Recommendation on how avoid Interference Issues in companion and organized avalanche rescue Manuel Genswein, Switzerland Dale Atkins, Recco AB and Vice President of the ICAR Avalanche Commission Joe Obad, CEO Canadian Avalanche Association Emily Grady, Education Officer Industry Training Programs, Canadian Avalanche Association Marc Piché, Technical Director, Association of Canadian Mountain Guides Todd Guyn, Mountain Safety Manager, Canadian Mountain Holidays Rob Whelan, Technical Advisor and Ski Guide, Canadian Mountain Holidays Kjetil Brattlien, Senior Engineer, Norwegian Geotechnical Institute Electronic avalanche rescue devices such as 457kHz transceivers and Recco are today the primary search tools in companion and organized rescue. The requirement for a long receive range in order to shorten rescue time asks for highly sensitive receivers. Such highly sensitive receivers are vulnerable to be influenced by interference from other electronic devices, but as well metal parts and passive electronics may detune the antennas or act as a unwanted reflector in the case of a Recco search. The percentage of users who carry a wide range of electronic devices such as mobile phones, helmet cameras, music players, heart rate monitors etc in the outdoors has considerably increased over time and therefore the negative influence on an efficient search effort has in several cases lead to loss of valuable rescue time and greatly disturbed the rescuers on the accident site. The study includes a detailed analysis on the mechanisms of interference, a matrix of influence and potential consequences as well as a new, user group specific recommendation on how to avoid interference issues in companion and organized rescue. Keywords: Avalanche rescue, interference, Transceiver, Recco Introduction Metal parts, magnets and any kind of passive or reduction of transmitted field strength active electronics potentially cause interference (TX) for a transceiver. This may lead to the following effects: inability for proper signal detection in digital search modes (RX) detuning of the antennas (TX and RX) reduction of receive range due to persistent magnetization of the receive filters opening up to a broader antennas (TX and RX) frequency range (RX) increased power consumption (TX) increase of noise in analog sound (RX). Whereas metal parts may detune the antennas and shield the signal, active electronic devices __________________________________ are likely to cause interference resulting in a higher noise floor and/or arbitrary distance and Corresponding author address: direction indications. The mass, dimension and characteristics of metals and the amplitude and Manuel Genswein frequency spectrum of the electronic and General Willestr. 375 CH-8706 Meilen electromagnetic interference influence the Switzerland extent of problems created for the transceiver. It Mobile +41 79 236 36 76 is important to understand that for many sources E-Mail: [email protected] of interference, the amplitude of the harmful interference increases with proximity by a power 1402 of three to distance, i.e. if a certain electronic however, this equally means low tolerance for device causes an interference ring amplitude of interference. level 2 to the transceiver at 20cm distance, the interference reaches an amplitude of level 8 at => the longer the range of a device, the more it 10cm distance. is susceptible to interference => the shorter the range, the lower the Concept of Interference and Consequences sensitivity of the device for „real“ signals as well for Transceiver Technology as for interference. => long range and high interference tolerance When speaking about electronic and are antagonists electromagnetic interference, it is important to => long range leads to shorter burial times and understand that an interfering signal may therefore increased survival chances (1) directly influence the electronic circuits of the => users have to know that their degree of transceiver and / or be picked up by the compliance to the rules on avoidance of antennas of the transceiver. The frequency interference directly influences the efficiency of spectrum of interference often includes the rescue actions frequencies exactly on or close to 457’000Hz, in particular when taking into account that In cases where rescuers experience strong multitudes of harmonics may be in this interference despite full compliance to the rules spectrum. Therefore the interference is in the of avoiding interference, such as in proximity to avalanche rescue transceiver frequency range high-voltage power lines, antenna masts, and can make exactly the same impression to cableways, buildings etc. , where the source of the receiver as the signal of a buried subject. interference cannot be removed or turned off, Electronic and electromagnetic interference with switching the device to analog mode with different characteristics influence the transceiver manual volume control may be the only option to in different ways, however, it is crucial to allow to search for the buried subject. Often this understand that an incoming interfering signal measure needs to be combined with a reduction may look to the receiver exactly the same as a of search strip width. Devices targeting the “real” signal transmitted by a buried subject. advanced recreational or professional user Therefore, rescuer may experience that the groups with the aim to provide a solution for transceiver shows arbitrary distance and 100% of the potential rescue situations such as direction indications exclusively caused by an Ortovox S1, ARVA Link or Pulse Barryvox interference in an area where there is no buried therefore offer such analog search options. subject or the distance to the buried subject is The reason behind the much higher tolerance much greater than the maximum range of the for interference in an analog search compared receiver (signal search phase). The difference in to a digital search is the better performance of amplitude of interference compared to the human hearing to detect to the “real” signal amplitude of the real transmit signal of a buried when a lot of interference is present and when subject is an important factor which influences to the signal to noise ratio (SNR) is bad. what extent the search may be compromised (SNR = Signal to Noise Ratio). At last, interference degrading the performance and efficiency of the transmit function should be Therefore, we may conclude: discussed: Transmit mode is less sensitive to interference than receive mode, therefore 1: acceptance of interference is higher and most of The weaker the signal of the buried subject, the the equipment and “gadgets” can be used with lower the tolerance for interference only minor restrictions such as respecting a minimum distance of 20cm between metal parts, 2: electronics (active or passive) and the A transceiver with high sensitivity has the transceiver in transmit mode. In case the capability to pick up very weak signals from recommended safety distance is compromised buried subjects in a far distance (=long range), as the equipment and clothing gets dislocated on the body during the course of the avalanche, 1403 the transmitted field strength within the nominal manufacturer. The appropriate rescue tactical transmit frequency range may be reduced measure in such cases is to cut the search strip leading to a shorter range in which the buried width in half, which practically means to search subject can be received. However, range on the middle lines of the signal search pattern reductions of more than 30% are seldom and (i.e. if in the first phase, 50m search strip width would require detuning of the antenna and/or has been applied without success, in the second shielding of the signal by a massive or large phase, the signal search strip width pattern is metal object. In particularly negative cases, this shifted by 25m. This approach is equal to a may lead to the fact that the weaker signal of the second coarse search in a probe line with a buried subject is not picked up when applying shifted probing pattern when the first grid did not the search strip width recommended by the lead to success. Matrix of Influence and Potential Consequences Distance Interference Interference at Amplitude Amplitude Outcome between at rescuer’s buried subject’s of of signal of rescue and position position Interference the buried at rescuer’s transceiver subject location of the buried subject at rescuer’s location Out of range, Low Irrelevant for Very low Lower than Signal search not signal search interference, rescuer’s position maximum compromised, no all rescuers receiver arbitrary distance on scene sensitivity and direction compliant to indications, white rules noise on low level in analog sound Out of range, Strong Irrelevant for Medium to Lower than Signal search signal search interference, rescuer’s position Strong maximum compromised, from receiver arbitrary distance interfering sensitivity and direction device with indications, normal increased noise interference level in analog level closer sound than 50cm or strongly interfering device in greater distance than 50cm or on other rescuer 1404 Coarse Low Irrelevant for Very low Very weak Coarse search search, 80+m interference rescuer’s position signal not compromised, distance, level, all weak, but analog sound rescuers on detectable analog only scene sound compliant to rules Limit of digital Low Irrelevant for Very low Weak Coarse search range, i.e. interference rescuer’s position signal not compromised, 50m distance