Friday, December 21, 2012

TECH TIPS: 457 kHz Frequency Deviation

457 kHz, right?
We all know that our avalanche beacons transmit at 457 kHz. Unfortunately, older beacons--or a beacon that has sustained damage--may be transmitting +/- 180 Hz. In order to account for these deviating signals, we build our beacons to receive at a wider range. Think of it like when you are listening to the radio--you may be able to listen to your favorite channel even when you turn the dial a little bit up or down. Of course it may be scratchy and intermittent, but it still works.

Beacons are similar. International norms require that we build our beacons so that they can still work even if a transceiver is sending a couple kilohertz off. If we knew that all beacons in the field were transmitting precisely at 457kHZ, then we could build our beacons on a narrower band which would provide greater accuracy. Unfortunately, because of the number of old or slightly damaged in the field, this is not possible. This is yet another reason to make sure you and your friends are using modern avalanche beacons.

So, owning and using a modern beacon not only makes the search easier, but it makes a potential search for you more accurate.

457 SEND ACCURACY
The Mammut Pulse and Element beacons test the frequency during the start up self test. A properly functioning PULSE will transmit at 457 kHz (+/- 80 Hz). Additionally, Mammut recommends that you have your PULSE run on our TESTER unit for a full diagnostic test every three years.

457 SEARCH ACCURACY
The international norms require that beacons receive +/- 180 Hz of 457 kHz. If the Mammut PULSE recognizes that a beacon that it is searching for has a frequency far out of the norm, it will recommend "reduce search strip to 25m." This narrow search strip will optimize your chances of finding a beacon that is transmitting outside of the norm.  As stated in the Reference Manual:
If your Barryvox® detects that the signal search stripwidth needs to be reduced due to a device trans-mitting far apart from the normative regulation, thereduced search strip width will be indicated.


Take Away Points
Modern beacons provide you with the ability to search for multiple victims and "mark" their locations (after you have found them with a probe.) More importantly, modern beacons do a much better job of transmitting an accurate 457 kHz signal. Will your Barryvox Opto 3000 work? Yes. But retiring older technology will help the entire industry provide greater search accuracy.

Additionally, it is important to test the accuracy of your signal. Mammut beacons do this during start up as well as recommending more detailed examinations every three years (done at the Mammut offices in Burlington, Vermont.)

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