>>That sounds intriguing and useful - Could you tell us more about the >>technique of triangulation? By using directional antennas and signal strength meters, one could find the general direction that the transmitting signal is coming from. With 3 or more ships or aircraft in different locations, they can plot on a map, the separate bearing readings from each position. Where the lines intersect is the general area the the signal is coming from. Here's a better explanation. http://hometown.aol.com/bmgenginc/Triangul.html Here's how GPS satellites do it: http://murray.newcastle.edu.au/users/staff/eemf/ELEC351/SProjects_98/Ashby/T riangulation.htm Steve *************************************************************************** PaddleWise Paddling Mailing List - Any opinions or suggestions expressed here are solely those of the writer(s). You must assume the entire responsibility for reliance upon them. All postings copyright the author. Submissions: PaddleWise_at_PaddleWise.net Subscriptions: PaddleWise-request_at_PaddleWise.net Website: http://www.paddlewise.net/ ***************************************************************************
From: "Stephen Wan" <Steve_at_OlsonArchitect.com> > >>That sounds intriguing and useful - Could you tell us more about the > >>technique of triangulation? > > By using directional antennas and signal strength meters, one could find the > general direction that the transmitting signal is coming from. With 3 or > more ships or aircraft in different locations, they can plot on a map, the > separate bearing readings from each position. Where the lines intersect is > the general area the the signal is coming from. The Canadian Coast Guard has many ground stations around the Great Lakes (presumably, so does the US) and can do triangulation easily. In fact, when I took my Restricted Operator's Certificate (Maritime) course this past spring, the instructors made a point (more than once) of advising folks not to use the radio _and_ try crossing the Canada-US border in their boats. They pointed out that these areas are monitored and that the monitoring has likely been stepped up in the past year. I'd also assume there are similar capabilities in the Pacific (BC-Wash.) and Atlantic (NB/NS - Maine). It's a useful feature for SAR and a security feature in both the so-called drug war and for fear of terrorists. Mike *************************************************************************** PaddleWise Paddling Mailing List - Any opinions or suggestions expressed here are solely those of the writer(s). You must assume the entire responsibility for reliance upon them. All postings copyright the author. Submissions: PaddleWise_at_PaddleWise.net Subscriptions: PaddleWise-request_at_PaddleWise.net Website: http://www.paddlewise.net/ ***************************************************************************
Stephen wrote >By using directional antennas and signal strength >meters, one could find the general direction Michael wrote >The Canadian Coast Guard has many ground stations >around the Great Lakes (presumably, so does the US) >and can do triangulation easily. G'day Thanks very much for the comments and explanations - the web site seems to indicate that this can be a special set up for emergencies and Michaels comments suggest it can also be a routine set up at some coast guard stations. In such a case what is the correct protocol for accessing information? Do you have to make a request and then continue talking while the triangulation is carried out - or is it nearly instantaneous? When I was a kid it took several minutes fiddling with the angle on a ferrite rod aerial to get a bearing on a radio station. I haven't heard of this facility in Australian Coast guard stations but will investigate after I understand the protocol a bit better. All the best, Peter *************************************************************************** PaddleWise Paddling Mailing List - Any opinions or suggestions expressed here are solely those of the writer(s). You must assume the entire responsibility for reliance upon them. All postings copyright the author. Submissions: PaddleWise_at_PaddleWise.net Subscriptions: PaddleWise-request_at_PaddleWise.net Website: http://www.paddlewise.net/ ***************************************************************************
From: "PeterO" <rebyl_kayak_at_iprimus.com.au> > In such a case what is the correct protocol for accessing > information? Do you have to make a request and then continue talking while > the triangulation is carried out - or is it nearly instantaneous? AFAIK, the triangulation is done automatically and quickly. I am not aware of any protocol to request the information on position from the Coast Guard. >From the way that the course instructor talked, it sounds like something they might not readily acknowledge if you ask informally on a routine call. Standard protocol on any priority message is for the person making the call to indicate their position and the Coast Guard doesn't turn around and tell the world where you are if you don't know. If SAR is involved, triangulation is used by them, but we weren't taught to expect the CG to broadcast a location based on this; it's handled entirely by a local military base that manages all SAR activities. Mike *************************************************************************** PaddleWise Paddling Mailing List - Any opinions or suggestions expressed here are solely those of the writer(s). You must assume the entire responsibility for reliance upon them. All postings copyright the author. Submissions: PaddleWise_at_PaddleWise.net Subscriptions: PaddleWise-request_at_PaddleWise.net Website: http://www.paddlewise.net/ ***************************************************************************
>AFAIK, the triangulation is done automatically and quickly. I >am not aware >of any protocol to request the information on position from the >Coast Guard. >something >they might not readily acknowledge if you ask informally on a routine >call. Standard protocol on any priority message is for the >person making >the call to indicate their position and the Coast Guard doesn't turn >around and tell the world where you are if you don't know. If SAR is >involved, triangulation is used by them, but we weren't taught >to expect >the CG to broadcast a location based on this; it's handled entirely by >a local military base that manages all SAR activities. Indeed, the equipment has been in place for decades and is common place on ships, ground stations, and SAR aircraft. Virtually every airport or flight service station has them for the air controllers as well. All a controller has to do is look at an indicator to get your bearing. And assuming sufficient separation between the two monitoring stations, only two receivers are required to deduce your location, more just confirm it. In fact in a more rudimentary sense, nearly every general aviation and commercial aircraft has similar equipment on board for navigation purposes (though not applicable for this use). It's a loop antenna and an instrument called an ADF (automatic direction finder), that simply points a needle on the bearing of the signal on the frequency it's tuned to. In this case generally covering the AM broadcast band. You tune to the station and listen in to confirm it's identity and home in on the known location. You can obtain your own physical position by getting the bearing of two or more known transmitters, and intersecting the bearings on your map. AM radio stations work just as well as official navigation beacons since they periodically state their call letters and transmitting towers are listed on aviation maps with their call letters beside. Official navigation beacons NDB's (Non Direction Beacons) are just AM radio stations of a standard output power (typically 50MW) and constantly transmit a morse code identifier (also listed on aviation maps). So this is just the reverse process. You as the kayaker are the "NDB" so to speak. And multiple "ADF's" compare their observed bearings to you, the station, to obtain your fix. If it's a SAR aircraft, they can home right in on you with no help from any other station if need be (as long as you're transmitting). Just as any aircraft can home in on an airport with an NDB, or home from station to station enroute from one place to another. As for the CG and it's implementation and policies I have no information, I'm just getting my feet wet in the kayaking realm (renting currently with a view to buy a Feathercraft Klondike). In order for an automatic position fix, it's presumable that their systems range anywhere from a bearing and signal strength (not a great indicator of distance, but better than nothing) indication as is found in airport towers, that a CG radio operator can glance at and compare with other operators bearings (verbally), all the way up to an automated system that monitors all VHF communications and relative fixes by comparing the bearings from networked but diverse receivers (putting the results on a map display for a CG or marine controller say at Comox). Without the advantage of the latter example, it's not possible for a single radio operator to tell you where you are, only your bearing from him. Perhaps that's why it's not as commonly used in marine situations. Your request may require him to call another CG station and compare notes. Whereas presumably a large CG center may have this computed and put on a display and it would be trivial. There may also be an element of legal responsibility involved in the reluctance to provide that information. It's up to the operator of a craft to make navigation decisions and accept responsibility for the results of those decisions. If the CG tells you where they think you are, and you act on it, but there was a system failure, or solar flares, or some RF anomaly in your location, and you get your self in hot water because you proceeded off in a direction based on erroneous information provided by the CG, then they run the risk of shared blame. It is less common these days in the aviation realm (which I'm familiar with as a licensed commercial pilot) for such services to be requested, but wasn't uncommon 15-20 years ago. I myself have requested a "DF Steer" a few times as a green private pilot, when in a lightly instrumented Cessna 150, and weaving my way around low and visibility limiting cloud. Every tower or flight service station could give you one, but that was just a bearing to the tower (which is often your intended destination). You'd ask for a DF Steer, he'd go over to the instrument and ask you to transmit again, and he'd read your bearing off the instrument (looks like a big compass, but with the "needle" pointing to the aircraft that's transmitting on the airport frequency). I'm not sure in the marine environment it's as useful a tool, since how often is your destination in your kayak, the coast guard station? To ask for a triangulation fix may well require some effort and inter-station communication, which when they're busy, may not be warmly received. Back in the aviation realm, typically, requesting a service more involved as a position fix, or assistance in navigation, prequires you to first declare an aircraft emergency. Then you get all the help in the world. The price however is all the paperwork in the world afterwards, and having to explain how your inept preparation and poor navigation skills got you into that predicament in the first place. At a minimum you can likely expect a mandatory ground school refresher to be demanded of you, and perhaps reimbursing the air traffic and SAR services for their time (woe to you if a SAR Hercules was dispatched, billing out at $5000 Canadian per hour). YMMV but a GPS may be cheaper ;-) -Craig Bowers Vancouver, Canada *************************************************************************** PaddleWise Paddling Mailing List - Any opinions or suggestions expressed here are solely those of the writer(s). You must assume the entire responsibility for reliance upon them. 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Peter said: <<< Thanks very much for the comments and explanations - the web site seems to indicate that this can be a special set up for emergencies and Michaels comments suggest it can also be a routine set up at some coast guard stations. In such a case what is the correct protocol for accessing information? <snip n' nip> >>> Sorry I never got back to you - I have only recently returned to the land of the living from migraine hell. I see you got a few responses already. In BC water, VTC (Vessel Traffic Control) can pinpoint your position. Mariners, where needed, can contact VTC with their trajectories where there could be interaction hazards with large moving vessels. For the paddler, fog-obscured crossings could prove hazardous where convection fog, etc. moves in unexpectedly. The authorities can pinpoint various vessels, including the lowly kayaker from what I understand, and let you or others know where you are or where to take remedial action. A paddler in trouble can merely click the talk button to gain signal triangulation. Paddlers should also know the morse code for SOS. I was once hit so hard on my Adams Apple by a paddle shaft, that I wasn't too far away from loosing my voice. I'm not aware of any protocol, other than most paddlers don't practice any with respect to crossing shipping lanes. Doug *************************************************************************** PaddleWise Paddling Mailing List - Any opinions or suggestions expressed here are solely those of the writer(s). You must assume the entire responsibility for reliance upon them. All postings copyright the author. Submissions: PaddleWise_at_PaddleWise.net Subscriptions: PaddleWise-request_at_PaddleWise.net Website: http://www.paddlewise.net/ ***************************************************************************
G'Day Doug and Craig, It seems as if there is quite a bit of variability in what is available. >From what Doug says the facility would be useful in a working harbour or near shipping lanes subject to fog (or smoke from bush fires in the case of Sydney Harbour). You've encouraged me to ask our local volunteer coast guard and see what they know about availability of triangulation information in foggy (or smokey) conditions. Craigs description suggests the bearings are likely to be calculated from an array of directional aerials rather than physically rotating an aerial, which makes sense of the fast speed of response. Last time I remember thinking about this was in early 1960's when reading "Practical Wireless":~) Thanks again for the information. All the best, PeterO *************************************************************************** PaddleWise Paddling Mailing List - Any opinions or suggestions expressed here are solely those of the writer(s). You must assume the entire responsibility for reliance upon them. All postings copyright the author. Submissions: PaddleWise_at_PaddleWise.net Subscriptions: PaddleWise-request_at_PaddleWise.net Website: http://www.paddlewise.net/ ***************************************************************************
>... Craigs description suggests the bearings are > likely to be calculated from an array of directional aerials rather than > physically rotating an aerial, which makes sense of the fast speed of > response. Last time I remember thinking about this was in early 1960's when > reading "Practical Wireless":~) Modern technique is to use a pseudo-Doppler array, which is a ring of 4 or more antennas that are switched using diodes. This can give you very fine resolution with no moving parts. In fact, it can be done with only two antennas, albeit with a 180 degree uncertainty that can generally be resolved with two bearings. -- mike *************************************************************************** PaddleWise Paddling Mailing List - Any opinions or suggestions expressed here are solely those of the writer(s). You must assume the entire responsibility for reliance upon them. All postings copyright the author. Submissions: PaddleWise_at_PaddleWise.net Subscriptions: PaddleWise-request_at_PaddleWise.net Website: http://www.paddlewise.net/ ***************************************************************************
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