Re: [time-nuts] Next Generation Time/Frequency Standards May Require Provisions Preventing Vertical Displacement
On 09/30/2010 06:14 AM, jimlux wrote: Magnus Danielson wrote: Doppler effects is much more important, and it's effects is being treated regularly, such as when talking in the GSM phone while driving the car... Hmm.. I think crystal oscillator frequency variation in the phone is a bigger factor. Let's say you're zipping down the road at 200 km/hr (55m/s), texting your friends. That's about 0.2ppm Doppler or around 400 Hz (for a 2 GHz carrier).. as noted.. the XO probably has 1ppm (at best.. more like 10ppm) On why there is a big market for small but stable TCXOs at 26 MHz. An even bigger problem in a mobile environment is multipath, which is far worse than the Doppler.. The effective propagation path distance could easily change 1000 meters in a fraction of a second. Depending on system, different approaches to handle fading and multipath is done. 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] Next Generation Time/Frequency Standards May Require Provisions Preventing Vertical Displacement
Magnus Danielson wrote: On 09/30/2010 06:14 AM, jimlux wrote: Magnus Danielson wrote: Doppler effects is much more important, and it's effects is being treated regularly, such as when talking in the GSM phone while driving the car... Hmm.. I think crystal oscillator frequency variation in the phone is a bigger factor. Let's say you're zipping down the road at 200 km/hr (55m/s), texting your friends. That's about 0.2ppm Doppler or around 400 Hz (for a 2 GHz carrier).. as noted.. the XO probably has 1ppm (at best.. more like 10ppm) On why there is a big market for small but stable TCXOs at 26 MHz. how stable? I'm sort of curious, I wonder what sort of temperature range cellphones are expected to really work over.. (not necessarily what they're specified for, but what the designers see as the sweet spot).. It's not like people carry their phones in pocket on the back of a backpack in -40 weather. I wonder if they're like pager receivers in some sense (e.g. they're on all the time, waiting for a call) And, as the phone heats up as you transmit, how much does the frequency change? It's a real cost sensitive huge volume market, so the specs for a cellphone reference oscillator could be highly tailored to a specific application. ___ 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] Next Generation Time/Frequency Standards May Require Provisions Preventing Vertical Displacement
On 9/30/2010 8:43 AM, jimlux wrote: how stable? The parts are generally ~ 1 ppm over temp and another ppm or two aging. I'm sort of curious, I wonder what sort of temperature range cellphones are expected to really work over.. depends on the vendor to some extent. Not all standards spec an operating temp range. The bottom end is usually -20 or -40 C though not at full spec, and -40 is pretty rare. (not necessarily what they're specified for, but what the designers see as the sweet spot).. It's not like people carry their phones in pocket on the back of a backpack in -40 weather. Most phones are not specified to operate this cold. Even standards that specify operating temperature range are often not fully complied with. I wonder if they're like pager receivers in some sense (e.g. they're on all the time, waiting for a call) No, a lot of effort is spent in letting them spend most of their time in standby and only wake up every second (or few seconds.) Most modern pagers do the same thing. They indicate to the receiver when they will be sending data, and when they will be sending device addresses (generally called the paging interval for cellphones and pagers both.) And, as the phone heats up as you transmit, how much does the frequency change? Once the phone is participating in the network it's locked to it. At that point the only thing we care about in the TCXO is short term (~ 1sec) drift and that's WAY better than 1 ppm. If you are transmitting you are still receiving several times a second and getting frequency offset updates at the same rate. It's closed loop. It's a real cost sensitive huge volume market, so the specs for a cellphone reference oscillator could be highly tailored to a specific application. Yup, and stamped out in the millions per month so they are really cheap. Well under a buck. Most are just a slab of silicon, a slab of quartz, and a package. All oscillator functions and compensation are provided in a custom bit of CMOS with EEPROM or fuse programmable compensation memory. I didn't think this was possible, but I saw one yesterday in a GS that was in an SSOT-23 package. Sheesh. -- 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] Next Generation Time/Frequency Standards May Require Provisions Preventing Vertical Displacement
See the following: http://www.nature.com/news/2010/100923/full/news.2010.487.html Of course, we're probably a few years away from seeing commercially available instruments with the required precision/accuracy...but it will come. Jeff Jeffrey K. Okamitsu, PhD, MBA +1-609-638-5402 US Mobile Phone +1-240-421-0692 GSM Mobile Phone ___ 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] Next Generation Time/Frequency Standards May Require Provisions Preventing Vertical Displacement
Actually, as I think about this, it will be impossible to calibrate another device unless one knows the vertical displacement between the standard and the DUT AND a suitably adequate (read: easy to use) algorithm for accounting for the effect of gravity can be developed. Jeff Jeffrey K. Okamitsu, PhD, MBA +1-609-638-5402 US Mobile Phone +1-240-421-0692 GSM Mobile Phone From: Jeffrey Okamitsu w...@w3kl.com To: time-nuts@febo.com Sent: Wed, September 29, 2010 12:43:36 PM Subject: [time-nuts] Next Generation Time/Frequency Standards May Require Provisions Preventing Vertical Displacement See the following: http://www.nature.com/news/2010/100923/full/news.2010.487.html Of course, we're probably a few years away from seeing commercially available instruments with the required precision/accuracy...but it will come. Jeff Jeffrey K. Okamitsu, PhD, MBA +1-609-638-5402 US Mobile Phone +1-240-421-0692 GSM Mobile Phone ___ 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] Next Generation Time/Frequency Standards May Require Provisions Preventing Vertical Displacement
More importantly, does this impose an upper limit on data transport speed over networks, in particular wireless networks? If and when one produces the network technology that would demand the accuracy and precision of these new standards, if one object is moving relative to the other, there could be loss of data as the moving clock goes out of sync with the stationary one. We know this was possible just from special relativity, but motion at normal speeds does not contribute appreciably at the currently achievable accuracies and precisions. However, with the next generation, driving in a car or certainly flying in a plane will limit bandwidth. And, of course there's the gravitation effect to contend with in the future as well, which could also limit bandwidth. As I am thinking about this, does this impose a limit on GPS accuracy and precision based on the next gen technology? Jeff Jeffrey K. Okamitsu, PhD, MBA +1-609-638-5402 US Mobile Phone +1-240-421-0692 GSM Mobile Phone From: Pieter ten Pierick time-nuts-m...@tenpierick.com To: Discussion of precise time and frequency measurement time-nuts@febo.com Sent: Wed, September 29, 2010 12:55:59 PM Subject: Re: [time-nuts] Next Generation Time/Frequency Standards May Require Provisions Preventing Vertical Displacement Hi, See the following: http://www.nature.com/news/2010/100923/full/news.2010.487.html Of course, we're probably a few years away from seeing commercially available instruments with the required precision/accuracy...but it will come. I read that the moving of NIST F1 1 floor indeed changed the frequency quite a bit. (The change in altitude was 11.5 feet) That article also mentioned that the warming up of the building itself in summer has an effect on some of the newest research clocks, because the environment changes shape... See http://www.wired.com/science/discoveries/news/2007/12/time_nist?currentPage=all (Not that those clocks are commercially available, though :-/ ) Greetings, Pieter. Jeff Jeffrey K. Okamitsu, PhD, MBA +1-609-638-5402 US Mobile Phone +1-240-421-0692 GSM Mobile Phone ___ 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] Next Generation Time/Frequency Standards May Require Provisions Preventing Vertical Displacement
On 09/29/2010 06:56 PM, Jeffrey Okamitsu wrote: Actually, as I think about this, it will be impossible to calibrate another device unless one knows the vertical displacement between the standard and the DUT AND a suitably adequate (read: easy to use) algorithm for accounting for the effect of gravity can be developed. You can compare two standards by levelling their gravitational centers (similar to phase centers of GPS antennas) to the same level or within same level to what degree they are comparable too. Wither they need to be within 1 mm, 100 mm, 10 m or 1 km depends on the quality of the oscillators. 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] Next Generation Time/Frequency Standards May Require Provisions Preventing Vertical Displacement
I was thinking more in terms of remotely located devices. That is, not at the same physical position where the sync signal is transmitted over some reliable medium. In that case, one will have to know the relative vertical displacement. Also, as I think further, in principle the local terrain at each location plays a role as well. Jeff Jeffrey K. Okamitsu, PhD, MBA +1-609-638-5402 US Mobile Phone +1-240-421-0692 GSM Mobile Phone From: Magnus Danielson mag...@rubidium.dyndns.org To: time-nuts@febo.com Sent: Wed, September 29, 2010 1:51:30 PM Subject: Re: [time-nuts] Next Generation Time/Frequency Standards May Require Provisions Preventing Vertical Displacement On 09/29/2010 06:56 PM, Jeffrey Okamitsu wrote: Actually, as I think about this, it will be impossible to calibrate another device unless one knows the vertical displacement between the standard and the DUT AND a suitably adequate (read: easy to use) algorithm for accounting for the effect of gravity can be developed. You can compare two standards by levelling their gravitational centers (similar to phase centers of GPS antennas) to the same level or within same level to what degree they are comparable too. Wither they need to be within 1 mm, 100 mm, 10 m or 1 km depends on the quality of the oscillators. 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] Next Generation Time/Frequency Standards May Require Provisions Preventing Vertical Displacement
More importantly, does this impose an upper limit on data transport speed over networks, in particular wireless networks? If and when one produces the network technology that would demand the accuracy and precision of these new standards, if one object is moving relative to the other, there could be loss of data as the moving clock goes out of sync with the stationary one. We know this was possible just from special relativity, but motion at normal speeds does not contribute appreciably at the currently achievable accuracies and precisions. However, with the next generation, driving in a car or certainly flying in a plane will limit bandwidth. And, of course there's the gravitation effect to contend with in the future as well, which could also limit bandwidth. That's not a serious problem. The receiver doesn't need a free running local clock that is exactly matched to the transmitter clock. It can use a PLL to derive a local clock from the received signal. Most (all?) Ethernet receivers and modems already work this way. Think of the Doppler shift from a train horn. If the train was sending morse code, you could still decode it if the train was moving toward or away from you. It's just different from what you would hear if the train wasn't moving. As I am thinking about this, does this impose a limit on GPS accuracy and precision based on the next gen technology? Relativity is already significant for GPS. The transmitters in the satellites arepre-corrected so it comes out right after the signal gets to a receiver on the surface of the Earth. See the recent discussion (a day or two ago) on the exact value of the frequency sent by the GPS satellites. Once you figure out what you want, you can probably figure out what corrections you need to get it. If you are comparing clocks at the level of national labs, you already have to correct for elevation of the receiver. Boulder (NIST) is at 5000 feet. That's the same elevation used by Poject GREAT. http://www.leapsecond.com/great2005/ Daniel Kleppner's, Time Too Good to Be True in Physics Today, March 2006, pointed out that atomic clocks will soon define what sea level means. -- 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] Next Generation Time/Frequency Standards May Require Provisions Preventing Vertical Displacement
On 09/29/2010 07:17 PM, Jeffrey Okamitsu wrote: More importantly, does this impose an upper limit on data transport speed over networks, in particular wireless networks? No, not really. If and when one produces the network technology that would demand the accuracy and precision of these new standards, if one object is moving relative to the other, there could be loss of data as the moving clock goes out of sync with the stationary one. We know this was possible just from special relativity, but motion at normal speeds does not contribute appreciably at the currently achievable accuracies and precisions. However, with the next generation, driving in a car or certainly flying in a plane will limit bandwidth. And, of course there's the gravitation effect to contend with in the future as well, which could also limit bandwidth. The imprecision of oscillators being used is so huge that gravitational effects is swamped in normal everyday life. You need significant elevation such as that of GPS satellites, but much of that effect can be treated using frequency offset and the remaining effect involves movement. As I am thinking about this, does this impose a limit on GPS accuracy and precision based on the next gen technology? No, gravitational effects is first degree compensated and only a minor second degree effect needs compensation for some case. These effects is very predictable. You can always find cases where a particular effect forms a limit, but relative theory doesn't form a practical limit for most of the day to day life and use of technology. For the case of telecommunication networks, the receiver will recover the symbol rate of the signal in order to sample the symbols and later those symbols is converted into bits. That the transmitter and receiver has different gravitational potential causes a small offset in frequency, but since the receiver PLL tracks the frequency then frequency errors due to oscillator offsets, temperature changes, doppler effects as one moves around etc. Doppler effects is much more important, and it's effects is being treated regularly, such as when talking in the GSM phone while driving the car... 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] Next Generation Time/Frequency Standards May Require Provisions Preventing Vertical Displacement
Jeffrey Okamitsu wrote: More importantly, does this impose an upper limit on data transport speed over networks, in particular wireless networks? If and when one produces the network technology that would demand the accuracy and precision of these new standards, if one object is moving relative to the other, there could be loss of data as the moving clock goes out of sync with the stationary one. We know this was possible just from special relativity, but motion at normal speeds does not contribute appreciably at the currently achievable accuracies and precisions. However, with the next generation, driving in a car or certainly flying in a plane will limit bandwidth. And, of course there's the gravitation effect to contend with in the future as well, which could also limit bandwidth. We already deal with relativistic corrections in GPS data, and also in deep space navigation (when you're measuring millimeter range differences in the distance to Saturn and back, everything counts).. A few years ago, I was working with some folks who were looking at time transfer among different spacecraft for the Constellation program (e.g. if you have relay satellites around the Moon or Mars or somewhere, and you want precision timing to someone on the back side of either (i.e. they can't see Earth directly). The velocities are high enough that you need to start contemplating relativistic effect: e.g. at 7 km/s sqrt(1-v^2/c^2) is about 1 part in 1E10.. If you need to synchronize events to, say, 1 millisecond out of a day, that's 1 part in 1E11 As I am thinking about this, does this impose a limit on GPS accuracy and precision based on the next gen technology? ___ 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.
