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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

   

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