amount of cable required. The audio signal is returned via earth.

I think they would suit your purpose. Whether there are any to buy or borrow, I don't know. You'd have to contact Stuart.

It is also worth posting your question to ukCaving.com which gets a wider audience than here.

Actually, there have been a number of SWT designs, over the years, in the CREG journal, so plenty to choose from. I might be mis-remembering, but I think that Michael Lake, in Australia, sells ready-built units. Let me know if you need his email address, Luc.

What kind of earth return do SWT need? I guess hand-body-rubber boots don't make a proper contact. Is a trailing wire enough, or must a spike be used? The passage I'm thinking about is water-washed bare rock.

Yes, Michael Lake's e-mail address is welcome.

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Luc Le Blanc
http://www.speleo.qc.ca/Auriga

Found it, but Michael Lake's stock is sold out:
http://www.speleonics.com.au/business/index.html

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Luc Le Blanc
http://www.speleo.qc.ca/Auriga