Tuesday, 10 March 2015

That 3rd Antenna

Hi folks. I thought I would make a quick post to all the many students who have done avy courses with me up at Glencoe Mountain this winter. Firstly to say thanks for coming, and I hope you enjoyed it, and secondly with a bit of tech info.
This year the beacon training park is well buried with the shallowest transmitter at 2.5m and the deepest now at 6m with some in between. Its a challenging environment for beacon searching as you have had to learn deep burial techniques which are not really part of a basic avy course. You will have noticed how much easier it is for your beacon to find the shallow burials when we hid transceivers around the area for you to find on ski.

Many of you have had to switch from search back to transmit then back to search as your beacons have locked out and stalled with the processor unable to update. Even then your "pinpoint" for probing is a large grid of about 6m square at times (depending on the buried beacon orientation). This is because of "null points". Contrary to what you will have read these do occur in 3 antenna beacons but most handle them well in shallow burials.

The 3rd antenna solves null points by switching on (most often at approx 3m as a rough average) during the close range final search when you are close to the victim.  On some models this is a circle that gets smaller with arrows pointing in out out depending on if you move in or away, or it can be the appearance of a landing strip, or just an increasing acoustic tone and volume with decreasing distance, or all of these depending on the make. Distance readings can be ok on some, or jump eratically from a small to very long range in some cases.

Regardless, all these beacons are well tried and tested and reliable, but the one you own is the one you must practice with to understand how it reacts to the different scenarios an avalanche burial might present.  This does include deep burials if you are learning more advanced skills.  At a basic level we just want you to be able to conduct a basic search from last seen point in series or in parallel and not rely on "marking" then once you have mastered the basic search patterns and recovery we introduce marking to those who have that feature. Should marking fail you have a backup search strategy to put in place.

These deep burials in the park on some ocassions are so deep that the 3rd antenna is not kicking in and therefore you are effectively operating a dual antenna beacon and getting these null points. In these situations as you will have seen, your find is limited by the length of your probe (if indeed you have a long enough probe), then deep burial techniques such as "pinpointing on a line" and systematic probing from the lowest reading point is very important. No one needs to carry probes longer than 3m but a probe of less than 240cm is perhaps too short and in any case not robust.  The latest stats show that survival of a victim is poorer at depth not because of the depth itself, just that its more digging and more time and the survival window of opportunity closes as that digging takes longer.

So folks there is nothing wrong with your beacons its just that they have been challenged as have you and I. The real thing might turn out to be easier - or might not!  The old adage of train hard fight easy has some merit. Keep practicing and get fast.

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