[time-nuts] eLORAN will be on the air GRI 99600

[paul swed]

I some tests I was fortunate to be a part of the eLloran system was able to
deliver very accurate time even in buildings. I won't quote numbers as it
was 5 years ago. But suspect the details are online. The extra data channel
allows for the transmission of various corrections.
Regards
Paul

On Thu, Aug 6, 2020 at 9:52 PM Forrest Christian (List Account) <
lists at packetflux.com> wrote:

> I probably need to clarify where I'm coming from in relation to my previous
> message.
>
> I have a fair bit of background in dealing with using GPS clock sources for
> synchronization at communication sites.   Many of these sites are lucky to
> have a rubidium oscillator in place for holdover, although some do (usually
> the larger ones).  And we're talking about thousands and thousands and
> thousands of these sites.
>
> Where I was coming from is that at these sites, GPS can be a challenge -
> it's in a narrow band, very low signal, and, at least from my worldview, it
> seems like GPS interference is becoming more prevalent instead of less.
>  As a result, whether terrestrial or via satellite, it would be nice to
> have a second alternative in a different band where one could obtain a
> reasonably aligned 1PPS (+-1uSish).
>
> I'm hopeful that eLORAN will result in this result.   I'm also curious
> about the GPS L5 signal once it becomes operational since that is far
> enough away frequency wise that one would hope that it wouldn't be affected
> by the same interference source.
>
> On Thu, Aug 6, 2020 at 6:19 PM jimlux <jimlux at earthlink.net> wrote:
>
> > On 8/6/20 4:28 PM, Forrest Christian (List Account) wrote:
> > > If you look at generally-available GNSS PNT solutions, you'll find a
> few
> > > failure modes:
> > >
> > > 1) Loss of a satellite (or two).   This is why the constellations have
> > more
> > > satellites than is strictly necessary, so not a big deal.
> > >
> > > 2) Loss of control/failure in the control system/constellation wide
> > > software failure, aka the recent Galileo failure.   This is why you
> have
> > > multiple GNSS constellations.
> > >
> > > 3) Ground based interference (jamming, spoofing), etc.    This is why
> you
> > > need a terrestrial backup, which doesn't really exist.
> > >
> > > For timing, I wouldn't be opposed to someone flying (or adding a
> payload
> > > to) a couple of geostationary satellites which live in a separate band
> > from
> > > GNSS.  It would be interesting to be able to put up a small satellite
> > dish
> > > and get a highly reliable and hard to interfere with timing alternative
> > to
> > > GNSS.    I know there are two way time transfer options out there, I'm
> > more
> > > thinking basically a fixed-location cesium clock in the sky.
> > >
> >
> > Well, the GPS folks found that a Rb works better than a Cs, and both
> > need ground monitoring and updating.
> >
> > One could rent a Single Channel Per Carrier transponder slot on a GEO
> > satellite, feed a carrier derived from your ensemble of clocks to the
> > uplink, and there you go.
> >
> > My google-fu is failing and I can't find even a rough cost for such a
> > service.  Maybe something like $50k/month? $600k/year.
> >
> > That 600k would probably buy you *one* space qualified Rb oscillator of
> > "good enough" performance, maybe.   USOs like used on GRAIL were
> > $1M/each sort of items in qty 4. And then you need some TWTAs to amplify
> > the signals for transmission - those are also pretty pricey.
> >
> > And then the launch cost.. I happen to know (because I just bought it at
> > work) that you can push about 100-120kg to a GEO+1000km orbit for right
> > around $10M.  Rocketlabs might do 20-30kg to a similar orbit for half
> that.
> >
> >
> > All in all, I suspect that there are better uses of the $50M it would
> > cost - You could buy a LOT of Cesium clocks for terrestrial use.
> >
> > If you're willing to do CSAC level performance, and you're willing to
> > have it be in LEO, so you see it a couple times a day for 20 minutes,
> > and you're willing to do some design and fab in your garage - under $5M.
> >
> > Look up CHOMPTT  - CSAC and optical links.
> >
> >
> >
> https://digitalcommons.usu.edu/cgi/viewcontent.cgi?article=4407&context=smallsat
> >
> >
> >
> >
> > _______________________________________________
> > time-nuts mailing list -- time-nuts at lists.febo.com
> > To unsubscribe, go to
> > http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com
> > and follow the instructions there.
> >
>
>
> --
> - Forrest
> _______________________________________________
> time-nuts mailing list -- time-nuts at lists.febo.com
> To unsubscribe, go to
> http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com
> and follow the instructions there.
>