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    Re: LORAN-C to be shut down.
    From: John Huth
    Date: 2009 Dec 6, 10:54 -0500
    I'm building my own so that I can play around with the antenna design to see what precision I can reach.  If I use a large loop antenna rather than a loopstick, I think I can do much better in angular measurement.  

    So far, with a cheap radio (Grundig) I got about 3 degrees - I'm hoping that with some improvisation with my own playing around I can do much better.   It's more of a labor of love than anything else.  

    It is admittedly crude, but being a navigation maven, I'm always curious about the limits of precision with  home-made schemes - which may explain better why/what I'm doing.   If one wants to get very precise, look at the HF/DF (Huff Duff) radio direction finding that was developed during WWII to find German U-boats.   The designs were extremely sophisticated - both in terms of the electronics and antenna design.  

    My interest is more of the variety - "what can I do with my simple knowledge of physics and junk lying around the house or readily available?"

    Another radio technique which is of interest, and I document below is the range of radio stations based on reception as a function of time of day/night.   AM radio waves will propagate with both a ground-wave (line of sight) and sky-wave (ionospheric bounce).   During the day, the bombardment of the ionosphere by junk from the sun disrupts it, but it settles down during the night.   When I was a kid, I could receive AM radio from New York and Los Angeles simultaneously, while camping on Isle Royale in Lake Superior.   

    As you approach an AM radio station from a great distance - a thousand + miles, you'll first only hear it at midnight, but as you get closer, you'll hear it closer and closer to sunrise, and then finally at mid-day when you're in the ground wave regime.  

    This was actually documented in a book by William Butler, titled 66 Days Adrift.   He and his wife Simone were sailing out of Panama, and were some 1200 miles offshore when their sailboat was attacked by a pod of pilot whales.   They had a walk-man with them as they drifted in the equatorial counter-current toward central America.   I've put down some clips of the radio transmission they got as they drifted toward land - you can see the use of both triangulation and ground/sky wave transmission as a function of the time of day during their drift:


     

    Of his 26th day adrift Butler writes of his use of triangulation at night:

     

    When I turn, Sim is listening to the radio.   She calls to me, “Bill, radio reception is good.   Shall we do it?”   I had asked Sim to call when she picked up two or more strong stations that didn’t fade out right away.  We hope we can locate the source of a radio signal by rotating the radio until the signal disappears.

                I tell Sim, “OK.  You tune to the station and I’ll do the fix.”

                She passes over the radio and earphones. “Here’s Radio Sandina in Managua, Nicaragua.”

                I put on the earphones and turn the Walkman until I can no longer hear the broadcast.   Sim, with the compass in one hand and the flashlight in the other, awaits my signal.  I rotate the radio until the station disappears and then place it over the compass.

                “Thirty degrees,” I call out.  “OK, Sim, get another station.”

                We repeat the process with a station in Costa Rica, which bears 60 degrees.   Thirty degrees to Nicaragua and 60 to Costa Rica puts us many hundreds of miles offshore.   We have probably traveled almost five hundred miles and have five or six hundred more to go.   But at least we are moving toward shore. 

     

    The next day

     

    Simonne picks up faint radio signals in the late afternoon.   Though she can’t make out words – it’s more like a rumble – she has no doubt it’s a shore station.   When she first listened four weeks ago, she heard absolutely nothing until midnight.  

     

     

    Of their 42nd day adrift, he writes:

     

    The sun slowly makes its appearance.   Clear skies promise a dry day.   Simonne, listening to the radio, is far away in her own world.

                She takes the earphones off.  “Every day I can hear stations later in the day.   A week ago, I received only static starting at six in the morning.   Now the sun is up, and I can still hear Costa Rican stations clearly.   Here, listen.”

                I put the earphones on.   The signal isn’t perfect but it’s not bad.  I hear music.   We can’t be much more than two hundred miles away, possibly less.  When we hear a station right through the day, even at high noon, we’ll be within a hundred miles.   Today’s signal lingers until ten, then fades away.   Land remains hundreds of miles to the east.

     

    On their 59th day adrift:

     

    Sim’s radio picks up signals from San Jose, the capital of Costa Rica, and from a town called Carthago.   Last night she again heard a station out of David, a small town in northern Panama, advertising a dancing, drinking and eating place with many girls.   Wow, we’re back in civilization.

                The direction of the radio signals tells us our drift is to the south.  I wish we had a map to locate all the cities, and how I wish I had paid a little more attention in high school to the geography of this part of the world.  The good news is that we are approaching the coast, slowly yet steadily.

     

    On their 64th day adrift:

     

    There, Bill, more to the left.”  I see it.  A halo of light, a loom, ever so faint.   It must be a small town.  On the other hand small towns normally don’t make a loom.   It must be a medium-sized city.   The direction of the radio signal indicates that it’s in southern Costa Rica.   Though faint and far away, this is our first visual sign of life onshore.  We see no distinct lights, but there are surely people.

                Sim again echoes the queries I ponder.  “What do you think it is?  How far?”

                “I can’t see the horizon, but I sense it is up high in the hills.   It can be thirty or so miles away.   It has to be a fair-sized city with mercury street lighting.   Otherwise the lights would not create a loom.”

     

    Two days later, they were rescued by a Costa Rican patrol boat.



    On Sat, Dec 5, 2009 at 8:58 PM, Lu Abel <lunav@abelhome.net> wrote:
    Why build your own??   Many cheap AM receivers use a loop antenna which is fairly directional.

    I also wonder what benefit one gets (other than "yes, it can be done" satisfaction) of creating a RDF with 3 degree accuracy.   Each degree of bearing inaccuracy gives 100' of inaccuracy per nautical mile of distance from the station.   Shoot a station from 10 nm offshore with your proposed RDF and you have a 1 nm inaccuracy in your LOP!

    Apache Runner wrote:
    Although this is a completely out-of-the-box idea, I've been working on an AM radio receiver/direction finder for fun.    The FCC publishes the lat/long for all stations in the US.   

    I haven't seen a variable capacitor in ages, but managed to find some beauties online, and am making my own antenna.    Right now, I think I can get an accuracy of maybe 3 degrees, but that's just a guess.  

    I'll post something when I have it up and running.

    On Sat, Dec 5, 2009 at 3:03 AM, glapook@pacbell.net <glapook@pacbell.net> wrote:
    I know we have some commercial air pilots on the list and was
    wondering if
    they thought an aircraft RDF unit could be easily mounted on a boat.
    The
    aircraft industry seems to be the only ones making small units these
    days.
    I might go ocean cruising with a friend who is presently re-fitting
    his
    boat, and I am a big fan of redundancy, and thought this might be a
    workable
    solution.

    ---------------------------------------------------------------------------

    An ADF will work on a boat but they aren't cheap, the readout is only
    marked every 5 degrees and the antenna has to be mounted somewhere. If
    you want RDF capability just by an inexpensive digitally tuned
    portable radio that covers the LF band such as the Grundig G5 which
    also covers HF and has SSB capability so you can get your time
    signals  too. These all have ferrite rod internal antennas which are
    highly directional. Get one and tune a distant station. Then orient
    the radio in different attitudes and rotate the radio until you get a
    null which will let you know the orientation of the ferrite rod. Then
    you can use the edge of the radio to indicate the direction to the
    station. Place it on top of a universal plotting sheet to use as a
    compass rose placed on a table or nav station desk and rotate the
    radio to get a null. You may want to make a calibration table for it.
    Don't worry about the lack of a sense antenna which are really only
    needed by an ADF since a human can easily determine which is the
    correct bearing, the 180 degree ambiguity, which is a big problem for
    an ADF, is not a problem for a human.

    gl

    On Dec 4, 11:48 am, Bruce Hamilton <brucerhamil...@gmail.com> wrote:
    > If GPS goes dark, Jeremy will be in a great position to negotiate a salary
    > raise.
    >
    >  I had great hope for e-loran as going to a single system with no redundancy
    > seems risky at best. Even when Loran C coverage was poor, even the
    > information from a single chain would give you something to work with. In
    > the middle of Lake Superior, coverage was always spotty, and on the East
    > Coast of Canada we would often be on a single chain only 50 miles off the
    > coast.
    >
    > Jeremy, do you still have a working RDF?  I used them on aircraft all the
    > time, but must admit the one on the first ship I was on was not often used
    > and this was pre-gps. I have a working portable (Ray Jefferson) RDF that I
    > am going to try in a friend's boat. It is a pity that the technology got
    > left behind in the GPS age as the modern RDF's are apparently very good and
    > very quick. The signal from the multiple antennas is instantly processed and
    > you get an bearing read out.  The Canadian Coast Guard use them to get
    > instant fixes from distress signals in pre-GMDSS days. They have remote
    > stations they use to get a cross bearings from. No GPS required.
    >
    > I know we have some commercial air pilots on the list and was wondering if
    > they thought an aircraft RDF unit could be easily mounted on a boat. The
    > aircraft industry seems to be the only ones making small units these days.
    > I might go ocean cruising with a friend who is presently re-fitting his
    > boat, and I am a big fan of redundancy, and thought this might be a workable
    > solution.
    >
    > A fine page of old RDF units <http://www.angelfire.com/space/proto57/rdf.html>
    >
    > On Fri, Dec 4, 2009 at 8:09 AM, <Anabasi...@aol.com> wrote:
    > >  I read the following on a maritime forum site.  Looks like LORAN-C
    > > systems run by the US will be shut down sooner than we thought.
    > > -----------------------------
    > > The US Coast Guard released an internal message advising of the imminent
    > > termination of the long range aid to navigation Loran-C. Current plans call
    > > for the termination process to commence on 4 January 2010. The process is
    > > expected to take several months. ALCOAST 675/09<http://www.uscg.mil/announcements/alcoast/675-09_alcoast.txt>(11/25/09).
    > > *Note: This will mark the end of an era that started during World War II.
    > > The Loran system has improved greatly over the years and was on the edge of
    > > yet another advance: to enhanced Loran (eLoran). It is unclear how other
    > > nations, which operate their own independent Loran-C systems, will react to
    > > this development. *
    > > Courtesy: Bryant’s Maritime Blog – 1 December 2009<http://bryantsmaritimeblog.blogspot.com/2009/12/bryants-maritime-blog...>
    > > ------------------------------
    >
    > > Not that this will affect many large ships.  My ship hasn't had LORAN
    > > capabilities since the antenna broke 3 years ago and the captain was too
    > > afraid to order a new antenna.  Most merchant ships are utterly dependent on
    > > GPS at this point, and would have a tough time remembering how to use the
    > > sextant if it came down to that point.  It will only get worse when the
    > > younger generations take command, having never known a time without GPS.
    >
    > > JCA
    >
    > > --
    > > NavList message boards:www.fer3.com/arc
    > > Or post by email to: NavList@fer3.com
    > > To , email NavList+@fer3.com<NavList%2B@fer3.com>
    >
    >

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