[time-nuts] Loran - any good for timekeeping?

[Brooke Clarke]

Hi Poul:

I don't think any commercial LORAN-C receiver takes advantage of the TOC 
between chains.  This is a similar concept to the "lane width" of the 
now obsolete Omega navigation system.  The lanes get wider when 
different stations are combined.  In a similar fashion when two 
different LORAN-C chains are watched for TOC to UTC then time between 
both matching the UTC second is much more that the sum to the individual 
TOCs.  Tom has a web page that I use giving the TOC for Middletown 
(9940), see:
http://www.leapsecond.com/java/gpsclock.htm

There's a lot that can be done to take advantage of LORAN-C for timing 
applications.

In GPS World there's been a couple of articles about problems with GPS.  
In one case all of the Monterey Bay was blacked out and after quite some 
investigation it was found that active UHF television antennas (that 
were powered 24/7) were the problem.  In another case it turns out that 
U.S. military ships radar can burn out commercial GPS active antennas 
and a lot of these are used on U.S. military ships.  In the 
recommendation to maintain LORAN-C they mentioned how the designers of 
the Titanic knew that the ship could not sink because it had water tight 
compartments so they did away with the backup system (lifeboats).
http://www.gpsworld.com/gpsworld/article/articleDetail.jsp?id=314679  <- 
Backup
http://www.gpsworld.com/gpsworld/article/articleDetail.jsp?id=43404 <- 
Monterey Bay Jammed
http://www.gpsworld.com/gpsworld/data/articlestandard/gpsworld/132006/315558/article.pdf 
<- Ships Radar

Have Fun,

Brooke Clarke

-- 
w/Java http://www.PRC68.com
w/o Java http://www.pacificsites.com/~brooke/PRC68COM.shtml
http://www.precisionclock.com


Poul-Henning Kamp wrote:

>In message <1565.1145648380 at critter.freebsd.dk>, "Poul-Henning Kamp" writes:
>  
>
>>In message <20060421.133311.35013386.imp at bsdimp.com>, "M. Warner Losh" writes:
>>
>>    
>>
>>>Can't you recover the time by tracking multiple chains and using the
>>>relationship between them to come up with at least small number of
>>>possible seconds?  Hasn't the US started broadcasting data that can be
>>>used to know which second you are at?
>>>      
>>>
>>This is called "Time Of Coincidence" and it works generally OK.
>>    
>>
>
>I should add that "TOC" is an overloaded term here: it's used
>both about when a chain coincides with a UTC second and when
>it does with another chain.
>
>All chains started at the top of the second 1958-01-01 00:00:00 UTC
>so you can just calculate forward using the gri.
>
>Remember leapseconds.
>
>- 
>Poul-Henning Kamp       | UNIX since Zilog Zeus 3.20
>phk at FreeBSD.ORG         | TCP/IP since RFC 956
>FreeBSD committer       | BSD since 4.3-tahoe    
>Never attribute to malice what can adequately be explained by incompetence.
>
>_______________________________________________
>