RE: [Paddlewise] VHF signal triangulation

>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
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