Avalanche transceiver

Avalanche transceivers are a class of radio transceivers specialized to the purpose of finding people or equipment buried under snow. They are variously called "ARVAs" (Appareil de Recherche de Victimes en Avalanche, in French), “avalanche beacons” or “avalanche transceivers” with many regional slang terms in effect. When transmitting, the device emits a pulsed signal which another transceiver can receive. Due to the nature of the radio pulse, a person holding the receiving beacon can orient it, and home in on the location of the transmitting beacon using techniques similar to radio direction finding.

The current standard specifies a frequency of 457 kHz, and many companies manufacture beacons that comply with this standard.

It is important to note that an avalanche beacon is not considered a preventative measure for possible avalanche burial, but rather it is a way to reduce the amount of time buried.

History
In 1968 Dr. John Lawton invented the first avalanche effective transceiver in 1968 at Cornell Aeronautical Laboratory in Buffalo, New York, with the first units being sold in 1971 under the “Skadi” brand name. This unit, functioning on 2.275 kHz, converted the radio frequency to a simple audible tone that a human can hear. By following the tone to where it was louder, the beacon operator could use it to locate the buried beacon by using a grid searching technique.

In 1986 IKAR adopted 457 KHz.

In 1996 ASTM adopted the 457KHz standard.

Standard:
 * 457 kHz
 * 200 hours transmitting at +10C
 * 1 hours receiving at -10C
 * operation from -20C to +45C
 * carrier keying (pulse period) 1000 ms +/- 300ms
 * frequency tolerance +/-80 Hz

Types of Beacons
There are two types of avalanche beacons: digital and analogue. They both adhere to the international standard as described above, and only differ in the method(s) used to indicate to the user where the buried beacon is located.

Analog
The original avalanche beacon was an analogue beacon which transmitted the pulsed signal as an audible tone to the user. The tone gets louder when the user is closer to the transmitting beacon. These beacons have also been augmented with LEDs that provide a visual indication of signal strength, and earpieces to increase the ability of the listener to hear the tone.

Digital
Digital beacons take the strength of the signal and the emitted dipole flux pattern and compute distance and direction to the buried transceiver

Search Techniques
Due to the highly directional nature of the 457 kHz signal at the ranges common for avalanche burial (and the range specified in the standards), there have been many techniques developed to search for buried beacons. Good beacon skills are considered to be a professional duty by recreational backcountry skiers and mountaineers, and by avalanche professionals such as ski guides, ski patrollers and search and rescue volunteers and professionals. Recreationalists and professionals alike take part in drills, practice and scenarios as a regular part of avalanche skills training.

The burial of a single beacon may involve search using one of several methods:
 * grid search
 * induction search
 * circle method

These search methods are adapted and extrapolated to scenarios where there is more than one burial.

Manufacturers

 * Ortovox - F1 (analogue) M2, X1, S1, d3 (digital)
 * Pieps - 457, OptiFinder and Opti-4 (analogue) and DSP (digital)
 * Backcountry Access - Tracker DTS (digital)
 * Survival On Snow SOS F1ND (analogue)
 * Mammut - Barryvox Opto 3000 and Mammut Pulse
 * Nic-Impex - ARVA Advanced, ARVA 8000, ARVA 9000 and Arva Evolution+ beacons