FYI: iPod / cell phone can interfere with beacon signal.

[1000-oaks]

From here: http://www.esavalanche.org/

"Another issue is radio frequency interference (”RFI”). With so many different electronic devices carried by backcountry recreationalists these days, complete testing of every possible device is infeasible so I’ll cover this briefly here. I have found that a *transmitting* cell phone (CDMA band) or FRS/GMRS radio can cause interference to varying degrees in some (but not all) beacons. But no beacons suffer RFI from an on-yet-not-transmitting phone or two-way radio. Far more importantly, playing an iPod will cause RFI to vary degrees in *all* avalanche beacons at close range. My general conclusions with RFI are: Be very careful if deciding to call for help while simultaneously searching with an avalanche beacon; and if you are touring with any brand of avalanche beacon, never listen to an iPod. (I am very serious about this: the potential for an iPod to be inadvertently left on and then cause interference in a beacon search is dangerous."

[Tye 1on]

Appreciate the heads up, there's been a few interesting threads on this topic. In this one, The Suit had some particularly alarming observations with an iPhone, that was on, but not in active use. Because of the data side, iirc, the iPhone interfered with the beacon even just sitting in a pocket. I don't recall the specifics, but the take home i got was that if you are serious about wearing and potentially using a beacon, keep your cell phone turned completely off when skiing/in hazard areas.

[Jonathan S.]

From here: http://www.esavalanche.org/ [...]

I started reading that and it seemed really familiar until I realized that . . . well, anyway, it's actually an excerpt from this series:
http://www.wildsnow.com/1476/avalanc...-review-intro/

And yes, iPod interference was way worse than other electronics I've tested, plus unlike any other device it intefered with *every* beacon on the market.

[Tye 1on]

heh, nice article J!

[pbourdon]

So ok, I'm lazy and didn't read the linked article....If I understand what you're saying the phones/ipods interfere with the search/recovery mode...that is if you're looking for someone your ipod or phone can cause problems. What about the person who is buried? Does their ipod or phone interfere with their signal being transmitted? Good heads up on this though...thanks.

[Jonathan S.]

Correct, I tested only the potential for a searcher's various electronic devices to cause RFI when searching.
I did not test the potential for a victim's various electronic devices to somehow interfere with signal transmission: although I am not an electrical engineer (or even anywhere close to it!) I'm pretty sure that would not be a problem.
But that might be an interesting test to set up . . .
(And realistically, only an iPod has the potential to be on and actively doing anything while on the body of a victim, unless somehow a radio or phone gets stuck in transmission when a victim is buried.)

[Tye 1on]

(And realistically, only an iPod has the potential to be on and actively doing anything while on the body of a victim, unless somehow a radio or phone gets stuck in transmission when a victim is buried.)

You sure? I can't even spel electrikal enjineer, but it seems to me, based on the way my crackberry sends goofyass tones through my work land line when i'm not even on it, that any phone with data or text message capability is sending signals out whether you are talking on it or not. Which may, or may not, interfere with a beacon.

I'd be interested in knowing, but imho the safest bet is to turn the phones and tunes off when in the zone...

[Jonathan S.]

You sure?

err, no, not really

But I do happen to have both an iPod and iPhone with me (or is that, i?) tomorrow, so I'll (i'Ll?) try to run some quick tests.

[pbourdon]

err, no, not really

But I do happen to have both an iPod and iPhone with me (or is that, i?) tomorrow, so I'll (i'Ll?) try to run some quick tests.

I'd like to hear what you come up with...I'm not anywhere near avy terrain right now (damn midwest) and won't really get too involved in that shit until I move out west again in another year or two, but I do enjoy having tunes while riding, but I think my safety would trump my audible enjoyment.

[Jax]

Interesting.

Nothing scietific, just something I've observed the last few days inbounds at LL. I keep my iphone in the chest pocket of my windshirt, underneath my jkt, to keep it warm and I can feel it vibe if I need to. iPod shuffle clipped to the same pocket. If I get a call or a text/email I can hear interference through the iPod. Also, at work if phone is near landline or computer speakers I also hear interference.

[H-wood]

Jonathan,
I actually read that on wildsnow and forwarded the link to Sue Burak, who runs ESAC, my local avalanche org--hope you don't mind. I'm sure she (and others) like to be in the loop for whatever other useful info you turn up.

[Jonathan S.]

That's perfectly fine -- better to have more awareness of these potential RFI problems.
What cracked me up though was that I started reading it and thinking, hmm, this is pretty interesting, and very similar to my own findings, I wonder who wrote it -- oh, wait a second...

[H-wood]

I've had that same feeling--when I saw a ski review on untracked.com and realized I had written it, for another ski shop. I should have asked Sue to credit you. Really, the beacon manufacturers should be doing this kind of testing, but it's great that you pointed out this issue, especially as more and more people are skiing w/ avalanche deflectors and ipods, phones, etc.

[SchralphMacchio]

folks, this is good discussion. I had written some detailed comments in a similar thread on splitboard.com.

It should be reiterated that there is no prerequisite for a device to have an RF transceiver (i.e., a radio component) in order to interfere with a digital avalanche beacon. I believe the power supply and the high-speed processing of any embedded electronics device (e.g., GPS, MP3 player) can cause sufficient near-field dynamic electromagnetic radiation to trip up the digital signal processor (DSP) of a digital beacon.

Current flowing through a wire generates a local magnetic field. If the current is constant, the field is constant and the inducted signal into a near field receiver (i.e., your avy beacon in search mode) would appear as a DC offset (sometimes something manageable). When the field is dynamic, the inducted signal is dynamic, and the DSP can have a problem depending on the nature of the noise injected into the signal. The processor and power supply of a high-speed electronic device (an MP3 player) are plenty capable of creating a very dynamic high frequency magnetic field ... in turn capable of polluting the signal into a beacon's DSP enough to trip it up.

Now, here is the disturbing part ... my recollection of the Suit's thread is that his PIEPS DSP beacon was in *TRANSMIT* and not receive mode when it was being rebooted by proximity to his iPhone.

This is very disturbing news indeed. I'll echo the thoughts of the TGR thread in saying that if you really want to have your iPod with you while touring, set the playlist and then wrap that sucker in foil.

Final food for thought - analog beacons are not susceptible to interference of this sort, because there is no DSP. Your brain is smart enough to filter the signal (the beeping) from the noise. The big problem is that three or four antennas on a DSP are much faster at calculating the angle of the flux lines than your thumb on the volume wheel. Because of all this discussion I've wondered about getting an M2 ... doesn't it have a volume wheel so that you can use it in analog style?

[nesta]

all very interesting. I actually need my cell phone in the field, as it doubles as my paging device for SAR. I use an Ortovox F1 beacon. I usually leave my cell phone behind when I am out doing avalanche control. Of course I am packing a Motorola 2 way VHF radio or ICOM.
But one thing I never do is listen to my iPod while ski touring in avalanche terrain. You have to be able to hear avalanches, especially the ones coming at you that you might not see.

[SchralphMacchio]

nesta, proximity is everything. I call the radiation "near field radiation" because it does not just radiate into free space like a radio signal, this is the kind of noise that swirls around locally ... think miniature flux lines of magnetic radiation being emanated from these devices. I suspect that with most devices, above 30 cm's the effects drop off very rapidly. Unfortunately most beacon slings put the device right under any left breast pocket of your shell ... where most people like their electronics!

Also, with F1 you have no DSP so I don't think you have any real problem on search mode, and the data about how someone might be affected searching you is marginal.

Final disclaimer, everything I say is technically informed conjecture. I'm not a beacon designer or an RF/EMI/EMC engineer. I have a basic physics and engineering background and I work at a company that builds embedded electronic devices that have RF transcievers, though I am barely involved in design and testing (I do implementation).

[likwid]

You sure? I can't even spel electrikal enjineer, but it seems to me, based on the way my crackberry sends goofyass tones through my work land line when i'm not even on it, that any phone with data or text message capability is sending signals out whether you are talking on it or not. Which may, or may not, interfere with a beacon.

I'd be interested in knowing, but imho the safest bet is to turn the phones and tunes off when in the zone...

Same thing with a Blackjack II (WinMo device), infact its WAY worse. My personal phone is a Blackberry, work cell is a Blackjack II. It could have something to do with the network too. BB: Verizon BJ: AT&T

[Jonathan S.]

Ran some more tests today for interference. The quick summary:

-- Neither an iPod nor an iPhone seemed to cause any problems with transmitting. (So if you care only about yourself and hence only about being found, play music and chat away.)

-- I didn't bother testing an iPod again while searching, since my previous tests caused all sorts of problems with ghosting, noises, and directional indicators gone astray.

-- The iPhone was scary. I stopped the formal testing after awhile because the potential for a problem was clearly really bad. But at its worst (i.e., close to a searching beacon, and making a call, although the actual GSM band transmission might not be the problem), a Pulse ghosted and had directional problems, a DSP showed 3+ victims even when the actual victim was still way out of range, and an S1 was unable to find the transmitting beacon until it was within 11 feet.

[Tye 1on]

Thanks Jonathan.

You have a blackberry too by chance?

[Jonathan S.]

Somehow I have so far managed to avoid getting a Crackberry or similar PDA or "smart" phone (thus checking my email every five minutes no matter where I am), but I did notice this afternoon while patrolling that one of my fellow patrollers has a Blackberry, so I might run some more tests with his.

Also, right after I ran the tests I went patrolling, and who was there but none other than one of my fellow patrollers who is both an electrical engineer and an NSP avalanche instructor.
His thoughts of my findings (in particular regarding the relative lack of interference from my basic CDMA-band basic phone versus the GSM-band iPhone) were that it's not the transmission band but rather the internal guts of the device. Perhaps the main processor or some peripheral. Could be the internal DC to DC convertor (typically running of a single lithium cell). Much of this is in the 100kz to 1mhz range, so the 457kHz beacon frequency falls within that. [Caveat: these are quickly scribbled notes from his verbal explanations, so if something doesn't make sense here, it's probably my fault, not his!]

[likwid]

I just forwarded the part about the cell signal vs RFI to a buddy of mine in the radio industry to see if he can clarify whether its the device itself or the cell signal causing the interference.

I'll post the answer as soon as I get it.

Regardless, I'd still say either way, turn em the eff off.