[time-nuts] Loran-C

Enrico Rubiola rubiola at femto-st.fr
Sun Jun 3 04:30:54 EDT 2007

Dear all,
the old good Loean-C is still alive, as I can see.

There is a funny thing about the receiver.  The case
of loran signal is that of finding the zero-crossings in
a very polluted signal.

The receivers designed in the '80s use a 1bit ADC
(hard limiter) sampling at some 10 MHz, and find the
zero crossings through the statistics of 0s and 1s at the
converter output.  They identify the envelope (needed
for the zero crossing at 30 microsec from the origin of
  the envelope) in this way.

It has been demonstrated that in the case of detecting the
zero crossings in highly polluted signals, if the hard limiter
is used instead of the full resolution of an ideal ADC (infinite
number of bits), the SNR is made worse by less than 2 dB.

There are a few articles written by Durke van Viilligen,
Delft University, somewhere between 1975 and 1980.
On request, I can dig deeper in my memory and hard disks.



Enrico Rubiola
professor of electronics

web:	http://rubiola.org
e-mail:	rubiola at femto-st.fr

FEMTO-ST Institute
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