Friday, October 5, 2012

TECH TIPS: "Stop, Stand Still"

SLOW IS SMOOTH, SMOOTH IS FAST: Understanding the "Stop Stand Still" Message

Earlier today I posted an explanation on the "457 SEND failure!" Below, I explain the "Stop Stand Still" message.

First, it's necessary to have a little background.  All digital beacons have limitations. It is interesting to recall, as Manuel Genswein noted at this year's ISSW Avalanche Rescue Workshop that early on, the professional community was reluctant to switch to digital technology. Why was this? Well, some of it was probably fear of the unknown and a bit of techno-phobia. But another component was based on the fact that ANALOG tones are real, raw data. Analog does not have the potential to MISinterpret information, whereas DIGITAL interprets the analog information--think of it like communicating with someone through a translator--information can be confused and lost. Yet, by now we've all accepted digital technology as the de-facto standard. It is therefore important that we are aware of and accept the shortcomings of digital technology and have a backup plan.

What are the practical limitations of digital avalanche transceivers? 
The advantages of digital beacons are well known to us: it allows the beacon to provide us with a distance indication as well as a direction. This saves us time formerly spent comparing signal strengths of different tangents on a flux line (remember the technique used with analog only beacons?). In short, digital beacons allow us to be faster because we do not have to do comparisons or deductions.

Now, the limitations: Digital beacons arrive at their distance and direction indications by using a mathematical algorithm in a processor to interpret the raw data they are recieving--they are interpreting the strength of a given signal for us. In single companion rescue this is easy and virtually all digital beacons perform easily and with near-perfection. In multiple burial situations however, the beacon must identify patterns to distinguish between the signals. If, at any time, two buried beacons "beep" at the same time, then the searching beacon may be unable to distinguish between these signals--this is signal overlap. Luckily, in time the buried beacons' respective signals will drift apart, so the simple solution (if you know that you have overlapping signals) is to Stop, Stand Still and let the overlapping signals drift back apart, which normally only takes a few seconds.

In the above picture, I set the iPhone directly on top of the PULSE during start up. This message is more often a result of over-lapping signals, but I used electrical interference to initiate this message as I was unable to get the Stop Stand Still message prompt while searching for 5 beacons.


Aha! So, when you get this message, your beacon has actually identified the fact that you have overlapping signals (huh, that's pretty smart!) and advised you as to the best solution. Remember folks, "slow is smooth, smooth is fast." Sometimes our desire to move quickly to find our partner needs to be tempered to have the best (fastest) end result.

Allowing time to separate overlapping signals may not be acceptable to all users. Mammut recommends that mountain guides, ski patrollers, and other advanced users take advantage of the PULSE's Advanced Settings in preparation for the most difficult rescue scenarios. In the Advanced Settings, you can pre-set your beacon to provide you with both ANALOG and DIGITAL information simultaneously. Accordingly, you will never be confused when you encounter overlapping signals because you will actually hear the raw analog signals throughout the course of your search. This is the setting used by most professionals who are aware of the limitations of digital beacons. Be forewarned however, that effectively using analog and digital at the same time takes practice. 

Using Analog and Digital simultaneously, an advanced technique to utilize analog tones while still benefitting from digital distance, direction capability, and marking functionality takes practice. That topic will be covered in a future blog post.  (UPDATE: More info on this can be found HERE and ALSO HERE.)

I hope this helps you understand your PULSE a little better. If you have any questions do not hesitate to contact me (Doug Workman) at mammutavalanchesafety@gmail.com.

No comments:

Post a Comment