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. But, a good quality terrestrial option would be useful too. On Thu, Aug 6, 2020 at 3:40 PM Bob kb8tq <kb...@n1k.org> wrote: > Hi > > > On Aug 6, 2020, at 4:40 PM, jimlux <jim...@earthlink.net> wrote: > > > > On 8/6/20 9:17 AM, Taka Kamiya via time-nuts wrote: > >> Someone in this thread mentioned "at least 2 satellite time and > frequency solutions" exists already. I only know of GPS (GNSS) > constellations. What's the other? > > > > Transit? > > > > I don't believe they are still operational, though. > > > > > > I wonder if one might be able to pick up time/frequency from a > commercial TV broadcast transponder. The transponders on the satellite are > typically bent pipes (for C-band anyway), I would assume that the uplinks > may or may not have stability comparable to terrestrial broadcast. > > > > One problem is, of course, that the satellites aren't in a stable > location (at least on a "meters" scale) - but one could certainly do > "common view" kinds of time transfer. > > Another couple of “up in the air” question: > > Some of the systems transmit “stand alone” signals in each of two or three > different bands. Does each > band count as a separate time source? > > If you know your location already, each sat in these systems can be a time > source all by it’s self. Do they > each count? > > I guess is depends a lot on just how you look at redundancy …. > > Bob > > > > > > > > > > > >> --------------------------------------- > >> (Mr.) Taka Kamiya > >> KB4EMF / ex JF2DKG > >> On Thursday, August 6, 2020, 12:01:27 PM EDT, paul swed < > paulsw...@gmail.com> wrote: > >> Magnus > >> Its honestly by luck that I know anything. From the bits I have read > Europe > >> seems far closer to eLORAN then we are. Perhaps 6 months ago the US > >> performed a series of tests 2 eLoran solutions and something like 6 or > more > >> satellite solutions. I know the old Iridium satellites were in the tests > >> and some other LEO satellites. > >> But thats about it. > >> What we need is a cheap SDR LORAN C sniffer. Low power runs 24 X 7 and > >> turns a LED on if the stations active. > >> Oh well another project in the someday pile. > >> Regards > >> Paul > >> WB8TSL > >> On Thu, Aug 6, 2020 at 2:42 AM Magnus Danielson <mag...@rubidium.se> > wrote: > >>> Hi Paul, > >>> > >>> I only ask as you seem to track this thing the best here on time-nuts, > >>> as far as I have seen, such that it is your emails that keeps me best > up > >>> to date with the progress. > >>> > >>> Cheers, > >>> Magnus > >>> > >>> On 2020-08-05 19:21, paul swed wrote: > >>>> Hi Magnus been a while since have emailed. > >>>> Its one site that was a test transmitter. Its in New Jersey, USA. > >>>> The goal of the testing I believe is to establish the viability of an > >>>> alternate PNT reference to GPS. Additionally the ability to > communicate > >>>> some level of message broadcast. This should be identical to > proposals I > >>>> have heard of in Europe. > >>>> But I have no direct relationship to any of this. Like you, a very > >>>> interested observer and hope that eLORAN wins the battle. > >>>> Unfortunately there are many alternate proposals such as using other > >>>> satellites. Hmmm if I wanted to advance my career in the Air Force or > >>> Space > >>>> Force (Yes thats actually real now). > >>>> Would I select the lowly reliable as heck eLORAN at sub $100 M/year to > >>>> operate. Or the glorious space based proposals in $B region. Never > mind > >>>> that at least 3 countries now have demonstrated killer satellites. > >>>> Sorry for that editorial. > >>>> Regards > >>>> Paul > >>>> WB8TSL > >>>> > >>>> On Wed, Aug 5, 2020 at 11:04 AM Magnus Danielson <mag...@rubidium.se> > >>> wrote: > >>>> > >>>>> Hi, > >>>>> > >>>>> Do you know that they would do test with two actual transmitter > sites? > >>>>> > >>>>> Cheers, > >>>>> Magnus > >>>>> > >>>>> On 2020-08-05 16:00, paul swed wrote: > >>>>>> Hello to fellow time nuts. > >>>>>> Warm up those old Austrons. eLORAN out of New Jersey has been on the > >>> air > >>>>>> intermittently prior to a test run next week. Due to the storm they > >>> have > >>>>>> lost power and should have it back today or tomorrow. > >>>>>> The intention will be on the air operation till the 20th. That's a > long > >>>>>> run. Nice. > >>>>>> Seems the Austron 2100s can be had for reasonable money these days > >>> also. > >>>>>> Enjoy. > >>>>>> Paul > >>>>>> WB8TSL > >>>>>> _______________________________________________ > >>>>>> time-nuts mailing list -- time-nuts@lists.febo.com > >>>>>> To unsubscribe, go to > >>>>> http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com > >>>>>> and follow the instructions there. > >>>>> _______________________________________________ > >>>>> time-nuts mailing list -- time-nuts@lists.febo.com > >>>>> To unsubscribe, go to > >>>>> http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com > >>>>> and follow the instructions there. > >>>>> > >>>> _______________________________________________ > >>>> time-nuts mailing list -- time-nuts@lists.febo.com > >>>> To unsubscribe, go to > >>> http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com > >>>> and follow the instructions there. > >>> > >>> _______________________________________________ > >>> time-nuts mailing list -- time-nuts@lists.febo.com > >>> To unsubscribe, go to > >>> http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com > >>> and follow the instructions there. > >>> > >> _______________________________________________ > >> time-nuts mailing list -- time-nuts@lists.febo.com > >> To unsubscribe, go to > http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com > >> and follow the instructions there. > >> _______________________________________________ > >> time-nuts mailing list -- time-nuts@lists.febo.com > >> To unsubscribe, go to > http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com > >> and follow the instructions there. > > > > > > _______________________________________________ > > time-nuts mailing list -- time-nuts@lists.febo.com > > To unsubscribe, go to > http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com > > and follow the instructions there. > > > _______________________________________________ > time-nuts mailing list -- time-nuts@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@lists.febo.com To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there.