Tuesday, March 19, 2019

About The Supplementary “Pro Check" Feature in the Barryvox S

To best understand how to use Pro Check some background is helpful. All avalanche transceivers worldwide adhere to the same legal standard, or “norm”. This norm ensures compatibility between all transceivers worldwide, thus every transceiver is able to search for others and to be found by others, independently of the transceiver brand and model. Although all manufacturers operate under the same standard, there are still many older transceivers in use and every manufacturer applies slightly different transmit parameters within the legal framework.  Rescuers should be aware that each different signal within the norm parameters will always work with other transceivers. Some differences between individual signals, in particular in pulse rate, is even an advantage in multiple burial situations as it reduces the likelihood of persistent signal overlap. At the same time, each different signal can create different scenarios when in combination with various other beacons—many of the questions we get can be traced to such issues, so we want to provide people with a tool to see what may be driving the way their beacon interacts with other beacons.

The three parameters you'll see tested in Pro Check are defined by the international norm for avalanche transceivers as shown in Figure 1. 

Figure 1:  Transmitter parameters ETSI 300718 


Frequency (Freq): This is the transmit frequency of an avalanche rescue transceiver: 457kHz. The legal standard allows a tolerance of +/- 80 Hz. For additional safety the Barryvox digital signal processor receives a wider range of frequencies than the norm allows transmitters to send within, but a transceiver that is out of transmit tolerance always leads to a lower probability of detection and thus unnecessary complexity and uncertainty when every minute counts to save your life! 
As devices often shift out of tolerance over a longer period of time and not as a sudden event, features like Pro Check may be used to detect developing problems before they show a serious impact. 

Period: This is the length of time of a full cycle of one pulse [“on time”] plus the length of gap (pause) in between transmitted signals [“off time”], measured in milliseconds (ms).  The norm is 1000ms +/- 300, in other words 700ms- 1300ms. There is a risk that a period under or over the norm length could be interpreted by the searching beacon as “not a signal from an avalanche transceiver” or even as “two signals” (although you would still hear the analog tone with Pro Search activated). Also of note, a signal with a shorter period will always cause overlap more frequently than one with a longer period when in combination with any other transmitter, especially in combination with a longer pulse.  

Pulse Length: This is the length of time that each transmitted signal lasts—The “on time”.  The norm dictates the pulse must be a minimum of 70ms. Very long lasting pulses, as you would see with older analog-only transceivers, result in more frequent and more long lasting signal overlaps when in combination with any other transceiver. This means that having one older transceiver with a long pulse in your group can make searching more difficult for every other transceiver in that group should they become buried within range of each other. On the other hand, a pulse shorter than the required 70ms minimum doesn’t allow sufficient signal acquisition time for the searching transceiver, which may lead to issues like inaccurate distance and direction indication or even failure to be recognized as a signal by another avalanche transceiver. 

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