[LEAPSECS] Executive Order on Strengthening National Resilience through Responsible Use of Positioning, Navigation, and Timing Services

[Warner Losh]

On Thu, Feb 13, 2020, 12:36 PM Tom Van Baak <tvb at leapsecond.com> wrote:

> > I thought of Loran...  but you need 2 stations for time, I thought...
>
> 2 (or more) Loran-C stations gave you more accurate time. But if you know
> where you are, and since the stations don't move, you can manually adjust
> for signal propagation delay to some extent. This is not unlike how one
> obtains time from WWV or WWVB.
>
One of the big issues with LORAN C, I thought, was that those variations
were measured in microseconds...

But I guess those average out over time so if you have a stable local
oscillator you can recover time fairly well.

Fun fact, LORAN has no leap seconds (since it is just a bunch of different
rates). So to calculate time of coincidences with UTC you had to basically
use TAI - 10s since the LORAN signal is paced with SI seconds. When I was
working on the replacement timing system for the LORAN chains, this was a
big deal since to start LORAN you needed to know both the UTC time and a
recent / near future table of leap seconds... This leads to a lot of edge
cases, especially when you needed to cope with the cold spare GPS reciever
case. :(. It's also where all the love I feel for leap seconds left my
body...

Warner

> /tvb
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