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 above images show the transmitting transceiver signal in a relatively noise free environment. If interference from another electronic device is introduced, the S/N ratio will decrease even further as spikes in noise will begin to drown out the desired transceiver signal making it indistinguishable. Can you tell the difference between the transceiver signal and noise spikes caused by active interference in Figure 3 below?  

The Testing:

The QA crew drove out to the Bonneville Salt Flats west of Salt Lake City to find a wide-open barren space, away from as many possible sources of electromagnetic interference found in the city. 

A transceiver in send mode was placed at the end of a 100m tape measure. It was then slowly approached with a searching transceiver until a steady signal, both distance and direction indicators, was indicated. The distance at this point was then recorded. 

Various electronics often found in the backcountry were used in our test, including smart watches, GPS watches, smartphones, two-way radios, action cameras, satellite communication devices, electronic airbag packs, and even a snowmobile. The searching transceiver was held at 50cm from the torso using a static tether to help maintain the appropriate distance. Each item was then placed in a normal use position as noted below.  

The goal was to determine how bad it might be to violate the 20/50 rule. To do so, many items were held closer than 50cm (i.e., heated gloves and smart watches). Each item was tested three times, and the average taken. We then calculated the reduction in range compared to a baseline with no other items present. 

The Results

As you can see, there was a wide range of reductions in performance depending on the power of the devices, and how close they are to the searching transceiver.  

Some Caveats:  

1.) These items were tested one at a time, and it is likely that there would be a compounding effect from multiple concurrent devices.  

2.) The testing was conducted using a single pair of transceivers and a random selection of electronic devices. They do not represent every device out there. Personal electronic devices will continue to get more powerful over the coming years. 

The takeaway here is that EMI is real, and it can have a significant impact on transceiver performance! And we can’t stress enough the importance of updating the firmware of your avalanche transceivers and electronic avalanche airbag packs.  

Firmware

Transceiver and electronic airbag pack manufacturers are continually refining their firmware to improve performance (much the same way the apps on your phone are continually being updated). Firmware updates can improve features, extend battery life, reduce harmful interference being generated, and improve the way interference signals are processed.

It is of utmost importance to keep your firmware updated for these products. But we know many people do not. Don’t be one of these people. Update your firmware now. It’s easy and can often be done using an app on your phone. Refer to the manufacturer’s website for information on performing firmware updates.

Conclusions / Key Takeaways and General Guidelines

1.     Be aware of EMI.

• It’s real, and it can have a significant negative effect on transceivers.
• It will have its largest influence during initial signal acquisition, which when you really don’t want to be wasting time.
• As you get closer to the transmitting transceiver and its signal becomes stronger, interference will have less of an effect.
• You will likely not be aware of or recognize that EMI is affecting your transceiver, especially in a high-stress avalanche event.
• The more powerful and closer the electronics are to the transceiver, the more likely they are to cause significant interference.

2.     Is EMI the most important factor in your backcountry safety?

• No. Avoiding avalanche terrain, having proper training, and carrying a transceiver, shovel, probe are all higher on the list. But managing EMI is part of comprehensive backcountry safety. And in some cases, it can make a big difference, and could significantly slow down your transceiver search if not managed.

3.     Some level of EMI is unavoidable but can be kept to a minimum by having awareness of what electronics are being used and where you place them. Good practice is to discuss this with your group at the trailhead before heading out.

4.     Keep your firmware up to date on your transceiver and electronic avalanche pack.

5.     Some modern transceivers can sense the presence of interference and will provide a visual indication on the screen that your search strip width should be reduced.

6.     Like many mountain safety and risk decisions, it is your responsibility to understand your equipment and your group’s risk tolerance.

• If you want the lowest amount of interference possible, turn off all non-essential electronics and/or move away from them.
• Otherwise, follow the 20/50 rule along with some generally accepted guidelines which are shown in the graphics below.