Avalanche Mobile Phone detection

A snowHead

Haggis_Trap, I should have made it clearer that I essentially support your position, but you weaken a strong case by overstating it. The comparison with Recco was to see if the proposed new search tool would offer any advatages over that system - and other than a possible sensitivity advantage it's not immediately obvious that there is. The heli example was to show that the Recco system does appear to have a very useful sensitivity already, and it is rather more useful than a chocolate teapot in that being able to track from a heli gives a huge advantage of mobility. Yes, it does then depend on heliservices being available, but I guess I saw about half-a-dozen helis a day (at least) when I was last in St Anton, and there are always some flying around Chamonix. As davidof confirms, Recco is no longer just a dead body locator, even though companion rescue should be the first line of defence (well 2nd actually - not getting caught in the first place should be the first line). And, in the vein of not overstating the case, the X1 is the spawn of the devil, and would be a disgrace to the noble calling of chocolate teapots Wink

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Steilhang, if you're the electronic engineer you claim to be, you should know that a 32kHz clock, unless it's a pure since wave (highly unlikely), will be radiating at dozens of harmonics of that frequency. 457kHz is between the 14th and 15th harmonic, so any approximation of a square wave will be radiating plenty of energy there, even if there are no other divided/multiplied signals in the design. (There appears to be a +/-80Hz spec on the transmitter frequency, but I don't know what spec if any there is on the receiver bandwidth, and rate of rolloff away from the centre frequency - i.e. how far away from 457kHz a signal needs to be before it will be say 30dB down).

I've just run a test using my Mamut/Barryvox Pulse. While the mobile is switched on it registers as a transmitter of indeterminate location and distance - the distance reading does decrease the closer the beep is to the phone, but those distances do not match. (Not that it would apply on the mountain, but there was also interference from my laptop, the laptop power supply and the wireless hub). Of course none of these broadcast the analogue beep, so would not be found using an audio tracker, but there was a significant level of background noise. To claim that a phone only interfering with a transeiver in receive mode is not a problem is ridiculous - if you're searching then your transceiver is in receive mode, and if the victim has a phone transmitting it's going to affect your reception. Yes, this is a case where your F1 will have an advantage over a digital, and if you're basing your argument on the F1 performance then I can see why you're holding the position you do. But that is extremely short-sighted, given that the vast majority of transeivers are now digital.

The way in which interference can mess with the digital direction/distance location is one reason why I will only ever use beeps with an analogue fallback facility - and know how to use it; if all else fails I can always go back to first principles. I have had experience of an X1 getting completely confused and being completely useless (and the UIAGM guide with me could not get anything useful out of it either).

A snowHead

The 32.768kHz quartz crystal WILL be oscillating with a pure sine wave - that's all it can do. Sure, the electronics will square this up (generating odd harmonics only) and then divide it down. However, the circuit actually doing this will all be on one chip and will be just microns wide and generating little interference. Steilhang's assertion that the rest of the phone is shut down is a reasonable one so it'll be doing even less than your digital watch is - that also operates from 32.768kHz.

But yes, when it wakes up, the phone will probably wreck havoc.

Well, the person's real but it's just a made up name, see?

OK, but something is clearly radiating - as the fact remains that there is a) a significant change in the audible background from the transceiver as it's brought near the idle phone (Samsung D600) and b) an indeterminate "body" that disappears when the phone's turned off.

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Haggis_Trap, I just looked at your Pieps reference - it does not say not to have your mobile switched on, it actually just says that there is an effect if the mobile is 5cm or less from the Transciever so you should maintain a separation (which I do - transceiver on my left, phone on my right).
Just going to look at the others.

Anyway, snowHeads is much more fun if you do.

Haggis_Trap, Your second reference did say this:

"It is preferable to turn off your electronics when transmitting. If it is not practical to turn them off, always keep them at least a few inches away from your transceiver. Metal objects should also be kept away from your transmitting beacon (e.g., pocket knifes, additional transceivers, etc).
When searching, the electronics and metal objects should be further away from your transceiver. Tracker says at least 15 cm (6 inches), Ortovox says least 30 cm (12 inches), and Barryvox says at least 50 cm (20 inches). My informal testing leads me to feel that Ortovox's 30 cm (12 inches) is a reasonable minimum. Of course, it is best if you turn the devices off (which is what most manufactures suggest), but turning off radios and cell phones during a search is not always realistic."

So in future I will certainly switch off my phone (if it is on) while searching.

Another of your references says : " But no beacons suffer RFI from an on-yet-not-transmitting phone or two-way radio." But he does warn against playing an iPod while skiing which several peole mention as being worse - a point I have not seen before (but doesn't affect me).

I'll have to think about reducing the times I have my phone switched on - just to when it seems necessary (eg skiing in trees or someone going ahead to check direction or safety, or when someone seems to have got lost or I've lost the others) since in the heat of the moment when searching I might well forget to switch off my phone.

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I usually leave my phone turned off while skiing for equally important reasons - to prevent anyone from work calling just to check on something wink

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GrahamN, wot altis said! Especially the bit about your watch!

After all it is free

I've just repeated the test and come up with mixed results. Went down the bottom of the garden as there's all sorts of interference within the house this evening (and a particularly strong radiation source from the other side of my party wall - maybe a plasma TV?). Took the watch off as well, so nothing electrical within about 30 yds, other than the phone. Move the phone, in idle mode and screen blank, near the transceiver (or move the transceiver close to the phone)and get an audible increase in background and false positive detection. Repeat the procedure with the phone turned off and no effect. So that clock, or whatever, is very definitely causing EMI. The false positives take about 30 secs to clear (I've noticed before that this device does expect whatever it's searching for to be stationary and constantly on - it really doesn't like the world around it changing).

Keep the phone more than about 30cm away from the transceiver though and the interference does not give rise to the false positive, even though the increase in background is just about audible. Also tried making phone calls, and that didn't seem to make much odds either. This does go a bit against what I was finding this lunchtime, and is also contrary to what I found on previous exercises (e.g. when we had a session in Richmond Park and were playing with rob@rar's equipment Wink

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Also tried with the digital watch. No observable effect on the transceiver even when touching, until turning on the backlight, when a false positive was registered about half the time (distance about 10-20cm).

The false positives from the phone seemed to be pretty reliable. While not a particularly relevant observation, those from the other interference sources within the house seemed a bit random - sometimes they were all over the place, and sometimes just registered as high background level. I guess it all depends what chance modulation patterns may be on them at any particular time.

So a bit of right on both sides. Yes it does cause interference that can result in false positive detections, even when the phone is idle. But keeping more than 30cm away (at least in this test) showed no false positive effect.

Unfortunately I don't have a second beep to act as a transmitter to see whether there was any effect on ranging/detection ability.

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Mobile Phones uses radio frequency (RF) to communicate with a base station and detect incoming calls / SMS. Even when idle mobiles still scan the airwaves to look for incoming data. An Avalanche beacon is a sensitive device for detecting changes in magnetic flux. Go figure what could happen...

Additionally the processors in avalanche beacons are very simple and slow - primarily to maximise battery life.
So they dont react very quickly to changes in magnetic flux. They expect to be following a constant flux pattern. The fact GrahamN had to do his experiment outside tells you something...

Here is a final pdf for anyone who may still be in total denial that EMI interferance might cause a problem -

http://www.pieps.com/images/stories/news/2009_Hinweis-Handy/ICAR_Statement_20090207_EN.pdf

Given the potential risk I personally choose to keep my own phone off.

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So if we are so worried I guess all Ski Patrol, Heliski Guides, Rescue Squads etc should turn their two was radios off in case there is interference. Wake up everyone this is not a perfect world we live in and the amount of interference from phones and radios is minimal if you maintain some small separation. A little bit of common sense would go a long way. If you read the manufacturers info is says there "might" be a problem. Sounds a bit like corporate bum covering rather than a statement of fact. When I am on the snow I often have beacon, phone and radio on at the same time and have done plenty of training with all this electronics on both the rescuer and "victim". No problem making the finds.

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^ Many UIAGM guide will ask clients to switch their mobile phones & radios off when skiing.
Only skied once with a guide myself (2004) - and he defn asked us to switch phones off in the cable car.
Never been heli skiing, but I presume the same applies.

GrahamN, experiment over theory every time!

You know it makes sense.

laundryman, ideally the two coexist in perfect harmony Wink

Otherwise you'll just go on seeing the one name:

I retried the experiment with my two (ancient) F1s. Similarly to GrahamN I went down the end of my garden to avoid interference from other sources. The results are that with the mobile phone in my pocket and the searching F1 in my hand ( about 30-40cm ) there was no discernible interference from the phone and the beacon lead me directly to the target. With the phone at a distance of about 1cm from the beacon I did however pick up a false target. I guess there will be differences from one phone to the other so this cannot be taken as definitive. For me that is sufficient proof that my phone at least will not hamper any search that I'm (hopefully never) engaged in!

I tried the same thing in the cellar of my house and was picking up all sorts of signals from power lines in the walls etc. So much so that I doubt I could have found the target in a real life search! I guess the moral of the story is : don't get buried in your house wink

A snowHead

On the subject of my ancient F1s, any recommendations on an idiot proof replacement for them? What's the current state of the art in beacons?

A snowHead

With practise the old F1 is just as quick as newer digital models.

The BCA Tracker is one of the easiest digital beacons to use - really intuitive and simple.
And they just brought out the Tracker2, which is very similar to the classic original model.

If I was buying a new beacon I would probably get the Mammut Pulse.
Really impressed with it, again easy to use - but it copes with (hopefully rare!) multiple burial scenarios way better than older digital beacons.
The Ortovox S1 is also worthy of consideration.

Well, the person's real but it's just a made up name, see?

So what differentiates the digital models from the old analog ones? Do they include some form of distance measurement and if so how does that work? Is it based purely on signal strength or is there some two way communication going on between the searcher and the transmitter, or do they derive a common time base from somewhere (e.g GPS)?

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GrahamN, if you were doing your experiment with only one transceiver I don't understand how this progresses things - if the phone is on the victim it is not a false positive. The point in question is: does a mobile on the victim (further than 5cm from his transceiver) affect the detection of the victim's transceiver in an actual test.

Anyway, snowHeads is much more fun if you do.

Steilhang, digital ones give distance and direction, so you're not tracking just on variation of the beep intensity. They take you directly towards the target, along a curved flux line, without having to do the grid search. Downside is that thy can get confused on occasion, particularly if there are multiple transmitters. The pulse (and S1, although I've not used that myself) allow you to isolate to individual transmitters in multiple burials. I got the Pulse after trying out the Tracker, older Barryvox and M2 and finding them all a bit weak in certain key areas, and didn't have the bulletproof fallback into F1 mode. The X1 is just a disaster. The Pulse does get confused from time to time, particularly if the transmitter moves, but it was the best I've used (range, simplicity in basic operation, analogue fallback). There's a new software update that's supposed to improve it further.

Bit surprised about your test - in what way did the interference affect the F1? I would have thought you would have been able to hear the transmitting beep through all sorts of static - I certainly would have been able to do so on the analogue output of the Pulse.

snowball, it's a false positive in the sense that it appears as a body, but of random distance and direction (one second it may appear to be 20m to rear left, the next 52m straight ahead, the next somewhere else). It shows up as something being around somewhere, but it's useless as a target to track, and so is a confusing interference, sending you off on wild goose chases. In that final test it seemed to only cause such effects when close by (<20cm ish), so not so much of a problem (as you should have a strong dominating true positive by then), but in previous tests (e.g. the one with [b]rob@rar[/v], although not quite so rigorous as this one) I have seen interferences at 5-10m distance.

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GrahamN,

After all it is free

Haggis_Trap, on the occasions when I've used an X1 the distance update has been so slow that it's significantly slowed down the search - maybe by a factor of 2 over what I can achieve with the Pulse. I was faster and more reliable with the M2 than I was with the X1. More experience with how it behaved would undoubtedly have improved that, but it's intended to be a very simple to use, relatively idiot-proof device, and on that count it failed (it certainly wasn't proof to this idiot). One of the really nice things about the Pulse is that, despite its complexity if you want to go there, in basic operation it's fast, sensitive and just works.

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Steilhang, the recent ones that give both direction and distance have three antennae. I don't know the details of the processing, but I assume it's from comparison of the signal levels from the different antennae, and relating that to the curvature of the flux lines (although on reflection that probably doesn't wash either). Distance measures are not particularly accurate, maybe within 20% if you're lucky, but it's their changes during the search that's important.

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In theory addition of a 3rd antenna only helps in the final stages of the search. The extra information should help locate the point on snow directly above the victim. However it is debatable is this helps much.... (link above has some great backround reading on spikes etc).

Davidof - As you described the Tracker multiple burial / special mode is far from simple ! There is no indication of multiple burials, and it still requires lots of practise... The 2nd gen digital beacons (such as Mammut Pulse / Ortovox S1) handle such scenarios way better ? However multiple scenarios should be rare. I havent used the pieps free-ride, however it certainly wouldnt be my first choice!

Thinking of buying a avvy tranceiver this season and do not know much about them so be gentle Very Happy

In a nutshell if I am caught in an avvy and I have my phone on it should not cause a problem for my tranceiver (separate pockets etc) or cause a problem for those hopefully searching for me (btw I seem to recall some one sending a message when they had taken a fall off a cliff and getting recues because of it last season), and if we are looking for a mate who has been buried is it best if we all turn off our phones?. Would it be ok for one of the group to keep their phone on but stay a few meters away from those searching with transceivers? because a phone can be useful in such circumstances.

You know it makes sense.

rayscoops, I think the conclusion is that it's probably best to strip off and do the search naked cos there are all sorts of things that can interfere with a beacon. That's provided you have not got any metallic objects in your body, like bits of shrapnel from normandy beach or a metal arm. Above all you shouldn't do the search while listening to music on your iPod. If you stick to those simple rules then the beacon should work just fine.

Seriously though, if you are buried there is little probability that the transmitter will be in any way impacted by your phone. My experiments, and I believe those of GrahamN show that if the phone is kept more than a few cm away from the searching beacon then there is no problem, but by all means switch the phone off at the beginning of a search if you feel like doing so!

Otherwise you'll just go on seeing the one name:

Guys, this is a great thread. I'm learning all about mobile phone electronics and all sorts. It's clear that there's no one definite school of thought on this, and therefore as responsible skiers, we have to work within the guidelines given to us knowing that they are guidelines only.

Here's a question though - if you're a victim of an avalanche (or really, any snow related incident) and you become separated from the rest of your group, if your mobile phone is switched on and one of your group phones it, it could be heard, thus enabling them to locate you?

A snowHead

snowqueen11,

A snowHead

If your buried with your phone and beacon then no worries as any interference is still going to send you to the correct location?, if the phone comes out of your pocket it' s unlikely to send a stronger signal than another beacon? so i cant see how any time will be wasted on it, so i cant really see a problem having a phone or ipod or whatever, if your the lucky searcher then yes perhaps chuck it away to search, but again i imagine you would get to the beacon through any interference... easy enough to test this winter though.

Well, the person's real but it's just a made up name, see?

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Now that twin peak thing is very interesting, I've never heard of that but it makes sense.

Anyway, snowHeads is much more fun if you do.

Here is another interesting link crossposted from the 'piste-hors' forum.
Posted yesterday warning that a motorola GP340 radio could accidentally turn a pieps-dsp off. <wow>

http://pistehors.com/news/forums/viewthread/373/

Davidof - magnetic reed switches provide very good shock immunity when a beacon is dropped / vibrated. Which is why Pieps will use them instead of a simple mechanical switch. Though its worrying that EMI from a radio could actually switch this beacon off. That really is worst case scenario - Eeeeeeek....

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A bit more evidence from in the field.

kristof and I did a bit of transceiver practice yesterday, while I noticed no difficulties searching with a phone turned on in my pocket at one point when kristof was searching someone walked past on their phone ~20m away, this sent his search completely haywire. Given you never know if someone is going to receive a call at any time it makes sense to me to switch your phone off (something I hadn't necessarily done in the past).

I wanted to get some data on search times and range in the presence/absence of a phone but didn't take a pen and paper.

Mind you I wouldn't have been able to collect enough data for the following reason:

Average time taken to find beacon in normal conditions ~2 min
Average time taken to find beacon when someone walks past on their phone ~ 3.5 min
Average time taken to find beacon when it wasn't turned on ~ 21 hours and 10 minutes including trip to buy metal detector, subsequent use of said detector in the dark, getting numerous nettle stings from rotting about everytime said detector beeped, getting pissed and going back the next day. Also time was taken for a quick ebay check for spurious transceiver listings. A further point of note the S1 is invisible to a metal detector above a range of about 10 cm while a tracker will be picked up at about 2 foot.

Tests were carried out with beacons hidden between a range of 50-150 m from the start point under long grass in sand dunes.

This is the second time I've tried to find a beacon that wasn't turned on ... it's beginning to get tedious.

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Swirly

so what we need is a beacon with embedded RECCO patch?

After all it is free

gorilla, I have, we thought it might be useful given our collective pole attrition rate.

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Swirly,

Help!!

Avalanche Mobile Phone detection

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