Avalanche Transceivers Beacons

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Anyone going off marked-pistes, and that includes skiers, snowboarders, walkers, climbers and snowshoers should wear an avalanche transceiver (beacon)and when riding in resort it is advisable to wear at least an inexpensive avalanche transmitter (doggy beacon) or Recco™.

Avalanche Transceivers
Avalanche Beacons

An avalanche transceiver is a small device, about the size of a paperback and weighing around 200 grammes. It enables a group of off-piste enthusiasts to mount their own search and rescue operation in the event of an avalanche. A group has a window of opportunity of roughly 15 minutes to rescue a buried victim, after that time the chance of survival drops rapidly. In France, it takes the rescue services an average 45 minutes to reach an accident scene, by that time 75% of victims will be dead.

Avalanche transceivers cost between 200 € ($200) for a basic model to 300 to 500 € ($500) for advanced digital beacons. But remember they are only as efficient as the skills of the user. Transceivers work in two modes: transmit and search. In transmit a signal is emitted by a transceiver and this can be detected by another transceiver set in search mode. Basic models emit a series of beeps, the frequency and volume can be used to localise a buried victim. More advanced digital transceivers may give an indication of distance and direction. In general they have an effective range of around 20 meters but the signal may be affected by rocks and other hidden obstructions.

Transceiver Types

There are two basic transceiver types, analogue and digital. They operate on a standard frequency of 457 KHz. Digital devices give a range and direction, analogue devices provide an audio indication of distance and direction and may also feature a flashing lamp showing signal strength. Analogue devices have a manual gain control. Analogue and digital avalanche beacons can interoperate but be aware of the characteristics of individual transceivers. Transceivers should be used with high quality alkaline type batteries. Do not use rechargeable batteries as their performance degrades rapidly at low charge. Digital devices can be further subdivided into single antenna (Arva 9000), dual antenna (Tracker DTS, Barryvox Opto 3000, ARVA ADvanced) and even triple antenna (Pieps DSP). There is even the hybrid Ortovox S1 which uses a single antenna and other sensors. The extra antennas are able to extract more information from the signal. They can give a better indication of direction and range and can speed up the search.

In transmit mode a transceiver creates an elliptical electromagnetic field, if a second device is set to search mode it will detect this field if it is in range. The maximum signal is obtained when the two antennas are parallel. The antenna is usually situated on the longest side of the transceiver. Conversely the signal is weakest when the two devices are at right angles. By moving the transceiver through an arc a searcher can pick up the strongest signal and follow this directly to the victim. This is easiest with digital devices that give a visual indication of signal strength and approximate distance to the victim. It is important to maintain the same orientation throughout each search phase.

Theoretical Maximum Range

The range is the maximum distance between two transceivers when a signal is first obtained. It depends on a number of criteria:

  • The make of device
  • The battery condition
  • The ambient temperature
  • The relative positions of the antennas
  • Electromagnetic and other interference

The maximum range can be established by using two transceivers of the same type with new batteries. Find a large flat area such as a football field and place one device on the ground in transmit mode. The other should be set to search mode on maximum gain and the antennas should be parallel. Move away from the device on the ground until the signal disappears.

The distance obtained is usually the range indicated by the manufacturer and is usually around 80 meters for analogue devices and somewhat less for digital devices.

Practical Range

The practical or minimum range is that obtained when the antennas are at right angles, that is the transmitting device is positioned horizontally. This is around 20% of the maximum range and is around 20 meters for analogue devices and as low as 10 meters for digital devices. Perform the same experiment as above but with old batteries and the antennas at right angles. Depth of burial will also affect range. This is the practical range that should be used when searching to avoid missing areas of the avalanche site. This gives us a search band of 20 meters.

A paper, On the practical use of Avalanche beacons - PDF Format, presented at the 2002 International Snow Science Workshop by Holler and Gibler compared digital and analogue transceivers. In practical tests they rated the Barryvox Opto 3000: very good, the Tracker DTS and Arva 9000 and revised Ortovox M2? and Ortovox F1 Focus: good and the Ortovox F1 and Pieps 457?: sufficient.

It would appear that after early problems the digital transceivers have a clear advantage over analogue models, particularly in the hands of less experienced searchers. The lack of range is compensated by the search speed. However they concluded that regular training and exercises are they key to successful rescues. PisteHors have also tested a number of avalanche transceivers and our conclusions can be found on the site.

Categories: Snow Safety

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