LORAN to come back?

[Mike O'Dell]

eLoran is indeed an improvement over Loran-C

first, a few comments about Loran-C vs GPS.
Loran has *always* been better than GPS with respect to *repeatability*
while GPS has always been superior about positioning accuracy.
Those are *different*.

Repeatability has to do with "marking" a location and returning to it
at some later point. Loran-C does a better job of getting you back
to a spot *that you have already visited* and "marked".

GPS lets me give you a Lat/Lon pair on the other side of the world
with the assurance that we will be within the error circle *the first
time*.

Loran-C is great for returning to the crab traps you've dropped
in the Bering Sea, while GPS is better for delivering an autonomous
payload to a distant target.

the eLoran ground station upgrades involve triple cesium clocks at
the stations coupled with a dedicated time distribution network
from the Naval Observatory, coupled with new solid-state transmitters
that dramatically include the phase noise in the signals.
eLoran also carries differential correction information within
the waveform of the carrier. Because of the transmitter improvements,
the 100KHz signal is as good a source for precision timing as GPS,
possibly better in periods of ionospheric disturbance.

the other part of eLoran is in the receivers.

all the work which has been done developing algorithms for
"all sats in view" GPS receivers turns out to be applicable
to eLoran receivers. The eLoran receiver I bought when the
deployment started can track up to 10 or 15 stations simultaneously
and does the same kind of calculations which reduce the error
radius dramatically in the "all sats in view" GPS receivers.
Between these algorithms and the significantly improved
ground station signals which allow phase tracking, both the
accuracy and repeatability are improved. Also contributing
to eLoran's improved performance is the computation ability
where the kinds of propagation distortion maps akin to the
deviation maps in GPS recievers that provide a "magnetic" heading.

the other thing my eLoran receiver has is a GPS receiver, the
output of which is combined with the eLoran solutions, providing
the accuracy of GPS and the repeatability of eLoran.

Had the deployment been allowed to continue, it would all be
done now and we'd have a super-solid backup PNT source that
would be as usable in your basement as on your roof.

Now that the OMB lamebrains have torn down several stations, 
including the antennas, it is going to cost multiple hundreds
of millions to rebuild them. The original deployment was *almost*
complete and the annual OPEX was less than $50 million.
and that decision to start destroying them to save $50mm/year
was done *after* the FAA selected eLoran as the backup PNT
system that was required to move forward with the NextGen
Air Traffic Control System which has been stalled ever since
it became clear there was no viable backup for GPS.

I've been following all this for over a decade now and
it's one of the worst examples of "death by wonkery"
i've ever heard of. Luckily some concerted efforts got
the destruction stopped and the ball rolling the right
direction again.

	  -mo