commgrp@silver.bacs.indiana.edu (06/18/87)
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.
Thanks in advance; my e-mail replies don't always go.
--
Frank Reid PO Box 5283
reid@gold.bacs.indiana.edu Bloomington, IN 47402
(812) 335-0711 (w)byrnes@ge-dab.UUCP (Arthur J. Byrnes) (06/20/87)
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
henkp@nikhefk.UUCP (Henk Peek) (06/24/87)
In article <24300011@silver> commgrp@silver.bacs.indiana.edu 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? Its orgin is British. The DECCA system works with chains of 4 transmitters. (1 master and 3 slaves). They transmit on the frequention range of 70 to 130 Khz. The frequentions are subharmonic related (about a few KHz). The system works with fase-relations between the trans- mitters. Those relations named lanes and are hyperbolic lines between transmitters on a special chart. There are a few modes with different lane wides. >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? The DECCA system was born in ww2 and patended by decca corparation. They own all the equipment and only hiring out the recievers. Only in the last few years you can buy recievers from other firms. The DECCA system is used in the hole West European coast and japan. DECCA is an old system, but it works with a good accuracy. henk peek ..!seismo!mcvax!nikhefk!henkp.UUCP
mb@camcon.co.uk (Mike Bell) (07/02/87)
> 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) I bounced this story off an ex-DECCA employee. He said it sounded unlikely, because the specification of the DECCA signals are actually layed down by legal statute, so unless the fellow's receiver relied on something which wasn't in that specification... [There was no love lost between the ex-DECCA employee and Racal-Decca, so I have no reason to doubt this...] Apocryphal story: apparently it used to be quite common for ships to travel along the lines of constant phase - resulting in the occasional collision between ships travelling along the same line in opposite directions (usual disclaimers...) -- --------------- UUCP: ...seismo!mcvax!ukc!camcon!mb -- Mike Bell -- or: mb%camcon.uucp --------------- Phone: +44 223 358855