Re: [time-nuts] June 30 2015 leap second
Such slewing solutions are OK for Google. They wouldn't work well for one of the systems I work with, which uses system time to calculate the position of a LEO satellite for purpose of pointing a 7.6 meter X-band dish. Half a second of error corresponds to a pointing error of 0.5 degrees, well outside the main lobe of the antenna beam. Anecdotally yours, Henry On Fri, Jan 9, 2015 at 2:30 PM, Hal Murray hmur...@megapathdsl.net wrote: t...@patoka.org said: 1s/24h = 1/86400 which is approximately 12ppm. That means that Aging Offset could slow down my clock for 1 second if I'll apply the maximum value one day ahead (roughly). I need to do some experiments first. ;-) Its looks too unreliable for me. If you do it that way, your clock will be off by a whole second just before midnight when the leap-second brings it back into sync. If you tweak your clock from noon-noon, it will only be off by 1/2 second at midnight when the sign-bit of the error flips. -- 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 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] question Alan deviation measured with Timelab and counters
Stephane, On 01/09/2015 12:53 PM, steph.rey wrote: Dear all, I'm trying to measure Alan Deviations using Timelab and some frequency counters. The device under test is a GPSDO using a TCXO as référence I've an HP58503B GPSDO which feeds my counters. I've tried an HP5342A, 0-18 GHz, 1 Hz resolution and a Philipps PM6654C, 0.01Hz resolution. In Timelab, the plot with the HP5342A is around 10e-7 which correspond to 1Hz and with the PM6654C, the plot is around 10e-10. I would suspect that this is still the counter which limits the actual response of my device under test. My question are : - how to measure Alan Deviations with levels below 10e-12/10e-13 ? What can be the application of measurement Alan deviation 10e-10 ? I guess most of the low frequency - The HP53503 GPS is given to be 10e-11 / 10e-12. I guess this will limit anyway the measurement floor. I've a Rb source, but it's stability is within the same range. What kind of reference would be more suitable for such measurements ? - With the PM6654C on 15h measurement, I can see some frequency jumps of 800 Hz which are not relevants with the GPSDO undertest. I suspect error in data transmission. This makes the overall measurement totally wrong (10e-5). The counter is in talk only mode. I'd like to get rid of these points maybe 40-50 points out of 1. Is there a way to do that from Timelab or the only option is to export the file and process manually the data ? I've use the PM6654C with TimeLab. I wire the 10 MHz from the GPSDO and then the PPS to Channel A. Channel B has whatever signal I want to measure. By letting TimeLab know the frequency, it can adjust for any slipped cycles on the fly. This works well. The PM6654C has a single-shot resolution of 2 ns, which comes from the internal 500 MHz counting clock. This gives ~ 2E-9/tau (very coarse level) measurement limit. If you want to reach the 1E-12 resolution mark you need another 2000 of resolution gain, which is what you get if you mix your 10 MHz signal with a 10,005 MHz clock or lower. The Dual Mixer Time Difference (DMTD) is more likely to work well, as it provides some cancellation of the transfer clock. Slew-rates needs to be shaped, so you probably need a lower frequency to get some additional gain (and thus margin) and then amplifier stages on the beat signal. It's a tricky subject which requires a lot of attention to a bunch of details. I'd stay of the HP5342A as it will create dead-time in the measurements, which has a bias factor to it. The comments and suggestions you have received so far is also good comments. 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] Four questions on Datum PRS-50
Hello and Happy new year to all list members. I have four questions regarding a Datum PRS-50: 1 - Is it similar to another Datum Cesium like the FTS 4060 or another FTS series Cesium ? 2 - Is there a list of commands and the data the with get out of the RS-232 port, which port (front or back ) should I use, and what are the COM parameters (baud rate, parity, etc) ? 3 - I checked on the web and found no manual (service or users) and no trace of the software use to control the unit. If someone has it and want to share, I would appreciate. 4 - I'm getting this unit from a friend as is, and I don't know if it is working or not. What would be a fair offer, I don't know the going price on these or how common are they. Thank you ! Claude ___ 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] question Alan deviation measured with Timelab and counters
Hi If your only instrument is a counter. — and — You never measure past 1x10^-10 with that counter — and — Measurements that bounce around with a standard deviation of the difference between readings of 1x10^-10 are ok. — then — No, you don’t need anything better than a 1x10^-10 ADEV. Most people would be bothered by a counter that has an typical jump of 1x10^-10 between every reading, so most would want a standard that’s a bit better than that. In addition, if you want to guarantee accuracy of a reading, you probably want something that’s 5X to 10X better than the level that stops the reading jitter. Simply put - ADEV is not standard deviation of frequency. Your frequency counter measures frequency. Going from one to the other means you want to have better ADEV than you might think. Bob On Jan 9, 2015, at 10:42 AM, steph.rey steph@wanadoo.fr wrote: Hi Bob, Many thanks for your prompt and detailled answer. My question on applications wasn't on good ADEV where I perfetcly understand the need, but actually what could be the applications of measuring BAD ADEV (10e-7). That was my point asking what king of application can we cover by measuring such high ADEV when you have counters with resolution not greater than 0.01Hz However you bring to me part of the answer when you talk about the reference and the way to get something cheap and better than 10e-12. I will investigate on DMTD. However, even if you have a beautiful Maser source, will you improve anything above the resolution of your counter. In other words, with my 0.01Hz counter, will I improve my measurement if I replace my GPSDO source with something much better ? I feel the resolution of the counter will anyway limit the ADEV floor, right ? If the last digit of the counter do not move how could we measure something smaller ? The counters I'm using are not running on their own reference (OCXO or TCXO) but with the HP58503b which is a GPS disciplined OCXO but with stability in the range of 10e-11 or 10e-12 at best. I'm working for a big lab where possibly I could have nice piece of equipment but this is always easier to find alternatives solutions at lower price. On the application I'm working on we're looking for phase stability in the range of fs at several GHz. One of the project I'm working will use a femtosecond laser modulated at 88 Mhz that some people want to use as RF reference for the 3 GHz source. I'm pretty sure this can't achieve the phase stability requirement and I'm trying to illustrate this. However even for my ham activites where I'm trying to design low noise LOs, I'd like to have a tool able to measure goog frequency and phase stability... Stephane On Fri, 9 Jan 2015 07:48:42 -0500, Bob Camp kb...@n1k.org wrote: Hi Welcome to the world of trying to measure this stuff … On Jan 9, 2015, at 6:53 AM, steph.rey steph@wanadoo.fr wrote: Dear all, I'm trying to measure Alan Deviations using Timelab and some frequency counters. The device under test is a GPSDO using a TCXO as référence I've an HP58503B GPSDO which feeds my counters. I've tried an HP5342A, 0-18 GHz, 1 Hz resolution and a Philipps PM6654C, 0.01Hz resolution. In Timelab, the plot with the HP5342A is around 10e-7 which correspond to 1Hz and with the PM6654C, the plot is around 10e-10. I would suspect that this is still the counter which limits the actual response of my device under test. Yes, the counters and TCXO are limiting your measurements. My question are : - how to measure Alan Deviations with levels below 10e-12/10e-13 ? How much money do you have to spend? ( There are expensive commercial ways to do this). No matter what, you will need a “better than” reference. That’s not going to be cheap. Most of us simply get a second GPSDO and compare them. The assumption is that they both are the same and you can allocate the error equally between them. With three you can more accurately allocate the error. A DMTD is the “cheap” way to get the actual measurement done. What can be the application of measurement Alan deviation 10e-10 ? I guess most of the low frequency There are a number of systems applications that very much need good ADEV. Getting into why this or that nav or com system needs it would take a bit of time. - The HP53503 GPS is given to be 10e-11 / 10e-12. I guess this will limit anyway the measurement floor. I've a Rb source, but it's stability is within the same range. What kind of reference would be more suitable for such measurements ? If you want to do it directly, a hydrogen maser is a good way to go. That’s silly expensive. Just compare GPSDO’s, that’s a lot cheaper. - With the PM6654C on 15h measurement, I can see some frequency jumps of 800 Hz which are not relevants with the GPSDO undertest. I suspect error in data transmission. This makes the overall measurement totally wrong
Re: [time-nuts] Mechanical 1PPS Oscillator Disciplining
Hi Tom dividing down wasn't always necessary I have sample from the UK GPO Crystal Factory of NT-cut bars, quartz tuning fork, and Gapped Ring crystals, the latter marked 400cps (pre Hertz :-)) ) I think these are post WWII because they are mounted in IO base GT style tube envelopes. Dividers were achieved with neons and locked multivibrators, where necessary, I believe. The original ( 1926 ) frequency source for Rugby GBR 16kHz radio station was an invar tuning fork with a tube maintaining amplifier. I cannot find any information on syntonising that but it probably was not necessary. Alan G3NYK - Original Message - From: Tom Van Baak t...@leapsecond.com To: Discussion of precise time and frequency measurement time-nuts@febo.com Sent: Friday, January 09, 2015 9:51 PM Subject: Re: [time-nuts] Mechanical 1PPS Oscillator Disciplining Andy, Yes, Neal Stephenson's Mother Earth Mother Board article is a classic that every time nut should read at some point. The one page version is at http://archive.wired.com/wired/archive/4.12/ffglass_pr.html Prior to quartz, pendulum clocks and tuning fork oscillators were the standard. Even until the 1950's or early 1960's tuning fork oscillators were used when one needed accurate frequency in the audio range. That's because dividing down high frequency quartz oscillators to, say, 60 Hz or 400 Hz required lots of circuitry. Not sure if Neal's reference to vibrating reed is what we would call a tuning fork, or if it's something else. Here in the US General Radio made precision tuning fork oscillators. Model numbers 213, 723, 813, 815. One example is at http://leapsecond.com/museum/gr815b/ Also check out old issues of General Radio Experimenter magazine for details on these wonderful instruments. Pendulum clocks were also used in power plants around the world to keep the grid synchronized. There is occasional discussion about this on clock collecting or horology forums. They are precious and can be extremely accurate, as good as a second a year. Since pendulum clocks were better long-term timekeepers and generated only 0.5 or 1 Hz signals, a PDTF (Pendulum Disciplined Tuning Fork) made sense. Has a nice ring to it, doesn't it. /tvb - Original Message - From: Andy Bardagjy a...@bardagjy.com To: Discussion of precise time and frequency measurement time-nuts@febo.com Sent: Friday, January 09, 2015 9:22 AM Subject: [time-nuts] Mechanical 1PPS Oscillator Disciplining From a fascinating (albeit long) article about transatlantic communication cables http://archive.wired.com/wired/archive/4.12/ffglass.html On the bottom of page 45 to the top of page 46 Each piece of equipment on this tabletop is built around a motor that turns over at the same precise frequency. None of it would work - no device could communicate with any other device - unless all of those motors were spinning in lockstep with one another. The transmitter, regenerator/retransmitter, and printer all had to be in sync even though they were thousands of miles apart. This feat is achieved by means of a collection of extremely precise analog machinery. The heart of the system is another polished box that contains a vibrating reed, electromagnetically driven, thrumming along at 30 cycles per second, generating the clock pulses that keep all the other machines turning over at the right pace. The reed is as precise as such a thing can be, but over time it is bound to drift and get out of sync with the other vibrating reeds in the other stations. In order to control this tendency, a pair of identical pendulum clocks hang next to each other on the wall above. These clocks feed steady, one-second timing pulses into the box housing the reed. The reed, in turn, is driving a motor that is geared so that it should turn over at one revolution per second, generating a pulse with each revolution. If the frequency of the reed's vibration begins to drift, the motor's speed will drift along with it, and the pulse will come a bit too early or a bit too late. But these pulses are being compared with the steady one-second pulses generated by the double pendulum clock, and any difference between them is detected by a feedback system that can slightly speed up or slow down the vibration of the reed in order to correct the error. The result is a clock so steady that once one of them is set up in, say, London, and another is set up in, say, Cape Town, the machinery in those two cities will remain synched with each other indefinitely. Does anyone know any other history about that particular piece of equipment? Cheers! Andy ◉ Bardagjy.com ◉ +1-404-964-1641 ___ 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 --
Re: [time-nuts] Mechanical 1PPS Oscillator Disciplining
yes, Ulrich's [ Rohde ] Father made a high precision clock around 1940, which had an electronically tuned mechanical oscillator. The vibrating 400Hz tuning fork is phase locked to a quartz crystal oscillator, that was the most precise clock at that time, and it worked as I have seen it at the company as I worked there in the sixties of the past century. 73 KJ6UHN Alex On 1/9/2015 9:22 AM, Andy Bardagjy wrote: From a fascinating (albeit long) article about transatlantic communication cables http://archive.wired.com/wired/archive/4.12/ffglass.html On the bottom of page 45 to the top of page 46 Each piece of equipment on this tabletop is built around a motor that turns over at the same precise frequency. None of it would work - no device could communicate with any other device - unless all of those motors were spinning in lockstep with one another. The transmitter, regenerator/retransmitter, and printer all had to be in sync even though they were thousands of miles apart. This feat is achieved by means of a collection of extremely precise analog machinery. The heart of the system is another polished box that contains a vibrating reed, electromagnetically driven, thrumming along at 30 cycles per second, generating the clock pulses that keep all the other machines turning over at the right pace. The reed is as precise as such a thing can be, but over time it is bound to drift and get out of sync with the other vibrating reeds in the other stations. In order to control this tendency, a pair of identical pendulum clocks hang next to each other on the wall above. These clocks feed steady, one-second timing pulses into the box housing the reed. The reed, in turn, is driving a motor that is geared so that it should turn over at one revolution per second, generating a pulse with each revolution. If the frequency of the reed's vibration begins to drift, the motor's speed will drift along with it, and the pulse will come a bit too early or a bit too late. But these pulses are being compared with the steady one-second pulses generated by the double pendulum clock, and any difference between them is detected by a feedback system that can slightly speed up or slow down the vibration of the reed in order to correct the error. The result is a clock so steady that once one of them is set up in, say, London, and another is set up in, say, Cape Town, the machinery in those two cities will remain synched with each other indefinitely. Does anyone know any other history about that particular piece of equipment? Cheers! Andy ◉ Bardagjy.com ◉ +1-404-964-1641 ___ 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] June 30 2015 leap second
t...@patoka.org said: 1s/24h = 1/86400 which is approximately 12ppm. That means that Aging Offset could slow down my clock for 1 second if I'll apply the maximum value one day ahead (roughly). I need to do some experiments first. ;-) Its looks too unreliable for me. If you do it that way, your clock will be off by a whole second just before midnight when the leap-second brings it back into sync. If you tweak your clock from noon-noon, it will only be off by 1/2 second at midnight when the sign-bit of the error flips. -- 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.
Re: [time-nuts] question Alan deviation measured with Timelab and counters
Hi Bob, Many thanks for your prompt and detailled answer. My question on applications wasn't on good ADEV where I perfetcly understand the need, but actually what could be the applications of measuring BAD ADEV (10e-7). That was my point asking what king of application can we cover by measuring such high ADEV when you have counters with resolution not greater than 0.01Hz However you bring to me part of the answer when you talk about the reference and the way to get something cheap and better than 10e-12. I will investigate on DMTD. However, even if you have a beautiful Maser source, will you improve anything above the resolution of your counter. In other words, with my 0.01Hz counter, will I improve my measurement if I replace my GPSDO source with something much better ? I feel the resolution of the counter will anyway limit the ADEV floor, right ? If the last digit of the counter do not move how could we measure something smaller ? The counters I'm using are not running on their own reference (OCXO or TCXO) but with the HP58503b which is a GPS disciplined OCXO but with stability in the range of 10e-11 or 10e-12 at best. I'm working for a big lab where possibly I could have nice piece of equipment but this is always easier to find alternatives solutions at lower price. On the application I'm working on we're looking for phase stability in the range of fs at several GHz. One of the project I'm working will use a femtosecond laser modulated at 88 Mhz that some people want to use as RF reference for the 3 GHz source. I'm pretty sure this can't achieve the phase stability requirement and I'm trying to illustrate this. However even for my ham activites where I'm trying to design low noise LOs, I'd like to have a tool able to measure goog frequency and phase stability... Stephane On Fri, 9 Jan 2015 07:48:42 -0500, Bob Camp kb...@n1k.org wrote: Hi Welcome to the world of trying to measure this stuff … On Jan 9, 2015, at 6:53 AM, steph.rey steph@wanadoo.fr wrote: Dear all, I'm trying to measure Alan Deviations using Timelab and some frequency counters. The device under test is a GPSDO using a TCXO as référence I've an HP58503B GPSDO which feeds my counters. I've tried an HP5342A, 0-18 GHz, 1 Hz resolution and a Philipps PM6654C, 0.01Hz resolution. In Timelab, the plot with the HP5342A is around 10e-7 which correspond to 1Hz and with the PM6654C, the plot is around 10e-10. I would suspect that this is still the counter which limits the actual response of my device under test. Yes, the counters and TCXO are limiting your measurements. My question are : - how to measure Alan Deviations with levels below 10e-12/10e-13 ? How much money do you have to spend? ( There are expensive commercial ways to do this). No matter what, you will need a “better than” reference. That’s not going to be cheap. Most of us simply get a second GPSDO and compare them. The assumption is that they both are the same and you can allocate the error equally between them. With three you can more accurately allocate the error. A DMTD is the “cheap” way to get the actual measurement done. What can be the application of measurement Alan deviation 10e-10 ? I guess most of the low frequency There are a number of systems applications that very much need good ADEV. Getting into why this or that nav or com system needs it would take a bit of time. - The HP53503 GPS is given to be 10e-11 / 10e-12. I guess this will limit anyway the measurement floor. I've a Rb source, but it's stability is within the same range. What kind of reference would be more suitable for such measurements ? If you want to do it directly, a hydrogen maser is a good way to go. That’s silly expensive. Just compare GPSDO’s, that’s a lot cheaper. - With the PM6654C on 15h measurement, I can see some frequency jumps of 800 Hz which are not relevants with the GPSDO undertest. I suspect error in data transmission. This makes the overall measurement totally wrong (10e-5). The counter is in talk only mode. I'd like to get rid of these points maybe 40-50 points out of 1. Is there a way to do that from Timelab or the only option is to export the file and process manually the data ? You can expand the data and zap the offending segments. It’s done on the phase plot. Have Fun. Bob Thanks cheers Stephane ___ 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
Re: [time-nuts] question Alan deviation measured with Timelab and counters
On 1/9/15 7:42 AM, steph.rey wrote: Hi Bob, Many thanks for your prompt and detailled answer. My question on applications wasn't on good ADEV where I perfetcly understand the need, but actually what could be the applications of measuring BAD ADEV (10e-7). That was my point asking what king of application can we cover by measuring such high ADEV when you have counters with resolution not greater than 0.01Hz However you bring to me part of the answer when you talk about the reference and the way to get something cheap and better than 10e-12. I will investigate on DMTD. However, even if you have a beautiful Maser source, will you improve anything above the resolution of your counter. In other words, with my 0.01Hz counter, will I improve my measurement if I replace my GPSDO source with something much better ? I feel the resolution of the counter will anyway limit the ADEV floor, right ? If the last digit of the counter do not move how could we measure something smaller ? The various heterodyne techniques (DMTD is but one) let you use your counter for many more digits than it has. Essentially what you do is beat your unknown against the standard, and count the difference frequency. What you really do is put an offset in one (say 100Hz on a 10 MHz standard) so you're accurately measuring a 100 Hz instead of a 10 MHz signal. Your counter then gets down into the microHz. The other approach is to use one standard to drive the ADC clock to sample the unknown, and then post process in software. Once you've got a series of numbers, you can get infinite precision in software. there's a variety of schemes here too. The counters I'm using are not running on their own reference (OCXO or TCXO) but with the HP58503b which is a GPS disciplined OCXO but with stability in the range of 10e-11 or 10e-12 at best. I'm working for a big lab where possibly I could have nice piece of equipment but this is always easier to find alternatives solutions at lower price. On the application I'm working on we're looking for phase stability in the range of fs at several GHz. One of the project I'm working will use a femtosecond laser modulated at 88 Mhz that some people want to use as RF reference for the 3 GHz source. I'm pretty sure this can't achieve the phase stability requirement and I'm trying to illustrate this. However even for my ham activites where I'm trying to design low noise LOs, I'd like to have a tool able to measure goog frequency and phase stability... Stephane On Fri, 9 Jan 2015 07:48:42 -0500, Bob Camp kb...@n1k.org wrote: Hi Welcome to the world of trying to measure this stuff … On Jan 9, 2015, at 6:53 AM, steph.rey steph@wanadoo.fr wrote: Dear all, I'm trying to measure Alan Deviations using Timelab and some frequency counters. The device under test is a GPSDO using a TCXO as référence I've an HP58503B GPSDO which feeds my counters. I've tried an HP5342A, 0-18 GHz, 1 Hz resolution and a Philipps PM6654C, 0.01Hz resolution. In Timelab, the plot with the HP5342A is around 10e-7 which correspond to 1Hz and with the PM6654C, the plot is around 10e-10. I would suspect that this is still the counter which limits the actual response of my device under test. Yes, the counters and TCXO are limiting your measurements. My question are : - how to measure Alan Deviations with levels below 10e-12/10e-13 ? How much money do you have to spend? ( There are expensive commercial ways to do this). No matter what, you will need a “better than” reference. That’s not going to be cheap. Most of us simply get a second GPSDO and compare them. The assumption is that they both are the same and you can allocate the error equally between them. With three you can more accurately allocate the error. A DMTD is the “cheap” way to get the actual measurement done. What can be the application of measurement Alan deviation 10e-10 ? I guess most of the low frequency There are a number of systems applications that very much need good ADEV. Getting into why this or that nav or com system needs it would take a bit of time. - The HP53503 GPS is given to be 10e-11 / 10e-12. I guess this will limit anyway the measurement floor. I've a Rb source, but it's stability is within the same range. What kind of reference would be more suitable for such measurements ? If you want to do it directly, a hydrogen maser is a good way to go. That’s silly expensive. Just compare GPSDO’s, that’s a lot cheaper. - With the PM6654C on 15h measurement, I can see some frequency jumps of 800 Hz which are not relevants with the GPSDO undertest. I suspect error in data transmission. This makes the overall measurement totally wrong (10e-5). The counter is in talk only mode. I'd like to get rid of these points maybe 40-50 points out of 1. Is there a way to do that from Timelab or the only option is to export the file and process manually the data ? You can expand the data and zap the offending segments. It’s done on the
Re: [time-nuts] Mechanical 1PPS Oscillator Disciplining
In message df7c7705-b1cc-4b8d-8bac-d471e2ab5...@bardagjy.com, Andy Bardagjy w rites: Does anyone know any other history about that particular piece of equipment? I seriously doubt those claims of precision. At datamuseum.dk we did a small booklet about the history of paper tape as a storage medium some years back, and the Great Nordic Telegraph Company was roughly half of the material. The first thing to notice is that most cables were simplex, you could only transmit in one direction at a time. The turnaround was suprisingly slow. Because of the dielectric absorption in many miles of cable you had to disconnect your (relatively high voltage) transmitter, short the cable for some time, before you could attach your (incredibly) sensitive receiver to the cable. Some time depended on cable type and length of cable, but up to five minutes were not unheard of. (The exact duration were often determined by the clerk putting his moistened finger across the terminal.) Needless to say this made it a paramount matter of efficiency to minimize turn-arounds, and therefore the general scheme of operation was that one side would transmit until they had cleared their backlog or until a certain maximum amount of time since last turnaround had elapsed. Some high-traffic cables ran on clockwork (minutes 0-15,30-45 A to B, minutes 15-30,45-00 B to A) -- this made it possible to predict how much papertape would be required. During each turning, the transmitter would be driven by papertape, each roll as large as physically practical, but there would still be a gap between individual messages on the tape and a longer gap between tapes. It was not uncommen for a high speed relay station to go through five miles of papertape a day at rates of several inches per second. This is even more astonishing when you realize that many of these relay stations were remotely situatated, like for instance the Eastern South African Telegraph Companys station on the island Bawe outside Zanzibar. For particular long cables repeater stations were necessary and since they only had two cables, there were never any doubt where the messages would go. Most, but not all of these skipped the paper-tape step, and had the receiving undulator drive the transmit relay directly. This is likely the kind of syncronized table described in the text. The majority of stations had more than two cables and therefore needed to make routing decisions, but messages would be batched as early as possible to minimize the number of paper tape splices required. Anyway... What all this boils down to is that the syntonization requirements were nowhere as dramatic as that text claims: +/- 5% were a very common specification. Driving the 30Hz reed with a pendulum clock would trivially do this. -- 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] Mechanical 1PPS Oscillator Disciplining
Andy, Yes, Neal Stephenson's Mother Earth Mother Board article is a classic that every time nut should read at some point. The one page version is at http://archive.wired.com/wired/archive/4.12/ffglass_pr.html Prior to quartz, pendulum clocks and tuning fork oscillators were the standard. Even until the 1950's or early 1960's tuning fork oscillators were used when one needed accurate frequency in the audio range. That's because dividing down high frequency quartz oscillators to, say, 60 Hz or 400 Hz required lots of circuitry. Not sure if Neal's reference to vibrating reed is what we would call a tuning fork, or if it's something else. Here in the US General Radio made precision tuning fork oscillators. Model numbers 213, 723, 813, 815. One example is at http://leapsecond.com/museum/gr815b/ Also check out old issues of General Radio Experimenter magazine for details on these wonderful instruments. Pendulum clocks were also used in power plants around the world to keep the grid synchronized. There is occasional discussion about this on clock collecting or horology forums. They are precious and can be extremely accurate, as good as a second a year. Since pendulum clocks were better long-term timekeepers and generated only 0.5 or 1 Hz signals, a PDTF (Pendulum Disciplined Tuning Fork) made sense. Has a nice ring to it, doesn't it. /tvb - Original Message - From: Andy Bardagjy a...@bardagjy.com To: Discussion of precise time and frequency measurement time-nuts@febo.com Sent: Friday, January 09, 2015 9:22 AM Subject: [time-nuts] Mechanical 1PPS Oscillator Disciplining From a fascinating (albeit long) article about transatlantic communication cables http://archive.wired.com/wired/archive/4.12/ffglass.html On the bottom of page 45 to the top of page 46 Each piece of equipment on this tabletop is built around a motor that turns over at the same precise frequency. None of it would work - no device could communicate with any other device - unless all of those motors were spinning in lockstep with one another. The transmitter, regenerator/retransmitter, and printer all had to be in sync even though they were thousands of miles apart. This feat is achieved by means of a collection of extremely precise analog machinery. The heart of the system is another polished box that contains a vibrating reed, electromagnetically driven, thrumming along at 30 cycles per second, generating the clock pulses that keep all the other machines turning over at the right pace. The reed is as precise as such a thing can be, but over time it is bound to drift and get out of sync with the other vibrating reeds in the other stations. In order to control this tendency, a pair of identical pendulum clocks hang next to each other on the wall above. These clocks feed steady, one-second timing pulses into the box housing the reed. The reed, in turn, is driving a motor that is geared so that it should turn over at one revolution per second, generating a pulse with each revolution. If the frequency of the reed's vibration begins to drift, the motor's speed will drift along with it, and the pulse will come a bit too early or a bit too late. But these pulses are being compared with the steady one-second pulses generated by the double pendulum clock, and any difference between them is detected by a feedback system that can slightly speed up or slow down the vibration of the reed in order to correct the error. The result is a clock so steady that once one of them is set up in, say, London, and another is set up in, say, Cape Town, the machinery in those two cities will remain synched with each other indefinitely. Does anyone know any other history about that particular piece of equipment? Cheers! Andy ◉ Bardagjy.com ◉ +1-404-964-1641 ___ 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] June 30 2015 leap second
Tom Van Baak wrote: I couldn't help noticing that Debian just issued an update to tzone, so that means Linux systems now know about the leap second. -Chuck Harris Hi Chuck, Linux systems now know about the leap second -- this is a very dangerous assumption. And one reason why leap seconds have gotten out of hand the past decade. Just because you observe one tz update from Debian does not imply that all Linux systems on planet earth (or in space) magically know about leap seconds. There must be millions (billions?) of embedded or isolated systems -- from web servers to desktops to military systems to gadgets to Raspberry Pi's to mobile phones, that have not, and will not ever receive this update. And that's where the new tzdist protocol comes into the game, which can be used to supply leap second information to time *servers* which need to send leap second warnings to their clients. Systems which are simply time clients can receive the leap second warning via the usual protocols like NTP or PTP/IEEE1588. Of cours it must be sure that the information is also *evaluated* by the client software. Martin ___ 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] June 30 2015 leap second
Reading about leap seconds for the past two days, I found that common solution for it - just encode leap second event proactively and wait for it. Of course that possible only if device has that option. For example, BC637PCI has a menu item 7. Program Leap Event Seconds. Which I did. Now, if I do the request for time settings, its shows me following: Time Settings: Mode : GPS Time Format: Binary Year : 2015 Local Offset : 0.0 Propagation Delay : 0 Current Leap Seconds : 16 Scheduled Leap Event Time : 1435708799 Scheduled Leap Event Flag : Insertion GPS Time Format: UTC Format IEEE Daylight Savings Flag : Enable Scheduled Leap Event Time - is so-called UNIX time. However, I am not sure where its take number 16 (Current Leap Seconds). Its definitely was not programmed there by me. Concerning of my clock project, I am thinking about best approach how to set up leap second procedure. I mean which time exactly I'll need to do correction for my clock (set time on RTC module). There is two options, I think. One: to reset RTC at July 1, 00:00:00 and set it back to June 30, 23:59:00. Or, at July 1, 00:00:01, set RTC back to July 1 00:00:00 and then at July 1 00:00:01 reset RTC with occurrance of raising edge of 1PPS. I would prefer to play with July 1, because in this case I don't need to do much calculations to transfer RTC time to number of seconds, decrement it by 1 second, transfer it back to BCD format and write it back to RTC. Instead, I'll need just read/write RTC register which keeps number of seconds inside. Regards, Vlad Just because you observe one tz update from Debian does not imply that all Linux systems on planet earth (or in space) magically know about leap seconds. There must be millions (billions?) of embedded or isolated systems -- from web servers to desktops to military systems to gadgets to Raspberry Pi's to mobile phones, that have not, and will not ever receive this update. -- WBW, V.P. ___ 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] Mechanical 1PPS Oscillator Disciplining
From a fascinating (albeit long) article about transatlantic communication cables http://archive.wired.com/wired/archive/4.12/ffglass.html On the bottom of page 45 to the top of page 46 Each piece of equipment on this tabletop is built around a motor that turns over at the same precise frequency. None of it would work - no device could communicate with any other device - unless all of those motors were spinning in lockstep with one another. The transmitter, regenerator/retransmitter, and printer all had to be in sync even though they were thousands of miles apart. This feat is achieved by means of a collection of extremely precise analog machinery. The heart of the system is another polished box that contains a vibrating reed, electromagnetically driven, thrumming along at 30 cycles per second, generating the clock pulses that keep all the other machines turning over at the right pace. The reed is as precise as such a thing can be, but over time it is bound to drift and get out of sync with the other vibrating reeds in the other stations. In order to control this tendency, a pair of identical pendulum clocks hang next to each other on the wall above. These clocks feed steady, one-second timing pulses into the box housing the reed. The reed, in turn, is driving a motor that is geared so that it should turn over at one revolution per second, generating a pulse with each revolution. If the frequency of the reed's vibration begins to drift, the motor's speed will drift along with it, and the pulse will come a bit too early or a bit too late. But these pulses are being compared with the steady one-second pulses generated by the double pendulum clock, and any difference between them is detected by a feedback system that can slightly speed up or slow down the vibration of the reed in order to correct the error. The result is a clock so steady that once one of them is set up in, say, London, and another is set up in, say, Cape Town, the machinery in those two cities will remain synched with each other indefinitely. Does anyone know any other history about that particular piece of equipment? Cheers! Andy ◉ Bardagjy.com ◉ +1-404-964-1641 ___ 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] June 30 2015 leap second
On Fri, Jan 9, 2015 at 3:21 PM, Martin Burnicki martin.burni...@burnicki.net wrote: Systems which are simply time clients can receive the leap second warning via the usual protocols like NTP or PTP/IEEE1588. Indeed, they can. Even when there hasn't been a leap-second. Practically all internet (and otherwise?) time distribution is unauthenticated, the leap second itself is unauthenticated. It's fragile enough that there have been accidental false leap-second events. ... one of many reasons I'd prefer leap seconds went away though I've personally had great fun observing them in the past. (and, I suspect, they may have been one of the first reasons I became interested in precise time keeping). ___ 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] June 30 2015 leap second
This is an issue indeed. Here is what I get from MySQL Data Base support site: Before MySQL 5.0.74, if the operating system is configured to return leap seconds from OS time calls or if the MySQL server uses a time zone definition that has leap seconds, functions such as NOW() could return a value having a time part that ends with :59:60 or :59:61. If such values are inserted into a table, they would be dumped as is by mysqldump but considered invalid when reloaded, leading to backup/restore problems. As of MySQL 5.0.74, leap second values are returned with a time part that ends with :59:59. This means that a function such as NOW() can return the same value for two or three consecutive seconds during the leap second. It remains true that literal temporal values having a time part that ends with :59:60 or :59:61 are considered invalid. Last time it was quite a pain: Machines running the mighty Amadeus Altea system were brought down soon after an extra second was added to Coordinated Universal Time (UTC) at midnight on Saturday, 30 June. The bonus second was inserted at the direction of time boffins to keep UTC synchronised with Earth's slowing rotation. The Altea system was taken offline for an hour, and staff at Qantas and Virgin Australia had to check in passengers manually, disrupting flight plans. Google's solution looks pretty amazing. The slowing down the clock by milliseconds as the event approach. May be that an option to play with Oscillator Aging register. In accordance with data sheet, the Aging Offset register takes a user-provided value to add to or subtract from the factory-trimmed value that adjusts the accuracy of the time base. The Aging Offset code is encoded in two’s complement, with bit 7 representing the SIGN bit and a valid range of ±127. One LSB typically represents a 0.12ppm change in frequency. The change in ppm per LSB is the same over the operating temperature range. Positive offsets slow the time base and negative offsets quicken the time base. So, using that I could achieve 127x0.12 = 15ppm change. 1s/24h = 1/86400 which is approximately 12ppm. That means that Aging Offset could slow down my clock for 1 second if I'll apply the maximum value one day ahead (roughly). I need to do some experiments first. ;-) Its looks too unreliable for me. On , Martin Burnicki wrote: Gregory Maxwell wrote: On Fri, Jan 9, 2015 at 3:21 PM, Martin Burnicki martin.burni...@burnicki.net wrote: Systems which are simply time clients can receive the leap second warning via the usual protocols like NTP or PTP/IEEE1588. Indeed, they can. Even when there hasn't been a leap-second. Practically all internet (and otherwise?) time distribution is unauthenticated, the leap second itself is unauthenticated. ... and even the time you get via NTP or PTP is usually not authenticated. So you can trust the time and leap second warning, or you shouldn't trust either. It's fragile enough that there have been accidental false leap-second events. Yes, for example if there have been GPS receivers which decoded the UTC parameters incorrectly, and started to announce a leap second when there wasn't one (end of September). That's why, for example, ntpd's leap second handling code has been changed in v4.2.6 to accept a leap second warning only if the warning is received from a majority of the configured servers. If you want to be sure you can also provide ntpd with a leap second file which is then (in current versions) considered as authentic source for leap second information. Martin ___ 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. -- WBW, V.P. ___ 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] June 30 2015 leap second
d0ct0r wrote: Reading about leap seconds for the past two days, I found that common solution for it - just encode leap second event proactively and wait for it. Of course that possible only if device has that option. For example, BC637PCI has a menu item 7. Program Leap Event Seconds. Which I did. Now, if I do the request for time settings, its shows me following: Time Settings: Mode : GPS Time Format: Binary Year : 2015 Local Offset : 0.0 Propagation Delay : 0 Current Leap Seconds : 16 Scheduled Leap Event Time : 1435708799 Scheduled Leap Event Flag : Insertion GPS Time Format: UTC Format IEEE Daylight Savings Flag : Enable Scheduled Leap Event Time - is so-called UNIX time. However, I am not sure where its take number 16 (Current Leap Seconds). Its definitely was not programmed there by me. 16 s is the current difference between GPS system time and UTC, which will increase to 17 after the next leap second. It is part of the UTC data set broadcasted by the satellites. I'd expect that in a few days the GPS satellites start broadcasting the leap second announcement, and then yourGPS receiver should also find out by itself *when* the leap second will occur, and what the UTC offset will be thereafter. When I looked this morning the sats did't broadcast this information, yet. Concerning of my clock project, I am thinking about best approach how to set up leap second procedure. I mean which time exactly I'll need to do correction for my clock (set time on RTC module). There is two options, I think. One: to reset RTC at July 1, 00:00:00 and set it back to June 30, 23:59:00. Or, at July 1, 00:00:01, set RTC back to July 1 00:00:00 and then at July 1 00:00:01 reset RTC with occurrance of raising edge of 1PPS. I would prefer to play with July 1, because in this case I don't need to do much calculations to transfer RTC time to number of seconds, decrement it by 1 second, transfer it back to BCD format and write it back to RTC. Instead, I'll need just read/write RTC register which keeps number of seconds inside. As said, once the sats start broadcasting this information your software should be able to read the time and leap second status from the PCI card, if the API supports this. How you can handle this to set your clock depends on the capabilites of your clock, and its API. Martin ___ 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] June 30 2015 leap second
Gregory Maxwell wrote: On Fri, Jan 9, 2015 at 3:21 PM, Martin Burnicki martin.burni...@burnicki.net wrote: Systems which are simply time clients can receive the leap second warning via the usual protocols like NTP or PTP/IEEE1588. Indeed, they can. Even when there hasn't been a leap-second. Practically all internet (and otherwise?) time distribution is unauthenticated, the leap second itself is unauthenticated. ... and even the time you get via NTP or PTP is usually not authenticated. So you can trust the time and leap second warning, or you shouldn't trust either. It's fragile enough that there have been accidental false leap-second events. Yes, for example if there have been GPS receivers which decoded the UTC parameters incorrectly, and started to announce a leap second when there wasn't one (end of September). That's why, for example, ntpd's leap second handling code has been changed in v4.2.6 to accept a leap second warning only if the warning is received from a majority of the configured servers. If you want to be sure you can also provide ntpd with a leap second file which is then (in current versions) considered as authentic source for leap second information. Martin ___ 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] June 30 2015 leap second
Correct me if I'm wrong, but as I understand it the tzfile in the tzone package is not used to update the system time - that relies on NTP or similar. Rather, the leap second info in the tzone files is made available for applications to use, primarily for calculating time differences in the past. Henry On Fri, Jan 9, 2015 at 6:17 AM, Tom Van Baak t...@leapsecond.com wrote: I couldn't help noticing that Debian just issued an update to tzone, so that means Linux systems now know about the leap second. -Chuck Harris Hi Chuck, Linux systems now know about the leap second -- this is a very dangerous assumption. And one reason why leap seconds have gotten out of hand the past decade. Just because you observe one tz update from Debian does not imply that all Linux systems on planet earth (or in space) magically know about leap seconds. There must be millions (billions?) of embedded or isolated systems -- from web servers to desktops to military systems to gadgets to Raspberry Pi's to mobile phones, that have not, and will not ever receive this update. /tvb ___ 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] question Alan deviation measured with Timelab and counters
Dear all, I'm trying to measure Alan Deviations using Timelab and some frequency counters. The device under test is a GPSDO using a TCXO as référence I've an HP58503B GPSDO which feeds my counters. I've tried an HP5342A, 0-18 GHz, 1 Hz resolution and a Philipps PM6654C, 0.01Hz resolution. In Timelab, the plot with the HP5342A is around 10e-7 which correspond to 1Hz and with the PM6654C, the plot is around 10e-10. I would suspect that this is still the counter which limits the actual response of my device under test. My question are : - how to measure Alan Deviations with levels below 10e-12/10e-13 ? What can be the application of measurement Alan deviation 10e-10 ? I guess most of the low frequency - The HP53503 GPS is given to be 10e-11 / 10e-12. I guess this will limit anyway the measurement floor. I've a Rb source, but it's stability is within the same range. What kind of reference would be more suitable for such measurements ? - With the PM6654C on 15h measurement, I can see some frequency jumps of 800 Hz which are not relevants with the GPSDO undertest. I suspect error in data transmission. This makes the overall measurement totally wrong (10e-5). The counter is in talk only mode. I'd like to get rid of these points maybe 40-50 points out of 1. Is there a way to do that from Timelab or the only option is to export the file and process manually the data ? Thanks cheers Stephane ___ 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] June 30 2015 leap second
I couldn't help noticing that Debian just issued an update to tzone, so that means Linux systems now know about the leap second. -Chuck Harris Hi Chuck, Linux systems now know about the leap second -- this is a very dangerous assumption. And one reason why leap seconds have gotten out of hand the past decade. Just because you observe one tz update from Debian does not imply that all Linux systems on planet earth (or in space) magically know about leap seconds. There must be millions (billions?) of embedded or isolated systems -- from web servers to desktops to military systems to gadgets to Raspberry Pi's to mobile phones, that have not, and will not ever receive this update. /tvb ___ 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] question Alan deviation measured with Timelab and counters
Hi Welcome to the world of trying to measure this stuff … On Jan 9, 2015, at 6:53 AM, steph.rey steph@wanadoo.fr wrote: Dear all, I'm trying to measure Alan Deviations using Timelab and some frequency counters. The device under test is a GPSDO using a TCXO as référence I've an HP58503B GPSDO which feeds my counters. I've tried an HP5342A, 0-18 GHz, 1 Hz resolution and a Philipps PM6654C, 0.01Hz resolution. In Timelab, the plot with the HP5342A is around 10e-7 which correspond to 1Hz and with the PM6654C, the plot is around 10e-10. I would suspect that this is still the counter which limits the actual response of my device under test. Yes, the counters and TCXO are limiting your measurements. My question are : - how to measure Alan Deviations with levels below 10e-12/10e-13 ? How much money do you have to spend? ( There are expensive commercial ways to do this). No matter what, you will need a “better than” reference. That’s not going to be cheap. Most of us simply get a second GPSDO and compare them. The assumption is that they both are the same and you can allocate the error equally between them. With three you can more accurately allocate the error. A DMTD is the “cheap” way to get the actual measurement done. What can be the application of measurement Alan deviation 10e-10 ? I guess most of the low frequency There are a number of systems applications that very much need good ADEV. Getting into why this or that nav or com system needs it would take a bit of time. - The HP53503 GPS is given to be 10e-11 / 10e-12. I guess this will limit anyway the measurement floor. I've a Rb source, but it's stability is within the same range. What kind of reference would be more suitable for such measurements ? If you want to do it directly, a hydrogen maser is a good way to go. That’s silly expensive. Just compare GPSDO’s, that’s a lot cheaper. - With the PM6654C on 15h measurement, I can see some frequency jumps of 800 Hz which are not relevants with the GPSDO undertest. I suspect error in data transmission. This makes the overall measurement totally wrong (10e-5). The counter is in talk only mode. I'd like to get rid of these points maybe 40-50 points out of 1. Is there a way to do that from Timelab or the only option is to export the file and process manually the data ? You can expand the data and zap the offending segments. It’s done on the phase plot. Have Fun. Bob Thanks cheers Stephane ___ 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.
