457 SEND failure!
Yikes. Sounds bad doesn't it? Well, it is not.
All beacons are affected to varying degrees by electrical interference. At this year's ISSW in Anchorage, John W. Barkhausen presented a paper (THE EFFECT OF EXTERNAL INTERFERENCE ON AVALANCHE TRANSCEIVER FUNCTIONALITY, ISSW 2012) on electrical interference with digital beacons. What he found was that electronic devices such as digital cameras, smartphones, vhf radios, and GPS devices will interfere with a beacon (we have known this for a long time but Barkhausen's experiments made an effort to quantify the interference.)
Barkhausen found that a distance of 40 centimeters between the beacon and the interfering device usually remedied the problem. The bottom line is that a beacons' ability to function properly can be hampered by electrical output from smartphones, digital cameras, VHF radios and many other high frequency devices.
The above picture demonstrates a 457 SEND failure! I was able to initiate this error message by setting an iPhone directly atop the PULSE while it was in SEND mode. As soon as I moved the iPhone away from the PULSE it immediately removed the 457 SEND failure! message.
When the PULSE shows "457 SEND failure!", it is letting you know that is has identified electrical interference. When you receive this message, relax: there is nothing wrong with your beacon. Take a moment to move any electronic device away from your beacon (as Barkhausen found in his experiments, 40 cms is usually adequate.) Digital cameras have been found to be some of the worst offenders, but smartphones and VHF radios are common culprits as well, and we've even heard reports of the foil wrapper on an energy bar (in a chest pocket right on top of the beacon) leading to an error message. Practically speaking, moving the offending device about an arms-length from your beacon will solve the problem.
While this message may be alarming, it is important for everyone to realize that smartphones, cameras, and other electronic devices pose a real risk of interfering with a rescue. The PULSE will remind you if someone in my party has neglected to turn off one of these devices (turn off your iPhone!!!)
Bottom Line: All digital beacons will suffer from such electrical interference. If you see the "457 SEND failure!", address the problem if possible by moving the offending device or turning it off, and continue. It is possible that you could receive this warning in an urban setting due to electrical interference from large buildings, power lines and appliances. Obviously, in these circumstances you will need to be aware, though there is little you can do to remedy the problem.
I hope this helps you understand your PULSE a little better. If you have any questions, do not hesitate to email me at mammutavalanchesafety@gmail.com.
Very interesting article. I did a similar series of experiments to see what effect items had on a compass - phones and cameras were the worst offenders, needing a range of up to 450mm to be outwith the affected zone. Here it did not matter if the device was off or on. I'd be interested to hear confirmation regarding the off/on point in the above article.
ReplyDeleteWhat is concerning is that 40cm is a long way - get a tape measure out and draw a radius from where your beacon sits and you'll find you can not have anything on the front of your body and as electromagnetic waves travel through your body most of your rucksack is within range too. Probably the only safe place to keep such items is in the top pocket of your rucksack - but this is where I keep my compass.
Some food for thought!
angus@yatsim.co.uk