--> Did you find usefull reference information? <--

Yes, there are a few places on the net where you can find the signal
specification, and how the system works. It's a lot simpler than GPS. Just
google for LORAN C Signal specification, and you should find it. That will
give you pretty much all the info you need for decoding the signal.

You'll need to build a tuned RF 100 kHz receiver. If you google for info
about VLF radio, you'll find amateurs who construct receivers that will pick
up the signal. In fact, many of the discussions relate to how to get rid of
that damned LORAN signal because it is transmitted with such high power.
Search also for WWVB receivers, as many of those are suitable. (Note, its
WWVB, which transmits at 60 kHz, not WWV which transmits at much higher
frequencies).

They usually use some kind of B field antenna, shielded from the E field.
I've seen plans for one that was made from the rim of a bicycle wheel. It's
all very doable, especially if you have a scope. Google for "loop antenna"
or "VLF antenna".

You can also buy LORAN antennas that are already tuned for the right
frequency. They use them for small aircraft and boats. There are usually a
few on eBay.

I suspect the RF part will be relatively simple, but then you'll have the
job of decoding the pulses and measuring their arrival time. Depending on
where you are in the world, the signal has different timing characteristics.
You have to recognise these patterns to know which LORAN chain you are
listening to. Then you have to identify the master transmitter in the chain,
and 2 or 3 slaves. You'll need a very precise, stable crystal oscillator. I
would suggest oven stabilized, or at least temperature compensated. Some
receivers generate their timing from the 100 kHz carrier, which is locked to
a caesium clock. WHatever method you use, you'll need to timestamp as
precisely as possible the time of arrival of each pulse in the chain. Each
pulse is a burst of carrier of an exactly defined shape. You have to
identify a particular point within the burst as the time reference for that
burst. The reference point is something like the third zero crossing of the
carrier. When you have the timestamps for all the pulses, you then apply the
math and solve for your position.

I still like the idea of building one of these, even though I have no use
for it now.

Neil


On 1/20/06, Wouter van Ooijen <wouter@voti.nl> wrote:
>
> > If you just want to extract timing info from the LORAN signal, it's
> > not too complicated. Using it for navigation requires a whole bunch of
> > precise math as well as the ability to time the arrival of the LORAN
> > pulses. You have to pick out a particular point on a particular cycle
> > of the 100 kHz signal as your timing reference.
>
> I fellow teacher was interested in the possibility of using it for
> mobile robot position information. We do electronics and embedded, some
> work was expected, both analog and digital.
>
> Did you find usefull reference information?
>
> Wouter van Ooijen
>
> -- -------------------------------------------
> Van Ooijen Technische Informatica: www.voti.nl
> consultancy, development, PICmicro products
> docent Hogeschool van Utrecht: www.voti.nl/hvu
>
>
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