From parsavan@boulder.Colorado.EDU Tue Oct 3 17:25:16 MDT 1995 Newsgroups: rec.skiing.backcountry Subject: avalanche beacons: has the direction finding problem been solved? i have been wondering for a while now if if anyone has come up with a solution to the direction finding problem with respect to avalanche beacons. there are several possible problems, but basically the goal would be to have a beacon in your hand that could indicate the exact direction to the buried beacon (say a projection of the vector onto the plane the device was held in plus a slope indicator) but range would be unknown. ideally, a solution to this problem without modification of the transmitter is the best, but i'm also interested in other research as well. my field is not electromagnetics, so i may be missing some obvious property of the transmitting frequency or antenna design that makes this problem intractable. however, a problem that seems tractable to me and i'm surprised it isn't solved and implemented in a beacon today is that of taking current transmitted signals and finding the direction of the induction line for use with the induction line search method. i quite like this method, but it could be a lot faster if one didn't have to re-estimate the direction of the induction line (projected on to the snow plane) every few meters. dara parsavand - parsavan@prony.colorado.edu "shift key - what shift key?" From Clyde_Soles@nile.com Sat Oct 21 12:08:24 MDT 1995 Subject: Re: avalanche beacons: has the direction findin Newsgroups: rec.skiing.backcountry In message ID on 10/6/95, Hugh Shane wrote: > One basic problem is the length of a wave at 457kHz. It's so long that > it's difficult to get any kind of resolution. 457kHz wasn't chosen > because it's a good band for this application, rather it was chosen > because it allows beacons to be manufactured using inexpensive and > readily available AM radio components. Actually it was chosen because tests showed it propogates through the snow more effectively. Hence the greater -- as in double -- range over the old 2275 hz. From v-pcamp@microsoft.com Sun Jan 21 22:03:24 MST 1996 Newsgroups: rec.skiing.backcountry Subject: Re: avalance trancievers In article <4cugho$8pq@news.pacifier.com>, gregs@wacom.com says... >Someone from a HP address was inquireing the possibility and the >interest in developing an avalance tranciever that would cost less than >the current high cost of $200+ for a fairly simple device (from a >technical standpoint). I would be interested in hearing more about >this. The DIN standards that govern the current avalanche beacons are pretty primitive but designed to be that way to satisfy European Communications Authorities (and because we already have them working this way.) You may not want to focus on the signal strength as much as on the speed of locating and discriminating between multiple signals. The new Ortovox 457KHz only beacons with the LEDs make identifying the direction of the strongest signal much faster. PS: Paul Ramer has been working with engineers in the Fort Collins area for several years to develop a beacon but still only has a prototype. Skadi is reported to be preparing a beacon for market but there are no North American manufacturers. -- The opinions expressed in this message are my own personal views and do not reflect the official views of Microsoft Corporation. From seapwc@halcyon.com Fri Dec 8 15:08:23 MST 1995 Newsgroups: rec.skiing.backcountry Subject: Re: Transceivers Enquiry ASTM considered revising the spec for beacons when they standardized the new frequency of 457KHz and the date of Jan 1, 1996. It was felt that it was inappropriate to try to change the standard adopted by the Europeans, when at the time there were no US manufacturers of beacons. By the way the standard only calls for them to operate between -10C +40C(transmitter) and -20(receiver) (Skadi may have resumed under new ownership and Paul Ramer is getting close, still.) Here are some numbers on the European Standard. (Not from an "official" copy.) CEN/TC 136 DIN 32 924 (CEPT CEN) From mje@pookie.pass.wayne.edu Tue Jan 16 14:27:29 MST 1996 Newsgroups: rec.skiing.backcountry Subject: Re: avalance trancievers What probably keeps the price up is the low volume. An avalanche tranceiver is basically a single channel reciever with very low requirements for sensitiviyty and selectivity and a low power transmitter. The critical requirements are ruggedness, good cold weather performance and reliability. You need the following componants to be designed: 1. Transmitter board 2. Receiver board 3. Antenna (probably etched on a piece of PC board) 4. Case, including battery compartment and recessed control switch. Using varous ICs the electronics part count could be made very small. There are one-chip receivers, and the transmitter can be made with a couple of transistors. : Anyone with the electronics expertise that would be willing to help, please : pipe up! Also, some plastics exp would be helpful, though I suspect a custom : case is prohibitive, as plastics dies & molds are VERY expensive. You need a non-metallic case that's transparent to radio. Urethane resins can be used to make both molds and cases at fairly low cost; a friend has done this for some low-production runs of equipment. There are also some small commercial boxes made of polycarbonate and other resins that are inexpensive and rugged. If someone could design the electronics, perhaps a set of PC boards and plans could be made availible inexpensively. But tooling up to actually produce units wouldn't be that much or a savings, given the labor involved. Ideally you'd have these made and assembled in the far east, but then you'd be talking volume production, FCC certification, etc. --mike From parsavan@boulder.Colorado.EDU Thu Oct 17 12:39:12 MDT 1996 Newsgroups: rec.skiing.backcountry Subject: indicator lights and tangent method (was: F1 Focus) In article <544flk$9np@news.sdd.hp.com>, Patrick Chase wrote: >I'm not convinced that the built-in visual signal strength indicator >is all that useful, because it only shows three levels. Anybody with >non-impaired hearing (highly experienced or not) will be able to resolve >signal strength more precisely than that by ear. The built-in meter >is also not precise enough in my opinion to accurately find the direction >of maximum signal strength when doing a tangent search, so if the user >can't "play it by ear" they're pretty much restricted to grid search i have an F1+ with just a single light and i claim that the information it provides is useful in a tangent search. it is usually possible at a given location to pick a volume control that causes the light to be on somewhere between 10 and 120 deg of continuous arc. if one bisects this angle, it seems to match the highest sound point (but maybe my hearing isn't that good). likewise, when doing a grid search, one can bisect the distance between when the light came on and when it went off. this isn't very practical for long distances, but in doing a fine grid search, the light may be going on and off in a distance of less than 2 meters and it is easy to bisect this short distance. what i wish is that av beacon manufacturers would come up with a design that allowed users to just stand still for a few seconds and the correct tangent direction would show up on the screen (either lcd if they can get a low temperature one, or simply a ring of led's). this might be a hard signal processing problem with multiple targets, but i would think it can be solved for single targets using different receiver antenna's and dsp chips. even better would be an arrow that pointed right to the victim, but this may not be possible with the standard frequency and transmitting antenna used. dara parsavand parsavan@prony.colorado.edu From parsavan@boulder.Colorado.EDU Thu Mar 6 13:02:26 MST 1997 Newsgroups: rec.skiing.backcountry Subject: Next generation beacons (in FAQ?) (was: wonder beacons) dbogan@hq.nasa.gov writes (}): }I have been told that new technology is soon to appear that will make }finding a buried victim trivially easy. I was told that it will be }able to point the direction in which to walk and tell you exactly how }far to walk before you start digging. the direction finding problem would be the most important to solve. if you could come up with a beacon that would tell you which direction to walk, the estimation of range is not really necessary as long as the device could give you a good indication of when you get there. however when i posed this problem a few years ago on this newsgroup, several thought that it was not possible to solve. i talked to a prof. in RF who gave me a book to look at which mostly talked about rotating loop antennas looking for max gain and i was so out of my area i couldn't figure out if the device would at all apply to 457kHz with a small transmitting dipole. a related problem, which if it could be solved would be almost as good in my opinion, is a constant readout of the induction line orientation - then you could run (really run - with no stopping to every meter or two) along the direction of the induction line (sometimes called the tangent method) until the signal strength maxed out. i thought this could be done with multiple receiving dipoles and software processing, but again i'm out of my area and i could be neglecting interference between the different antennas or other issues. both of these problems are compounded when there are multiple targets. last time i practiced with my low-technology Ortovox F1+, my partner buried two beacons about 3-5 meters apart without telling me (i had never practiced this which is pretty silly now that i think about it). it confused the heck out of me and i didn't get the second one out until almost 10 minutes had elapsed which is pretty pathetic. murray@pa.dec.com wrote: (>) >One could imagaine a GPS receiver in the transmitting >unit. It could transmit it's location. The receiving >unit could use differential GPS to tell you where to go. unfortunately, this will probably never be invented. i proposed this several years ago, and several posters pointed out that the GPS signal will not penetrate any significant depth of snow (when GPS first came out, i tried to borrow one to take in a snow cave and find out for myself, but i never did - anybody else ever try?). a related problem might be the use of multiple searching beacons that know their position from GPS and communicate with each other about the nature of the signal they are receiving from the buried beacon (whose signal is probably going to have to convey more information than it does now - i.e. a spread spectrum signal of some kind) to calculate a position. i was never that keen on this problem though since i often ski with just two or three people. i think this area would make an excellent addition to the FAQ if there was someone very knowledgeable in the field of RF and signal detection who was willing to write it. dara parsavand | parsavan@prony.colorado.edu (do not use header address) From hugh.grierson@trimble.co.nz Fri Mar 7 09:59:35 MST 1997 Newsgroups: rec.skiing.backcountry Subject: Re: Next generation beacons (in FAQ?) (was: wonder beacons) parsavan@boulder.Colorado.EDU (Dara Parsavand) wrote: >unfortunately, this will probably never be invented. i proposed this >several years ago, and several posters pointed out that the GPS signal >will not penetrate any significant depth of snow (when GPS first came >out, i tried to borrow one to take in a snow cave and find out for >myself, but i never did - anybody else ever try?). I keep meaning to borrow one from work to test this. Maybe this winter. Back to the original idea, I think a continuous induction line display would be the single biggest potential improvement for tranceivers. I heard a rumour that implied that the Ramer might do something like that, but I have to say it scores pretty low on my veracity meter. -H From dawson@rof.net Sat Mar 8 11:20:44 MST 1997 Newsgroups: rec.skiing.backcountry Subject: Re: Wonder beacons I've used the Tracker DTS. It works. It's amazing. I didn't use it enough to experience any "gotchas," I'm sure there are a few. But from what I saw it must have the euros scrambling to make something similar. My only gripe was that it was too bulky and heavy and didn't use AA batteries, for which I've standardized all my gear. We'll see what the production unit looks like... >>In article <5fkce1$6h4@centauri.hq.nasa.gov>, dbogan@hq.nasa.gov writes: >>> >>> I have been told that new technology is soon to appear that will make >>> finding a buried victim trivially easy. I was told that it will be able to >> >>> point the direction in which to walk and tell you exactly how far to walk >>> before you start digging. Does anybody know about this? If true and if >>> it is soon to appear on the market, it might be a good idea to wait before >>> laying down your money. Unless you are going into imminent danger soon. -- 'best, Lou Dawson (Carbondale, Colorado, USA) -- From parsavan@boulder.Colorado.EDU Mon Mar 10 09:07:45 MST 1997 Newsgroups: rec.skiing.backcountry Subject: Directional beacons (was: Wonder beacons) > wrote: >>Some information from the brochure: >>457 kHz digital transceiving system >>Directional LED's Philip Patrick Fortier wrote: >Don't several beacons already have this? It shows the direction of >'induction lines' not the victim. Is this any different? to perform the induction line search method, one stops every meter or so and moves the beacon rotationally (along the vertical axis) looking for the maximum signal strength and then heads in that direction. no beacon today will do this computation for you regardless of the stupid arrow shape on the LED's (arrgh - why did they do that). it was my assertion a few years ago that this computation is possible and the claim is that this new company has done it - if so, bravo! but i'll be more convinced when i have one in my hands of course. >>Numeric distance display (approx distance in meters, changing >> to tenths of meters for pinpoint search) probably very approximate since i'm guessing snow attenuation is different than air and without knowing how deep the beacon is, i would think it would be difficult to say how far away it is. this information isn't even very necessary as long as the direction is known - one just needs to go in that direction unntil you find it. and as Phillip points out, it is probably just a scale factor times the signal strength raised to some power. the big question i have when i first thought of this problem is how the device handles multiple targets. is it capable of locking into one by filtering out the others? it will be interesting to check out. dara parsavand | parsavan@prony.colorado.edu (do not use header address) From dawson@rof.net Tue Mar 11 08:48:12 MST 1997 Newsgroups: rec.skiing.backcountry Subject: Re: Wonder beacons All: FWIW, the Tracker has a computer function that handles multiple signals. It's quite effective, though like any artificial "intelligence" it probably could work against you in certain weird or unusual situations . -- 'best, Lou Dawson (Carbondale, Colorado, USA) -- From andrew@bdel.com Thu Mar 6 13:28 MST 1997 Subject: Re: Next generation beacons (in FAQ?) (was: wonder beacons) Status: RO Hi Dara, At the Feburary Outdoor Retailer show, a company from Colorado was showing a directional transciever. You turned it on and walked right to the hidden beacon. It was a 457kHZ, so it would work with all other 457's and gave you the range to target as well. Very, very slick, and many people (skiers anyway) thought it was the hot new product of the show. From parsavan@boulder.Colorado.EDU Sun Mar 16 17:24:26 MST 1997 Newsgroups: rec.skiing.backcountry Subject: GPS in beacons (was: wonder) In article , Alan Brunelle wrote: >I don't think that the location info would have to be transmitted in the >same frequency range as the GPS uses for location. correct - in fact, there may not be a publically usable radio band near there anyway. since the bit rate needed to send the last couple digits of a latitude/longitude pair and what satellites were used to do the computation in a few seconds is so low, you could use just about any frequency you want. [note: if two GPS receivers use the same satellites, they can compute differential positions as accurate as DGPS. DGPS is not motivated by the need to calculate differential positions but to be precise about your absolute position] the big catch is of course, GPS signals will not penetrate the snow, or so i've been told. hopefully i'll have a Garmin 12xl in a few weeks and i'll go check it out for myself. it's too bad this wouldn't work, because you could have this transceiver for many other uses as well if you threw a keypad on it for use with the data channel. you could search for your lost dog, kid, use it on climbs where you can't hear your partner, etc., etc. dara parsavand | parsavan@prony.colorado.edu (do not use header address)