Oxford University Cave Club
Huerta del Rey Expedition 1992
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This year OUCC decided to use CB radios on our expedition. The expedition is split between a base camp accessible by road, and a higher camp, Ario, about 2 hours walk up the mountain. We decided that radio communication would help to improve the organisation of the expedition, mainly by making it possible for those at Ario to radio down to Base before people started walking up in the morning, and to control the flow of essential supplies. They also proved very useful when people were unable to keep to a pre-arranged plan, because instead of having a caving trip delayed while cavers at Ario waited for someone to arrive from Base, they could be warned by Base and could make other arrangements.
The equipment we were using consisted of two Team TRX404 radios. These are European CEPT specification, rather than the original UK CB standard, which means that they are legal both in the UK and in Europe. Most countries in Europe have arrangements whereby a UK licence allows you to operate abroad; however Spain is one of the exceptions, and we had to obtain a Spanish licence for each radio. One radio was mounted either in the minibus with a centre loaded aerial on a magmount, or in the main tent, using two 10m lengths of cable from the van for power and the aerial. The other radio, for use at Ario, was mounted inside a steel box to protect it from cavers. This was powered from a separate 12V 6Ah sealed lead-acid cell with three 4.5V flat-packs built into the ammo box for emergency use, although we found that the emergency batteries were used in preference to carrying the heavy lead acid one around. We intended using a large 'base-station' type aerial at Ario, on the end of a 7m pole, but for portable use we also had a small helical aerial, as used on hand-held radios. The battery was charged from a solar panel which produced 180mA in full sunlight.
The distance between the two camps is about 5 km, and almost line-of-sight. Base Camp is beside a lake in a bowl, the main obstruction between it and Ario being a steep 200m high hill some 400m from the camp. The Ario campsite is on the far side of a ridge, 500m from and 30m below, the ridge. Whilst carrying the radio up to Ario I managed occasional communication with Base Camp which improved steadily as I climbed higher, and dropped off very rapidly after passing the ridge, as expected. At both camps we suffered from interference from other CB users, some as far away as Germany, and even one in the UK. The amount varied throughout the day, but a noticeable drop in interference was noticed when the mist came down.
The big aerial we had planned to use at Ario proved to be almost useless. After failing to make contact from the camp we moved the aerial closer to the ridge. Eventually we managed to get a very broken and almost unintelligible signal. When we moved closer to the ridge, we lost this signal altogether. Getting tired of carrying the aerial about, we left it guyed down overnight. The following day we found it lying on the ground with two broken poles and a broken guy rope. We had to resort to using the portable aerial, and walking to the top of the ridge when we wanted to use the radio. This limited us to calling from Ario to Base only. This actually was not too much of a problem because most of the important messages would be from Ario anyway, e.g. rescue callouts, 'Send some people up the hill to go caving', and 'Go and buy some bread, we've run out!'. To this end, the radio at Base was left on continuously and we tried to make regular calls from Ario every morning to see if there were any messages.
We found that the quality of reception at both camps was heavily dependent on the position of the van at Base. The van was never in line of sight of Ario, because the view was blocked by the large hill mentioned above. However, moving the van 5m towards the line of sight made the difference between a garbled message and a clear signal. In spite of the problems with the aerial, we found the radios very useful. There were a couple of times when we were able to avoid having to put the schedule back by a day when people couldn't go caving, and we also found them worthwhile for passing messages regarding supplies of food and caving gear at Ario. A further improvement in the system would be a third, portable, radio to use for rescue call-outs to 2/7, especially in misty weather, to let the advance rescue team talk to people at Ario.
This year Martin Hicks, a highly accomplished cave photographer, came on the expedition with the main aim of taking a successful photograph of Just Awesome, the huge chamber at the bottom of Pozu Jultayu. To coordinate the discharge of flash guns in different parts of the chamber he took four CB Walkie-Talkies bought from Tandy) on his photography trip. The radios worked successfully underground, but he found that although the four were nominally on the same channel, they only worked as two separate pairs underground. We can only assume that this is due to the pairs being at slightly different frequencies, and a loss in signal strength caused by the surrounding rock and water.
The walkie talkies were to the standard UK specification, and not compatible with the system we were using on the surface, so it was not possible to use them to extend our surface communication network. In fact we found that the performance of the walkie talkies on the surface was very disappointing, and we would not recommend them for serious use.
This year we were fortunate to be loaned some Mitchie-phones by Nigel Lovell. We had been hoping to investigate the possibility of providing a reliable communications link between the underground camp on the Big Ledge in Pozu Jultayu and the surface. The reasoning behind this was mainly that with good telecommunications the time taken to get rescuers to the underground camp could be cut from 10 hours to 3, vital in the event of an accident. It would also be useful for more mundane communication between the camping team and the surface ('Where exactly was that 5 second drop?' and 'Send Tony down with a 200m rope!').
The phones we were lent are high impedance earth return types. They require a single wire between the instruments, and an earth connection, usually provided through the person holding the instrument. Any number of instruments can be connected to the system, but they will eventually increase the signal drain and the volume will drop. Devices of this type have been tested to a range of 4km. The limitations on the range are the resistance of the cable and of the earth return path, and current leakage from the cable to earth. We were loaned three instruments: one large, base station which ran off two 4.5v batteries with 'Call' and 'Push to Talk' buttons, and two hand-sized units, one with a rotary switch for 'Off, 'Receive', 'Talk' and 'Call', and one with just an on/off push switch and a 'Push to Talk' switch. The base station was the loudest unit, and of the hand held units, the second was much more sensitive, giving a louder signal even when not well earthed.
We had hoped to lay a cable from the entrance all the way to the Big Ledge, but we decided that we couldn't afford to buy any cable specifically for this so we used some cotton-covered enamelled wire which we had been given. Although we had hoped to lay the cable while the cave was being rigged, the delay to the van meant that the cave was almost completely rigged by the time the wire reached Spain, and it was not until the third camping trip that we tried to lay the cable. We left Chris Lloyd at the entrance with the base station and started down the entrance pitches with a reel of cable. We had expected the pitches to be easy, with the rifts posing more problems, but it turned out to be surprisingly difficult to fix the wire far enough from the rope to avoid swinging into it, there was also a problem with the wire getting wrapped round the rope. If we had had a stronger wire which could have been dropped down pitches then this would not have been a problem. By the time we had reached the bottom of Seventh Heaven we were starting to realise how long it would take to run the cable all the way to Just Awesome, and then the cable broke somewhere above us. We gave up, and continued down to camp. Since the Just Awesome chamber is one of the worst places to try and communicate over any distance, we also tried running a cable from the camp on the Big Ledge down to the bottom of the Just Awesome pitch. At the bottom the air was full of spray, with water running down the cable, b'ut we experienced no problems in talking to people at camp once we had attracted their attention. It was obvious that a call tone was essential to make people at the other end listen to the phone, and we also decided that a rotary switch that could be accidentally left in the 'Talk' position was not a very good idea.
Despite our lack of success at rigging a wire through the cave this year, we found that the phones were very effective, and we hope to be able to do the job better next year, maybe with a radio link at the entrance to relay signals back to Ario.