Wednesday, December 26, 2018

Pro Check in the Barryvox S

The Pro Check feature is an extension of the Barryvox S Group Check that is available only when the "Pro Search" capability is activated.  Instructions for activating the Pro Check function are in the Barryvox S Extended Reference Guide.(link).  This new feature is intended for guides and advanced users to have visibility of all the relevant parameters of each transmitter within their group, as a tool to identify when the parameters of one transmitted signal might cause searching problems such as shortened range or a higher incidence of signal overlap within the group. It's not something most rescuers should use every day and it is not considered a “critical check” like the group check.
The Pro check is an additional option available in the Pro Settings of the Barryvox S.  It tests all parameters of the transmitted signal of another transceiver to identify a signal that might be out of tolerance or cause problems during a search.  The parameters shown are that of a new Barryvox transceiver and represent an ideal signal because: 1) the frequency is within the norm requirements, 2) the period is relatively long which reduces overlap; 3) the pulse is very short, which reduces overlap, and 4) the pulse is slightly above the required minimum in order to provide plenty of time for a searching transceiver to measure the signal for accurate distance and direction.

Most guides and professionals would use Pro Check with an unfamiliar group of transceivers once at the beginning of a trip to get a better quantified (rather than qualified) idea of  the signals within the group and how they may react with each other, or to help diagnose what’s causing a problem during a practice search. 
After this initial check the standard Group Check mode is recommended for everyday use.  Note that since Pro Check is not a calibrated test it is not a substitute for running each transceiver through the manufacturers diagnostic equipment on the recommended schedule. Mammut recommends that every Barryvox transceiver get a calibrated functional test at the country Service Center at least once every 3 years or 3000 hours of use, and we offer this service in both our US and Canadian Service centers, as well as in Europe.   Many large fleet operators maintain their own Barryvox tester  as well.  

To best understand how to use Pro Check some background is helpful. All avalanche transceivers worldwide adhere to the same standard, or “norm” (link). This norm ensures that all brands and models of transceivers function reliably with each other. Although all manufacturers use the same 457 kHz frequency band, there are still many older transceivers in use and every manufacturer uses a slightly different cadence of signals because doing so provides that transceiver with slightly different characteristics and capabilities when searching and when being searched-for.  Rescuers should be aware that each different signal within the norm parameters will always work with other transceivers, but each different signal can create different scenarios when in combination with various other beacons—many of the questions we get can be traced to this issue, 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. 

They are:

Figure 1:  norm parameters tested during Pro Check.  Click on the photo to see it larger.

Freq: This is the transmit frequency of the beacon--457kHz, +/- 80 Hz. If you have a beacon that is out of transmit tolerance, it can exhibit as being difficult to RECEIVE that signal when searching at your normal max search strip width--so a beacon that is very close to 80Hz off might be a reason to assume a shorter search strip width than normal, or you might just ask a client to use a different beacon for that trip to ensure maximum search effectiveness.

Period: This is the length of time of a full cycle of one Pulse [“on time”] plus the length of gap 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” 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: This is the length of time that each transmitted signal lasts—The “on time”.  Although it's not a "beep", think of it as the difference between a long "beeeeeeeep" versus a short "beep". The norm dictates the pulse must be a minimum of 70ms. In this case very long pulses as you would see with an older analog-only transceiver result in frequent 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 a searching transceiver to measure each signal for very long—this can lead to less reliable signal acquisition and distance/direction indication, especially in poorer coupling orientations.

Relative to both signal Period and Pulse, multiple beacons within a group with very similar signals, once overlapped, can take a long time to separate. Identifying when this is happening before it becomes a problem is the key, and a long-duration overlap is frequently the issue causing beacons to appear to not be picked up during a practice search. This situation is exactly why Mammut recommends the “Pro Search” function to advanced rescuers.  Most manufacturers of modern transceivers agree that the "best" signal is one with a long Period, and a Pulse that is slightly longer than the minimum--this accomplishes both minimizing signal overlap in combination with other signals, as well as provides enough time for any receiving transceiver to fully measure that signal with all antennas even when coupling isn't ideal.  Also, most manufacturers of modern transceivers utilize multiple slightly different signals within one model of transceiver specifically to optimize for signal overlap.  As an example, Mammut utilizes 10 slightly different signals because having different signals shortens the duration of any overlap that does happen.

The guidelines above about issues caused by various signal parameter-lengths are simply rules of thumb, and Pro Check is designed to be a tool to give you visibility of this so you can anticipate any issues and so if you do find any issues in a practice setting you can perhaps have a better idea of what some of the major factors that can cause them are. These factors are in large part what is behind many common beacon searching problems that even highly trained professionals don’t realize, so we are hoping to give people a tool to make this more transparent.

Some people have reported consistent Pro Check Pulse “out of tolerance” readings with specific model transceivers. This can happen when measuring a signal that is at the absolute minimum Pulse length allowed by the transceiver norm, especially in combination with unfavorable coupling positions between the sending and testing device. For this reason make sure to perform the Pro Check in an ideal antenna coupling between both devices, as indicated on the device screen in the Pro Check mode and in Figure 2 below.  Should you encounter the described situation the “Pro Check” result will be an out of tolerance “pulse” test, usually in combination with a very short measured Period in the 700’s – 800’s ms range (the absolute minimum period allowed being 700ms). 

If a transmitting beacon has too short a pulse it is possible a searching transceiver will have difficulty obtaining complete signal measurements, leading to less-reliable distance and direction information. This is why it is important for a transmitters' signal to have a Pulse within the Norm requirement--because a receiving transceiver needs as much time as possible to measure the signal with all antennas.  However, on some transceivers the signal is as short as is allowed right down to the last decimal--this allows a searching beacon to receive more signals faster which can make the perceived update rate on a searching transceiver slightly faster, but it can cause problems because there is only an absolute minimum amount of time possible for any searching transceiver to get enough information from each transmitted signal to provide reliable search direction. The norm dictates the duration of a transmitted signal must be at least 70ms—the beacons in question typically send exactly a 70ms Pulse. Even an additional couple milliseconds would make this signal more optimized with regard to providing other searching transceivers with enough info to provide reliable distance and direction indication, while still maintaining exceptionally good update rates and minimizing overlap. We don’t want to simply “OK” a beacon that tests at 69ms because a too-short pulse length can cause problems in providing accurate search info.  In this case the Pro Check result is often a “false negative” if conditions for measuring are not perfect. Because Pro Check is a non-critical pro or advanced-user-only function, we think this is preferable to a false-positive—the professional user group who has activated this function is exactly the group that has the knowledge and discretion to make an informed judgement of how to use this information and whether it warrants taking action.

The image shows a Pro Check result that could be a false negative.  Note the Pulse measurement is out of tolerance, and the Period is at the extreme low-end of the norm requirement.  The tested transceiver has a Pulse of exactly 70ms, which, due to less than perfect antenna coupling was measured as out of tolerance.  A false negative can be verified using the quick secondary test below.

If you encounter an out of tolerance Pulse measurement during Pro Check (usually with a measured Period in the 700’s-800's range), then here is how you can verify a false-negative:
·    For any beacon, this information should always be used in conjunction with a group check using the “Group-Check” mode .  Assuming a good Group Check with the expected receiving range, if you get what you suspect to be a "false negative" Pro Check result, utilizing a quick test can differentiate between a beacon with a 70ms Pulse versus one that is truly out of tolerance:
o   Put the transmitter being tested in SEND, and the receiving transceiver in ALTERNATE SEARCH mode, at least 3-5 meters apart (to ensure the fine-search cross icon does not activate).  Make sure the two transceivers are oriented in parallel as shown in fig. 2 for best coupling.
o   Let the distance and direction indication settle and note the arrow direction and distance. 
o   Physically turn the sending transmitter 90-degrees, as shown in figure 2.
§  If the distance decreases and direction indication turns, then the signal pulse is long-enough to allow proper measurement, and a daily “Group Check” should suffice for the remainder of your trip.
§  If the distance and direction indication does NOT change to reflect that of the transmitter orientation, then the “Pro Check” results indicate a Pulse that is actually out of tolerance, which should be tested by the manufacturer. 

Figure 2Additional quick-test to verify a "false negative" Pro Check result.  In the image, on rotating the sending transceiver 90-degrees the distance decreased and the arrow changed direction as the transceiver moved--this indicates the sent signal is long enough to measure on multiple antenna axes.  

Again, this allows you to not only test the presence of a signal (what we at Mammut refer to as "Send Confirmation") it gives you a great deal of information about the integrity of the signal. Although it's not intended to replace regular maintenance, if a transceiver does not receive regular diagnostic testing from the manufacturer this function allows you to have confidence in that beacons signal. Accordingly, this is a very useful tool for guides testing unfamiliar client beacons, or simply a way to test your friends beacons to ensure that they are not just working, but working well.  
The advanced rescuer using “Pro Check” should simply be aware that in a multiple burial situation involving searching for any combination of beacons where one transmitter has an extremely short Period or very long Pulse it is more likely that you will encounter signal overlap, and if you have multiple transmitters with nearly the same pulse and period in a group, that any overlap that does happen may last quite a while.
The rescuer can anticipate any difficulties this causes by utilizing the “Pro Search” function during any search and doing 10m and 3m tone checks to verify that the digital display info matches the tones heard, and if they do not match switching to alternate mode to search using an alternate search method such as Micro strips or Micro box. These are the same techniques a rescuer would use in any such situation (link), the difference is that due to the transmitted signal of these devices being less optimized for minimizing signal overlap such a situation is more likely, and more likely to last longer, and will affect any beacon utilizing a marking function.

We hope this helps you to make informed decisions about the Barryvox S “Pro Check” function, and how to use it and how to interpret the results. If you have further questions please give us a call.

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