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 level, all no arbitrary rescuers on distance and scene direction compliant to indications, rules multiple burial algorithms work properly, clean analog sound

Limit of Low Rescuer/receiver: Very low Very weak Search strip width recommended interference Irrelevant for signal may be signal search level, all rescuer’s position compromised, if strip width, i.e. rescuers on search with 25m distance scene Buried recommended (2x25m = compliant to subject/transmitter: search strip width 50m) rules Very strong, does not lead to caused i.e. by success, cut mobile phone search strip width turned on, running in half. video camera with wireless functions or larger metal object and safety distance compromised due to displacement of equipment on the body during the course of the avalanche

Limit of Strong Irrelevant for Medium to Weak to Search strip width recommended interference, rescuer’s position Strong medium may be signal search from signal compromised, strip width, i.e. interfering arbitrary distance 25m distance device with and direction (2x25m = normal indications 50m) interference possible, level closer performance of than 50cm or multiple burial strongly algorithms interfering compromised,

1405 device in increased noise greater level in analog distance sound than 50cm or on other rescuer

10m distance Low Strong, buried Low Strong Coarse search interference subject uses not compromised, level, all strongly interfering no arbitrary rescuers on device in minimum distance and scene allowed safety direction compliant to distance such as indications, rules mobile phone multiple burial turned on, running algorithms work video camera with properly, clean wireless functions analog sound etc.

10m distance Extremely Extremely strong Very strong Strong Digital signal strong interference due to detections are interference high voltage power likely to fail due to high line, antenna mast. completely, voltage Affected radius multiple burial power line, may be larger than algorithms are antenna 150m, depending very likely to fail mast. on voltage / completely, Affected transmit power. maybe only radius may analog search be larger with manual than 150m, volume control depending possible, apply on voltage / strongly reduced transmit search strip width. power.

1m distance Low Strong, buried Strong Extremely Fine search not interference subject using Strong compromised, no level, all strongly interfering arbitrary distance rescuers on device in minimum and direction scene allowed safety indications, compliant to distance such as Tracking of rules mobile phone multiple burials in turned on, running medium to longer video camera with distance wireless functions compromised, etc. clean analog sound on low volume/sensitivity level

1406 Recommendations Concerning Potentially Definitive List of Equipment Which Can Be Used Interfering Equipment for Professional and With a Transceiver institutional Users and Special Applications (Detailed) List of objects and equipment (conclusive), which can be used with a transceiver respecting General Rules the rules as mentioned above. This conclusive list includes rescue or operationally critical Clothing equipment and equipment which is an integral Avoid wearing clothes with magnetic buttons or part of mountain excursions. larger metallic and/or conductive parts (e.g. nets For equipment which is critical for rescue or of heated gloves)! operationally, but require more restrictive rules than the 20cm safety distance in transmit and Storage 50cm in receive mode, the exceptions are Do not store the transceiver close to strong specifically mentioned. magnetic fields as they can magnetize the antennas with a long term effect. General equipment: - metallic frames of backcountry backpacks Magnets and electromagnetic fields - camping and cooking equipment, metallic Some transceivers of several brands have a vacuum bottles magnetic ON / OFF or OFF / SEND / SEARCH - non engine driven snow sport equipment (skis, switch and therefore magnets in close proximity snowboards, snowshoes) can turn the unit OFF, to SEARCH or SEND at - climbing gear (carabineers, ice axes, any given moment. crampons, etc.) - electric head lamps excluding headlamps with Some transceivers of several brands contain an switching power voltage regulators electronic compass and are, especially during - snow study kits incl. metallic snow saw search, highly sensitive to magnets and - improvised repair equipment and tools like electromagnetic fields. pocket knives and pocket multi-purpose repair Transmit mode tools - writing tools In transmit mode a minimum distance of 20cm - wrist watch without radio functions on the wrist; has to be respected between the avalanche large, multi-functional watches with large rescue transceivers and any metal object or screens electronic device. Although the distance where should not be worn on the same hand like the serious interference of transmit mode has to be searching transceiver is held. expected is for many objects and devices - Any kind of food, candy or cigarette box considerably shorter (<3cm), the likely wrapping with metal foil displacement of a carrying system, clothing and potentially interfering objects due to the Search, rescue and survival equipment: mechanical impact to the person taken by an - flotation devices (incl. remote release device), avalanche has to be taken into account and Avalung, Avalanche Ball therefore the recommended distance has to - avalanche rescue transceivers leave some safety margin. - devices providing a backup transmit function in case of a secondary avalanche - RECCO search devices (3m distance and do not point directly to another rescuer) Search mode - RECCO reflectors (reflectors may be placed at any distance without any risk of interference) In search mode, a minimum distance of 50cm - avalanche probes and shovels has to be respected between the beacon and (metallic and carbon probes may not be placed the listed objects below which can be used with parallel to the snow surface during fine and a transceiver. pinpoint search)

- high performance lights and generators for

1407 night searches in organized rescue is in progress, use of these device (strong interference may occur and affect a on the entire avalanche should be restricted to larger zone around the equipment. Interference short-lasting emergency calls in minimum should be checked with an analog receiver on distance of 25m to the closest searching the highest sensitivity setting and appropriate rescuer. Based on new measurements, measures taken accordingly) actively searching rescuers must completely turn off cellular phones as some specific, but Vehicles: popular models show even in “air plane mode” - snow mobiles, snow grooming machines, cars, in distances up to 100cm interferences which snowploughs, snow blowers trigger erratic distance / direction (The search from such vehicles can be indications on the screen in areas where there severely disturbed by interferences from the is no real transceiver signal). running engine, metal plates and the vehicle electronics. In transmit mode, reduction of Orientation equipment: range is possible depending on proximity of - electronic and mechanical altimeters the transmitter to metal parts of the vehicle. - electronic and mechanical compasses Search accuracy might be compromised in - handheld GPS receivers (except devices with close proximity of the vehicle.) radio transmit functions) - helicopters (The search from a helicopter is only efficient Equipment of armed forces and law enforcing with specialized transceivers) agencies: - guns and pistols, ammunition Medical equipment: (weapons incl. optics, but excluding electronic - pacemakers and ICDs systems; if the weapon is carried diagonally on (Users of pacemakers/ICDs are advised to the front side of the body, the transceiver must carry the device on their right side (adjust the be carried sidewise) length of the carrying straps. Consult the - body armor systems (carry transceiver manufacturer’s instructions of the pacemaker sidewise) with regards to the interference impact.) - portable heart rate monitors (needs to be switched off during search or in Non Rescue, Mountain or Operationally 50cm distance to the receiver) Relevant Equipment (= all equipment not listed - first aid equipment incl. metallic splints above) - toboggan, immobilization equipment, stretchers The variety of electronic equipment (entertainment, video, photo, remote controls, Communication equipment: etc) that rescuers have been trying to use in - analog VHF and UHF radios up to 5W transmit combination with their avalanche rescue power (interference may occur during transmit transceiver has tremendously grown in the past of the searching rescuer. Loudspeakers of years. Whereas some of the equipment might radios produce a strong electromagnetic field not cause an interference problem in and should therefore not directly point towards combination with a particular transceiver, it does the transceiver) with others and vice versa. It is therefore - digital VHF and UHF radio up to 5W transmit impossible to make a recommendation for each power (interference may occur during transmit, individual device and transceiver. Several radio needs to be turned off during search) reports from failed or severely disturbed and - cellular phones, satellite phones, PLB delayed rescue action in the last years have (personal locator beacon) shown that electronic equipment can have a (inference may occur during communication very unpredictable and severe influence on (incl. synchronization with the network, avalanche rescue transceivers. communication of text messages and data), Therefore, while a search is in progress on the devices need to be turned off during search for avalanche, all equipment not listed above must all searching rescuers. As long as the search be turned off and remain off on the entire

1408 avalanche for the short duration of the search Source of Interference in Recco Searches compared to the entire duration of rescue. RECCO reflectors use a specially tuned diode to High voltage power lines and radio towers may cast back the directional signal. Diodes are as well dramatically reduce the performance of generally used to control the direction of current an avalanche rescue transceiver. Often, the but can be used to modulate or shift radio digital search mode completely fails and it is frequencies. RECCO reflectors use a diode to necessary to carry out an analog search by double the RECCO frequency. There are four applying signal search strips with a very limited situations where diodes or diode-like materials width. can result in interference or distracting RECCO signals: Recommendations Concerning Potentially Interfering Equipment for Recreational Users Electronic Devices (Short Version) Potentially, any device – even when turned off – Avoid wearing clothes with magnetic buttons or with a diode can produce a reflected RECCO larger metallic and/or conductive parts (i.e. signal. However, for most devices this range is heated gloves). Be aware that food, candy or only millimeters to centimeters but can range up cigarette box wrapping often include thin metal to several meters. foils which therefore count as a metal object! Different Metals (generally found in equipment) In transmit mode a minimum distance of 20cm Diodes are made of two different conductive has to be respected between the avalanche materials or metals, so a reflected RECCO rescue transceivers and any metal object or signal can be produced from items made of electronic device. different metals. This can include boot buckles,

skis and snowboards, bindings, rusted steel, or In search mode, a minimum distance of 50cm even rivets made of a different type of metal has to be respected between the transceiver, from steel shovel blades. electronic equipment and metals parts. All equipment on the searching rescuer has to Mineralization (rocks) be turned off, except: - radio Since diodes are made of two different - head lamp without switch power voltage conductive metals, rocks that are heavily regulator (usually found in high power devices mineralized may reflect RECCO signals. The with external battery packs) signal is generally very weak and is often more - wrist watch without radio functions on the wrist; problematic early in the winter when the snow large, multi-functional watches with large cover is shallow. Because the signal is so weak, screens should not be worn on the same hand it generally disappears when the power is like the searching transceiver is held. reduced one or two steps. A RECCO reflector - devices providing a backup transmit function in will continue to produce a strong signal unless case of a secondary avalanche the snow is exceptionally deep or wet.

Reflectors on Rescuers All equipment on all non-searching rescuers on the avalanche has to be turned off, except: Reflectors on rescuers produce a very strong - Cellular phones, satellite phones, PLB source of interference and should be avoided by As long as a search is in progress on the principle. An experienced Recco operator may avalanche, use is restricted to short-lasting be able to work around reflecting rescuers - thus emergency calls/messages in minimum avoiding to point the device towards them - but distance of 25m to the closest searching the avoidance strategies at the same time may rescuer. increase the risk to oversee a weak reflection of - devices providing a backup transmit function in a deeply buried subject. Backup- / Rescue case of a secondary avalanche SEND functions of modern avalanche - head lamp transceivers are a more appropriate solution to

1409 allow fast rescue in case of a secondary detector operator, if necessary, can wrap their avalanche accident. transceiver or other device with a shield or Pouch. Even a vest is available by a third party. Solution to Manage Distracting RECCO When used over a transceiver the fabric will not Signals affect the transceiver’s signal.

While the reasons for interference are varied Train and different, the solution is the same for all situations. There are five techniques that will The detector operator should practice in the help minimize distracting RECCO signals. In presence of interference. This means searching some situations one technique may solve any while wearing radios, cameras, mobile phones, challenges, while in other situations all the GPS, etc. and amongst other reflector-equipped techniques will need to be applied. rescuers. However, this should only be done once the operator has good skills and Aim experience with the detector. Novice instructors should learn initial skills free from the challenges Strictly limit the search horizon by aiming the of interference. With good skills they can then detector downwards the snow and avoid add interference issue into their trainings and rotations motions which make the antenna practice. temporarily point towards other rescuers, equipment or towards the sky. Reducing power to eliminate interferences?

Manage Only reduce the power to limit interference as a last resort. Reducing power reduces range and The detector operator should, ideally, keep is therefore a highly unattractive solution. rescuers behind the operator; basically don’t point the detector towards other rescuers. Searching uphill makes it easier to avoid an undesired extension of the search horizon. Acknowledgements: Searching sidewise/traversing on an inclined slope needs special attention of the rescuer in The author would like to thank to the following the moment where the device is pointed individuals and organizations for their downslope as the search horizon quickly corrections, linguistic review and contributions to includes the entire debris. Searching downhill in this paper: step terrain is therefore strongly suboptimal and Joe Obad, CEO Canadian Avalanche should be avoided if possible. Association Emily Grady, Education Officer Industry Training Position Programs, Canadian Avalanche Association Todd Guyn, Mountain Safety Manager, The detector operator should wear their Canadian Mountain Holidays transceiver and other electronic devices on their Rob Whelan, Ski Guide and Technical Advisor, back. If the transceiver is equipped with a Canadian Mountain Holidays reflector, the reflector side should worn securely Marc Piché, Technical Director, Association of against their back. As previously mentioned, Canadian Mountain Guides reflectors on rescuers add unnecessary Daniel Forrer, Head of Software Engineering, challenges to a rescue operation, which should Adaxys Solutions be avoided.

Shield References:

If the previous three techniques are not reducing (1) Genswein, M., Reiweger, I. and Schweizer, distracting signals for the detector operator, J., 2009. Survival chance optimized search strip RECCO makes available a specialized width in avalanche rescue. Cold Regions metalized fabric that can shield a reflector or Science and Technology, 59(2-3): 259-266. other device(s) from the RECCO signal. The

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