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The 2002 edition of Bowditch that you can download from NGA.mil has
this to say about correcting long range radio bearings for plotting on
a Mercator chart: "The relatively short range of those stations
remaining has made this process obsolete."

gl

On Dec 6, 4:53�pm, Lu Abel  wrote:
> Good point, Irv. � I've been navigating since navigation texts included
> a chapter on RDF. �Almost invariably they mentioned that there was
> danger in using commercial AM stations for RDF -- antennas often inland,
> sometimes mismarked on charts or other publications, etc. � Advice was
> generally to stick to CG RDF beacons -- low frequencies assured
> groundwave (vs skywave) propagation, locations accurately marked on
> charts and available in the Light List, etc. � �I even remember when
> Bowditch had a table for compensation for great-circle propagation of
> signals from distant transmitters (ie, you got a direction to the
> transmitter, but it was the initial direction of a great circle which
> all of us expert navigators know (right?) is not the rhumb line bearing
> to the destination.
>
> Lu
>
> Irv Haworth wrote:
>
> > Might I also add that the towers associated with civilian radio
> > stations are generally inland. This may (depending upon bearing taken)
> > be several degrees off due to refraction.
>
> > As an aside and depending upon radio used (freq./mode �etc.) one is
> > also able to use antennae associated with airports. Needless to say to
> > use these on needs either �an air map or get � & � from google .
>
> > VE7CVL
>
> > *From:* Lu Abel [mailto:lu...@abelhome.net]
> > *Sent:* Saturday, December 05, 2009 5:58 PM
> > *To:* navlist@fer3.com
> > *Subject:* Re: [NavList 10950] Re: LORAN-C to be shut down.
>
> > 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, glap...@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  > > 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
> > 
>
> > > On Fri, Dec 4, 2009 at 8:09 AM,  > > 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(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
>
> > > > ------------------------------
>
> > > > 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
>
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