[time-nuts] US considers shutting down Loran

[Brooke Clarke]

Hi Rob:

Thanks.  I have subbmitted the following comment:

Brooke Clarke

w/Java http://www.PRC68.com
w/o Java http://www.pacificsites.com/~brooke/PRC68COM.shtml
http://www.precisionclock.com
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I think that LORAN-C is a necessary system and it should not be shut 
down.  There are a number of reasons for this.

(1)   The GPS system operates at a microwave frequency in the area of 
1,500 MHz whereas the LORAN-C system operates at a frequency of 0.1 MHz, 
i.e. very much separated in frequency from GPS.  This is not the case 
with the Russian and European satellite navigation systems that operate 
in a similar manner to GPS making all three satellite navigation systems 
susceptible to a common jamming signal.  Hence the European and Russian 
satellite navigation systems can not be thought of a backups to GPS.  
But the frequency of LORAN-C is far from the band used by the three 
satellite navigation systems and would not be effected by a GPS jammer 
in any way.

(2)   The signal strength of GPS is below the noise level at the surface 
of the Earth so it can be jammed by a weak signal.  There have been a 
number of confirmed cases of this happening by accident.  For example a 
defective television antenna on a boat in Monterey Bay, California 
jammed all the GPR receivers for some time until it was tracked down and 
turned off.  Harmonics of some UHF television channels will jam the GPS 
signal.  Harmonics from aircraft receivers have been known to jam GPS.  
There is a home brew jammer that's smaller than a shoe box designed to 
jam GPS described on the internet.  By contrast the signal from LORAN-C 
is measured in megawatts rather than is micro watts and so would be very 
difficult to jam.  There have been articles in "GPS World" that have 
details of these GPS failures.

(3)   Because of it's high power and low frequency the LORAN-C signal 
can be received where GPS is blacked out.  For example in urban canyons 
or inside buildings.

(4)   If GPS is going to be used for critical functions then there is a 
need for a backup system and LORAN-C has been demonstrated to be a good 
choice.  This applies in diverse areas.  For example:

·        Automated landing of passenger aircraft

·        synchronization of telecommunication systems

·        separation of high speed trains

·        in the not too far future automated highway systems

(5)   One drawback of the LORAN-C system is that there is no data being 
sent, i.e. it's a pure navigation system.  For example you can not set a 
clock using LORAN-C by itself.  But the new data channel adds a number 
of data fields (I think this is part of the eLoran upgrade) so that you 
can set a clock.  The LORAN-C station at Middletown, California (near 
me) just started sending the data channel October 2006 and I have 
started working on a receiver to decode it in order to set a precision 
clock.


Since LORAN-C stations are spread pretty much all over the world when 
they are upgraded to eLORAN stations it would allow for a global method 
of accurately setting clocks.  Note that now there is a U.S. "atomic 
time" station (WWVB at 60 kHz) and a station in Germany using a 
different frequency and data protocol and a different station in the UK 
that's on 60 kHz but with a different protocol from WWBV, a station in 
Japan that's different, etc.  So the market for automatic radio 
synchronized clocks is fragmented.  Note that GPS is not suitable for 
indoor clock setting because it requires an outside antenna unlike WWVB 
at 60 kHz or LORAN-C at 100 kHz which work fine indoors.

 

(6)   LORAN-C was designed for coastal navigation but it has grown.  
Prior to GPS, LOARN-C receivers were popular in aircraft allowing much 
more freedom in choosing routes than the old system that depended on 
flying to or from air navigation beacons.  And LORAN-C does offer better 
repeatability than GPS and this is a much liked feature for boats that 
need to return to the same spot, like to retrieve crab traps to find the 
correct slip in a foggy harbor.

 From an economic point of view the cost to upgrade the LORAN-C system 
and to maintain it is far far lower than the cost for one GPS 
satellite.  Note that satellites have a limited life (need to be 
replaced) and their cost includes not only the actual hardware in space 
but also the launch and continuous maintenance.  But in return there is 
a great benefit from eLORAN both in terms of GPS backup and in terms of 
capability that GPS can not supply.
-------------------------------------------------------------------------------------
Rob Kimberley wrote:

>http://www.fcw.com/article97298-01-08-07-Web
>
>Rob Kimberley
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