NavList:

   

Reply

Herbert:

Thanks for your reply.  In my original post I should have noted that I had
already researched the Loran-C handbook, the USCG NavCen web site, and done
a Google search.  All came up empty with any specifics on how L/Lo
calculations are actually done in Loran receivers.

As you point out, a number of sources including the Loran-C Handbook
provide the equations for the hyperbolic LOPs.  But the ones in the Loran-C
Handbook at least are flawed:  (1) they assume the Master and Secondary
stations are on the same parallel of Latitude, and (2) the work all their
mathematics in miles of distance rather than L/Lo (which where we want to
end up).  In other words, they are the standard equations found in a
standard high school algebra text, not equations suitable for real-world
use.  And there is absolutely no information on how one might intersect a
pair to get a fix.

And, again, using the hyperbolic LOP equations might or might not be the
way it was done in real Loran units.

Lu Abel


At 09:02 PM 7/22/2001 +0000, you wrote:
>It's a combination of both. You have to start with TDs to get an approximate
>position. Because the TDs give you hyperbolic surfaces, and you know your
>altitude, you get a system of  3 quadratic equations in 3 dimensions.
>
>Then you have to correct for Primary Phase Factor, Secondary Phase Factor and
>Additional Secondary Phase Factor. The latter is for varying propagation speed
>of the signal over different types of surfaces. Since the route of the signal
>and hence the decomposition into the various segments of the signal path are
>only known after the approximate position of the receiver is known,
>iteration is
>unavoidable.
>
>I cannot speak for Micrologic or Furuno, but anything less then the above
>would
>not have been state of the art.
>
>A technical description of Loran-C can be found in "Loran-C User Handbook",
>1992, COMDTPUB P16562.6 available from the US GPO.
>
>Herbert Prinz (from 1368950/-4603950/4182550 ECEF)
>
>
>Lu Abel wrote:
>
> > Does anyone have specific knowledge of how Loran receivers calculate L/Lo?
> >
> > It seems to me there are two possibilities:
> >
> > 1.  Pseudo-ranging as is done in GPS receivers.  This involves guessing at
> > a position (L, Lo, and time) and seeing if it's consistent with the
> > received signals.  If not, the position is adjusted and rechecked.  This is
> > repeated until the AP is consistent with all received signals and therefore
> > can be called a fix.
> >
> > 2.  Starting with the TDs as received and grinding them through some set of
> > equations which produce L/Lo directly from the TDs.
> >
> > I'd appreciate knowing how folks like Micrologic and Furuno actually
> did it.
> >
> > Thanks.
> >
> > Lu

   

Reply