Re: [time-nuts] Timing Distribution in Mountainous Terrain
Hi Quebec Hydro and I suspect others use it to regulate power generation facilities. Keeps them from simply cross feeding power through the reactance of the distribution network. They have some pretty long lines between source and load Bob On Sep 11, 2010, at 10:53 PM, Brian Kirby wrote: > I believe the primary reasons for GPS receivers for the power industry is > power line fault location. They use time tagging to measure disturbances to > locate a fault and it's accuracy directly determines its resolution. > > On 9/11/2010 7:33 PM, jimlux wrote: >> Stan, W1LE wrote: >>> If the odd harmonics were filtered out, would the zero crossing of the >>> 60 (50) Hz fundamental >>> be stable enough ? >>> >>> >> not to 30 ns >> >> >> Interestingly, one of the markets that Symmetricom/TrueTime/Datum sells >> into is GPS disciplined receivers used for power control. Power >> transmission is managed by controlling relative phases in the system, >> not to mention things like synchronizing generators. >> >> >> ___ >> time-nuts mailing list -- time-nuts@febo.com >> To unsubscribe, go to >> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts >> and follow the instructions there. >> > > ___ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. > ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Timing Distribution in Mountainous Terrain
I believe the primary reasons for GPS receivers for the power industry is power line fault location. They use time tagging to measure disturbances to locate a fault and it's accuracy directly determines its resolution. On 9/11/2010 7:33 PM, jimlux wrote: Stan, W1LE wrote: If the odd harmonics were filtered out, would the zero crossing of the 60 (50) Hz fundamental be stable enough ? not to 30 ns Interestingly, one of the markets that Symmetricom/TrueTime/Datum sells into is GPS disciplined receivers used for power control. Power transmission is managed by controlling relative phases in the system, not to mention things like synchronizing generators. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Timing Distribution in Mountainous Terrain
Stan, W1LE wrote: If the odd harmonics were filtered out, would the zero crossing of the 60 (50) Hz fundamental be stable enough ? not to 30 ns Interestingly, one of the markets that Symmetricom/TrueTime/Datum sells into is GPS disciplined receivers used for power control. Power transmission is managed by controlling relative phases in the system, not to mention things like synchronizing generators. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Timing Distribution in Mountainous Terrain
Hi Since the harmonics are locally generated, each site will see different crossings. The same is true of the local load impedance. Bob On Sep 11, 2010, at 5:54 PM, "Stan, W1LE" wrote: > If the odd harmonics were filtered out, would the zero crossing of the 60 > (50) Hz fundamental > be stable enough ? > > Thanks Stan,W1LE Cape Cod FN41sr > > > > > On 9/11/2010 5:08 PM, Bob Camp wrote: >> Hi >> >> You also have load dependent harmonic energy on there that messes up the >> zero crossings at the micro second level. >> >> Bob >> >> >> >> On Sep 11, 2010, at 3:45 PM, "Poul-Henning Kamp" wrote: >> >>> In message<8459b572-1428-4f6a-8375-afb4f7225...@cox.net>, "Thomas A. Frank" >>> wr >>> ites: >>> If so, being within 300 miles of each other suggests that they are most likely all on the SAME section of the grid, in which case the phase time of arrival of the electric power waveform should be constant between them (the zero crossing may not be perfectly aligned, but it should always be the same differential). >>> Won't work. Utility transformers have load-dependent parasitics >>> which mess this up. It is one of the biggest challenges in >>> doing "autonomous cell based grid control" and similar schemes. >>> >>> -- >>> Poul-Henning Kamp | UNIX since Zilog Zeus 3.20 >>> p...@freebsd.org | TCP/IP since RFC 956 >>> FreeBSD committer | BSD since 4.3-tahoe >>> Never attribute to malice what can adequately be explained by incompetence. >>> >>> ___ >>> time-nuts mailing list -- time-nuts@febo.com >>> To unsubscribe, go to >>> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts >>> and follow the instructions there. >>> >> ___ >> time-nuts mailing list -- time-nuts@febo.com >> To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts >> and follow the instructions there. >> > > > ___ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. > ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Timing Distribution in Mountainous Terrain
If the odd harmonics were filtered out, would the zero crossing of the 60 (50) Hz fundamental be stable enough ? Thanks Stan,W1LE Cape Cod FN41sr On 9/11/2010 5:08 PM, Bob Camp wrote: Hi You also have load dependent harmonic energy on there that messes up the zero crossings at the micro second level. Bob On Sep 11, 2010, at 3:45 PM, "Poul-Henning Kamp" wrote: In message<8459b572-1428-4f6a-8375-afb4f7225...@cox.net>, "Thomas A. Frank" wr ites: If so, being within 300 miles of each other suggests that they are most likely all on the SAME section of the grid, in which case the phase time of arrival of the electric power waveform should be constant between them (the zero crossing may not be perfectly aligned, but it should always be the same differential). Won't work. Utility transformers have load-dependent parasitics which mess this up. It is one of the biggest challenges in doing "autonomous cell based grid control" and similar schemes. -- Poul-Henning Kamp | UNIX since Zilog Zeus 3.20 p...@freebsd.org | TCP/IP since RFC 956 FreeBSD committer | BSD since 4.3-tahoe Never attribute to malice what can adequately be explained by incompetence. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Timing Distribution in Mountainous Terrain
On 09/11/2010 11:08 PM, Bob Camp wrote: Hi You also have load dependent harmonic energy on there that messes up the zero crossings at the micro second level. Not to speak about the highly shifting reactive load, which can shift both negative and positive... and mess about the transitions. Cheers, Magnus ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Timing Distribution in Mountainous Terrain
Hi You also have load dependent harmonic energy on there that messes up the zero crossings at the micro second level. Bob On Sep 11, 2010, at 3:45 PM, "Poul-Henning Kamp" wrote: > In message <8459b572-1428-4f6a-8375-afb4f7225...@cox.net>, "Thomas A. Frank" > wr > ites: > >> If so, being within 300 miles of each other suggests that they are >> most likely all on the SAME section of the grid, in which case the >> phase time of arrival of the electric power waveform should be >> constant between them (the zero crossing may not be perfectly >> aligned, but it should always be the same differential). > > Won't work. Utility transformers have load-dependent parasitics > which mess this up. It is one of the biggest challenges in > doing "autonomous cell based grid control" and similar schemes. > > -- > Poul-Henning Kamp | UNIX since Zilog Zeus 3.20 > p...@freebsd.org | TCP/IP since RFC 956 > FreeBSD committer | BSD since 4.3-tahoe > Never attribute to malice what can adequately be explained by incompetence. > > ___ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. > ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Timing Distribution in Mountainous Terrain
On 09/11/2010 08:24 PM, Ralph Smith wrote: On Sep 11, 2010, at 12:13 PM, Magnus Danielson wrote: On 09/11/2010 05:29 PM, jimlux wrote: If it's far enough in the future.. Hg ion traps have a lot of potential.. smaller, lower power, etc. than Cs Commercial availability is somewhat limited. that's for sure.. I think all the Hg ion traps are still laboratory curiosities.. but, 10 years from now? Sure, but that assumes his target deployment is 10 years ahead. Much closer than 10 years. The idea is to use existing or soon to be deployed infrastructure from the US ADS-B installation to also perform multilateration. I assumed within 1 or 2 years. This rules out waiting for commercialisation of new standards or new approaches on ADS-B receivers unless you control that process yourself. Yes, yes... I understood perfectly what you where describing and no doubt such a hint would be most useful, but it may not be applicable to his problem. The question is really if he has complete boxes to build with or can alter their design. Additional delta-channels is best handled in a combined receiver, as being done in many other similar heading receivers... such as GPS receivers with angular orientation such as used in airplanes and on ships. Multilateration can be performed with existing radios being deployed, deriving time synchronization from GPS. Future revision of radio specifications are possible, but are more likely to be incremental changes of existing design rather than more significant architectural changes. As expected. The concept for ADS-B multilateration is already set down, so the available parameters is really providing a timing system, algorithms of multilaterations and possibly aiding to sort things out. Cheers, Magnus ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Timing Distribution in Mountainous Terrain
In message <8459b572-1428-4f6a-8375-afb4f7225...@cox.net>, "Thomas A. Frank" wr ites: >If so, being within 300 miles of each other suggests that they are >most likely all on the SAME section of the grid, in which case the >phase time of arrival of the electric power waveform should be >constant between them (the zero crossing may not be perfectly >aligned, but it should always be the same differential). Won't work. Utility transformers have load-dependent parasitics which mess this up. It is one of the biggest challenges in doing "autonomous cell based grid control" and similar schemes. -- Poul-Henning Kamp | UNIX since Zilog Zeus 3.20 p...@freebsd.org | TCP/IP since RFC 956 FreeBSD committer | BSD since 4.3-tahoe Never attribute to malice what can adequately be explained by incompetence. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Timing Distribution in Mountainous Terrain
Sites communicate via landline telco. If there are sufficient mutually visible networked sites to form a solution on an aircraft visible to stations not in the timing network that would work, and is one of the options we are studying. May it be assumed that the sites are on the regular electric grid? If so, being within 300 miles of each other suggests that they are most likely all on the SAME section of the grid, in which case the phase time of arrival of the electric power waveform should be constant between them (the zero crossing may not be perfectly aligned, but it should always be the same differential). Whether you can measure it to within 30 ns I'm not sure... Simpler thought - is the telco fiber? Could they drop a second dedicated one to link the sites? The notion that GPS will suddenly 'go away', without any other issues being present, is rather silly. That same solar flare that takes out GPS for all your sites is going to most likely render your other gear inoperative as well... Tom Frank, KA2CDK ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Timing Distribution in Mountainous Terrain
On Sep 11, 2010, at 12:13 PM, Magnus Danielson wrote: > On 09/11/2010 05:29 PM, jimlux wrote: If it's far enough in the future.. Hg ion traps have a lot of potential.. smaller, lower power, etc. than Cs >>> >>> Commercial availability is somewhat limited. >> >> that's for sure.. I think all the Hg ion traps are still laboratory >> curiosities.. but, 10 years from now? > > Sure, but that assumes his target deployment is 10 years ahead. Much closer than 10 years. The idea is to use existing or soon to be deployed infrastructure from the US ADS-B installation to also perform multilateration. > Yes, yes... I understood perfectly what you where describing and no doubt > such a hint would be most useful, but it may not be applicable to his > problem. The question is really if he has complete boxes to build with or can > alter their design. Additional delta-channels is best handled in a combined > receiver, as being done in many other similar heading receivers... such as > GPS receivers with angular orientation such as used in airplanes and on ships. Multilateration can be performed with existing radios being deployed, deriving time synchronization from GPS. Future revision of radio specifications are possible, but are more likely to be incremental changes of existing design rather than more significant architectural changes. Ralph ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Timing Distribution in Mountainous Terrain
On 09/11/2010 05:29 PM, jimlux wrote: If it's far enough in the future.. Hg ion traps have a lot of potential.. smaller, lower power, etc. than Cs Commercial availability is somewhat limited. that's for sure.. I think all the Hg ion traps are still laboratory curiosities.. but, 10 years from now? Sure, but that assumes his target deployment is 10 years ahead. A problem with Hg ion traps would be ROHS, unless they can be exempted or assumed to be within the telco exempt, which would be a legal twist on the commercialisation aspect. And Cs or Rb don't have the same sorts of issues? No. http://en.wikipedia.org/wiki/Restriction_of_Hazardous_Substances_Directive Another aspect I have been wondering about is the trap hold-length, I think I recall that there was some issues relating to that... I think, though, that some sort of self calibrating array using the target of interest is a better scheme.. multiple receivers at each site separated by some distance. Getting milliradian angular resolution is a piece of cake. That moves the expense, and I don't think the available receivers have that option. They intend the spatial separation to be in kms and not m. I was thinking about changing the problem somewhat. Yes, but now you shifted from "time-support system of transciever boxes" to modifications of the boxes themselves or at least use multiple boxes for angle determination only (wasting much of the rest of the receiver structure). You'd have your stations separated by km, but each station has several receivers and can compare the phase of the signals. You can solve for range rate (Doppler) and angle (delta phase), and that can go into your position solution. (this is how we navigate spacecraft, after all, and it's also used for a variety of target tracking systems) Yes, yes... I understood perfectly what you where describing and no doubt such a hint would be most useful, but it may not be applicable to his problem. The question is really if he has complete boxes to build with or can alter their design. Additional delta-channels is best handled in a combined receiver, as being done in many other similar heading receivers... such as GPS receivers with angular orientation such as used in airplanes and on ships. Cheers, Magnus ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Timing Distribution in Mountainous Terrain
If it's far enough in the future.. Hg ion traps have a lot of potential.. smaller, lower power, etc. than Cs Commercial availability is somewhat limited. that's for sure.. I think all the Hg ion traps are still laboratory curiosities.. but, 10 years from now? A problem with Hg ion traps would be ROHS, unless they can be exempted or assumed to be within the telco exempt, which would be a legal twist on the commercialisation aspect. And Cs or Rb don't have the same sorts of issues? Another aspect I have been wondering about is the trap hold-length, I think I recall that there was some issues relating to that... I think, though, that some sort of self calibrating array using the target of interest is a better scheme.. multiple receivers at each site separated by some distance. Getting milliradian angular resolution is a piece of cake. That moves the expense, and I don't think the available receivers have that option. They intend the spatial separation to be in kms and not m. I was thinking about changing the problem somewhat. You'd have your stations separated by km, but each station has several receivers and can compare the phase of the signals. You can solve for range rate (Doppler) and angle (delta phase), and that can go into your position solution. (this is how we navigate spacecraft, after all, and it's also used for a variety of target tracking systems) Changing it from a rho-rho nav problem into a theta-theta problem (triangulation vs trilateration). The goal is to get target position to 10 meters, at a distance of, say, 20km, so you need angular measurements on the order of 0.5 milliradian (0.03 degree). Offhand, that might be easier than time to 30 ns. There are some significant issues here.. is the pulse long enough and enough power to make the required differential phase measurement, are there propagation issues (refraction, diffraction, multipath) that make milliradian precision impossible. The added hardware cost at each receiver site isn't much (compared to site costs, etc.) especially since you probably already need at least dual redundancy, so you can do N+1 redundancy, using 3 antenna/receivers at each site, using 2 of them at any given time. The wavelength at the transponder frequency is about 30cm, so with a moderate spacing of the receive antennas (say a meter), you'll get grating lobes and an angle ambiguity, but I think that could be resolved with the other information available (e.g. a coarse fix) Cheers, Magnus ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Timing Distribution in Mountainous Terrain
Don Latham wrote: jees, Bob, it's called a TDR - Original Message - From: "Bob Camp" To: "Discussion of precise time and frequency measurement" Sent: Friday, September 10, 2010 9:27 PM Subject: Re: [time-nuts] Timing Distribution in Mountainous Terrain Hi The assumption is that you can "bounce" a pulse off the far end of a single fiber or coax to read it's delay. Bob Actually, they don't use a TDR for this kind of thing.. you want to measure continuously in real time, so you propagate signals in both directions (at different frequencies) and look at phase differences, etc. With multiple fibers in the same jacket, you can assume that the fibers are the same, which makes life easier. On antenna ranges, with coax, the approach is similar, but you rely on a known mismatch at the probe. It's a fascinating metrology problem, especially if you want to actually "compensate" in real time, rather than just getting knowledge of the delay and using that in post processing. http://ipnpr.jpl.nasa.gov/progress_report/42-167/167C.pdf is a paper by Bob Tjoelker and others about how they do it for DSN. it has to be hotswappable, etc. there's some company in Colorado who makes the equipment, as I recall. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Timing Distribution in Mountainous Terrain
It is my understanding that test equipment is exempt from all RoHS requirements. -Chuck Harris Magnus Danielson wrote: Commercial availability is somewhat limited. A problem with Hg ion traps would be ROHS, unless they can be exempted or assumed to be within the telco exempt, which would be a legal twist on the commercialisation aspect. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Timing Distribution in Mountainous Terrain
On 09/10/2010 07:17 AM, jimlux wrote: Ralph Smith wrote: On Sep 9, 2010, at 8:01 PM, Rick Karlquist wrote: I would like to point out that the environmental sensitivities of the 5071A are unmeasureable, and the measurement threshold is far below 5.8E-14. I would estimate that the 5071A (and ONLY the 5071A among commercial clocks) could get the job done provided that you could compare its frequency to GPS to the stated accuracy. This would be using the 5071 as a secondary standard. You still need to deal with the short term stability of the 5071A, depending on your system needs. JPL uses H masers as flywheels. I would imagine the cost of a 5071A per radio station would make the check writers swallow hard, and adding an H Maser into the mix would really get their attention. Especially if you need redundancy. there's also the possibility mentioned earlier of using a lower quality standard at each station and flying (driving) a higher quality clock (5071) around often enough to keep them trued up. If it's far enough in the future.. Hg ion traps have a lot of potential.. smaller, lower power, etc. than Cs Commercial availability is somewhat limited. A problem with Hg ion traps would be ROHS, unless they can be exempted or assumed to be within the telco exempt, which would be a legal twist on the commercialisation aspect. Another aspect I have been wondering about is the trap hold-length, I think I recall that there was some issues relating to that... I think, though, that some sort of self calibrating array using the target of interest is a better scheme.. multiple receivers at each site separated by some distance. Getting milliradian angular resolution is a piece of cake. That moves the expense, and I don't think the available receivers have that option. They intend the spatial separation to be in kms and not m. Cheers, Magnus ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Timing Distribution in Mountainous Terrain
On 09/10/2010 11:50 PM, jimlux wrote: Ralph Smith wrote: OK, stop me if this is really stupid. The initial site is in Colorado. Would it be possible to use WWV? In particular: 1) Lock a reference to the carrier of one of the WWV signals 2) Generate PPS off of WWV-locked reference 3) Periodically send difference of GPSDO PPS and WWV-locked PPS home, along with GPS lock indication 4) When GPS goes away do the math at home and correct for the timing drift of the GPSDO compared to WWV-locked reference I don't think a received WWV (or WWVB) signal is stable to 30ns... The critical aspect here is stable to 30 ns _relative_. I.e. common mode changes mostly cancels. I think it is problematic... the frequency of the carrier is too low. The vector sum of reflections may shift the group delay, and in this case the time error of such sums can be expected to be proportional to the wavelength. I would use one wavelength as the rule of thumb as long as it is not better quantified, and I would assume that individual changes can range that full range... Cheers, Magnus ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Timing Distribution in Mountainous Terrain
jim...@earthlink.net said: > I seem to recall that the returned beam divergence was no narrower than the > incident beam divergence, so if you want a X km footprint on Earth, you > need a X km footprint on the Moon. Please let me know if you find that again. I poked around on the web and can't find anything that confirms my impression that they picked the size of the corner cubes to make sure the beam was large enough to cover the telescope motion due to the Earth's rotation. They are made out of fused silica. Thermal distortions are important. There are arrays from Apollo 11, 14, and 15. 11 and 14 are 100 cubes in a 10x10 array. 15 is 3x bigger. There is also an array of larger French cubes on Lunokhod, a Russian rover. There are brighter than Apollo 11 adn 14, even though the total reflecting area is smaller. http://www.physics.ucsd.edu/~tmurphy/apollo/lrrr.html (That's at night. During day, thermal distortion costs a factor of 30.) This page says the beam is 7 km dia on the moon due to atmosphere and 20 km back on the Earth due to diffraction. http://www.lpi.usra.edu/lunar/missions/apollo/apollo_11/experiments/lrr/ Dickey et al, 1994 is a good review article. http://www.physics.ucsd.edu/~tmurphy/apollo/doc/Dickey.pdf http://trs-new.jpl.nasa.gov/dspace/bitstream/2014/32452/1/94-0193.pdf (The second looks like an early version of the paper.) It confirms the beam diameters above. My calculation for the motion due to the Earth's rotation while the beam is in flight is 1or 2 km so 20 km easily covers that problem. There is a comment about correcting for something like the telescope not being in the center of the beam. Overall optical efficiency is about 1E-21. At 10 pulses per second with 1E19 photons each pulse, that's 1 photon every 10 seconds. A run is several hours. (The numbers get better over time.) In 1994, the RMS error was about 3 cm. A French station is getting a lot of good data. They have to consider solid tides and a zillion other details that I don't understand. (So add that one to the tides in solid rock list.) The Earth-moon distance is increasing by about 3.8 cm per year. I remember another story from long ago that one of the variables they had to add to their model was the location of the telescope on the surface of the Earth. The data fit better with the telescope a mile down the road from their coordinates from the USGS maps. I don't know if they ever tracked that down. -- There is a new Lunar Laser Ranging program called APOLLO. Apache Point Observatory Lunar Laser-ranging Operation http://www.physics.ucsd.edu/~tmurphy/apollo/apollo.html They are aiming for mm precision. They have a 3.5 meter telescope. Good geek data (graphs) here: http://www.physics.ucsd.edu/~tmurphy/apollo/first_range.html (Other stuff is good too, AKA time sink warning.) -- These are my opinions, not necessarily my employer's. I hate spam. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Timing Distribution in Mountainous Terrain
jees, Bob, it's called a TDR - Original Message - From: "Bob Camp" To: "Discussion of precise time and frequency measurement" Sent: Friday, September 10, 2010 9:27 PM Subject: Re: [time-nuts] Timing Distribution in Mountainous Terrain Hi The assumption is that you can "bounce" a pulse off the far end of a single fiber or coax to read it's delay. Bob On Sep 10, 2010, at 10:09 PM, "J. L. Trantham" wrote: -Original Message- From: time-nuts-boun...@febo.com [mailto:time-nuts-boun...@febo.com] On Behalf Of Stanley Reynolds Sent: Friday, September 10, 2010 7:13 PM To: Discussion of precise time and frequency measurement Subject: Re: [time-nuts] Timing Distribution in Mountainous Terrain How to keep hundreds of miles of copper stable or predict it's delay ? Stanley Would temperature changes over any consecutive 6 day period create a 30 change (assuming the 'central station' is indeed central)? And, if so, would that make any difference in position accuracy since all stations would have the same or similar error? Oops, there I go again thinking as a 'user' :>). Joe ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Timing Distribution in Mountainous Terrain
ground wave has variation due to changes in refractive index over the path. - Original Message - From: "WB6BNQ" To: "Discussion of precise time and frequency measurement" Sent: Friday, September 10, 2010 6:46 PM Subject: Re: [time-nuts] Timing Distribution in Mountainous Terrain Hal, The LORAN frequency was picked to have predominately ground wave acquisition over the less preferred skywave. The only signal worth considering from Fort Collins is the WWVB signal which is at 60 KHz. For Ralph's application in Colorado, the WWVB signal would probably do it. Particularly considering the short distance between the sites and Fort Collins. LORAN and WWVB are about the same as far as stability goes at the actual transmitter site with WWVB having a slight edge. The value is 1x-E11 or better. For Ralph, the WWVB would be more stable due to his site proximity to the transmitter over any LORAN signal (when working) which is much further away. BillWB6BNQ Hal Murray wrote: ra...@ralphsmith.org said: > There are probably several fatal flaws with this approach. In > particular, > the following are required: > 1) Ability to maintain constant lock to WWV > 2) Common-mode error. Will the propagation from WWV be similar > enough for all stations to it be a practical common reference. > 3) Adequate resolution. Even if, for some reason 1 and 2 are possible, > would the result be good enough to use. My quick guess is that WWV would be worse than LORAN since LORAN got to pick the frequency that would work best. If you want more info, you probably need to contact a radio propagation wizard. Unless you are very close, the signal will be bouncing off the ionosphere and that isn't stable. There are big changes from day to night, and I think you can measure the tiny changes during the day if you have a good clock at the receiver. Didn't one of the recent FMT discussions mention something like this? I think they were measuring a frequency shift which would translate into velocity of the layer. Dave Mills has drivers for NTP that decode WWV/H signals from a short wave radio going into a PC audio chip. http://www.eecis.udel.edu/~mills/ntp/html/drivers/driver36.html In general, he's getting sub ms rather than few ns. -- These are my opinions, not necessarily my employer's. I hate spam. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Timing Distribution in Mountainous Terrain
Stanley Reynolds wrote: How to keep hundreds of miles of copper stable or predict it's delay ? Stanley these days, you'd use optical fiber, but the answer is the same, you measure it in real time. Send a signal down it and see when the reflection comes back. Off the shelf hardware these days. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Timing Distribution in Mountainous Terrain
Hal Murray wrote: [Lunar Laser Ranging] Hmm.. the SNR isn't all that huge on the echo. The target is say, 1 square meter, at a distance of 300,000 km. The beam divergence coming back is about the same as the outbound (that is, in order to cover 300km on earth, you need to have a spot on the moon about 300km in diameter).. So the laser power will be spread out by a factor of 71E9.. (about 110 dB). The power reflected back, if intercepted by a 1 square meter aperture will have the same "loss" for a round trip loss of around 220dB. I don't see why the outgoing beam has to be that big. Anything that doesn't hit the corner cubes is wasted. I thought the size of the corner cubes was picked so that diffraction would spread the beam enough so the telescope would be in the reflected beam might be... I seem to recall that the returned beam divergence was no narrower than the incident beam divergence, so if you want a X km footprint on Earth, you need a X km footprint on the Moon. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Timing Distribution in Mountainous Terrain
Hi The assumption is that you can "bounce" a pulse off the far end of a single fiber or coax to read it's delay. Bob On Sep 10, 2010, at 10:09 PM, "J. L. Trantham" wrote: > > > -Original Message- > From: time-nuts-boun...@febo.com [mailto:time-nuts-boun...@febo.com] On > Behalf Of Stanley Reynolds > Sent: Friday, September 10, 2010 7:13 PM > To: Discussion of precise time and frequency measurement > Subject: Re: [time-nuts] Timing Distribution in Mountainous Terrain > > > How to keep hundreds of miles of copper stable or predict it's delay ? > > Stanley > > > > Would temperature changes over any consecutive 6 day period create a 30 > change (assuming the 'central station' is indeed central)? > > And, if so, would that make any difference in position accuracy since all > stations would have the same or similar error? Oops, there I go again > thinking as a 'user' :>). > > Joe > > > ___ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. > ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Timing Distribution in Mountainous Terrain
~ 1ft = 1 ns for coax, but 1000-2000 us is common delay for long phone lines which is very frequency dependent, you would want unloaded circuits, loading coils would make for more problems. My experience with metallic circuits is limited to less than 10 miles at some point you would need an amplifier/repeater. I do know noise and cross talk and other impairments are common. Data modem design is quite complicated but I don't think they are very predictable as far as delay goes, except delay increases and transfer rate decreases with impairments. Stanley - Original Message From: J. L. Trantham To: Discussion of precise time and frequency measurement Sent: Fri, September 10, 2010 9:09:29 PM Subject: Re: [time-nuts] Timing Distribution in Mountainous Terrain -Original Message- From: time-nuts-boun...@febo.com [mailto:time-nuts-boun...@febo.com] On Behalf Of Stanley Reynolds Sent: Friday, September 10, 2010 7:13 PM To: Discussion of precise time and frequency measurement Subject: Re: [time-nuts] Timing Distribution in Mountainous Terrain How to keep hundreds of miles of copper stable or predict it's delay ? Stanley Would temperature changes over any consecutive 6 day period create a 30 nS change (assuming the 'central station' is indeed central)? And, if so, would that make any difference in position accuracy since all stations would have the same or similar error? Oops, there I go again thinking as a 'user' :>). Joe ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Timing Distribution in Mountainous Terrain
-Original Message- From: time-nuts-boun...@febo.com [mailto:time-nuts-boun...@febo.com] On Behalf Of Stanley Reynolds Sent: Friday, September 10, 2010 7:13 PM To: Discussion of precise time and frequency measurement Subject: Re: [time-nuts] Timing Distribution in Mountainous Terrain How to keep hundreds of miles of copper stable or predict it's delay ? Stanley Would temperature changes over any consecutive 6 day period create a 30 nS change (assuming the 'central station' is indeed central)? And, if so, would that make any difference in position accuracy since all stations would have the same or similar error? Oops, there I go again thinking as a 'user' :>). Joe ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Timing Distribution in Mountainous Terrain
On Sep 10, 2010, at 7:44 PM, J. L. Trantham, M. D. wrote: > I guess I am thinking about this from a user perspective rather than an > engineering design and implementation perspective. If the requirement is > aircraft separation, LORAN should be adequate for that, if it was still up. > You would only have to transmit your position and altitude to a ground > receiving station that then would relay it to the Center Controllers to be > displayed on a map along with all the other aircraft. What you are talking about here is already implemented in ADS-B which is currently being fielded in the US. ADS-B stands for automatic dependent surveillance - broadcast. It is dependent in the sense that the aircraft tells you where it thinks it is. If the aircraft is mistaken or lying you have a problem, although there are ways of validating a report if heard by multiple ground stations. > However, it seems they want to do this by use of an upside down but > otherwise 'GPS like method', i.e., the 'satellites' are fixed to > mountaintops and the aircraft still moves. Mathematically it is similar, both using multilateration, determining position from knowing the comparative difference in distance between the unknown position and multiple known points. Multilateration, like radar, is an independent surveillance method. The aircraft position is calculated by means external to the aircraft itself. You know where the aircraft is, even if the aircraft doesn't. > That being the case, what about a fixed, land-line, connection for every > mountaintop to a central location that broadcasts the time signal, calibrate > the system using GPS then rely on the central ground station to keep it > running? As mentioned by others, that can be difficult to do while maintaining the timing tolerances necessary for accurate position determination. Ralph ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Timing Distribution in Mountainous Terrain
Hal, The LORAN frequency was picked to have predominately ground wave acquisition over the less preferred skywave. The only signal worth considering from Fort Collins is the WWVB signal which is at 60 KHz. For Ralph's application in Colorado, the WWVB signal would probably do it. Particularly considering the short distance between the sites and Fort Collins. LORAN and WWVB are about the same as far as stability goes at the actual transmitter site with WWVB having a slight edge. The value is 1x-E11 or better. For Ralph, the WWVB would be more stable due to his site proximity to the transmitter over any LORAN signal (when working) which is much further away. BillWB6BNQ Hal Murray wrote: > ra...@ralphsmith.org said: > > There are probably several fatal flaws with this approach. In particular, > > the following are required: > > 1) Ability to maintain constant lock to WWV > > 2) Common-mode error. Will the propagation from WWV be similar > > enough for all stations to it be a practical common reference. > > 3) Adequate resolution. Even if, for some reason 1 and 2 are possible, > > would the result be good enough to use. > > My quick guess is that WWV would be worse than LORAN since LORAN got to pick > the frequency that would work best. > > If you want more info, you probably need to contact a radio propagation > wizard. Unless you are very close, the signal will be bouncing off the > ionosphere and that isn't stable. There are big changes from day to night, > and I think you can measure the tiny changes during the day if you have a > good clock at the receiver. > > Didn't one of the recent FMT discussions mention something like this? I > think they were measuring a frequency shift which would translate into > velocity of the layer. > > Dave Mills has drivers for NTP that decode WWV/H signals from a short wave > radio going into a PC audio chip. > http://www.eecis.udel.edu/~mills/ntp/html/drivers/driver36.html > In general, he's getting sub ms rather than few ns. > > -- > These are my opinions, not necessarily my employer's. I hate spam. > > ___ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Timing Distribution in Mountainous Terrain
That's why you need sufficient bean divergence on the outgoing beam Sent via BlackBerry by AT&T -Original Message- From: Stanley Reynolds Sender: time-nuts-boun...@febo.com Date: Fri, 10 Sep 2010 15:34:42 To: Discussion of precise time and frequency measurement Reply-To: Discussion of precise time and frequency measurement Subject: Re: [time-nuts] Timing Distribution in Mountainous Terrain If you have to work with the existing corner cubes, I don't see how to start with a pulse at one site, bounce it off the moon, and get it back to another site that isn't nearby. If you didn't send the pulse it would be hard to time the trip anyway no start time. But it one site is transmitting a series of accuratly spaced pluses then ... Stanley ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Timing Distribution in Mountainous Terrain
How to keep hundreds of miles of copper stable or predict it's delay ? Stanley - Original Message From: "J. L. Trantham, M. D." To: Discussion of precise time and frequency measurement Sent: Fri, September 10, 2010 6:44:35 PM Subject: Re: [time-nuts] Timing Distribution in Mountainous Terrain I guess I am thinking about this from a user perspective rather than an engineering design and implementation perspective. If the requirement is aircraft separation, LORAN should be adequate for that, if it was still up. You would only have to transmit your position and altitude to a ground receiving station that then would relay it to the Center Controllers to be displayed on a map along with all the other aircraft. However, it seems they want to do this by use of an upside down but otherwise 'GPS like method', i.e., the 'satellites' are fixed to mountaintops and the aircraft still moves. That being the case, what about a fixed, land-line, connection for every mountaintop to a central location that broadcasts the time signal, calibrate the system using GPS then rely on the central ground station to keep it running? Joe -Original Message- From: time-nuts-boun...@febo.com [mailto:time-nuts-boun...@febo.com]on Behalf Of Oz-in-DFW Sent: Friday, September 10, 2010 12:21 PM To: Discussion of precise time and frequency measurement Subject: Re: [time-nuts] Timing Distribution in Mountainous Terrain On 9/10/2010 7:26 AM, Ralph Smith wrote: > On Sep 10, 2010, at 7:50 AM, J. L. Trantham wrote: > >> Loran was used as an area navigation method in aviation for many years. It >> was available nation wide with a number of chains. I had assumed that the >> area of interest was the Rocky's but if the Appalachians, even better. > The site currently under consideration is in Colorado. Only problem with Loran, of course, is that is has been killed, thus the operative word "was" above. If the design and approach bears out it could be deployed over a much wider scale. > > Ralph Even if LORAN was alive it wouldn't meet the requirement. You'd still have 20-30 M position uncertainty in a differental application - way more than your 30 ns. I thiink that dropping LORAN was a really big mistake, but it wouldn't meet this need. I used to see several 100 ns of time drift and jitter when I was in San Antonio and watching Boise City, OK (~600 Mi) -- mailto:o...@ozindfw.net Oz POB 93167 Southlake, TX 76092 (Near DFW Airport) ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Timing Distribution in Mountainous Terrain
I guess I am thinking about this from a user perspective rather than an engineering design and implementation perspective. If the requirement is aircraft separation, LORAN should be adequate for that, if it was still up. You would only have to transmit your position and altitude to a ground receiving station that then would relay it to the Center Controllers to be displayed on a map along with all the other aircraft. However, it seems they want to do this by use of an upside down but otherwise 'GPS like method', i.e., the 'satellites' are fixed to mountaintops and the aircraft still moves. That being the case, what about a fixed, land-line, connection for every mountaintop to a central location that broadcasts the time signal, calibrate the system using GPS then rely on the central ground station to keep it running? Joe -Original Message- From: time-nuts-boun...@febo.com [mailto:time-nuts-boun...@febo.com]on Behalf Of Oz-in-DFW Sent: Friday, September 10, 2010 12:21 PM To: Discussion of precise time and frequency measurement Subject: Re: [time-nuts] Timing Distribution in Mountainous Terrain On 9/10/2010 7:26 AM, Ralph Smith wrote: > On Sep 10, 2010, at 7:50 AM, J. L. Trantham wrote: > >> Loran was used as an area navigation method in aviation for many years. It >> was available nation wide with a number of chains. I had assumed that the >> area of interest was the Rocky's but if the Appalachians, even better. > The site currently under consideration is in Colorado. Only problem with Loran, of course, is that is has been killed, thus the operative word "was" above. If the design and approach bears out it could be deployed over a much wider scale. > > Ralph Even if LORAN was alive it wouldn't meet the requirement. You'd still have 20-30 M position uncertainty in a differental application - way more than your 30 ns. I thiink that dropping LORAN was a really big mistake, but it wouldn't meet this need. I used to see several 100 ns of time drift and jitter when I was in San Antonio and watching Boise City, OK (~600 Mi) -- mailto:o...@ozindfw.net Oz POB 93167 Southlake, TX 76092 (Near DFW Airport) ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Timing Distribution in Mountainous Terrain
> If you didn't send the pulse it would be hard to time the trip anyway no > start time. If you know the start time and the receive time, you can compute the distance. If you know the start time and the distance you can compute the receive time and hence synchronize clocks. For this discussion, we know the distance to a small fraction of the 30 ns target. -- These are my opinions, not necessarily my employer's. I hate spam. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Timing Distribution in Mountainous Terrain
Well; maybe more to it. Ballon tether carries a few watts to transmit from the ballon altitude to all other sites. At predetermined times the master site balloon transmits to the other sites. The other sites respond with their estimated time. The master provides corrected time. Knowing past history of path properties & precise (ballon) location at each transmission (data sent with transmission); the rest should be easy. The master has to precisely locate its own balloon just prior to transmitting to the other sites. even if it's balloon is wandering, a short (10ms) delay to transmit will create negligible error. Ballons might be at each site to create redundant data & suffer a few lost ballons while waiting for replacements, or to switch time master. It might be necessary to update path properties just prior to timing. Pete Rawson On Sep 10, 2010, at 12:14 PM, Mark J. Blair wrote: > > On Sep 10, 2010, at 10:47 AM, Pete Rawson wrote: >> Can you use tethered balloons at each site to obtain adequate S/N >> in their position to permit time calculations to 30ns uncertainty? > > > Tether a single balloon to three sites to reduce the balloon's displacement > due to wind, and then measure its position relative to the three sites by > laser or radar ranging! :-D > > > > > -- > Mark J. Blair, NF6X > Web page: http://www.nf6x.net/ > GnuPG public key available from my web page. > > > > > > ___ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Timing Distribution in Mountainous Terrain
If you have to work with the existing corner cubes, I don't see how to start with a pulse at one site, bounce it off the moon, and get it back to another site that isn't nearby. If you didn't send the pulse it would be hard to time the trip anyway no start time. But it one site is transmitting a series of accuratly spaced pluses then ... Stanley ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Timing Distribution in Mountainous Terrain
ra...@ralphsmith.org said: > There are probably several fatal flaws with this approach. In particular, > the following are required: > 1) Ability to maintain constant lock to WWV > 2) Common-mode error. Will the propagation from WWV be similar > enough for all stations to it be a practical common reference. > 3) Adequate resolution. Even if, for some reason 1 and 2 are possible, > would the result be good enough to use. My quick guess is that WWV would be worse than LORAN since LORAN got to pick the frequency that would work best. If you want more info, you probably need to contact a radio propagation wizard. Unless you are very close, the signal will be bouncing off the ionosphere and that isn't stable. There are big changes from day to night, and I think you can measure the tiny changes during the day if you have a good clock at the receiver. Didn't one of the recent FMT discussions mention something like this? I think they were measuring a frequency shift which would translate into velocity of the layer. Dave Mills has drivers for NTP that decode WWV/H signals from a short wave radio going into a PC audio chip. http://www.eecis.udel.edu/~mills/ntp/html/drivers/driver36.html In general, he's getting sub ms rather than few ns. -- These are my opinions, not necessarily my employer's. I hate spam. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Timing Distribution in Mountainous Terrain
[Lunar Laser Ranging] > Hmm.. the SNR isn't all that huge on the echo. The target is say, 1 square > meter, at a distance of 300,000 km. > The beam divergence coming back is about the same as the outbound (that > is, in order to cover 300km on earth, you need to have a spot on the moon > about 300km in diameter).. So the laser power will be spread out by a > factor of 71E9.. (about 110 dB). The power reflected back, if intercepted > by a 1 square meter aperture will have the same "loss" for a round trip > loss of around 220dB. I don't see why the outgoing beam has to be that big. Anything that doesn't hit the corner cubes is wasted. I thought the size of the corner cubes was picked so that diffraction would spread the beam enough so the telescope would be in the reflected beam footprint after Earth's rotation had moved it from the transmit position. My back-of-envelope says that's about 1 km in dia. If you have to work with the existing corner cubes, I don't see how to start with a pulse at one site, bounce it off the moon, and get it back to another site that isn't nearby. -- These are my opinions, not necessarily my employer's. I hate spam. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Timing Distribution in Mountainous Terrain
On 9/10/2010 4:04 PM, Ralph Smith wrote: > OK, stop me if this is really stupid. The initial site is in Colorado. > Would it be possible to use WWV? In particular: > > 1) Lock a reference to the carrier of one of the WWV signals > 2) Generate PPS off of WWV-locked reference > 3) Periodically send difference of GPSDO PPS and WWV-locked PPS home, > along with GPS lock indication > 4) When GPS goes away do the math at home and correct for the timing drift > of the GPSDO compared to WWV-locked reference > > There are probably several fatal flaws with this approach. In particular, > the following are required: > 1) Ability to maintain constant lock to WWV > 2) Common-mode error. Will the propagation from WWV be similar enough for > all stations to it be a practical common reference. > 3) Adequate resolution. Even if, for some reason 1 and 2 are possible, > would the result be good enough to use. > > Like I say, probably completely unworkable, but what are your thoughts? > > Ralph > There are a number of problems I see with this, each of which is sufficient to eliminate this as an option. 1. Propagation varies with temperature, humidity, and other atmospheric effects like dust content. Over a several hundred mile path this is going to be at least an order of magnitude greater error term than the overall budget. 2. This is HF and skip paths are common. The WWV wave form provides no mechanism for discriminating between ground and skywave. LORAN accomplished this by using a short pulse. The Skywave path was always later than the groundwave, and for most cases was completely distinct. This can be 100s of microseconds. 3. It's conceivable that you could have long-path propagation that makes a complete circuit of the earth - really long delays and no good way to know in the absence of a stable reference. About 150 milliseconds... 4. Multipath with sky and ground waves adds yet another variable. And WWVB doesn't really fix much of this. -- mailto:o...@ozindfw.net Oz POB 93167 Southlake, TX 76092 (Near DFW Airport) ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Timing Distribution in Mountainous Terrain
First thought is that the doppler shift associated with sky wave propogation will likely present issues.Wwvb might be a better choice if locking an oscilator to a received rf carrier will work. On Fri Sep 10th, 2010 5:04 PM EDT Ralph Smith wrote: >OK, stop me if this is really stupid. The initial site is in Colorado. >Would it be possible to use WWV? In particular: > >1) Lock a reference to the carrier of one of the WWV signals >2) Generate PPS off of WWV-locked reference >3) Periodically send difference of GPSDO PPS and WWV-locked PPS home, >along with GPS lock indication >4) When GPS goes away do the math at home and correct for the timing drift >of the GPSDO compared to WWV-locked reference > >There are probably several fatal flaws with this approach. In particular, >the following are required: >1) Ability to maintain constant lock to WWV >2) Common-mode error. Will the propagation from WWV be similar enough for >all stations to it be a practical common reference. >3) Adequate resolution. Even if, for some reason 1 and 2 are possible, >would the result be good enough to use. > >Like I say, probably completely unworkable, but what are your thoughts? > >Ralph > >___ >time-nuts mailing list -- time-nuts@febo.com >To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts >and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Timing Distribution in Mountainous Terrain
Ralph Smith wrote: OK, stop me if this is really stupid. The initial site is in Colorado. Would it be possible to use WWV? In particular: 1) Lock a reference to the carrier of one of the WWV signals 2) Generate PPS off of WWV-locked reference 3) Periodically send difference of GPSDO PPS and WWV-locked PPS home, along with GPS lock indication 4) When GPS goes away do the math at home and correct for the timing drift of the GPSDO compared to WWV-locked reference I don't think a received WWV (or WWVB) signal is stable to 30ns... ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Timing Distribution in Mountainous Terrain
OK, stop me if this is really stupid. The initial site is in Colorado. Would it be possible to use WWV? In particular: 1) Lock a reference to the carrier of one of the WWV signals 2) Generate PPS off of WWV-locked reference 3) Periodically send difference of GPSDO PPS and WWV-locked PPS home, along with GPS lock indication 4) When GPS goes away do the math at home and correct for the timing drift of the GPSDO compared to WWV-locked reference There are probably several fatal flaws with this approach. In particular, the following are required: 1) Ability to maintain constant lock to WWV 2) Common-mode error. Will the propagation from WWV be similar enough for all stations to it be a practical common reference. 3) Adequate resolution. Even if, for some reason 1 and 2 are possible, would the result be good enough to use. Like I say, probably completely unworkable, but what are your thoughts? Ralph ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Timing Distribution in Mountainous Terrain
Hi A lunar setup would only give you data for part of the day. You would relax the flywheel requirement. Net result likely would still be a maser / cesium combo at each site. Not real clear how you would model clouds and weather into the availability equation. Some of the things that 100% take out GPS also kick up a LOT of dust. There is a point where the dust locks up all the turbines and there's nothing to track Bob On Sep 10, 2010, at 2:42 PM, jimlux wrote: > Stanley Reynolds wrote: >> On the crazy side another common view object is the lunar laser ranging >> retroreflector array. Has been improvements in cost of lasers and telescopes >> in the past 41 years and it doesn't appear to be headed for shutdown anytime >> soon. >> > > Hmm.. the SNR isn't all that huge on the echo. The target is say, 1 square > meter, at a distance of 300,000 km. > > The beam divergence coming back is about the same as the outbound (that is, > in order to cover 300km on earth, you need to have a spot on the moon about > 300km in diameter).. So the laser power will be spread out by a factor of > 71E9.. (about 110 dB). The power reflected back, if intercepted by a 1 square > meter aperture will have the same "loss" for a round trip loss of around > 220dB. > > Radiate 10 Watts, and you're seeing -210dBW coming back.. That's going to be > tough to detect. Just how many photons/second is that? And what's the dark > current/shot noise of your detector (a PM tube, presumably) > > The first experiments with the Apollo 11 reflector were done with the 3.1m > antenna at the Lick observatory.. that's a pretty big telescope. The work at > the McDonald observatory used almost as big a telescope, but did provide > ranging to 1 cm, which is 0.03 ns... > > If we make the assumption that a degradation in position accuracy to 10m > requires 1/10,000 the power.. that would imply you could use a telescope with > 1/100th the area, or about 1/10th the diameter.. that's in the reasonable > range..30-45 cm aperture is an off the shelf commodity item. > > http://www.physics.ucsd.edu/~tmurphy/apollo/apollo.html talks about "few > picoseconds"... > > they use a pulsed laser with a few watts average power 115mJ/pulse at 20Hz > with a 3.5 meter telescope making a 1.8 km spot on the moon. For common view > sync, you need to have the spot bigger, as mentioned above, which is nice, > because it means you don't need as big a telescope to collimate the beam. > (interestingly, they use a XL-DC GPS disciplined oscillator as their > reference) > > > In other parts of that site, they say that getting cm scale precision > requires about 10 photons.. > > ___ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. > ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Timing Distribution in Mountainous Terrain
On 9/10/2010 11:19 AM, Oz-in-DFW wrote: On 9/10/2010 12:26 PM, Stanley Reynolds wrote: On the crazy side another common view object is the lunar laser ranging retroreflector array. Has been improvements in cost of lasers and telescopes in the past 41 years and it doesn't appear to be headed for shutdown anytime soon. Stanley Can they even shut this down? I thought it was passive. Last I heard they were worried about it becoming unusable as the loss was rising, presumably because of dust accretion. But even that seems to have stabilized. Some failure modes that cause every GPS satellite to be unusable might also affect the moon. Of course, you'll have bigger problems to worry about when this happens. Matthew Kaufman ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Timing Distribution in Mountainous Terrain
Stanley Reynolds wrote: On the crazy side another common view object is the lunar laser ranging retroreflector array. Has been improvements in cost of lasers and telescopes in the past 41 years and it doesn't appear to be headed for shutdown anytime soon. Hmm.. the SNR isn't all that huge on the echo. The target is say, 1 square meter, at a distance of 300,000 km. The beam divergence coming back is about the same as the outbound (that is, in order to cover 300km on earth, you need to have a spot on the moon about 300km in diameter).. So the laser power will be spread out by a factor of 71E9.. (about 110 dB). The power reflected back, if intercepted by a 1 square meter aperture will have the same "loss" for a round trip loss of around 220dB. Radiate 10 Watts, and you're seeing -210dBW coming back.. That's going to be tough to detect. Just how many photons/second is that? And what's the dark current/shot noise of your detector (a PM tube, presumably) The first experiments with the Apollo 11 reflector were done with the 3.1m antenna at the Lick observatory.. that's a pretty big telescope. The work at the McDonald observatory used almost as big a telescope, but did provide ranging to 1 cm, which is 0.03 ns... If we make the assumption that a degradation in position accuracy to 10m requires 1/10,000 the power.. that would imply you could use a telescope with 1/100th the area, or about 1/10th the diameter.. that's in the reasonable range..30-45 cm aperture is an off the shelf commodity item. http://www.physics.ucsd.edu/~tmurphy/apollo/apollo.html talks about "few picoseconds"... they use a pulsed laser with a few watts average power 115mJ/pulse at 20Hz with a 3.5 meter telescope making a 1.8 km spot on the moon. For common view sync, you need to have the spot bigger, as mentioned above, which is nice, because it means you don't need as big a telescope to collimate the beam. (interestingly, they use a XL-DC GPS disciplined oscillator as their reference) In other parts of that site, they say that getting cm scale precision requires about 10 photons.. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Timing Distribution in Mountainous Terrain
On 9/10/2010 12:26 PM, Stanley Reynolds wrote: > On the crazy side another common view object is the lunar laser ranging > retroreflector array. Has been improvements in cost of lasers and telescopes > in > the past 41 years and it doesn't appear to be headed for shutdown anytime > soon. > > Stanley Can they even shut this down? I thought it was passive. Last I heard they were worried about it becoming unusable as the loss was rising, presumably because of dust accretion. But even that seems to have stabilized. -- mailto:o...@ozindfw.net Oz POB 93167 Southlake, TX 76092 (Near DFW Airport) ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Timing Distribution in Mountainous Terrain
On Sep 10, 2010, at 10:47 AM, Pete Rawson wrote: > Can you use tethered balloons at each site to obtain adequate S/N > in their position to permit time calculations to 30ns uncertainty? Tether a single balloon to three sites to reduce the balloon's displacement due to wind, and then measure its position relative to the three sites by laser or radar ranging! :-D -- Mark J. Blair, NF6X Web page: http://www.nf6x.net/ GnuPG public key available from my web page. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Timing Distribution in Mountainous Terrain
Can you use tethered balloons at each site to obtain adequate S/N in their position to permit time calculations to 30ns uncertainty? Pete Rawson On Sep 10, 2010, at 11:07 AM, Oz-in-DFW wrote: > > > On 9/9/2010 2:03 PM, Ralph Smith wrote: >> 1e-11 only buys you 3000 seconds of drift before blowing the 30 ns budget. >> Without going to cesium we will most likely need some form of mutually >> visible synchronization. > Is Cesium even enough? The requirement looks like about 6 parts in > 10e-14. That's hydrogen maser territory isn't it? > > Given the application you could probably achieve this with fiber > back-haul that you continually range and jitter filter to achieve that > resolution. Not gonna be off the shelf, though. Your could probably > layer data transmission on top of this. > > Why not just periodically release a metalized weather balloon as a > calibration target, or use one to lift a calibrated reflector in the > event of an outage? Or pick a conventionally tracked target as a > calibration source? > > -- > mailto:o...@ozindfw.net > Oz > POB 93167 > Southlake, TX 76092 (Near DFW Airport) > > > > > > ___ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Timing Distribution in Mountainous Terrain
On the crazy side another common view object is the lunar laser ranging retroreflector array. Has been improvements in cost of lasers and telescopes in the past 41 years and it doesn't appear to be headed for shutdown anytime soon. Stanley - Original Message From: Mark J. Blair To: Discussion of precise time and frequency measurement Sent: Fri, September 10, 2010 11:49:49 AM Subject: Re: [time-nuts] Timing Distribution in Mountainous Terrain I presume that there's a good reason for the selection of antenna sites which don't have LOS to each other. However, would it be possible to select additional sites at which to install repeaters to allow timing calibrations to be made between pairs of primary receiving sites? These repeaters could also provide backup communications so that a primary receiving site isn't necessarily taken out of action if its communication channel (wireline?) gets cut by a wandering backhoe. Each repeater site would be selected to have LOS to two or more primary receiving sites, or when that's not possible, to one primary receiving site and another repeater that can see a different site. While multiplying the number of sites wouldn't be cheap (even considering that the repeater sites may host much less expensive equipment than the primary receiving sites, and may be able to operate without wireline communications or power lines to the sites), it might be cheaper than installing hydrogen masers and radio telescopes, designing custom aircraft and flying them overhead every 20 minutes, etc. -- Mark J. Blair, NF6X Web page: http://www.nf6x.net/ GnuPG public key available from my web page. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Timing Distribution in Mountainous Terrain
Hi An event that totally takes out every single GPS sat probably takes out everything else in orbit. A single GPS sat, no longer under ground control would be fine for timing a system like this. You don't need a full constellation or ground segment steering. About the only non-end of the world 6 day no GPS situation would be a jammer. Directional antennas could take care of terrestrial sources. You might need a steered dish, but those are available items (you can all look at the same sat at the same time). That get you to fleets of orbital jammers sync'd to the GPS birds. Pretty far out Bob On Sep 10, 2010, at 10:02 AM, jimlux wrote: > Peter Monta wrote: >>> Aren't pulsars a reliable accurate time source or do they not provide the >>> 30nS over ten days accuracy? >> By using them in common view, though, any absolute error would drop >> out. I'm not sure pulsar pulses are fast enough to do discrimination >> at 30 ns time scales, though. VLBI with broadband sources (quasars) >> would be fine here, but large amounts of data would need to be >> exchanged, and the sources are weak, requiring large antennas. >> Satellite laser ranging using LAGEOS and friends? But the original >> poster said no satellites (not even passive rocks in MEO?), and >> weather is a problem. > > > > Hmm.. here's an idea > look for the 217 MHz signals reflected from LEO satellites and NAVSPASUR.. > big illuminating fence, fairly easily detectable signals, LEO satellite so > ionosphere isn't a big deal. You get many satellites per hour crossing the > fence. > > Actually, if any satellites are available, how about using TV signals from > GEO relays? (or is the presumption that everything above 50,000 ft MSL has > been wiped out?) Some folks at JPL have used such signals to do microwave > holography on big antennas (big signal, essentially plane wavefront, etc.) > > For that matter, LEO satellites aren't that far away, and your Lband > interrogator for the transponder could probably light them up and reflect > some power back. You'd have to run the radar equation and see how much power > you get back... I have no idea about the RCS of a LEO satellite, but I'll bet > its "many" square meters (if you count ISS as a candidate.. thousands of > square meters RCS) ISS passes over several times a day, and while its orbit > isn't particularly well known or controlled (at least not to a scale of > meters), it might be good enough for you. > > > > > ___ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. > ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Timing Distribution in Mountainous Terrain
On 9/10/2010 7:26 AM, Ralph Smith wrote: > On Sep 10, 2010, at 7:50 AM, J. L. Trantham wrote: > >> Loran was used as an area navigation method in aviation for many years. It >> was available nation wide with a number of chains. I had assumed that the >> area of interest was the Rocky's but if the Appalachians, even better. > The site currently under consideration is in Colorado. Only problem with > Loran, of course, is that is has been killed, thus the operative word "was" > above. If the design and approach bears out it could be deployed over a much > wider scale. > > Ralph Even if LORAN was alive it wouldn't meet the requirement. You'd still have 20-30 M position uncertainty in a differental application - way more than your 30 ns. I thiink that dropping LORAN was a really big mistake, but it wouldn't meet this need. I used to see several 100 ns of time drift and jitter when I was in San Antonio and watching Boise City, OK (~600 Mi) -- mailto:o...@ozindfw.net Oz POB 93167 Southlake, TX 76092 (Near DFW Airport) ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Timing Distribution in Mountainous Terrain
On 9/9/2010 2:03 PM, Ralph Smith wrote: > 1e-11 only buys you 3000 seconds of drift before blowing the 30 ns budget. > Without going to cesium we will most likely need some form of mutually > visible synchronization. Is Cesium even enough? The requirement looks like about 6 parts in 10e-14. That's hydrogen maser territory isn't it? Given the application you could probably achieve this with fiber back-haul that you continually range and jitter filter to achieve that resolution. Not gonna be off the shelf, though. Your could probably layer data transmission on top of this. Why not just periodically release a metalized weather balloon as a calibration target, or use one to lift a calibrated reflector in the event of an outage? Or pick a conventionally tracked target as a calibration source? -- mailto:o...@ozindfw.net Oz POB 93167 Southlake, TX 76092 (Near DFW Airport) ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Timing Distribution in Mountainous Terrain
> The application in question seems to be concerned with the realitive time > difference between sites as opposed to absolute accuracy so depending on how > close they were together the propgation variances in a loran type solution > may not be that signficant as they may be common to the a group of receiver > sites. It's even better than that. You can use GPS to calibrate the delays. The question is stability. If you know the delays at noon, how much will they shift when the sun sets or the weather changes or ...? -- These are my opinions, not necessarily my employer's. I hate spam. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Timing Distribution in Mountainous Terrain
30ns for six days? You will probably will have to install Cesiums or Hydrogen Masers, a good Rubidium can drift 1.1us per day. Even with GPS it is hard to achieve, try to find a GPSDO that specifies +/-30ns to UTC some specify 30ns RMS, i.e. being < 30ns in ~70% of the time. Rob Kimberley -Original Message- From: time-nuts-boun...@febo.com [mailto:time-nuts-boun...@febo.com] On Behalf Of Ralph Smith Sent: 09 September 2010 5:49 PM To: Discussion of precise time and frequency measurement Subject: Re: [time-nuts] Timing Distribution in Mountainous Terrain The network is spread over about 250-300 US miles. Ralph On Thu, September 9, 2010 12:01 pm, Didier Juges wrote: > How widely spread is your network? > > > Sent from my BlackBerry Wireless thingy while I do other things... > > -Original Message- > From: "Ralph Smith" > Sender: time-nuts-boun...@febo.com > Date: Thu, 9 Sep 2010 11:37:46 > To: > Reply-To: Discussion of precise time and frequency measurement > > Subject: [time-nuts] Timing Distribution in Mountainous Terrain > > We have a requirement for approximately ten radio sites to be > synchronized to within 30 ns of each other. Ordinarily you could throw > in an appropriate GPSDO and be done with it. However, we also have the > reqirement to be able to operate independent of GPS for up to six > days. If we were able to have each site within line of sight of > another, and could form a network including all sites, we could do > differential time measurement between the mutually visible sites and correct in that way. > Unfortunately, that is not the case. Absolute time accuracy is not > critical, but relative time accuracy is. Does anyone out there have > any ideas? > > Thanks, > Ralph > AB4RS > > ___ > time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to > https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. > ___ > time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to > https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. > ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Timing Distribution in Mountainous Terrain
I presume that there's a good reason for the selection of antenna sites which don't have LOS to each other. However, would it be possible to select additional sites at which to install repeaters to allow timing calibrations to be made between pairs of primary receiving sites? These repeaters could also provide backup communications so that a primary receiving site isn't necessarily taken out of action if its communication channel (wireline?) gets cut by a wandering backhoe. Each repeater site would be selected to have LOS to two or more primary receiving sites, or when that's not possible, to one primary receiving site and another repeater that can see a different site. While multiplying the number of sites wouldn't be cheap (even considering that the repeater sites may host much less expensive equipment than the primary receiving sites, and may be able to operate without wireline communications or power lines to the sites), it might be cheaper than installing hydrogen masers and radio telescopes, designing custom aircraft and flying them overhead every 20 minutes, etc. -- Mark J. Blair, NF6X Web page: http://www.nf6x.net/ GnuPG public key available from my web page. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Timing Distribution in Mountainous Terrain
On 9/9/2010 12:49 PM, k6...@comcast.net wrote: > Ralph-- > > As far as getting a signal through mountainous terrain, look at NVIS antennas > for HF -- we use them for Field Day for just that kind of communications, 200 > - 300 miles in mountainous terrain. Figuring out propagation delays is going > to be interesting with NVIS though. > > 73 de Bob K6RTM > -- Actually, it's not too hard. layer sounding for single site DF has been pretty well documented for a long time. Getting it with accuracy to 15 feet is probably impossible though. -- mailto:o...@ozindfw.net Oz POB 93167 Southlake, TX 76092 (Near DFW Airport) ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Timing Distribution in Mountainous Terrain
On Fri, September 10, 2010 11:43 am, Mark Spencer wrote: > The application in question seems to be concerned with the realitive time > difference between sites as opposed to absolute accuracy so depending on > how > close they were together the propgation variances in a loran type solution > may > not be that signficant as they may be common to the a group of receiver > sites. Correct, it is the relative accuracy that is important, so common-mode errors will cancel out. Lot's of good comments coming through here. Thanks all for the input. Ralph ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Timing Distribution in Mountainous Terrain
The URL I posted earlier has an indpedth discussion of this (: It seems to imply to me that with processing a standard deviation of 8ns could be obtainable but I may have missed somethign in my quick skim thru the paper. If I have time this weekend I'll read thru it in more detail. It would be nice if a case could be made to restart a loran like system as GPS backup (: The application in question seems to be concerned with the realitive time difference between sites as opposed to absolute accuracy so depending on how close they were together the propgation variances in a loran type solution may not be that signficant as they may be common to the a group of receiver sites. - Original Message From: Hal Murray To: Discussion of precise time and frequency measurement Sent: Thu, September 9, 2010 9:18:16 PM Subject: Re: [time-nuts] Timing Distribution in Mountainous Terrain > Loran? What was the stability of Loran when used to distribute time? (I'm assuming I can use something like GPS for calibration.) Wikipedia says: The absolute accuracy of LORAN-C varies from 0.10-0.25-nautical-mile (185-463 m). Repeatable accuracy is much greater, typically from 60-300-foot (18-91 m). 60 feet would make it hard to get 30 ns accuracy, and that's probably at sea rather than in the mountains. -- These are my opinions, not necessarily my employer's. I hate spam. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Timing Distribution in Mountainous Terrain
Peter Monta wrote: Aren't pulsars a reliable accurate time source or do they not provide the 30nS over ten days accuracy? By using them in common view, though, any absolute error would drop out. I'm not sure pulsar pulses are fast enough to do discrimination at 30 ns time scales, though. VLBI with broadband sources (quasars) would be fine here, but large amounts of data would need to be exchanged, and the sources are weak, requiring large antennas. Satellite laser ranging using LAGEOS and friends? But the original poster said no satellites (not even passive rocks in MEO?), and weather is a problem. Hmm.. here's an idea look for the 217 MHz signals reflected from LEO satellites and NAVSPASUR.. big illuminating fence, fairly easily detectable signals, LEO satellite so ionosphere isn't a big deal. You get many satellites per hour crossing the fence. Actually, if any satellites are available, how about using TV signals from GEO relays? (or is the presumption that everything above 50,000 ft MSL has been wiped out?) Some folks at JPL have used such signals to do microwave holography on big antennas (big signal, essentially plane wavefront, etc.) For that matter, LEO satellites aren't that far away, and your Lband interrogator for the transponder could probably light them up and reflect some power back. You'd have to run the radar equation and see how much power you get back... I have no idea about the RCS of a LEO satellite, but I'll bet its "many" square meters (if you count ISS as a candidate.. thousands of square meters RCS) ISS passes over several times a day, and while its orbit isn't particularly well known or controlled (at least not to a scale of meters), it might be good enough for you. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Timing Distribution in Mountainous Terrain
David C. Partridge wrote: Jim is it possible you just gave a workable solution: Equip each site with a small radio telescope and watch pulsars. Aren't pulsars a reliable accurate time source or do they not provide the 30nS over ten days accuracy? Pulsars *are* pretty stable.. the problem is whether propagation is stable enough. Maybe with a flywheel.. GIMF (pulsar time stability) and it turns up a paper by Petit on DTIC (the research was done in 1995 at BIPM in France) http://www.google.com/url?sa=t&source=web&cd=1&sqi=2&ved=0CBcQFjAA&url=http%3A%2F%2Fwww.dtic.mil%2Fcgi-bin%2FGetTRDoc%3FLocation%3DU2%26doc%3DGetTRDoc.pdf%26AD%3DADA502306&rct=j&q=pulsar%20time%20stability&ei=-DOKTLXwKouqsAO2vNHZBA&usg=AFQjCNEH_epMW_tthuGiX50n93HH4xPxfg&cad=rja Covers performance and all the perturbations (gravitation effects from stars alongside the propagation path, propagation through atmosphere, etc.) take home value: for tau of few years, ADEV of few parts in 1E15. OTOH this paper also says the measurement uncertainty is 1 microsecond.. Also, one might look at: tf.nist.gov/general/pdf/2166.pdf Relativity and Timing in X-ray Pulsar Navigation This paper is about XNAV (think GPS in deep space, using X-ray pulsars as the S/Vs)... it seems to show that ModifiedADEV is 1E-13 (an order of magnitude worse than "atomic clock"; presumbably Cs) at tau of 0.1 year. ANother chart shows the relative performance of a whole raft of clocks (and you can see why everyone is excited about JPLs Hg-ion clock...) In any event PSR 1937+21 is about 1E-12 at tau of 500,000 seconds.. probably not good enough for the OP's need. (PSR 1937+21 has a period of about 1.5 msec, by the way.. if pulsars are really a spinning star, that's mighty impressive) thesis.library.caltech.edu/3590/ describes work on another millisecond pulsar.. the abstract says 100ns uncertainties, and long term (3yr) residuals of 500 ns. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Timing Distribution in Mountainous Terrain
Hi Satellites appear to be out. Best case, pulsars would be a once a day thing. You would need a bit better than 30 ns on the transfer (10?) to get the system to perform. To put an order of magnitude on the difficulty: I believe that 20 ns is in the same range as the error national standards labs hold relative to UTC. http://tf.nist.gov/pubs/bulletin/nistusnoarchive2009.htm That's with a lot more effort than any rational system is going to put into timing. Also that's with GPS available to allow precision time transfer. Bob On Sep 10, 2010, at 5:15 AM, Peter Monta wrote: >> Aren't pulsars a reliable accurate time source or do they not provide the >> 30nS over ten days accuracy? > > By using them in common view, though, any absolute error would drop > out. I'm not sure pulsar pulses are fast enough to do discrimination > at 30 ns time scales, though. VLBI with broadband sources (quasars) > would be fine here, but large amounts of data would need to be > exchanged, and the sources are weak, requiring large antennas. > > Satellite laser ranging using LAGEOS and friends? But the original > poster said no satellites (not even passive rocks in MEO?), and > weather is a problem. > > Cheers, > Peter Monta > > ___ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. > ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Timing Distribution in Mountainous Terrain
On Sep 10, 2010, at 7:50 AM, J. L. Trantham wrote: > Loran was used as an area navigation method in aviation for many years. It > was available nation wide with a number of chains. I had assumed that the > area of interest was the Rocky's but if the Appalachians, even better. The site currently under consideration is in Colorado. Only problem with Loran, of course, is that is has been killed, thus the operative word "was" above. If the design and approach bears out it could be deployed over a much wider scale. Ralph ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Timing Distribution in Mountainous Terrain
Loran was used as an area navigation method in aviation for many years. It was available nation wide with a number of chains. I had assumed that the area of interest was the Rocky's but if the Appalachians, even better. In aviation, 0.25 nm is 'precise'. If you get me to within 0.25 nm of the airport, I can probably find it. However, it would not be precise enough for a 'precision approach'. Joe -Original Message- From: time-nuts-boun...@febo.com [mailto:time-nuts-boun...@febo.com] On Behalf Of Hal Murray Sent: Thursday, September 09, 2010 11:18 PM To: Discussion of precise time and frequency measurement Subject: Re: [time-nuts] Timing Distribution in Mountainous Terrain > Loran? What was the stability of Loran when used to distribute time? (I'm assuming I can use something like GPS for calibration.) Wikipedia says: The absolute accuracy of LORAN-C varies from 0.10-0.25-nautical-mile (185-463 m). Repeatable accuracy is much greater, typically from 60-300-foot (18-91 m). 60 feet would make it hard to get 30 ns accuracy, and that's probably at sea rather than in the mountains. -- These are my opinions, not necessarily my employer's. I hate spam. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Timing Distribution in Mountainous Terrain
> Satellite laser ranging using LAGEOS and friends? On second thought, this wouldn't work anyway (besides being too expensive)---stations would have to be very close together to have common view. Cheers, Peter Monta ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Timing Distribution in Mountainous Terrain
> Aren't pulsars a reliable accurate time source or do they not provide the > 30nS over ten days accuracy? By using them in common view, though, any absolute error would drop out. I'm not sure pulsar pulses are fast enough to do discrimination at 30 ns time scales, though. VLBI with broadband sources (quasars) would be fine here, but large amounts of data would need to be exchanged, and the sources are weak, requiring large antennas. Satellite laser ranging using LAGEOS and friends? But the original poster said no satellites (not even passive rocks in MEO?), and weather is a problem. Cheers, Peter Monta ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Timing Distribution in Mountainous Terrain
Jim is it possible you just gave a workable solution: Equip each site with a small radio telescope and watch pulsars. Aren't pulsars a reliable accurate time source or do they not provide the 30nS over ten days accuracy? Regards, David Partridge -Original Message- From: time-nuts-boun...@febo.com [mailto:time-nuts-boun...@febo.com] On Behalf Of jimlux Sent: 10 September 2010 06:14 To: rich...@karlquist.com; Discussion of precise time and frequency measurement Subject: Re: [time-nuts] Timing Distribution in Mountainous Terrain Rick Karlquist wrote: > > I would like to point out that the environmental sensitivities of the > 5071A are unmeasureable, and the measurement threshold is far below > 5.8E-14. I would estimate that the 5071A (and ONLY the 5071A among > commercial clocks) could get the job done provided that you could > compare its frequency to GPS to the stated accuracy. This would be > using the 5071 as a secondary standard. You still need to deal with > the short term stability of the 5071A, depending on your system needs. > JPL uses H masers as flywheels. We also use the maser as a very low phase noise signal in the 10-1000 second tau range.. We multiply it up and send the (very clean) signal out to the spacecraft, it gets tracked by a loop with a few Hz BW, then sent back to earth where it's compared to the maser again to measure Doppler. Basically we measure doppler and doppler rate over a few minutes, assuming that the transmitted signal is constant during that time (which the maser is, for all practical purposes). Over a longer time span (e.g. the time between transmit and receive, which could be many hours, implying that we are transmitting from one station and receiving from another) I assume we use atomic standards and/or astronomical sources (pulsars). ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Timing Distribution in Mountainous Terrain
Each pair of sites could maybe do two-way time transfer over VHF or UHF meteor scatter. I don't know what the achievable resolution might be; I suppose it would depend on the size of the scattering entity (plasma cloud) and its geometry relative to the two sites. Sparse and unpredictable measurement times shouldn't be a problem so long as they're not too sparse. Even if 30 ns were unachievable single shot, averaging over multiple events would help given reasonable flywheel oscillators (say rubidium). The common-view UAV or mountaintop ideas would be simpler, though, if they pass muster in other respects. The mountaintop could also be passive if that helps: pairs of antennas connected by a transmission line and appropriately pointed. Cheers, Peter Monta ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Timing Distribution in Mountainous Terrain
Ralph Smith wrote: On Sep 9, 2010, at 8:01 PM, Rick Karlquist wrote: I would like to point out that the environmental sensitivities of the 5071A are unmeasureable, and the measurement threshold is far below 5.8E-14. I would estimate that the 5071A (and ONLY the 5071A among commercial clocks) could get the job done provided that you could compare its frequency to GPS to the stated accuracy. This would be using the 5071 as a secondary standard. You still need to deal with the short term stability of the 5071A, depending on your system needs. JPL uses H masers as flywheels. I would imagine the cost of a 5071A per radio station would make the check writers swallow hard, and adding an H Maser into the mix would really get their attention. Especially if you need redundancy. there's also the possibility mentioned earlier of using a lower quality standard at each station and flying (driving) a higher quality clock (5071) around often enough to keep them trued up. If it's far enough in the future.. Hg ion traps have a lot of potential.. smaller, lower power, etc. than Cs I think, though, that some sort of self calibrating array using the target of interest is a better scheme.. multiple receivers at each site separated by some distance. Getting milliradian angular resolution is a piece of cake. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Timing Distribution in Mountainous Terrain
Rick Karlquist wrote: I would like to point out that the environmental sensitivities of the 5071A are unmeasureable, and the measurement threshold is far below 5.8E-14. I would estimate that the 5071A (and ONLY the 5071A among commercial clocks) could get the job done provided that you could compare its frequency to GPS to the stated accuracy. This would be using the 5071 as a secondary standard. You still need to deal with the short term stability of the 5071A, depending on your system needs. JPL uses H masers as flywheels. We also use the maser as a very low phase noise signal in the 10-1000 second tau range.. We multiply it up and send the (very clean) signal out to the spacecraft, it gets tracked by a loop with a few Hz BW, then sent back to earth where it's compared to the maser again to measure Doppler. Basically we measure doppler and doppler rate over a few minutes, assuming that the transmitted signal is constant during that time (which the maser is, for all practical purposes). Over a longer time span (e.g. the time between transmit and receive, which could be many hours, implying that we are transmitting from one station and receiving from another) I assume we use atomic standards and/or astronomical sources (pulsars). ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Timing Distribution in Mountainous Terrain
Ralph Smith wrote: O We are not syncing time slots for communications. The timing requirement is for determining aircraft position by multilateration. Timing errors translate into position uncertainty. What's your carrier freq? In mountainous regions you'll probably have better luck at the lower end. Please tell me you're not trying this at GHz freqs at higher, rocky elevations. Signal emitted by the aircraft is 1090 MHz, pulse-position modulated transponder squitter (Mode C/Mode S). Radio stations receive signal, determine time of reception, and forward the timestamped transmission via landline to a central facility for correlation and position determination. and presumably, you have only one interrogation transmitter, and many listeners? (otherwise you could pulse each one in turn and essentially get a set of 2 way ranges to solve with) I realize you're trying to do multilateration.. BUT, if you measure angle of arrival too, then you can throw that into the solution, and you can tolerate a greater uncertainty in the range measurement. There's also the whole "using physics constraints"... combine multiple measurements, and model the vehicle dynamics. You've basically got a "make a bunch of measurements and combine them, hoping to get a root(N) improvement" problem. As you've noted, to get from 1000 ft to 30 ft requires a 30 fold improvement, implying a 1000 measurements.. Yow.. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Timing Distribution in Mountainous Terrain
Ralph Smith wrote: On Thu, September 9, 2010 1:10 pm, Matthew Kaufman wrote: On 9/9/2010 8:37 AM, Ralph Smith wrote: We have a requirement for approximately ten radio sites to be synchronized to within 30 ns of each other. 30 ns seems a little closer than most radio site applications need... what drives this requirement? Aircraft surveillance using multilateration. and presumably some form of bistatic radar with an illuminator and multiple receviers isn't going to cut it? You're fairly close.. is any RF method out of bounds? Could you radiate a low frequency signal that propagates by ground wave? (e.g. Omega.. but I don't think it was anywhere near nanoseconds..) Even a really, really good ovenized quartz oscillator isn't going to be that good. You're looking for 1E-13 sorts of precision, right (50 ns out of 500,000 seconds). I seem to recall numbers like 1 part in 1E10 over 400 days. You might do better with selected units, but this is million dollar a copy sort of units. The Cassini USO drifts between 1E-12 and 1E-11 per day. You're really looking at Cs standards... (about 2E-14 at 1E6 seconds) Ordinarily you could throw in an appropriate GPSDO and be done with it. However, we also have the reqirement to be able to operate independent of GPS for up to six days. Wow, ok, and what drives *that* requirement? Can you use any other Paranoia. People making the requirements are concerned with GPS going away due to solar flare or some other reason. mutually visible thing, or do we assume all satellites have vanished from orbit? No satellites. Thanks, Ralph ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Timing Distribution in Mountainous Terrain
On Fri, Sep 10, 2010 at 06:17, Mark J. Blair wrote: > Or, a specially-equipped aircraft which is periodically flown along paths > visible to multiple antenna sites during an extended holdover in order to > adjust out drift based on measured round-trip times between the sites and > aircraft? In effect, flying your own low-altitude satellite over the sites > when the GPS system is down. > Assuming there are multiple overflights per hour, which are visible at more than 4(?) sites at the same time, would there be enough information to steer the clocks? The correction would not need to be in real time, either. -- Sanjeev Gupta +65 98551208 http://www.linkedin.com/in/ghane ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Timing Distribution in Mountainous Terrain
> Loran? What was the stability of Loran when used to distribute time? (I'm assuming I can use something like GPS for calibration.) Wikipedia says: The absolute accuracy of LORAN-C varies from 0.10-0.25-nautical-mile (185-463 m). Repeatable accuracy is much greater, typically from 60-300-foot (18-91 m). 60 feet would make it hard to get 30 ns accuracy, and that's probably at sea rather than in the mountains. -- These are my opinions, not necessarily my employer's. I hate spam. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Timing Distribution in Mountainous Terrain
Loran? Joe -Original Message- From: time-nuts-boun...@febo.com [mailto:time-nuts-boun...@febo.com] On Behalf Of Mark J. Blair Sent: Thursday, September 09, 2010 1:48 PM To: Discussion of precise time and frequency measurement Subject: Re: [time-nuts] Timing Distribution in Mountainous Terrain On Sep 9, 2010, at 10:42, "Ralph Smith" wrote: > Paranoia. People making the requirements are concerned with GPS going > away due to solar flare or some other reason. Hmm... So the decision makers think that after a solar flare or "some other reason" (hostile destruction of the birds, perhaps?) takes out the GPS system, it'll be back up and running within six days? That sounds optimistic to me. It sounds to me more like you would need to function indefinitely without GPS, and just use GPS for initial position survey and as a convenient way to synchronize to external time reference (with ground-based backup methods in place and periodically tested). ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Timing Distribution in Mountainous Terrain
We should start seeing used Loran transmitters on ebay pretty soon (!), and it should not be too hard to build a timing receiver using this signal. If you just want timing, one transmitter may be enough to cover the area of interest. The low frequency Loran signals do go relatively well over hills, but mountains, I am not sure. Now, I do not know if this would provide the needed precision directly, but it might be enough to servo high quality references through a PLL. Didier Sent from my BlackBerry Wireless thingy while I do other things... -Original Message- From: Mark Spencer Sender: time-nuts-boun...@febo.com Date: Thu, 9 Sep 2010 17:36:39 To: Discussion of precise time and frequency measurement Reply-To: Discussion of precise time and frequency measurement Subject: Re: [time-nuts] Timing Distribution in Mountainous Terrain Some form of low frequency broadcast system might work as a GPS backup. This paper provides a comparison of Loran C vs GPS for time transfers. While Loran C is history in the US, this might give some indication of what could be expected from a low frequency broadcast system. http://www.dtic.mil/cgi-bin/GetTRDoc?Location=U2&doc=GetTRDoc.pdf&AD=ADA427851 I suspect buying cesium oscilators is likely to be cheaper than setting up a low frequency broadcast system,designing receivers etc. But there might be a more or less off the shelf way to do this ? Just a random thought. - Original Message From: Hal Murray To: Discussion of precise time and frequency measurement Sent: Thu, September 9, 2010 2:57:50 PM Subject: Re: [time-nuts] Timing Distribution in Mountainous Terrain Neat problem. Please let us know what you finally do. > 1e-11 only buys you 3000 seconds of drift before blowing the 30 ns budget. > Without going to cesium we will most likely need some form of mutually > visible synchronization. How many Cesiums do you need? What do they cost these days? (at that volume and govt rates) What's the long term maintenance cost? Can you afford to design, debug, and qualify something else at that total price? My straw man for an alternative would be to use the transmitter on the airplanes as the signal source. I think that works if you have extra ground stations covering at least some regions which will have enough airplanes in them to keep the system calibrated. But maybe you need those extra ground stations anyway so that the whole system doesn't fall apart when fire/earthquake/tornado/whatever takes out one ground station. (If so, you have to think about what happens if one station does go out.) -- These are my opinions, not necessarily my employer's. I hate spam. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Timing Distribution in Mountainous Terrain
On Sep 9, 2010, at 8:01 PM, Rick Karlquist wrote: > I would like to point out that the environmental sensitivities of > the 5071A are unmeasureable, and the measurement threshold is > far below 5.8E-14. I would estimate that the 5071A (and ONLY the 5071A > among commercial clocks) could get the job done provided that you could > compare its frequency to GPS to the stated accuracy. This would > be using the 5071 as a secondary standard. You still need to > deal with the short term stability of the 5071A, depending on > your system needs. JPL uses H masers as flywheels. I would imagine the cost of a 5071A per radio station would make the check writers swallow hard, and adding an H Maser into the mix would really get their attention. Especially if you need redundancy. Thanks for all the input. Being asked to design for Armegeddon begs the question of what will the system do after that. Ralph ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Timing Distribution in Mountainous Terrain
On Sep 9, 2010, at 9:27 PM, Bob Camp wrote: > Hi > > If 30 ns is the system goal, then you have a lot more to budget for than > simple clock error. You could easily be below 10 ns for just the clock > portion of the budget. I suspect that multiple 5071's and a maser or two at > each site will be the ultimate solution if each must stand alone for 6 days > and the set of 10 stay within 30 ns p-p. If reliability planning includes 6 > days past end of GPS it also likely includes significant redundancy and more > than a few 9's in the confidence factor. > > I suspect it's cheaper to buy the 5071's than to have a half dozen SR-71 > category aircraft ready to climb high enough to act as common view targets. > High altitude balloons might work pretty well and they would be cheaper to > keep in hot standby mode. I expect the more likely outcome to be a reality adjustment and relaxing of the requirements, possibly with some form of satellite common view target. Ralph ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Timing Distribution in Mountainous Terrain
Radar calibration: You could do a clock calibration if you knew some fixed reference points to sweep. Put some towers up on a few of the taller peaks in the area. Measure them while the GPS is running and use them for reference to keep the clocks right when GPS is down. But masers sound like more fun. -- Chris ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Timing Distribution in Mountainous Terrain
Hi If 30 ns is the system goal, then you have a lot more to budget for than simple clock error. You could easily be below 10 ns for just the clock portion of the budget. I suspect that multiple 5071's and a maser or two at each site will be the ultimate solution if each must stand alone for 6 days and the set of 10 stay within 30 ns p-p. If reliability planning includes 6 days past end of GPS it also likely includes significant redundancy and more than a few 9's in the confidence factor. I suspect it's cheaper to buy the 5071's than to have a half dozen SR-71 category aircraft ready to climb high enough to act as common view targets. High altitude balloons might work pretty well and they would be cheaper to keep in hot standby mode. Bob On Sep 9, 2010, at 8:01 PM, "Rick Karlquist" wrote: > Adrian wrote: >> Ralph, >> >> so you're talking about 5.8E-14, right? >> I'd think no off the shelf caesium, even when run in a temperature >> controlled environment, will get you there. >> Well, at a first glance, a 5071A with high performance tube would, if >> you keep any environmental effects out. >> So you'll likely need to sync them through a reliable and reproduceable >> link. >> Just a quick shot though. >> >> Adrian > > I would like to point out that the environmental sensitivities of > the 5071A are unmeasureable, and the measurement threshold is > far below 5.8E-14. I would estimate that the 5071A (and ONLY the 5071A > among commercial clocks) could get the job done provided that you could > compare its frequency to GPS to the stated accuracy. This would > be using the 5071 as a secondary standard. You still need to > deal with the short term stability of the 5071A, depending on > your system needs. JPL uses H masers as flywheels. > > Rick Karlquist N6RK > member 5071A design team > > > ___ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. > ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Timing Distribution in Mountainous Terrain
Some form of low frequency broadcast system might work as a GPS backup. This paper provides a comparison of Loran C vs GPS for time transfers. While Loran C is history in the US, this might give some indication of what could be expected from a low frequency broadcast system. http://www.dtic.mil/cgi-bin/GetTRDoc?Location=U2&doc=GetTRDoc.pdf&AD=ADA427851 I suspect buying cesium oscilators is likely to be cheaper than setting up a low frequency broadcast system,designing receivers etc. But there might be a more or less off the shelf way to do this ? Just a random thought. - Original Message From: Hal Murray To: Discussion of precise time and frequency measurement Sent: Thu, September 9, 2010 2:57:50 PM Subject: Re: [time-nuts] Timing Distribution in Mountainous Terrain Neat problem. Please let us know what you finally do. > 1e-11 only buys you 3000 seconds of drift before blowing the 30 ns budget. > Without going to cesium we will most likely need some form of mutually > visible synchronization. How many Cesiums do you need? What do they cost these days? (at that volume and govt rates) What's the long term maintenance cost? Can you afford to design, debug, and qualify something else at that total price? My straw man for an alternative would be to use the transmitter on the airplanes as the signal source. I think that works if you have extra ground stations covering at least some regions which will have enough airplanes in them to keep the system calibrated. But maybe you need those extra ground stations anyway so that the whole system doesn't fall apart when fire/earthquake/tornado/whatever takes out one ground station. (If so, you have to think about what happens if one station does go out.) -- These are my opinions, not necessarily my employer's. I hate spam. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Timing Distribution in Mountainous Terrain
See TVB's site for an experiment with moving CS standards around... Adrian > Ralph, > > so you're talking about 5.8E-14, right? > I'd think no off the shelf caesium, even when run in a temperature > controlled environment, will get you there. > Well, at a first glance, a 5071A with high performance tube would, if > you keep any environmental effects out. > So you'll likely need to sync them through a reliable and reproduceable > link. > Just a quick shot though. > > Adrian > > Ralph Smith schrieb: >> We have a requirement for approximately ten radio sites to be >> synchronized >> to within 30 ns of each other. Ordinarily you could throw in an >> appropriate GPSDO and be done with it. However, we also have the >> reqirement to be able to operate independent of GPS for up to six days. >> If >> we were able to have each site within line of sight of another, and >> could >> form a network including all sites, we could do differential time >> measurement between the mutually visible sites and correct in that way. >> Unfortunately, that is not the case. Absolute time accuracy is not >> critical, but relative time accuracy is. Does anyone out there have any >> ideas? >> >> Thanks, >> Ralph >> AB4RS >> >> ___ >> time-nuts mailing list -- time-nuts@febo.com >> To unsubscribe, go to >> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts >> and follow the instructions there. >> >> > > > ___ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to > https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. > -- "Neither the voice of authority nor the weight of reason and argument are as significant as experiment, for thence comes quiet to the mind." R. Bacon Dr. Don Latham AJ7LL Six Mile Systems LLP 17850 Six Mile Road POB 134 Huson, MT, 59846 VOX 406-626-4304 www.lightningforensics.com www.sixmilesystems.com ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Timing Distribution in Mountainous Terrain
Adrian wrote: > Ralph, > > so you're talking about 5.8E-14, right? > I'd think no off the shelf caesium, even when run in a temperature > controlled environment, will get you there. > Well, at a first glance, a 5071A with high performance tube would, if > you keep any environmental effects out. > So you'll likely need to sync them through a reliable and reproduceable > link. > Just a quick shot though. > > Adrian I would like to point out that the environmental sensitivities of the 5071A are unmeasureable, and the measurement threshold is far below 5.8E-14. I would estimate that the 5071A (and ONLY the 5071A among commercial clocks) could get the job done provided that you could compare its frequency to GPS to the stated accuracy. This would be using the 5071 as a secondary standard. You still need to deal with the short term stability of the 5071A, depending on your system needs. JPL uses H masers as flywheels. Rick Karlquist N6RK member 5071A design team ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Timing Distribution in Mountainous Terrain
Ralph, so you're talking about 5.8E-14, right? I'd think no off the shelf caesium, even when run in a temperature controlled environment, will get you there. Well, at a first glance, a 5071A with high performance tube would, if you keep any environmental effects out. So you'll likely need to sync them through a reliable and reproduceable link. Just a quick shot though. Adrian Ralph Smith schrieb: We have a requirement for approximately ten radio sites to be synchronized to within 30 ns of each other. Ordinarily you could throw in an appropriate GPSDO and be done with it. However, we also have the reqirement to be able to operate independent of GPS for up to six days. If we were able to have each site within line of sight of another, and could form a network including all sites, we could do differential time measurement between the mutually visible sites and correct in that way. Unfortunately, that is not the case. Absolute time accuracy is not critical, but relative time accuracy is. Does anyone out there have any ideas? Thanks, Ralph AB4RS ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Timing Distribution in Mountainous Terrain
On Sep 9, 2010, at 12:03 PM, Ralph Smith wrote: > 1e-11 only buys you 3000 seconds of drift before blowing the 30 ns budget. > Without going to cesium we will most likely need some form of mutually > visible synchronization. How about a rubidium or cesium standard at each site for holdover, with an extra cesium standard that is physically carried from site to site (say, by helicopter) during an extended holdover period to distribute a common time reference around? Or, a specially-equipped aircraft which is periodically flown along paths visible to multiple antenna sites during an extended holdover in order to adjust out drift based on measured round-trip times between the sites and aircraft? In effect, flying your own low-altitude satellite over the sites when the GPS system is down. These may be silly ideas, but brainstorming is fun. -- Mark J. Blair, NF6X Web page: http://www.nf6x.net/ GnuPG public key available from my web page. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Timing Distribution in Mountainous Terrain
Neat problem. Please let us know what you finally do. > 1e-11 only buys you 3000 seconds of drift before blowing the 30 ns budget. > Without going to cesium we will most likely need some form of mutually > visible synchronization. How many Cesiums do you need? What do they cost these days? (at that volume and govt rates) What's the long term maintenance cost? Can you afford to design, debug, and qualify something else at that total price? My straw man for an alternative would be to use the transmitter on the airplanes as the signal source. I think that works if you have extra ground stations covering at least some regions which will have enough airplanes in them to keep the system calibrated. But maybe you need those extra ground stations anyway so that the whole system doesn't fall apart when fire/earthquake/tornado/whatever takes out one ground station. (If so, you have to think about what happens if one station does go out.) -- These are my opinions, not necessarily my employer's. I hate spam. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Timing Distribution in Mountainous Terrain
I would agree with the many comments. Loran first choice in europe. Oooops we killed it here. 30ns speed of light issues. Think you need a synchronized RB or CS. But what on earth needs 30ns in a radio. On Thu, Sep 9, 2010 at 5:11 PM, Chris Howard wrote: > > 1) Your own LORAN? > > 2) MASERS! > > > > > ___ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to > https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. > ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Timing Distribution in Mountainous Terrain
1) Your own LORAN? 2) MASERS! ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Timing Distribution in Mountainous Terrain
On Thu, September 9, 2010 3:17 pm, John Anderson wrote: > Hmmm...I design such timing systems for Moto data radios, and 30nS sync is > going to be very hard to achieve in reality. Over a few hundred miles > you're going to have OTA time of flight issues, temperature dependencies, > etc. Over the years this has been tried, usually with dismal success in > the reliability department. You might get the system working in the > summer, and then when winter hits and snow builds up on the GPS antennas > your network goes down. Or, spring hit with a lot of atmospheric > turbulance and you get all sorts of reflection / refraction effects, and > trying to sync up time slots that close will be almost impossible. It > might work oneweek, and not the next. We are not syncing time slots for communications. The timing requirement is for determining aircraft position by multilateration. Timing errors translate into position uncertainty. > What's your carrier freq? In mountainous regions you'll probably have > better luck at the lower end. Please tell me you're not trying this at > GHz freqs at higher, rocky elevations. Signal emitted by the aircraft is 1090 MHz, pulse-position modulated transponder squitter (Mode C/Mode S). Radio stations receive signal, determine time of reception, and forward the timestamped transmission via landline to a central facility for correlation and position determination. > You might find +-1uSec is a good number to shoot for is cost and > reliability is a concern. Just a suggestion. 1 us = 1000 ft, which is more uncertainty than they want to deal with. I don't make the requirements, we just have to live with them. We definitely do provide feedback on cost and reliability to those that do dream up the requirements. Ralph ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Timing Distribution in Mountainous Terrain
Hmmm...I design such timing systems for Moto data radios, and 30nS sync is going to be very hard to achieve in reality. Over a few hundred miles you're going to have OTA time of flight issues, temperature dependencies, etc. Over the years this has been tried, usually with dismal success in the reliability department. You might get the system working in the summer, and then when winter hits and snow builds up on the GPS antennas your network goes down. Or, spring hit with a lot of atmospheric turbulance and you get all sorts of reflection / refraction effects, and trying to sync up time slots that close will be almost impossible. It might work oneweek, and not the next. What's your carrier freq? In mountainous regions you'll probably have better luck at the lower end. Please tell me you're not trying this at GHz freqs at higher, rocky elevations. You might find +-1uSec is a good number to shoot for is cost and reliability is a concern. Just a suggestion. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Timing Distribution in Mountainous Terrain
On 9/9/2010 11:57 AM, Ralph Smith wrote: You're making the mistake of applying logic. ;) Actually, aircraft can continue to fly VFR or navigate using VOR/DME and inertial navigation. The radios are part of an ADS-B installation. Yes, and they can make routine position reports and ATC can apply time-based sequencing for IFR traffic... see all sorts of past solutions to this problem. VFR aircraft don't need anyone to know where they are anyway, and IFR only need it if they're being provided radar (or equivalent) separation services. Things would work just fine after a period of adjustment, and during that period of adjustment the planes that need this kind of position determination would be grounded. I run GPS-disciplined oscillators at mountaintop radio sites *and* am a pilot, so this thread is particularly interesting to me. Matthew Kaufman ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Timing Distribution in Mountainous Terrain
1e-11 only buys you 3000 seconds of drift before blowing the 30 ns budget. Without going to cesium we will most likely need some form of mutually visible synchronization. Ralph On Thu, September 9, 2010 2:01 pm, Jason Rabel wrote: > What about Symmetricom XPRO Rubidium? It says on the data sheet they have > a low aging rate option (1e-11 / month). ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Timing Distribution in Mountainous Terrain
On Thu, September 9, 2010 1:55 pm, Matthew Kaufman wrote: > On 9/9/2010 10:42 AM, Ralph Smith wrote: >> On Thu, September 9, 2010 1:10 pm, Matthew Kaufman wrote: >>>On 9/9/2010 8:37 AM, Ralph Smith wrote: We have a requirement for approximately ten radio sites to be synchronized to within 30 ns of each other. >>> 30 ns seems a little closer than most radio site applications need... >>> what drives this requirement? >> Aircraft surveillance using multilateration. > So timing errors just become position errors. How do the sites talk back > to the display? Can't you null out position errors if enough sites can > see a single plane, and thus learn the timing error of the drifting > (relative to other) site? Sites communicate via landline telco. If there are sufficient mutually visible networked sites to form a solution on an aircraft visible to stations not in the timing network that would work, and is one of the options we are studying. Ordinarily you could throw in an appropriate GPSDO and be done with it. However, we also have the reqirement to be able to operate independent of GPS for up to six days. >>> Wow, ok, and what drives *that* requirement? Can you use any other >> Paranoia. People making the requirements are concerned with GPS going >> away >> due to solar flare or some other reason. > Once everyone relies on GPS approaches and ADS-B, the planes will be > grounded long before 6 whole days of GPS outage anyway. You're making the mistake of applying logic. ;) Actually, aircraft can continue to fly VFR or navigate using VOR/DME and inertial navigation. The radios are part of an ADS-B installation. >>> mutually visible thing, or do we assume all satellites have vanished >>> from orbit? >> No satellites. >> >> > Ok then. My best answer is to use the planes themselves as the common > reference, at least the ones high enough that enough sites can see them. > > Also consider that you might be able to find additional mountaintop > sites to plant fixed squitter-emitter transponders at that can be seen > by 2 (or more) sites. Thanks, all of these are various options we are considering, considering all of the engineering trade-offs. Ralph ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Timing Distribution in Mountainous Terrain
On Sep 9, 2010, at 10:42, "Ralph Smith" wrote: > Paranoia. People making the requirements are concerned with GPS going away > due to solar flare or some other reason. Hmm... So the decision makers think that after a solar flare or "some other reason" (hostile destruction of the birds, perhaps?) takes out the GPS system, it'll be back up and running within six days? That sounds optimistic to me. It sounds to me more like you would need to function indefinitely without GPS, and just use GPS for initial position survey and as a convenient way to synchronize to external time reference (with ground-based backup methods in place and periodically tested). ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Timing Distribution in Mountainous Terrain
What about Symmetricom XPRO Rubidium? It says on the data sheet they have a low aging rate option (1e-11 / month). ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Timing Distribution in Mountainous Terrain
On 9/9/2010 10:42 AM, Ralph Smith wrote: On Thu, September 9, 2010 1:10 pm, Matthew Kaufman wrote: On 9/9/2010 8:37 AM, Ralph Smith wrote: We have a requirement for approximately ten radio sites to be synchronized to within 30 ns of each other. 30 ns seems a little closer than most radio site applications need... what drives this requirement? Aircraft surveillance using multilateration. So timing errors just become position errors. How do the sites talk back to the display? Can't you null out position errors if enough sites can see a single plane, and thus learn the timing error of the drifting (relative to other) site? Ordinarily you could throw in an appropriate GPSDO and be done with it. However, we also have the reqirement to be able to operate independent of GPS for up to six days. Wow, ok, and what drives *that* requirement? Can you use any other Paranoia. People making the requirements are concerned with GPS going away due to solar flare or some other reason. Once everyone relies on GPS approaches and ADS-B, the planes will be grounded long before 6 whole days of GPS outage anyway. mutually visible thing, or do we assume all satellites have vanished from orbit? No satellites. Ok then. My best answer is to use the planes themselves as the common reference, at least the ones high enough that enough sites can see them. Also consider that you might be able to find additional mountaintop sites to plant fixed squitter-emitter transponders at that can be seen by 2 (or more) sites. Matthew Kaufman ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Timing Distribution in Mountainous Terrain
Ralph-- As far as getting a signal through mountainous terrain, look at NVIS antennas for HF -- we use them for Field Day for just that kind of communications, 200 - 300 miles in mountainous terrain. Figuring out propagation delays is going to be interesting with NVIS though. 73 de Bob K6RTM -- Message: 3 Date: Thu, 9 Sep 2010 11:37:46 -0400 From: "Ralph Smith" Subject: [time-nuts] Timing Distribution in Mountainous Terrain To: time-nuts@febo.com Message-ID: Content-Type: text/plain;charset=iso-8859-1 We have a requirement for approximately ten radio sites to be synchronized to within 30 ns of each other. Ordinarily you could throw in an appropriate GPSDO and be done with it. However, we also have the reqirement to be able to operate independent of GPS for up to six days. If we were able to have each site within line of sight of another, and could form a network including all sites, we could do differential time measurement between the mutually visible sites and correct in that way. Unfortunately, that is not the case. Absolute time accuracy is not critical, but relative time accuracy is. Does anyone out there have any ideas? Thanks, Ralph AB4RS ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Timing Distribution in Mountainous Terrain
On Thu, September 9, 2010 1:10 pm, Matthew Kaufman wrote: > On 9/9/2010 8:37 AM, Ralph Smith wrote: >> We have a requirement for approximately ten radio sites to be >> synchronized >> to within 30 ns of each other. > 30 ns seems a little closer than most radio site applications need... > what drives this requirement? Aircraft surveillance using multilateration. >> Ordinarily you could throw in an >> appropriate GPSDO and be done with it. However, we also have the >> reqirement to be able to operate independent of GPS for up to six days. > Wow, ok, and what drives *that* requirement? Can you use any other Paranoia. People making the requirements are concerned with GPS going away due to solar flare or some other reason. > mutually visible thing, or do we assume all satellites have vanished > from orbit? No satellites. Thanks, Ralph ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Timing Distribution in Mountainous Terrain
If you need that kind of timing accuracy in the absence of GPS then Cs is probably the only answer. Dark fiber would also work but the infrastructure and fiber leasing costs would probably be much more expensive than local Cs Sent from my Verizon Wireless BlackBerry -Original Message- From: "Ralph Smith" Sender: time-nuts-boun...@febo.com Date: Thu, 9 Sep 2010 12:48:54 To: Discussion of precise time and frequency measurement Reply-To: Discussion of precise time and frequency measurement Subject: Re: [time-nuts] Timing Distribution in Mountainous Terrain The network is spread over about 250-300 US miles. Ralph On Thu, September 9, 2010 12:01 pm, Didier Juges wrote: > How widely spread is your network? > > > Sent from my BlackBerry Wireless thingy while I do other things... > > -Original Message- > From: "Ralph Smith" > Sender: time-nuts-boun...@febo.com > Date: Thu, 9 Sep 2010 11:37:46 > To: > Reply-To: Discussion of precise time and frequency measurement > > Subject: [time-nuts] Timing Distribution in Mountainous Terrain > > We have a requirement for approximately ten radio sites to be synchronized > to within 30 ns of each other. Ordinarily you could throw in an > appropriate GPSDO and be done with it. However, we also have the > reqirement to be able to operate independent of GPS for up to six days. If > we were able to have each site within line of sight of another, and could > form a network including all sites, we could do differential time > measurement between the mutually visible sites and correct in that way. > Unfortunately, that is not the case. Absolute time accuracy is not > critical, but relative time accuracy is. Does anyone out there have any > ideas? > > Thanks, > Ralph > AB4RS > > ___ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to > https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. > ___ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to > https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. > ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Timing Distribution in Mountainous Terrain
Does the GPS backup include other sats ? As long as all sites could see the same sat then using it as a standard they would drift together. Stanley - Original Message From: Ralph Smith To: Discussion of precise time and frequency measurement Sent: Thu, September 9, 2010 11:45:04 AM Subject: Re: [time-nuts] Timing Distribution in Mountainous Terrain The requirement is 30 nanoseconds, so individual rubidium holdover over six days won't cut it. Ralph On Thu, September 9, 2010 11:58 am, Robert Darlington wrote: > Symmetricom makes GPS based NTP time servers with excellent holdover > capability. I think our "SyncServer" with an OXCO is good for +/- 0.5 > second holdover over something like 60 days. They have options for Rb > oscillators installed that will make that much much better and it might > fall > inside of your requirements. Give them a look. You're welcome to mail me > directly with questions about mine if you like. > > -Bob > > On Thu, Sep 9, 2010 at 9:37 AM, Ralph Smith wrote: > >> We have a requirement for approximately ten radio sites to be >> synchronized >> to within 30 ns of each other. Ordinarily you could throw in an >> appropriate GPSDO and be done with it. However, we also have the >> reqirement to be able to operate independent of GPS for up to six days. >> If >> we were able to have each site within line of sight of another, and >> could >> form a network including all sites, we could do differential time >> measurement between the mutually visible sites and correct in that way. >> Unfortunately, that is not the case. Absolute time accuracy is not >> critical, but relative time accuracy is. Does anyone out there have any >> ideas? >> >> Thanks, >> Ralph >> AB4RS >> >> ___ >> time-nuts mailing list -- time-nuts@febo.com >> To unsubscribe, go to >> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts >> and follow the instructions there. >> > ___ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to > https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. > ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Timing Distribution in Mountainous Terrain
On 9/9/2010 8:37 AM, Ralph Smith wrote: We have a requirement for approximately ten radio sites to be synchronized to within 30 ns of each other. 30 ns seems a little closer than most radio site applications need... what drives this requirement? Ordinarily you could throw in an appropriate GPSDO and be done with it. However, we also have the reqirement to be able to operate independent of GPS for up to six days. Wow, ok, and what drives *that* requirement? Can you use any other mutually visible thing, or do we assume all satellites have vanished from orbit? Matthew Kaufman ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Timing Distribution in Mountainous Terrain
The network is spread over about 250-300 US miles. Ralph On Thu, September 9, 2010 12:01 pm, Didier Juges wrote: > How widely spread is your network? > > > Sent from my BlackBerry Wireless thingy while I do other things... > > -Original Message- > From: "Ralph Smith" > Sender: time-nuts-boun...@febo.com > Date: Thu, 9 Sep 2010 11:37:46 > To: > Reply-To: Discussion of precise time and frequency measurement > > Subject: [time-nuts] Timing Distribution in Mountainous Terrain > > We have a requirement for approximately ten radio sites to be synchronized > to within 30 ns of each other. Ordinarily you could throw in an > appropriate GPSDO and be done with it. However, we also have the > reqirement to be able to operate independent of GPS for up to six days. If > we were able to have each site within line of sight of another, and could > form a network including all sites, we could do differential time > measurement between the mutually visible sites and correct in that way. > Unfortunately, that is not the case. Absolute time accuracy is not > critical, but relative time accuracy is. Does anyone out there have any > ideas? > > Thanks, > Ralph > AB4RS > > ___ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to > https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. > ___ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to > https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. > ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Timing Distribution in Mountainous Terrain
The requirement is 30 nanoseconds, so individual rubidium holdover over six days won't cut it. Ralph On Thu, September 9, 2010 11:58 am, Robert Darlington wrote: > Symmetricom makes GPS based NTP time servers with excellent holdover > capability. I think our "SyncServer" with an OXCO is good for +/- 0.5 > second holdover over something like 60 days. They have options for Rb > oscillators installed that will make that much much better and it might > fall > inside of your requirements. Give them a look. You're welcome to mail me > directly with questions about mine if you like. > > -Bob > > On Thu, Sep 9, 2010 at 9:37 AM, Ralph Smith wrote: > >> We have a requirement for approximately ten radio sites to be >> synchronized >> to within 30 ns of each other. Ordinarily you could throw in an >> appropriate GPSDO and be done with it. However, we also have the >> reqirement to be able to operate independent of GPS for up to six days. >> If >> we were able to have each site within line of sight of another, and >> could >> form a network including all sites, we could do differential time >> measurement between the mutually visible sites and correct in that way. >> Unfortunately, that is not the case. Absolute time accuracy is not >> critical, but relative time accuracy is. Does anyone out there have any >> ideas? >> >> Thanks, >> Ralph >> AB4RS >> >> ___ >> time-nuts mailing list -- time-nuts@febo.com >> To unsubscribe, go to >> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts >> and follow the instructions there. >> > ___ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to > https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. > ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Timing Distribution in Mountainous Terrain
How widely spread is your network? Sent from my BlackBerry Wireless thingy while I do other things... -Original Message- From: "Ralph Smith" Sender: time-nuts-boun...@febo.com Date: Thu, 9 Sep 2010 11:37:46 To: Reply-To: Discussion of precise time and frequency measurement Subject: [time-nuts] Timing Distribution in Mountainous Terrain We have a requirement for approximately ten radio sites to be synchronized to within 30 ns of each other. Ordinarily you could throw in an appropriate GPSDO and be done with it. However, we also have the reqirement to be able to operate independent of GPS for up to six days. If we were able to have each site within line of sight of another, and could form a network including all sites, we could do differential time measurement between the mutually visible sites and correct in that way. Unfortunately, that is not the case. Absolute time accuracy is not critical, but relative time accuracy is. Does anyone out there have any ideas? Thanks, Ralph AB4RS ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
