Hi Yup, and over something the size of a harbor, that works ok. It was done with the “old” Loran in a similar fashion and a couple of other ways as well. Expanding any of it to cover a country is a very different thing …..
I spent a lot of years trying to sell the designers of these systems on backup solutions. Not because I’m some kind of end of the world type. I figured selling them four boxes for every tower was at least twice as good as selling them two boxes. I was far from the only one making that pitch. None of us got a bite in 30 years of trying …. Bob > On Sep 8, 2018, at 5:16 PM, Bob Martin <aph...@comcast.net> wrote: > > Bob, > > That seems pretty conclusive to me but wait there's more.. > > By adding a letter to the name they are attempting to address the very issue > you've raised. > > https://rntfnd.org/wp-content/uploads/eDLoran-Reelektronica-Paper.pdf > > I'm sure after a few more prefix letters are added to Loran it will work for > everyone! > > Time for a new house to flip or dead horse to flog, > > Bob Martin > > > > > > On 9/8/2018 2:44 PM, Bob kb8tq wrote: >> Hi >> The differential approach to eLoran involves running two local receivers. >> You look at the time of arrival on one >> and use it to “calibrate" the time of arrival on the other. Put another way >> - you look at the difference between the >> two arrival times. They can both “wander” over a 250 ns range, as long as >> they stay within 50 ns of each other >> they meet the “differential spec”. >> For disciplining a local reference, you really need an absolute number. The >> fact that both are wandering over a >> pretty big range *does* matter if you are looking at a stable local source >> (and trying to make it more stable). What >> would / does work is having a very accurate standard at one of the locations >> and using the difference measure >> to “distribute” that source. That gets into bandwidth. >> Since the difference information is *very* local, there really isn’t a >> practical way to distribute it on the eLoran signal. >> As you pile on more correction stations, your data bandwidth goes up. There >> are a very limited number of bits >> available on the eLoran signal. >> Another way to look at it: If you have a standard sitting in your basement, >> and don’t have a buddy in town with a >> better standard. Does a difference measure to his house do you any good? >> Bob >>> On Sep 8, 2018, at 2:58 PM, Bob Martin <aph...@comcast.net> wrote: >>> >>> Bob, >>> >>> I believe that information is transmitted with the eloran signal. Way back >>> when, I remember there was an added pulse called the LDC pulse. I had to >>> modify that pulse with each transmission based on >>> an input to the transmit timing unit from the computer. >>> >>> I found the following on it: >>> http://www-personal.umich.edu/~tmikulsk/loran/ref/eloran_ldc.pdf >>> >>> Also, the article referenced previously on The Great Britain >>> system mentions that the differential corrections are sent on the LDC pulse. >>> >>> To be honest, I don't know if this addresses your "gotcha". >>> >>> Best, >>> >>> Bob Martin >>> >>> On 9/8/2018 12:38 PM, Bob kb8tq wrote: >>>> Hi >>>> The gotcha is the differential corrections. That’s not the way these >>>> systems are set up to work. They >>>> function with no external input other than the timing signal its self. >>>> Providing bandwidth to do correction >>>> signaling just isn’t part of the overall system design. If you wanted to >>>> use bandwidth, you would go >>>> with 1588. Then you have a backup and no fiddling with anything else. >>>> Indeed with an area wide 1588, you can do it all without even a GPS >>>> primary. Simply agree on a >>>> “something” as the master source. The man with one watch *always* knows >>>> what time it is …. >>>> The 250 ns "without correction" is the number that directly compares to >>>> the ~10 ns number for GPS. >>>> Stretch out the distances to “USA” sort of stuff and it does not improve >>>> things at all. >>>> Bob >>>>> On Sep 8, 2018, at 1:40 PM, Bob Martin <aph...@comcast.net> wrote: >>>>> >>>>> Bob, >>>>> >>>>> I agree that eloran needs to be analyzed with regard to it's >>>>> usefulness for each potential application. You are also 100% correct that >>>>> timing requirements get tighter and tighter as technology advances. In >>>>> some ways the question isn't whether eloran can >>>>> match GPS but rather would it suffice in a pinch were GPS to go down? >>>>> >>>>> I think the 50ns accuracy is actually "as received" not "as transmitted". >>>>> >>>>> The link below is an analysis of eloran in Great Britain. The >>>>> receiver/transmitter distance was 300 miles. >>>>> >>>>> http://www.ursanav.com/wp-content/uploads/On-the-Uses-of-High-Accuracy-eLoran-Time-Frequency-and-Phase-2015.pdf >>>>> >>>>> I've attached a screen capture of one of the pages that compares >>>>> eloran with GPS in case anyone is interested. This is where it >>>>> appears that the 50ns is received as opposed to at the transmitter. >>>>> >>>>> >>>>> >>>>> Best, >>>>> >>>>> Bob Martin >>>>> >>>>> On 9/8/2018 9:35 AM, Bob kb8tq wrote: >>>>>> Hi >>>>>> I believe the 50 ns is the “as transmitted” signal from the tower. The >>>>>> “as received” signal after going >>>>>> through all the various gyrations is not that good on a ~1 second basis. >>>>>> ==== >>>>>> One of the gotchas here is that we lump “systems” into one giant bag. >>>>>> That’s not a good way >>>>>> to analyze things. One system may be quite happy with 10 ms timing >>>>>> another may be happy >>>>>> with 10 us and yet another may die completely at 1 us and only run right >>>>>> at 100 ns. All of that >>>>>> is on a 2 second basis for CDMA (they time every other second). >>>>>> By far the biggest / baddest / most venerable system out the that uses >>>>>> GPS timing is the >>>>>> cell tower system. They started out back in the 80’s with a 10us max >>>>>> timing / 1 us running >>>>>> spec on CDMA. AFIK they were the first major system to adopt GPS time as >>>>>> their reference >>>>>> (rather than UTC). >>>>>> This worked out fine for a few decades while companies got a lot of >>>>>> towers built. People started >>>>>> using those systems and they became congested. Others started streaming >>>>>> video over them >>>>>> and they ran out of bandwidth. Upgrades followed. There have been a lot >>>>>> of them. Much of what >>>>>> we TimeNuts buy on the surplus market comes to us as a result of older >>>>>> systems being scrapped >>>>>> out. >>>>>> The latest set of upgrades does / will / is getting them into the sub 1 >>>>>> us range at the end of holdover. >>>>>> In normal operation they are spec’d at 100 ns worst case. To do that, >>>>>> you need a timing source in >>>>>> the roughly 10 ns range. No you don’t see those GPSDO’s on the surplus >>>>>> market. You will see >>>>>> them someday …. >>>>>> Again, they went this way a decade ago. Rolling that all back …. not at >>>>>> all easy. >>>>>> Are there other systems that have issues with sync? Of course there are. >>>>>> There also are a lot >>>>>> of instances where miss-configuration ( or junk implementation) is a >>>>>> much bigger issue. Sorting >>>>>> that all out requires a deep dive into the timing of each individual >>>>>> system / implementation. No >>>>>> two systems do things quite the same way. Unless you want to deal with >>>>>> the numbers and the >>>>>> implementation details, simply moaning and groaning isn’t going anywhere. >>>>>> Bob >>>>>>> On Sep 8, 2018, at 3:23 AM, Hal Murray <hmur...@megapathdsl.net> wrote: >>>>>>> >>>>>>> >>>>>>> kb...@n1k.org said: >>>>>>>> You are not trying to run a cell system when checking your local >>>>>>>> oscillator >>>>>>>> against LORAN. >>>>>>> >>>>>>> The eLoran committee said 50 ns. Is that good enough for cell towers? >>>>>>> >>>>>>> Too bad it isn't up so we could collect some data. >>>>>>> >>>>>>> >>>>>>> -- >>>>>>> These are my opinions. I hate spam. >>>>>>> >>>>>>> >>>>>>> >>>>>>> >>>>>>> _______________________________________________ >>>>>>> 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. >>>>> <Capture.JPG>_______________________________________________ >>>>> 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.