Jonathan’s WildSnow Beacon Test Notes

Post by blogger | July 14, 2009      
Avalanche Beacons

Avalanche Beacons

WildSnow Beacon Reviews Intro and Index

[January 2012 Update: Some small revisions throughout, plus an additional section for the new 5-25/5-20 Walk-the-Line Test]

Much of the basis for my reviews comes simply from lots of practice, often running searches in unusual or demanding circumstances. I’ve also run the beacon practice stations at various avalanche courses and ski patrol events, which provide an interesting opportunity to watch how other backcountry skiers react to different designs. I find this to be especially important, since often a feature that seems intuitively obvious to me will nevertheless baffle other users.

With that caveat aside, here are some brief descriptions of my formal testing. I also solicited feedback from all the beacon companies, and received very constructive information from all.

User Friendliness
The very first thing I do when I get a new beacon is try to conduct a search without reading the user manual. Now to some extent I’m already somewhat familiar with the beacon design from what I’ve read beforehand. But I feel that the ability to use a beacon without any user manual familiarity is a good test of the inherent ease-of-use of the design. (Plus how many typical users are really going to read their beacon’s user manual carefully?)

Electronic Interference (RFI)
I conducted three types of tests for potential electronics interference.

First, I set up a target beacon to transmit, and then set up a nearby semicircle of test beacons in search mode. I approached each beacon with a GPS, a digital camera, an FRS/GMRS radio, and a basic CDMA-band (e.g., Verizon) cell phone, one at a time. While doing this I noticed no changes in the searching beacons’ displays.

Then I repeated the testing  with the FRS/GMRS radio and the cell phone making a call. Noticeable interference occurred in some,  but not all models,  with ghosting,  distracting noise, incorrect directional indicators,  and other problems.

Next, I added an iPod to the mix of devices:   now the interference was much worse, and occurred in all beacon models. My conclusion: never tour in potential avalanche terrain with an iPod! The potential to have the iPod still on (yet not noticed) during a search could cause serious problems with any avalanche beacon.

I tested a “smart” phone, specifically an iPhone, which runs on the GSM band (i.e., AT&T). I changed my testing protocol this time to mimic my prior range tests for initial signal acquisition, i.e., start from far outside the acquisition range and then keep walking straight toward the target until a signal was acquired.

I held the iPhone (while making a call, although this probably doesn’t make any difference, since the actual cell transmission band is unlikely to be the source of the interference) close to the searching beacon. I tested three beacons, all of which fared far worse than with the previously tested electronics devices.

Specifically, the Pieps DSP immediately ghosted with its symbols for more than three victims, a distance readout of about four meters, and nonsensical directional indicators. I stopped the test right there,  since clearly the actual victim would be impossible to find with that kind of interference.

The Ortovox S1 immediately yet briefly ghosted, but then the screen cleared . . . and stayed clear until I was less than four meters from the actual victim:  this was even more scary, since the searcher would be entirely unaware of the interference problem.

The Barryvox Pulse ghosted, but seemed to fare a bit better than the others, although the interference was still a serious problem. Given the obvious problems caused by a “smart” phone, I didn’t bother testing any additional beacons. My conclusion: keep any “smart” phone entirely off while touring in potential avalanche terrain!

Lastly,  I tested whether an iPod or iPhone could interfere with a victim’s transmission. Instead of merely placing the target beacon (which here was a Pieps Freeride) on the snow, an assistant held the beacon pointing toward me, but also held either an iPod or iPhone close to the transmitting beacon. My range results while searching with an S1, DSP, and Pulse were the same as when the beacon  was on the snow with no electronic devices on either end. My conclusion: if you care only about yourself  (i.e., your ease of being found), then feel free to play those tunes and chat away!

Box Size
My pinpoint phase accuracy test was inspired by an avalanche beacon review in the New York Times last year. As a native North Easterner, I feel obliged to take seriously everything the NYT writes, even on subjects where its editors probably know absolutely nothing. The NYT review commented on the large “box size” of one model, so I devised a test to attempt to replicate such results, as shown :

Avalanche beacon testing.

Avalanche beacon testing.

I suspect this would matter only if a full burial were somehow still relatively shallow. Therefore, although I report the results, and although they vary widely among beacons, I don’t think they’re very important.

Range for Initial Signal Acquisition
You would think range testing would be relatively straightforward.  So did I. Wrong.

The first problem is what to count as initial signal acquisition. In general, I did not count a brief signal acquisition that then immediately disappeared (which often happens, i.e., a kind of brief “blip” that has you thinking, “wait, what was that?”).  But if the acquisition was continuous, I then stopped my slow advance toward the target beacon to record the distance.  By contrast, what to count as initial signal acquisition for analog acoustics is even far more subjective, but in general I counted a faint yet distinct “chirping” against any background sound.

Another problem is that many beacon models keep coming out with new firmware upgrades, which means having to run new range tests (as well as other tests). I appreciate their continuous innovation, but it sure complicates testing!

Next wrinkle is coupling – no, not that type of coupling (this is a family-oriented website!), but rather the orientation of the victim’s antenna (all beacons transmit on only a single antenna) relative to the orientation of the main axis of the searcher’s beacon’s housing (which can contain up to three receive antennas).  So, do you test range during optimal coupling or worst-case coupling?  My answer is, yes!  In other words, I test for both, but focus only on the latter, as I think worst-case coupling is more important especially in establishing the minimum range that you can rely upon consistently (i.e., the search strip width).

The Tricky Perpendicular Search
I set up a tricky perpendicular search to test the respective abilities of the Pulse’s 360-degree rotating arrow and the S1’s grid-like screen to accurately locate a beacon whose transmitting antenna is pointing directly at the searcher while the searcher is pointing at a 90-degree angle to the transmitting beacon. I also included a DSP in this test just to confirm my hunch as to how a “traditional” beacon with a more narrow arc of directional indicators would perform.

Imagine an avalanche path or deposition zone that is twice the width of a beacon’s range in worst-alignment coupling. The victim is buried at the extreme edge of the beacon’s range, with the transmitting antenna pointing toward the center of the slide path. The searcher enters the slide path with the beacon pointing toward the center. I attempted to replicate this scenario by approaching a target beacon that was pointed toward me, but with my beacon at a 90-degree angle to the target.

Close-Proximity Triple-Burial (Signal Separation Models Only)

Multiple burial beacon test.

Multiple burial beacon test.

I have run many informal tests for the signal separation capabilities of the various marking/masking/flagging models, but I also set up the formal test diagrammed to right for a close-proximity multiple-victim burial.

Looks like a nice controlled test, but unfortunately this is still subject to significant variation. Why? In [very] quick summary, because of ever-shifting signal overlap, each test was actually different, as each test beacon was facing a different set of signals with respect to their timing with one another. Nevertheless, after at least several trials with each beacon, consistent differences between models become apparent.

Marking/Masking/Flagging Trade-Offs: The Triangle Range Test
I set up a triangle range search to test see whether the impressively reliable marking/masking abilities of some signal separation beacons might compromise their respective abilities to locate another beacon toward the edge of their initial signal acquisition ranges. I included the DSP to see whether its less reliable (though much improved over various firmware versions) marking/masking/flagging had the benefit of not compromising its ability to search for other beacons in a real life backcountry skiing avalanche accident.

Imagine a large triangle, with the searcher at one end, and a transmitting beacon at each of the other two ends (pointed toward the searcher’s end). The sides of the triangle are long enough to be toward the outer end of initial acquisition range (taking into account coupling alignment). The searcher walks toward whatever target the searching beacon gives priority. Once at the first beacon, that beacon is marked, and then the searcher sees whether the searching beacon can find the second transmitting beacon. If no signal is shown by the searching beacon, then the first target beacon is turned off, just to verify that indeed the problem with signal acquisition was caused by the focus on the first beacon, and not a range issue.

This test has now been discontinued in favor of the more demanding yet still realistic and quite revealing:

Marking/Masking/Flagging Trade-Offs: 5-25/5-20 Walk-the-Line Test
I have now discontinued my Triangle Range Test in favor of this new test to see whether the impressively reliable marking/masking abilities of some signal separation beacons might compromise their respective abilities to locate another beacon toward the edge of their initial signal acquisition ranges.

This test sounds really easy, but the results can be surprising (in a bad way). Place the Far Target beacon 25 meters from the starting point, with its transmission antenna (typically in line with the long axis of the housing, though BCA beacons are at 45-degree angles, and Ortovox 3+ and S1+ beacons have the ability to shift among two perpendicular antennas, so they make for poor targets in tests like this) perpendicular to the searcher’s direction of travel. Turn the test beacon to Search. The test beacon should quickly acquire the signal of the Far Target beacon.

Okay, that was easy. Now let’s make it less easy. Turn the test beacon back to Transmit. Place another beacon, the Near Target beacon, 5 meters from the starting point. (Orientation doesn’t really matter since it’s so close — goal is keep the Near Target outside the 3-meter final search phase, but close enough so that its signal is very strong.) Go back to the starting point, and turn the test beacon to Search.

Any test beacon will lock on the signal of the Near Target. The Pieps DSP / DSP Tour will also pretty much right away show two victim icons, then once you take a few strides and mark the Near Target (which often will take two tries with the button), it will show the distance and direction to the Far Target. Sounds pretty easy, right?

Other signal separation beacons I’ve tried with this test will initially show only one victim symbol. Once the Near Target is approached and marked, even after taking several more strides so that the test beacon is partway in between the Near Target and the Far Target (i.e., the “Far Target” is no longer all the far away), the time for the second victim symbol to appear plus provide directional and distance information has varied from a few seconds to a few minutes.

Sometimes I’ve walked all the way up to the Far Target, standing directly over it, and counted out the time until I finally received a signal. I’ve even had one beacon often receive a second signal, but unfortunately the signal was not for the Far Target, but instead for the Near Target: following the beacon’s information, I reversed direction and went back to the Near Target to mark it again. [Note that I’m not providing results here for particular models, but rather in the individual beacons reviews — my vague references to various beacon beacon behaviors are just to provide examples of what these tests can reveal.]

Changing this test from the 5-25 variation to the 5-20 variation (i.e., the Far Target is only 20 meters from the starting point) makes this test much easier for the other signal separation beacons to perform well.


That’s it (for now). Also, remember that all of these tests are designed to examine the performance characteristics of new beacons that are presumed to be in good working order. By contrast, if you have a suspect older beacon, then check out this post:
Older Avalanche Beacon? How to Test It

If I can provide any clarification feel free to leave comments.


Please Enjoy A Few Suggested WildSnow Posts


10 Responses to “Jonathan’s WildSnow Beacon Test Notes”

  1. Kevin July 14th, 2009 6:13 pm

    In your write up I did not see a test of the iphone Avi beacon application that Wildsnow reviewed on April 1st 🙂

    On a serious note I must say the mere thought of having a cell phone on while in the back country is troubling. But when I come down Vail pass and see all of the tracks on one of the more deadly exposures in this country it becomes more believable that folks would leave their phones on knowing they have coverage in this area.

  2. Mark July 15th, 2009 8:43 am

    Testing for interference with things like iPhones, iPods, cell phones, and the like is certainly smart. It is a little frightening to note how some of these devices foul up beacons’ functions.

  3. Andy_L July 15th, 2009 10:29 am

    Lou & Jonathan,

    The interference info is critical stuff! Linked over to you, and I’ll try to remember to bring it up again when winter’s here.

  4. Jonathan Shefftz January 3rd, 2010 9:48 pm

    I recently ran some add’l RFI tests, with some interesting results, both concerning new devices and new beacons (or rather, combinations I hadn’t previously tested of new devices + old beacons).

    First, previously I had found that a CDMA (Verizon) basic phone (i.e., makes phone calls and does nothing else) does not cause interference when on yet not transmitting, and does cause interference when transmitting. However, this time I happened to notice that the phone briefly causes interference when being flipped open, even when not making a call.

    Second, previously I had been unable to detect any interference from a Garmin 60Cx GPS unit. This time though I tried the GPS when some old M2 and F1 beacons (which are generally not the subject of my various tests). When held very closely, the GPS caused interference.

    Third, a tried a Spot satellite messenger, second generation. When on, but not attempting to send a message, no interference. When transmitting a message, caused interference in some beacons.

    Overall, my conclusions from all this are that:
    – RFI issues can be very specific to certain beacon + device combinations; and,
    – RFI is often not caused by transmission but rather by power issues.

  5. Bruce Cheshire March 31st, 2010 2:38 pm

    Was the iPhone ‘on’ during your test? Did you happen to test it with the Airplane mode on?

  6. Jonathan Shefftz March 31st, 2010 7:01 pm

    The iPhone was on, but not making a call.
    Given that my electrical engineer friend thinks the interference has nothing do with the signal, and instead is related to the power step-down (apologies if I mangled the techno talk there), then I strongly suspect that the airplane mode would still produce the same interference.

  7. Sharon December 19th, 2011 4:44 pm

    Interesting article. I guess you didn’t test other smartphones (android or blackberry) but assume results would be similar?

  8. Jonathan Shefftz December 21st, 2011 7:23 am

    I’ve deliberately shied away from reporting on a various combinations of consumer electronics and individual beacon models, since the number of combinations has no end in sight, and the results are potentially misleading.
    Bottomline is that “smart” phones have some very scary potential interference problems, if you’re touring with your phone on, remember to keep lots of distance between phone and searching beacon.

  9. Jonathan January 5th, 2012 2:23 pm

    Just a quick comment to note that I’ve made some small revisions throughout, plus added another section for the new 5-25/5-20 Walk-the-Line Test.

  10. Matt February 11th, 2012 2:19 pm

    Great article. I, and many others, are guilt of this… thanks for the information. I’ll definitely be changing my habits.

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