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From: byrnes@ge-dab.UUCP (Arthur J. Byrnes)
Newsgroups: sci.electronics
Subject: Re: Info Wanted:  DECCA Navigation
Message-ID: <642@ge-dab.UUCP>
Date: Sat, 20-Jun-87 00:25:34 EDT
Article-I.D.: ge-dab.642
Posted: Sat Jun 20 00:25:34 1987
Date-Received: Mon, 22-Jun-87 06:29:53 EDT
References: <24300011@silver>
Reply-To: byrnes@ge-dab.UUCP (Arthur J. Byrnes)
Organization: GE Simulation & Control Systems Dept., Daytona Beach, FL
Lines: 50

In article <24300011@silver> commgrp@silver.UUCP writes:
>
>
>
>How  does the DECCA navigation system work?   My understanding is 
>that it's a British or European system similar to LORAN-A.  There 
>are  several "chains" of transmitters 70 and 130  kHz.   What  is 
>DECCA's range,  coverage area, and signal format?  I have seen no 
>DECCA  equipment advertized in marine electronics catalogs in the 
>U.S.   Is  it used in the Western or  Southern  hemispheres?   Is 
>DECCA  considered  a modern system?   Ian Fleming mentions it  in 
>"Thunderball," aboard the bad guy's yacht.
>
>
>--
>
>Frank Reid                                   PO Box 5283          
>reid@gold.bacs.indiana.edu                   Bloomington, IN 47402
>                                             (812) 335-0711 (w)

As a technician who worked for Decca Marine for several years I can 
tell you a little about the Decca Navigation system.  You are r
right about the frequency range.  It is a continous wave system
where as LORAN is a pulse system. The transmitters (3 or more)
transmit signal on a specific frequency and the receiver measures
the phase difference between the signals. Each transmitter is on n
a different frequency, but they are locked to a frequency 
standard such as a cesium (sp?) beam clock.  
The Decca system is very popular in Europe, and is (claimed to
be) more acurate than LORAN.  But Decca makes money by leasing the r
the recievers to ships, and since LORAN is free, there is
no market in the USA for the Decca system.  I think there is
a Decca chain on the east coast of Canada, but I'm not sure.

Also the system is not pure cw, some type of info is encoded 
but I'm not sure what.  (The techs from the UK told us about
a European fellow who decided he was going to get rich, he
designed a digital reciever that used the Decca system. 
The Decca recievers used big dials like analog clocks, kinda
looked like the altimeters in old crashing airplane movies,
the hands would spin wildly untill it locked onto the signal.
Anyway, this fellow's receiver worked real well and sold for 
the price of about a 6 month Decca lease.  After many canceled 
leases the boys at Decca found out what was going on and they
got one of his receivers, analyzed it and found that by 
slightly changing the signal the bogus receiver dooesn't
track anymore. But it didn't effect the mechanical works in a
"real" Decca receiver.

Arthur