Sunday, December 29, 2019

Group Check: Myths and Misnomers

Recently an experienced user posited the question, "Is is dangerous, when doing a group check, for the two beacons to touch?"

First of all, there is absolutely no hazard in 2 beacons coming into contact during a trailhead check or any other time--it will not affect the future performance of either of the devices.

Likewise, you cannot harm your beacon by touching it with an iPhone. Electromagnetic noise is just that, noise. It makes searching for a victim difficult if it is within 20cms of the transmitting unit, but it does no permanent damage to the actual beacon. It is quite simply that the "noise" is so loud that the "beep" cannot be heard by a searching beacon.

The only issue with doing a trailhead check in extremely close proximity--or touching--is that there is a chance the beacon being tested has a broken antennae or other problem that cause it to have a WEAK signal. In this case the receiving device will still "beep" and produce a low number on the screen, even though the signal isnt strong enough to detect normally in a real beacon search--a "false positive" so to speak.

So, if you chose to do a beacon check in this manner (we at Mammut refer to this as a SEND CONFIRMATION) be aware that you have confirmed a 457 kHz signal, you simply do not know anything about the strength of that signal.

A "Send Confirmation" is an
appropriate test when you have a high level of confidence in the unit being tested, perhaps because it is part of a fleet that receives regular diagnostic testing (as the Tester 2.0 is capable of doing). When doing a trailhead check with an assortment of units, this not the best practice.

Enter "Group Check." This is a specific function found on many modern avalanche transceivers. Group Check Accomplishes multiple things:

#1: You check that the strength of the unit being tested is adequate to transmit at the manufacturers recommended search strip width (verbose for, you have confirmed adequate signal strength). You now know, if the unit being tested has a recommended search strip width of 70m, that you can count on that. You have essentially done a range check.

#2: You have de-activated the beacon's attempt to "lock" onto any one transceiver. Remember, beacons with a marking function will identify the strongest signal--usually but not always the closest signal-- and then lock on to it. This is a helpful function for simplifying multiple burial searches. But for a trailhead check this feature causes confusion. Additionally, the List of Buried Subjects can only accommodate 15 transmitters. So, if you attempt to do a trailhead check with a very large group your list can max out and not give you any information about user 16, 17, etc.

In fact, done properly, a proper Group Check at 1 meter will verify that the sending beacon's recommended search strip width is accurate to its' manufacturers specifications. You have essentially done a range check as well, and confirmed the strength of the signal is up to the job. Much better than the aforementioned Send Confirmation.

The "Group Check" option appears during start-up. Click on the orange button on the from tof the beacon at this time to access the Group Check Mode. This is the only way to access Group Check. 


Once you have entered the Group Check Mode you will see this screen. It demonstrates how to properly perform the test. To return to send, press the Orange button at this time.


If you refuse to maintain a 1 meter distance during Group Check, you will see this screen. Nonetheless, this can be an effective way to do a test if you are only interested in Send Confirmation (for example, when you have frequently tested fleets.)


Essentially, Group Check is not different than putting your Barryvox S into Analog Mode at gain setting 4. In fact, many guides already use the analog mode during the trailhead check for this very reason. Mammut choses setting 4 because it is the perfect setting for a 1 meter distance, which is convenient for the task at hand.

There are times when a proper Group Check at 1 meter is inconvenient and unnecessary. If you are confident in integrity of your fleet then a Send Confirmation is faster. To accomplish this you should still be in Group Check mode. Your beacon will tell you that you are too close, but you can disregard that warning and simply pay attention to the number. This technique will certainly get 50 ski patrollers out the door faster and is sufficient when Diagnostic Testing has been performed at regular intervals.

However, if you are guiding 6 new guests and they all show up with their own gear, a Group Check at 1 meter has significant advantages. This does not need to be performed in this manner every day, but certainly is a great idea on day 1.

Our Pro Check function is another advanced feature (only available if your Barryvox S is in Pro Mode) that will test the Frequency (457 kHz, +/- 80 mHz), the Pulse (time in milliseconds of ON time) and Period (time of ON/OFF cycle in milliseconds.)

So, to bust the myth, beacons can touch, kiss, and get all sorts of hanky-panky. Just know that extremely close proximity tests are limited in what they accomplish, and Group Check functions have a lot of merit. Send Confirmations may be sufficient in some circumstances, but are not always the best practice when checking beacons before going in the field.


2 comments:

  1. I am slightly confused... I thought that the searching unit was the one with a recommended search strip, not the sending unit. In other words, that the search strip is a factor of the searching unit's sensitivity. I understand that the signal needs to be strong enough to be picked up, of course, but do we have to worry about knowing which beacons someone is wearing and adjust our search strip in consequence?

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  2. You are correct, the receiver determines range and search strip width. You never have to adjust your search strip width in regards to what you are searching for.

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