Re: [time-nuts] TymServe 2100 and the 1995 GPS issue
Sean, I have one on the way as well along with an MTI 240-0530-D OCXO. Looks like my TS-2100 is getting a complete makeover. I'll provide feedback as well. On Thu, Jun 4, 2015 at 11:38 AM, Sean Gallagher s...@wetstonetech.com wrote: Hey everyone, Just wanted to send this out. It is The documentation that Heol has sent me regarding the GPS replacement boards in the 2100. According to them so far they were able to correct the issues with some fancy firmware on their N024 board. He also told me they are going to support firmware updates up to 2035 in case more issues arise. He is sending me one of these new units and should arrive within the next 2 weeks and I'll let you know if it works in my 2100's and my Datum/Symmetricom BC635pci cards. Respectfully, Sean Gallagher Malware Analyst 571-340-3475 ___ 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] Nature: Hyper-precise atomic clocks face off to redefine time
Nice picture: A strontium-ion optical clock housed at the National Physical Laboratory in Teddington, UK. Over the past decade, various laboratories have created prototype optical atomic clocks, which use different elements such as strontium and ytterbium that emit and absorb higher-frequency photons in the visible spectrum. This finer slicing of time should, in principle, make them more accurate: it is claimed that the best of these clocks gain or lose no more than one second every 15 billion years (1E18 seconds) -- longer than the current age of the Universe -- making them 100 times more precise than their caesium counterparts. Optical clocks are claimed to be the best timekeepers in existence, but the only way to verify this in practice is to compare different models against each other and see whether they agree. Starting on 4 June, four European laboratories will kick off this testing process -- the National Physical Laboratory (NPL) in Teddington, UK; the department of Time-Space Reference Systems at the Paris Observatory; the German National Metrology Institute (PTB) in Braunschweig, Germany; and Italy's National Institute of Metrology Research in Turin. Between them, the labs host a variety of optical clocks that harness different elements in different experimental set-ups. -- These are my opinions. 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] METAS tour report (was Tour of METAS (Swiss Federal Institute of Metrology) time lab: any questions or requests?)
On 5/7/2015 11:38 AM, Pete Stephenson wrote: I recently inquired about taking a tour of the METAS time lab[1] and they said they'd be willing to show me around. Is there anything in particular that fellow time-nuts would be interested in me asking them about or (if possible) photographing? Hi all, On Friday I toured the METAS Time Frequency lab with two others: Patrick, a colleague from work and Atilla, a fellow time-nut. I'd like to report a bit about what we learned today that may be of interest to other time-nuts. UTC(CH) is composed of an ensemble of four commercial HP 5071A cesium clocks and an active hydrogen maser. METAS changed the definition of UTC(CH) several years ago. Details regarding the old and new systems were presented at a conference in 2006. The only archive I can find of the conference paper is, for some reason, available at a US military website[1]. I've mirrored the paper at my site[2]. I'll quickly summarize the two systems below: = Old Definition of UTC(CH) = UTC(CH) had previously been defined as a computed paper clock named UTC(CH.P) which was the weighted average of the four HP 5071As and the maser. This paper clock was steered monthly to track UTC. In the old system, the maser (the reference clock) drives a micro phase stepper and the output of the stepper is steered to the paper clock to form UTC(CH.R), the hardware real-time realization of UTC(CH). UTC(CH.R) is connected to the distribution hardware. Using a paper clock had two main advantages: - It's more stable than any of the individual clocks in the ensemble. - It is tolerant of hardware failure of the non-reference clocks. For example, if the ensemble normally has N clocks and one fails, it continues to work with N-1 clocks. However, there are several disadvantages: UTC(CH.P) was computed for only a single epoch each day so time measurements made at other epochs can only be related to UTC(CH.P) via interpolation. Also, if the reference clock fails the whole system is disrupted. = New Definition of UTC(CH) = In the new system, UTC(CH) is defined in real-time without interpolation instead of being computed for a single instant each day. UTC(CH) is now defined as a hardware master clock named UTC(CH.RT). To quote the paper, The UTC(CH.RT) hardware definition of UTC(CH) is chosen from one of two independent master clocks: UTC(CH.A) and UTC(CH.B). Each is the output from a DDS synthesizer, used as a MicroPhase Stepper (MPS). Each is driven by one of the free-running atomic clocks, and steered to track the paper time scale UTC(CH.P). Auto-sense Fault Switches (AFS) are used to choose UTC(CH.RT) between the A/B master clocks. The hardware redundancy between UTC(CH.A) and UTC(CH.B) has two advantages. One is reliability: if one master clock fails, switching to the backup master clock is instantaneous. The second is continuity of service: if some maintenance of one master clock becomes necessary, for example for the purpose of calibration, it is possible to switch to the other master clock at one’s convenience without interruption of service. Typically clock A is the hydrogen maser and clock B is an HP 5071A. In addition to both being reference clocks for UTC(CH.RT), both contribute to the paper time scale. = Clock Vault = In addition to the maser and four HP 5071A clocks, there are several other clocks that are used for various purposes but which do not contribute to UTC(CH): a passive hydrogen maser, several rack-mountable quartz oscillators, and at least one rubidium oscillator. All the clocks are kept in a single thermally-regulated clock vault in the basement at METAS. While it won't be used to contribute to UTC(CH), a continuous-beam cesium fountain is being constructed in the room next to that containing the UTC(CH) clocks. Details of this clock are available at [3] with a mirror at [4]. Although the Swiss are well-known for their fine watches and other timekeeping devices, METAS is a rather small national time lab (compared to, say, PTB, NIST, or USNO) with comparatively limited resources. Their primary function is to provide a service to customers or users rather than advance the state of the art of timekeeping: for example, they provide NTP service to the public and UTC-traceable calibration service to paying customers. In the past they were the time source for the long-wave time signal radio station HBG, but that service was discontinued in 2011. They are doing some interesting research in regards to time and frequency, but that is not their main focus. = Questions Answers = Several fellow time-nuts had sent me questions that they wanted me to ask METAS. Here's the questions and answers, paraphrased from my shorthand notes: 1. Q: How does METAS generate UTC(CH)? A: With four HP5071As and a hydrogen maser that contribute to a paper clock. See above, [1], or [2]. 2. Q: How is the Swiss time scale linked to the rest of the world? GPS? Two-way satellite
Re: [time-nuts] Using CPLD/FPGA or similar for frequency divider
I used a CPLD in a 900 GHz (that's right 900 GHz) optical sampling scope timebase. It was great because you just write a 17 bit counter in VHDL and there it is. You don't have to know anything about building digital hardware any more (40 years of experience wasted). Nobody cares about look ahead carry, etc. I cleaned up the timing with conventional logic, so I don't know what the jitter of the CPLD was. We needed jitter in the low fs, so I am sure the CPLD was not OK without cleaning up, but then that was a lunatic fringe project. Rick Karlquist N6RK On 6/2/2015 6:13 AM, David C. Partridge wrote: Is this a sensible thing to consider doing? Or would I be better sticking to AC/HC/AHC/LVC logic? Regards, David Partridge ___ 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] Nature: Hyper-precise atomic clocks face off to redefine time
Can someone explain to me how this is going to work in light of the fact that each clock is in a different gravitational field? Or is accuracy not the measurement, but rather stability? No, that can't be because any lab that wants to measure stability merely needs to build two or three copies of their favorite clock and insure against synchronization. They in principle shouldn't need to compare against a dissimilar type of clock. Therefore, we are back to the gravity issue. When we worked on the 5071A, we barely had enough sensitivity to notice a few parts in 10^13 between Santa Clara and Boulder (~5000 feet). Rick Karlquist N6RK On 6/3/2015 12:18 AM, Hal Murray wrote: Nice picture: A strontium-ion optical clock housed at the National Physical Laboratory in Teddington, UK. Over the past decade, various laboratories have created prototype optical atomic clocks, which use different elements such as strontium and ytterbium that emit and absorb higher-frequency photons in the visible spectrum. This finer slicing of time should, in principle, make them more accurate: it is claimed that the best of these clocks gain or lose no more than one second every 15 billion years (1E18 seconds) -- longer than the current age of the Universe -- making them 100 times more precise than their caesium counterparts. Optical clocks are claimed to be the best timekeepers in existence, but the only way to verify this in practice is to compare different models against each other and see whether they agree. Starting on 4 June, four European laboratories will kick off this testing process -- the National Physical Laboratory (NPL) in Teddington, UK; the department of Time-Space Reference Systems at the Paris Observatory; the German National Metrology Institute (PTB) in Braunschweig, Germany; and Italy's National Institute of Metrology Research in Turin. Between them, the labs host a variety of optical clocks that harness different elements in different experimental set-ups. ___ 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.
