[time-nuts] Loran - any good for timekeeping?
M. Warner Losh
imp at bsdimp.com
Fri Apr 21 16:14:27 EDT 2006
In message: <444937B6.6020405 at pacific.net>
Brooke Clarke <brooke at pacific.net> writes:
: Theoritically you could use stations from different chains to get a
: position fix.
As long as you can see more than one station from each chain, since
the position fix is established using the differential time of
arrival. If you only have one station from two different chains, you
can't be sure which of the stations from each of the chains you have
unless you already know about where you are. I don't know if the
addition of data has now given each station an ID or not, to be
honest. If you do happen to know which stations you are seeing, then
you can indeed work out a position fix, but the math is much harder.
: It's my understanding from talking to the people that run
: the Middletown, Calif. station that in the not to distant future all
: the U.S. LORAN-C stations will be transmitting their pulses based on UTC
: rather than on some delay from the master station as it is now.
Kinda. All the loran stations have multiple cesiums that are steered
to GPS that are used for their notion of UTC. The transition is
between tuning the network so that varying weather conditions are
accounted for at each of the monitoring stations so the pulses that
arrive there give a position fix that matches the surveyed location.
Each additional station in the chain still is offset from the master
by a fixed amount (and from eachother, so that the X station chirps at
a different time than the W station). The change is that everyone
recovers UTC and then base their transmission on UTC rather than
having each station tuned from the monitoring stations.
: station has multiple Cesium standards and each has a phase adjuster.
Yes. Each station monitors the time of transmittion relative to the
cesium clocks and adjusts delays to keep certain benchmark times
within spec. These adjustments can be made automatically by the
software, or manually by humans.
: This should have the effect of reinforcing the concept of "all in view"
: and now I can see also supports adding a time code.
I know of at least one time recovery receiver for LORAN-C that uses
all the stations it can see to refine its notion of time.
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