EMI, it’s a thing. Items found in the closet/pack that could interfere with an avalanche transceiver. Note: pictured here are heated gloves–these are not recommended for backcountry skiing! Missing from the pile—a cell phone (used to take the photo). The point is, we are carrying lots of devices that cause active EMI.
Confirming or denying what you already do in practice; the UIAA released recommendations for minimizing electromagnetic interference in avalanche transceivers. Here’s the latest.
On Dec. 6, the International Climbing and Mountaineering Federation (UIAA) released their recommendations for the use of avalanche transceivers in proximity to other devices we carry (or that might be in the environment, like overhead power lines) that emit electromagnetic radiation.
Electromagnetic radiation can cause electromagnetic interference, known as EMI. EMI is a big deal when considering the use of avalanche transceivers.
In the past decade, the number of personal devices we carry that emit electromagnetic radiation has increased—think cell phones, InReach type devices, GPS watches, heated socks/gloves, FRS/GMRS radios, Go Pro type cameras, and even headlamps. Depending on the individual, the list could likely go on. And we didn’t go into metal objects (including foils) and magnets, which can also cause interference.
Wearing an Avalanche Transceiver
Traditionally, we think of two primary places to carry a transceiver while touring: in a dedicated pants pocket with a sewn-in/reinforced clip to secure the unit or a proprietary harness (supplied with the unit) that positions the transceiver somewhere between the belly button and sternum. We bring this up because the graphics we include in the article, one from the UIAA and the other from Avalanche Canada, illustrate the transceiver when in transmit mode as being worn in the chest harness. The new recommended guidelines apply if you wear a transceiver in the harness or pant pocket.
Let’s take a short break in our programming. Much of what we write about here isn’t new, which sorta makes it not news. Over the years, EMI and solutions-oriented fixes have been bantered about. The revered The Avalanche Review (TAR) often publishes on the topic. A random search derives a piece from the April 2013 issue titled Interference Concerning Avalanche Rescue Transceivers by Manuel Genswein.
In short, here’s an excerpt from that paper’s recommendations: “In transmit mode a minimum distance of 20cm must be kept between avalanche rescue transceivers and any metallic object or electronic device. In search mode, keep a minimum distance of 50cm.”
Here we are a decade later. After combing through the literature and real-world experience, the 20-50 rule reigns. We’ll break down the UIAA recommendations by transmit and search modes.
Back to the scheduled programming by first discussing modes of interference.
Passive Interference Impacting Both Send & Search
Passive interference defines EMI as caused by objects/materials not actively consuming energy. The UIAA states, “Metal parts, electronic devices with metal cases, foils and wire mesh; magnets.
➔Keep >20cm distance from metal parts and magnets.”
Passive interference is known to cause “misleading distance and direction indications,” which, in the avalanche scene, we know as range reduction and false positives—all things that can critically impact rescue efficiency.
Active Interference Affecting Search
Active interference comes from any gear/equipment “consuming energy.” All these gadgets emit electronic noise. The UIAA advises following the rules outlined in their recommendations for searching, which we’ll get to in a bit, to reduce and eliminate the likelihood of range reduction and a “false positive.”
We raised this point in our first piece on transceivers and EMI; it is well worth watching Bruce Edgerly’s talk on the topic. We are relinking it below. Edgerly goes deep, describing the nuances of passive and active interference and how to recognize how EMI might affect a search. It is also worth noting and honoring Edgerly’s advice: go out and practice rescue scenarios in electronically noisy environments.
If you are new to the concept of EMI and are looking for an intermediate level discussion on the topic, this presentation by BCA’s Bruce Edgerly on transceivers and EMI is excellent.
The UIAA
Transmit mode recommendations from the UIAA
> 20cm from sources of interference:
- electronic devices
- metal parts
- metallic foils (e.g., to preserve heat)
- magnets
- heating elements
The UIAA also advises to be mindful of how a transceiver and cell phone, for example, might come into close contact in a victim burial and perhaps interfere with the send signal. Consider this another point to inform us how we orient/position electronic devices on our bodies.
UIAA Search Recommendations. Screenshot from UIAA document regarding EMI and avalanche transceivers.
SEARCH—Receive mode recommendations from the UIAA
The UIAA states to turn off any items that may cause EMI. Yes, “turn off” means off, as in power down. As you’ll read, “no airplane mode.” Heated gloves, toss them aside; the heated socks…turn them off. The UIAA does make exceptions but provides guidelines for a cell phone used to make an emergency call—keep that “active” phone at least 10m from a transceiver in search mode. Below are the specific recommendations for the search.
- Take off heated gloves.
- Switch off communication and other electronic devices (completely OFF, no airplane mode).
- Switch off heated socks and boots.
- When using a watch with an electronic screen, or bracelet with electronics for activity or heartbeat monitoring, hold the transceiver in the opposite hand.
- >50cm distance from devices absolutely necessary to conduct the search, for example a head lamp for a search at night.
- >10m distance from a turned on mobile phone, radio or satellite communication device.
- >10m distance from a snowmobile with running engine
- Reduce the search strip width to max. 20m if interference cannot be contained by the distance rule.
- Some electric airbag systems may cause interference. When using an affected system, you may need to consider searching without your electric airbag.
Companion rescue in a group:
To save time, or in case you are not familiar with turning your devices off, consider handing electronic devices to someone who is not actively searching.
UIAA Search Recommendations. Screenshot from UIAA document regarding EMI and avalanche transceivers.
Click here to see the full UIAA graphic.
Avalanche Canada
Referenced up top was Avalanche Canada. Their EMI graphic includes similar information to the UIAA recs, but is a bit cleaner in its presentation. We just want you to digest the information. With that in mind, here is the Avalanche Canada graphic. Please be safe.
Avalanche Canada’s graphic for minimizing EMI in transceivers.
I had not thought about this before, but just thought of this if you use radios:
Having a radio clipped to the outside, like Rocky Talkies , or a power switch on the mic, like the BCA Link 2.0, is really an essential feature.
Our current radios are inexpensive, and have worked well. But , they sit inside my pack, with a mic clipped to the shoulder. I’d hate to have to dig in my pack after an avalanche to turn the radio off.
Slim, had a similar thought as I thread the Rocky Talkie handheld mic from the pack’s innards to secure it on the shoulder strap…no on/off switch on the handheld mic. That means a step or two to access the radio unit (zipped into an electronics pocket inside the pack’s main compartment) to turn the unit off. That’s something I’ll consider moving forward—do I want the handheld mic if it in fact takes me longer to power down the unit in the even of a victim search?
Watch Bruce Edgerly’s talk at 52 min in he puts up a chart of the interference potential causes and distances – FRS radios (bca link, original rocky talky) are not a significant source of interference and don’t generally need to be turned off, he sorta discusses some newer VHF’s as a bigger issue (this may end up including the new rocky talky 5w). I find FRS’s indispensable and I personally would never tell anyone to turn one off in an avalanche, nor have had any issues with them when doing drills. If you are worried I feel like the go to take away from edgerly’s talk is – arms length generally gets you away from basically everything that is not a snowmobile.
Certainly lots to consider, and it is interesting to watch Bruce’s talk (which is excellent) in the context of the UIAA recommendations. I’ve always used a 2W radio (no handheld mic). Certainly it will be a power uptick with a 5W radio. The video does get into the VHF radios and mentions the issues some ski patrollers have noticed—it sounds like those are 5W radios they are using, but the model/make is not defined. And the arm’s length go-to has always been, generally speaking, my rule too. That noted, it was eye opening to see the >10m distance from a turned on phone, radio, or satellite communication device recommended by the UIAA. That’s a big difference between arm length (50cm) and 10m. And still, yeah, the UIAA states to “Switch off communication and other electronic devices (completely OFF, no airplane mode).” Best for me to go practice in the field with the 5W radio and transceiver in search mode.
San Juan Snowcast had a good episode recently that shared some interesting test results from a course with Edgerly that perhaps introduce some additional nuance. Ex: passive interference from a phone (can’t recall if the phone was powered on but inactive or powered off) only interfered with a beacon in send mode when the phone was literally against the beacon battery in the same pocket. Seems like maybe there is a little bit of room to make your own informed decisions about beacons and interference in send mode (ex. maybe it’s fine to just keep your phone in one pants pocket and your beacon in the opposite pocket). But it definitely seems wildly irresponsible to not maintain at least 50 cm in search when you’re being counted on for a rescue. (At least until fine search, when it appears that leaning over and accidentally lowering the distance from interference isn’t so a big deal because of how strong the beacon signals are at that point). I’d be pretty interested in the raw data that the 10m from phone/radio rec is coming from. Unless it’s truly necessary to go rooting through your pack powering down devices that time seems better used starting the search.
I’m sure the UIAA and manufacturers have done much more comprehensive research than I have, but here’s my personal experience. Using my own beacon (Barryvox S) and devices I normally have with me, I did a series of backyard experiments. Based on what I saw, the iPhone was by far the biggest problem, maybe the only problem piece of electronic equipment. In search mode, with the phone in my front pocket, I saw ghost signals, random changes in distance and direction, and less range to initially pick up the transmitting signal. It was really bad if I moved the phone closer. Interestingly, just moving the phone to my back pocket seemed to completely eliminate the interference. I didn’t see any perceptible effects with a GoPro, inReach (not transmitting) 2W BCA radio (standby or transmitting) or even a 5W Baofeng with the transmitter held down and holding it essentially right next to the beacon.
So based on my admittedly limited and personal experience, I really doubt any radio base unit in a backpack with a remote shoulder mic would have any effect on a beacon search. But I would absolutely not argue with the UIAA or manufacturer recommendations. I think we should all periodically incorporate some interferences into our ongoing training scenarios so everyone could recognize what EMI looks like on their beacons and not waste a lot of time chasing ghosts.
I may have just missed this, but are certain CLASSES of airbag packs “worse” than others? I’m picturing supercapacitor fan-style packs to have more electronic gadgetry and EMI than a canister system, but do realize that is total conjecture on my part and may be wildly wrong?
Our experience at Snowbird doing beacon drills while using commercial Motorola radios was that there was significant interference between radio and beacon. The radio would cause ghosting of 2+ burials and make direction guidance jump all over the place. About 1m of distance was required between radio and beacon, which meant that a patroller doing a hasty search had to shut off their radio. This was present with normal VHF radios and got MUCH worse when switching to a modern trunked/encrypted radio system, which is increasingly the system used by resorts. I think it’s reasonable to think that a radio with a higher transmitting power is more likely to interfere. Anyone with a programmable Baofeng radio could do a quick backyard experiment on this one.
Also published in Wilderness and Environmental Medicine within the last year was a study showing interference from heating clothing, particularly gloves. I do t recall if there were heated boot liners included but those would be a concern as well.