eLORAN

[Mike O'Dell]

The British eLoran system is a an extension of Loran C.
All the US Loran stations were upgraded to eLoran capability
before the morons in OMB decided to save $35mm/year by scrapping
$100mm of upgrades and infrastructure that will cost $500mm to
recreate. Yes, they have dropped a number of the big antennas.

This was AFTER the FAA picked eLoran as the GPS backup for NextGen.

The newest version is DeLoran - differential extended Loran.
it carries differential corrections as well as the other extended
Loran payload. 

the upgrades to the Loran stations included dual cesium clocks
at each site, a fiber time distribution network for all the stations,
and new high-power solid-state transmitters because they have much
much lower phase noise than the old tube units. 

It isn't widely known, but even Loran C has superior repeatability
over standard GPS, while GPS has higher accuracy. How's that different?

when you throw a trap into the ocean, you don't care about it's
exact location expressed as Lat/Lon, you care about being able
to go back to that same spot again and again. Loran C beats GPS
for that which is why commercial fishermen were the last to give
up on Loran.

If someone gives you a Lat/Lon on the other side of the world
and you are supposed to meet someone there, nothing does that
better than GPS, but the "point" is about 10 meters in size
(better if they ever get enough new GPS birds up with the new
signals). it was 100 meters before Selective Availability 
was turned off. 

The new eLoran receivers are very different from the old receivers.
Now the eLoran receivers use the algorithms developed for GPS to
allow a receiver to listen to "all chains in view" just like good
GPS receivers listen to "all satellites in view". With the ability
to hear multiple stations on multiple chains, the solutions are
easily as good as GPS used to be although not as good as GPS
carrier phase tracking can produce.

The radio front-ends are much better, too. Rather better semiconductors
and they are essentially all SDR so can use lots of computes to dig
signals out of the noise.

There are efforts under way to try and get this horrible mess sorted out
but the fact it was allowed to get screwed up in the first place
is absolutely infuriating.  We lost most of a decade out of sheer
fuckwittedness. That put the ATC NextGen system behind, etc, etc.

Stupid stupid stupid stupid.....

       -mo