[time-nuts] The Demise of LORAN (was Re: Reference oscillator accuracy)

David I. Emery die at dieconsulting.com
Mon Nov 16 03:33:07 UTC 2009


On Sun, Nov 15, 2009 at 08:56:36PM -0600, Didier Juges wrote:
> 
> I don't disagree that it would be fairly easy to disrupt the consumer
> devices, but other than a few missed appointments and frustrated gadget
> freaks, and the occasional emergency vehicle not finding its way to the
> scene of an accident, that would be more of a problem) I am not too worried
> about the consequences of that.

	GPS has been widely used for time and frequency sync in radio
systems of various sorts - some depend on it for successful simulcast
from multiple transmitters (including many public safety radio systems)
and while there is SUPPOSED to be significant holdover, there is are
always those situations where nobody has EVER checked that it works...
And what will holdover do about LONG TERM outages of GPS ?   Perhaps 
folks are willing to bet the whole infrastructure on the supposition that
we could NEVER see a complete long term loss of signal (using civilian
receivers with modest anti jam abilities) in a particular location or
region - I am not exactly sure what alternative might exist though I
guess there are some for time and frequency - terrestrial GPS beacons
from high points that could lock up a cell system in a region come to
mind...

	And more and more and more stuff depends on more or less
ignorant and sometimes not very bright operators expecting that the GPS
positions are always there or they don't know what to do.   And if GPS
is almost always reliably there there may well be little or no practical
training about what to do if it fails.   Failure modes and paths in code
and procedures (and sometimes even actual hardware) which aren't often
tested or exercised usually fail when actually needed and often in
entirely unanticipated ways - maybe the backup ALSO depends on GPS in
some way the system designers never thought about (or knew could
happen)...

	LORAN C represents a viable (albeit not often deployed) backup
to time and frequency control and could be implemented in modern
hardware as a backup location service at reasonably low cost for those
applications where that is important enough.	

> 
> The thread started with the loss of the LORAN system, and nobody (maybe I am
> going out on a limb here) ever used a LORAN receiver in his car to find the
> nearest restaurant :)

	Actually readers of this list have, though not in recent times I guess.
> 
> I think the people who should complain the most about the loss of LORAN are
> the boaters, but they are the one who embrassed GPS the first and are it's
> biggest advocates!!! I know, I live on the coast of Florida.

	An enhanced LORAN that has some of the accuracy and automation
of a GPS receiver exists... I suspect boaters care most about
convenience (and accuracy) and found GPS easier.   Certainly so compared
to earlier LORAN C gear.

	And of course there is another issue with GPS, it is controlled
by the DOD and is supposed to have the ability to deny service in a
region if conditions are sufficiently apocalyptic to require it.   For
folks worried about this (more outside than inside the US obviously)
LORAN is a local resource they may control and certainly can if they
make a more or less modest investment in the ability to do so.   Some
(large) players are of course planning their own space based systems for
just this reason but LORAN can be implemented by most nation states...

-- 
  Dave Emery N1PRE/AE, die at dieconsulting.com  DIE Consulting, Weston, Mass 02493
"An empty zombie mind with a forlorn barely readable weatherbeaten
'For Rent' sign still vainly flapping outside on the weed encrusted pole - in 
celebration of what could have been, but wasn't and is not to be now either."




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