SCMC Gadgets - Radios

Unable to afford the expensive Rescue Radios (for surface work) and Mole-phones (for underground use) we have been forced to compromise.

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, that they could still talk to the surface, lead to a range of experiments with 'guide wires' for the radio signals.

Main Gadgets

• The 'Bipod'
• The Club Winch
• Underground Radios
• Underground Electronic location device
• MineCam - Remote controlled video camera for shaft exploration
• Borg - helmet mounted video camera

Present System

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 take a turn of wire around the radio aerial to improve the signal.

Advantages

• No direct connection to the wire is necessary, so radio operators are free to roam underground or help out with the activities.
   
• Using radios means that others near to the operator can hear any messages passed on - unlike telephones.

Problems

The wire can get in the way in small passages, so has to be rigged sensibly. In rescue situations it's 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!

HeyPhone

Since we began our experiments with the use of radios underground, the Club has been able to acquire a HeyPhone (largely as a result of funding raising by friends of Club member Peter Owen, who died suddenly).

This "through-rock" radio system was developed for underground rescue teams and removes the need for laying wire through the workings - we have conducted a number of successful trials in Shropshire Mines and 3 HeyPhones were used very effectively during the 2003 rescue in Otter Hole.

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), but our loop does not yet have this facility. 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 are now experimenting with building their own versions of the Hayphone to increase the number (and variety) of underground radios that we have available to us.

Above, left: The two Heyphone sets and the Pelican case housing the ‘underground’ set (featuring a Robinson boot for scale)

Above, right: The Function switch and the ON/OFF Volume switch on the top of the Heyphone.

Left: Detail of the sockets and switches on the top of the Heyphone.

Pictures: Kelvin Lake & Alan Robinson

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