Tuesday, November 13, 2018

Tech Tips: Barryvox S Group Check Mode

Best Practices: Why To Use The Barryvox S Group Check Mode

It is the simple things that keep us alive and allow us to thrive--and the simple beacon check before headed out in the backcountry is no different.

While doing trailhead beacon checks I have found beacons that are not on, beacons that have dead batteries, and beacons that can send but not search. Simply put, a beacon check can save your life. But is it so simple? Can a beacon check be done incorrectly? What is the “best practice?”

Of course, just about any beacon check is better than no beacon check. The simplest form of a beacon check involves turning your beacon to SEARCH and moving towards your partner, who is in SEND. The number on your beacon should get smaller and smaller as you get closer, confirming that your 
A diagram of a simple group check from the Barryvox S Extended Reference Guide



partner is sending a signal. If you are testing multiple partners at once, they should all spread out 3m apart and walk past you, and you should see a low number on your screen with each pass.Is this good enough? Not exactly. 



You may notice in the above diagram that the Leader is using the "Group Check" mode as opposed to using SEARCH mode. Why would that be?

Let me start by reviewing some characteristics of modern beacon technology.

Most modern digital beacons use a MARKING function to assist with multiple burial scenarios. In order for a beacon to employ MARKING, the beacon must first be able to identify different victims’ signals. This means that Signal Separation Algorithms are being used to identify potentially chaotic signals. Once the Signal Separation Algorithms have done their job (the Barryvox can identify up to 16 signals) then the beacon must decipher which of those signals is the closest, based on signal strength. Once this decision has been made, the beacon will give the rescuer a number that corresponds with the closest signal based on its Signal Selection Process.

And herein, lies the rub.

A decision has been made by the transceiver. The rescuers beacon is now “locked” on the victims signal that it deems the closest. If the rescuer moves away from this victim, towards a different victim, the rescuer’s beacon will resist unlocking. This means the rescuer could move close to a different victim and get no indication of its’ presence!

This “locking” function is intentional. This is what prevents chaos in multiple burial scenarios. Rather than your beacon spastically jumping between victims, it makes a selection so that the rescuer can move calmly from one victim to the next.

Hopefully a light bulb is going off? How could this locking function be problematic during a group check? Well if, as the first person passes and then moves away, the Rescuer’s beacon is still locked on it, as the second person approaches the numbers may not indicate that the second person is closer. Now, hopefully, you understand why this is happening.

So, what to do about it?

GROUP CHECK MODE.
Mammut, and many other beacon manufacturer’s, have a Group Check Mode. To access, select Group Check by pressing the orange FLAG button while the Group Check indication is visible during the startup cycle.  Group Check mode can only be accessed during the startup cycle.









From Group Check mode the beacon is now receiving at an analog gain (combination of volume and range) that is appropriate for 1 meter. The signal separation algorithms are not at play, nor is the signal selection--the sound you hear is purely reflective of signal strength. For those of you with analog experience, think of this like using an old analog receiver set at low range.






The advantages of using the Group Check Function are many. The most important piece of the puzzle is that you can now do an easy beacon check without worrying that your beacon may be locked onto a user moving away from you.

But of even more value, you have not simply identified the presence of a signal (Signal Confirmation), you have verified the INTEGRITY of the signal. Because your beacon’s “gain” has been set very low to have a 1-meter receiving range and you can still hear you partners’signal, assuming you can estimate a 1-meter actual distance you can therefore assume your partner’s signal is strong enough to be reflective of it’s recommended search strip width. Aha! You just did a range check without having to do a "range check". 

Some added features of Group Check help ensure the integrity of the signal.





If you see the above icon (exclamation point above person) it means the beacon you are testing is out of tolerance--meaning, it is more than +/- 80Hz from 457 kHz, i.e. Signal Drift is a factor. Identify the problematic beacon and send it back to the manufacturer immediately.

If you see the "Too Close" screen message, you need to back up from the transmitter to maintain 1-meter distance.  We use this message to repetitively reinforce the 1m distance Group Check so you get in the habit of estimating and utilizing this distance, which is what allows you to verify signal integrity as opposed to only confirm there is a signal.

To review, Group Check Mode has 2 distinct advantages to using Search Mode for doing a trailhead check. The main advantages are that in a beacon with a marking function it prevents a brief "signal lock" from causing you to get a reading from the wrong transceiver in a group test, and it allows you to check the integrity, not just the presence, of the signal.

In the next blog post we will cover PRO CHECK, an added feature that became available with Firmware 3.0.

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