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QC Lab: Beacon Interference

Viri motenj pri iskanju lavinskega oddajnika: kako pametni telefoni itd. vplivajo na našo varnost

QC Lab: Beacon Interference

Ski season is here! It’s an exciting time of year, and many have started waxing skis, breaking in boots, cutting skins, practicing transceiver searches, and brushing up on backcountry travel skills. But wait, let’s not forget to change out the batteries and update the firmware on all our critical snow safety electronics as well.
Why?

Electromagnetic interference (aka EMI). EMI is real and can have significant impacts on avalanche transceiver performance, potentially jeopardizing backcountry safety. The bottom line is that many electronic devices we bring into the backcountry have the potential to interfere with an avalanche transceiver’s search mode.

 

In this QC Lab, we explore electromagnetic interference (EMI), how it affects backcountry safety, and why keeping your firmware up to date should be on everyone’s preseason checklist.

A definition of electromagnetic interference.

There has been an increasing amount of discussion around EMI and its negative effects on the performance of avalanche transceivers among the snow safety community. Although this is not a new topic, it is taking on a heightened level of awareness and importance as the number of winter backcountry users increases and people are carrying more personal electronic devices such as smart phones, smart watches, GPS devices, heated clothing, and electronic airbag packs.

The Basics

Avalanche transceivers are essentially radios that work by communicating on an internationally accepted frequency band, 457 kHz. A transceiver in send mode transmits a signal pulse every second which is defined by ETSI EN 300 718-1. When switched into search mode, the transceiver will listen for nearby signal pulses and display distance and direction information to aid in locating transmitting transceivers (avalanche victims). The further away you get from a transmitting transceiver, the fainter the signal becomes. At the maximum useable ranges, a searching avalanche transceiver is “listening for a whisper.” It is here that the transceivers are most susceptible to EMI.  

There are three major sources of interference that can negatively affect your transceiver’s functions. 

Passive

  • Metal objects like shovel blades, tin foil, foil backed clothing, and magnets.  
  • Passive sources affect transceivers in both send and search modes.  
  • Active
    • Personal electronic devices: smart phones, smart watches/rings/bracelets, two-way radios, satellite communicators, heated gloves, etc.   
    • Snowmobiles or any motorized vehicles  
    • Active sources produce more significant effects on transceivers in search mode   
    Environmental
    • Powerlines, ferrous rock, etc.   
    • Environmental sources produce more significant effects on transceivers in search mode   

In this QC Lab article, we will focus on active sources of EMI as they are often the highest concern and can generally be mitigated through some basic user knowledge and actions. Most electronic devices generate EMI at various frequencies, and at various strengths. When the EMI happens to be near the 457kHz frequency band, it can negatively affect the performance of transceivers. Keep in mind that most consumer electronics are not specifically designed for backcountry travel and have little regard for the sacred 457KHz frequency band. 

Let’s start with some simple spectrum analyzer images to understand the concepts better. The signal from an avalanche transceiver in a relatively noise-free environment is shown in Figure 1 below. Some level of background noise is unavoidable in the real world. A truly noise-free environment can only be created in a laboratory setting. As you can see, the signal level is significantly higher than the noise level. The difference between these levels is known as the signal-to-noise (S/N) ratio. The S/N ratio is important as the transceiver’s processor utilizes this information to identify a true transceiver signal from everything else going on.  ... >>> BDE - 09.01.2024

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