Loran C off the air
mo at ccr.org
Mon Aug 9 17:19:50 CDT 2010
the timing application of Loran relies upon the
stability of the carrier. in the upgrade, all the
stations were given cesium clocks (disciplined to
Naval Observatory) and new very-low-phase-noise
solid-state transmitters. after the upgrade, the
Loran stations were probably *better* than GPS
because of the superior propagation of that big
honking VLF ground wave completely devoid of
ionospheric scintillation and differential
multi-path which plays hob with the phase noise
as received on the ground.
the most interesting point is that all the algorithms
developed to handle all-in-view processing and
carrier phase tracking for GPS turn out to be applicable
to Loran. the eLoran receivers routinely track 10-20
stations on multiple chains simultaneously, making for
*very* good fixes. moreover, eLoran can provide absolute
heading (2D orientation fix) by using quadrature H-loop
antennas to give angle of arrival data. combine that
with the extremely precisely known location of all
the stations and a Kalman filter will give you very
good compass *without* requiring any motion in the platform.
the GPS compasses require 3 receivers and differential
carrier phase tracking to accomplish the same thing,
except if you go under a bridge, you lose your heading
they had already paid to upgrade the system, and the operations
cost is "couch change" compared to damn near everything else.
i'm cynical enough to believe there is more behind it.
being able to deny cellular communication by just
turning off the civilian GPS signals would seem
to be the kind of "OFF" switch Gubmint might want to have.
of course, the continunity-of-gubmint networks would use
the military signals so they would keep working.
i assume just about everyone here is old enough to remember
Burt Lancaster and the meaning of "ECOMCON" ??
Well, paradoxically, it's now a lot EASIER to do than ever before.
and it would take the Internet with it, btw. it uses the same
optical transmission infrastructure.
Yours for better nightmares,
On 8/9/10 8:35 AM, Tom Azlin N4ZPT wrote:
> Hi Mike.
> I suppose this could be a failed gold watch tactic. Or a "I will let it
> fail if you are so convinced it will work" strategy we are watching.
> But obviously not everybody said to keep Loran. Congress is frequently
> funding stuff the administration or DoD wants to kill. So why not now? I
> agree that what I read on line is uniformly in support of keeping Loran
> running as a backup timing system (which was always a secondary use I
> thought). So why did it not get prioritized within the Coast Guard when
> the initial calls for un-needed programs went out? Or if so inexpensive
> did not someone else pick up the mission, facilities, people, etc as the
> Coast Guard offered? Or if GPS were so vulnerable did DHS not tell the
> Coast Guard to just keep it going for infrastructure protection. And so on.
> Not a very interesting debate seems to me.
> 73, tom n4zpt
> On 8/8/2010 11:16 PM, Mike O'Dell wrote:
>> everybody that looked at it said to keep Loran-C
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> Tacos at amrad.org
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