SCMC Gadgets - Radios
The Field telephone in use
Back in the 1980s & 90s the Club was unable to afford the expensive VHF Rescue Radios (for surface work) and Mole-phones (for underground use) so we were forced to compromise. The Club had used ex-military field telephones since it was formed in 1961. To use them underground lengths of telephone wire had to be laid through the cave or mine, but the phones were effectively 'tied' to each end of the cable and it was felt that something more mobile was required.
Several Club Members had CB radios (working on 27MHz), but these were only any good for line of sight work - and no good underground.
However, a chance observation during a rescue practice, when someone was at the bottom of a ladder pitch (wire electron ladder), that they could still talk to the surface, lead to a range of experiments with 'guide wires' for the radio signals.
Guide wire radio using a CB handset
The present system uses a length of twin core cable run out along a tunnel or dropped down the side of a shaft.
Normal CB hand-sets can be used to talk to others underground or to the surface by holding them near the wire.
As underground explorers get further from the entrance it is necessary to hold the radio close to the wire or even take a turn of wire around the radio aerial to improve the signal.
The wire can get in the way in small passages, so has to be rigged sensibly. In rescue situations its advantages out-weigh this problem.
There does tend to be a maximum distance (depending on the power of the CB used) that you can travel before signals become too weak, although this can be solved by using intermediate stations to pass on messages.
Connecting a vehicle based CB into the end of the guide-wire would dramatically improve the system. A complete link through Snailbeach Lead Mine was achieved with over 800m of wire going down a hole on one hillside, via several hundred metres of workings, then up a 100m shaft on the opposite hillside!
Since we began our experiments with the use of radios underground, the Club was able to acquire a pair of HeyPhones (largely as a result of fund raising by friends of the late Club member Peter Owen).
This "through-rock" radio system was developed for underground rescue teams and removes the need for laying wire through the workings - the Heyphones have been successfully used on a number of underground rescues and rescue practices in Shropshire mines, and caves in neighbouring areas. Three HeyPhones were used very effectively during the 2003 rescue in Otter Hole cave (by the River Wye), a rescue which due to the tidal nature of the cave entrance took over 12 hours.
The 2 Heyphone sets and Peli case housing the 'underground' set
Detail of the sockets and switches on the Heyphone.
The HeyPhone has been described as a magnetic induction system that uses grounded antenna. To obtain this in practical terms you must have a unit that transmits a signal into the ground through an earthing point, which is then picked up a distance away by a similarly earthed unit. To achieve the 'earth' -a wire is simply run-out each side of the transceivers and each end attached to an earth spike or to a length of braided wire. This is then buried in mud or placed into water.
It is also possible to transmit a signal using a loop antenna (similar to the Club location device). There seems to be some confusion as to exactly how these radios work, but the phenomenon of conduction of baseband (i.e. no carrier) signals through the ground pre-dates radio.
While the HeyPhones are great for talking "through-rock", there is still a place for the guide wire radios, particularly for communicating down shafts and pitches where there isn't room to lay-out the HeyPhone aerials or where geological conditions disrupt their signals.
A couple of Club members have now built their own versions of the Heyphone using modern surface mount components (watching them being built is like watching someone glueing pepper grains to postage stamps!). Known as the µHeyphone (micro-Heyphone) This increases the variety of underground radios that we now have available to us.
Pushing the idea of 'development' even further, experiments have also been carried out with the µHeyphone and Heyphone using slow-scan TV to transmit photographs from underground to surface (and vice-versa) with the aid of a couple of free mobile phone apps to encode the images. The images are restriced to 320x 256 pixels by the apps - but it's a start!
The µHeyphone - built by Ian Cooper
A picture transmitted from underground!
Other recent developments have seen the production of the Nicola 3 radios by the British Cave Rescue Council (BCRC) to replace/supplement the Heyphones with a modern digital technology device. They are also smaller and lighter than the original Heyphones.
Cave Link (from Switzerland) a text based system is also proving popular with Cave Rescue teams. It allows text messages to be sent to upto 15 'terminals' on the surface or underground and despite being restricted to text only they are very effective, although the sets are quite expensive. In Burrington Combe (Mendip) multiple Cave Link sets were in use and cavers in one cave found that they could 'talk' to others in neighbouring caves as well as sets at various locations on the surface.
The BCRC's Nicola 3 radio
The Swiss Cave Link radio
Steve Holding using a Cave Link set underground
Nicola 3, Heyphone and µHeyphone