Jim Frankenfield

Avalanche Safety Courses and Services

1338 Foothill Dr. #170; Salt Lake City, UT 84108
1-877-604-0166; 1-209-315-9220 (Fax); snowman@csac.org

Snowmans Avalanche FAQ - [Contents]

Back to Technical Questions

History

The avalanche transceiver was introduced in this country about 25 years ago. The original units operated at a frequency of 2275Hz. Further development of the technology in Europe led to widespread use of units operating at 457kHz (457000Hz) there. In 1986 the European frequency was adopted as the international standard. 457kHz has been adopted as the US standard effective January 1, 1996.

Due to the adoption of the European frequency as the international standard, dual-frequency units dominated the US market for several years. Single-frequency 457kHz are the standard in the US market now.

Range

There seems to be a lot of confusion concerning the effective range of the various units. The higher world-standard frequency (457kHz) is a better operating frequency, and beacons operating at only this frequency will transmit further (per unit of power) than beacons operating at only the lower (2275Hz) frequency. This is due to the electromagnetic properties of snow and their variation with frequency. Dual-frequency units have a lower range partly due to the fact that part of their power goes into transmitting at the lower less efficient frequency and partly because the antenna coil can not be designed to be ideal for both frequencies at once.

Search Methods, Features, and Practice

In addition to the 'traditional' (or 'grid') search method there is another method known as the 'field line' or 'induction' method. This involves following the magnetic field lines towards the source. References have been made, erroneously, to 'beacons which work this way'. This is a method of searching, not a type of transceiver. The method can be used with any type of beacon, and has been in use by some people for quite some time. When done properly, it is claimed to be a faster method.

New units are touting all kinds of features, some of which may help one conduct a field-line search more efficiently. While some of the new features are probably helpful, they do not reduce the need for practice. Very few people invest enough time in practice. Learning to use a new method involves an even larger investment of time. Practice often. If you are unfortunate enough to have to search for a person use the method you know best from your practice sessions.

Implications

With the advent of single frequency 457kHz units on the US market there is now a possibility that two units will not be able to 'communicate' with each other. People owning the old 2275Hz-only units should purchase new units now. It would be advisable to do a beacon test at the trailhead or parking area. All participants should put their units in receive mode, and then one person at a time should transmit. Make a note of any beacons which cannot hear each other. This also checks that each unit is functioning properly. Put new batteries in now, and carry a spare set in your pack in case you find you need them at the trailhead check.

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Avalanche cords are long bright (usually red) cords which a person can trail behind them when in hazardous terrain. The idea is that after an avalanche the cord can be followed to the victim. Cord designed for this purpose has arrows on it to point the right direction. The advent of avalanche beacons has made this method obsolete.

From the 1950/51 season through 1994/95 season there was a total of 2 people recovered by avalanche cord. One was alive and one was dead. These figures are not likely to change since this method is rarely used anymore.

The figures are complicated by a few incidents. In January of 1978 four people were buried with avalanche cords but were not found until the snow melted. This has not been included in the above figures since they were not found by the cord. Some statistics may reflect this differently.

There have also been cases of climbers being roped together. I have heard of one instance where an ice climber was avalanched off a climb and buried. His partner tried to follow the rope but had too difficult a time and had to get help. When the buried climber was finally recovered he was dead.

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