ISSW 2012: avalanche beacons and electrical interference

Posted on November 19th, 2012 by | 8 Comments

We’re not done yet with our blog series on ISSW! Here’s a summary of the presentation by John Barkhausen on how electrical interference can affect avalanche beacons.

ISSW 2012

You might have seen some of the posts on TGR (Teton Gravity Research) and other forums recently in which a chap with a British accent (Stuart Pitches, fun co-owner of English retailer Facewest ), encounters problems when avalanche beacon searching with a GoPro camera attached to his chest. The video reinforces the point that electrical devices can definitely affect avalanche transceiver performance. But how much?

Barkhausen, a student at Alaska Pacific University, attempted to answer this question at the ISSW (International Snow Science Workshop) by placing various electronic devices near a transmitting avalanche beacon and near a searching avalanche beacon. Then he determined how it affected both the receive range and the search pattern of the receiving unit. He tried this with a cell phone, iPod, digital camera, RFID tag (Alyeska lift ticket), Spot emergency locator, a GPS unit, and a small radio. For searching beacons, he used a Tracker DTS, Barryvox Pulse, and Pieps DSP.

His first finding was that these electronic devices have no affect on a transmitting beacon, which is consistent with our experience. His second finding was that these electronic devices can definitely throw off the transceiver search if they’re held within 40 cm (about 17 in.) of the receiving unit. This is also consistent with our experience, which is why we recommend in our owner’s manuals to keep all electronic devices at least 30 cm (about 12 in.) away from the searching unit–or turn those electronic devices off entirely. In other words, keep your searching avalanche transceiver at arm’s length if you have a GoPro on your chest and you can’t figure out how to turn it off.

What are the symptoms when your avalanche beacon receives electrical interference? It will either lose receive range or it will show you “false triggers” on the distance display. This is usually in the form of erratic distance readings and directions; the distance readings are usually quite high, but not always. Can you avoid this if you use an analog beacon (like an Ortovox F1 Focus) ? Not really. You’re going to get so much static that you won’t even be able to pick out the “beep” in the background.

Barkhausen tried to capture this by tracking his search path on a GPS  with each receiving unit (the person holding the GPS was well behind the searcher, for the reasons above). Unfortunately, this part of the study was not conclusive.

In a previous blog, we gave a good example of how electrical noise from a snowmobile engine can affect searching with an avalanche transceiver. Moral of that story: get off your sled if you plan to do a beacon search.

OK, so which beacons are less susceptible to false triggers and range loss than others? It’s clear in the snowmobile blog above. At ISSW, Barkhausen didn’t go there, but of course I had to follow up with him. He provided the following graph:

Beacon interference graph

Click on the picture to see the full size graph.

The x-axis represents the various beacons at distances of 0, 10, 20, 30, and 40 cm from the electrical device. The y-axis is the “Theta” value, which is the difference between that beacon’s normal effective receive range and the effective range it got with the electrical device 0, 10, 20, 30, and 40 cm away. If the colored lines are low on the y-axis, that means that transceiver is less susceptible to noise than the beacons on either side of it on the x-axis. So the Tracker DTS is the least susceptible to noise and the Pieps DSP is the most susceptible.

You’ll also notice that the iPod (orange line) and the GPS (red line) are the biggest culprits in creating interference, which is consistent with our experience.

So we give John an A- on his paper. His findings make good sense, although they could have been presented more clearly. He definitely reinforces what we’ve been saying for years: keep your searching beacon at arm’s length!

We’re looking forward to the next installment of John’s research at the ISSW 2014 conference in Banff.

 

  • Bartholomule

    What about searching from within a heli?

  • andyL

    line graph was a terrible choice…

    Otherwise great info!

  • Tor Andre

    When searching from a helicopter the rescuers use an external, omnidirectional antenna suspended 5 meters under the machine.

    Like this: http://www.girsberger-elektronik.ch/Barryvox/Avalanche_Victim_Search_by_Helicopter_EN.html

  • skian

    great work edge

  • Tim N.

    Your article is appreciated. However, there is a critical phrase that you mispelled “have ne effect” – this might be “have an effect” or “have no effect” – and the context doesn’t distiguish – please correct this. Also – you posted a graph without giving us the labels – you mention ipods and GPS but we have no way of knowing what the other lines represent. Thanks for sharing but its not as helpful as it could be due to the error and oversight.

    • Chief

      Gotta click that graph. The Legend is outside of the compressed size.

  • Dave.s@yamnuska.com

    Hi Bruce

    We have just had two situations in a row with guests useing the new wi-fi enabled Go pro cameras. In both cases on two seperate weekends we had guests with Go-Pros turned on and everyone within 3 meters of the person had variable and off readings while searching with Tracker 2. It was virtually impossible to search with the camera turned on and in each case once the camera was turned off readings on the beacon returned to normal. These are brand new Go-Pros that are wi-fi enabled to work with a remote and with a smart phone. Haven’t seent his before. The old Go-pros as you stated were not so much of an issue when more than 40cms from the searching transceiver. Yet thses new ones seem to be a whole different ball game.
    Dave Satrk
    Director of Operations Yamnuska Mountain Adventures

  • Nate Corona

    Has it been tested that electronics in the off position have no interference at any given distance???