Re: [time-nuts] Sources for Mission Time Clock
I know precisely what you are saying and I get the feel. Nixie clocks seem so much cooler than seven-segment LED clocks. (And vacuum fluorescent just seems cheesy. Go figure.) So early '60s is retro but late '60s is not. From my view 50 years down the road that seems just ... humorous. Brian, and other time nuts, And if you don't get enough retro here, note there is an very fine Nixie mailing list at: https://groups.google.com/d/forum/neonixie-L If I had started it, it would have been called nixie-nuts ;-) /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] Current state of optical clocks and the definition of the second
At those low levels, how does one differentiate between phase or AM noise? Thanks Regards - Mike Mike B. Feher, EOZ Inc. 89 Arnold Blvd. Howell, NJ, 07731 732-886-5960 office 908-902-3831 cell -Original Message- From: time-nuts [mailto:time-nuts-boun...@febo.com] On Behalf Of Bruce Griffiths Sent: Wednesday, January 14, 2015 1:22 AM To: Discussion of precise time and frequency measurement Subject: Re: [time-nuts] Current state of optical clocks and the definition of the second Although the phase noise when using optical combs to generate Rf signals is low there is no mention of the am noise. Bruce ___ 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] Current state of optical clocks and the definition of the second
Interestingly they use regenerative dividers. Pretty good read. Thanks Paul WB8TSL On Tue, Jan 13, 2015 at 4:49 PM, Tom Knox act...@hotmail.com wrote: I think the key to this concept is an optical comb filter. Archita Hati of the Phase Noise measurement Group at NIST has been researching ultra low phase noise 5MHz references using an optical standard and comb filter as well as extensive RF components to down converting to the desired frequency. In experiments I believe she has achieved phase noise better then -154db @ 1Hz offset. It does appear to be the future but currently is far to large and complex for most if any practical use. I believe this link is the paper by Archita Hati I referred addressing State-of-the-Art RF Signal Generation From Optical Frequency Division. http://tf.boulder.nist.gov/general/pdf/2646.pdf Enjoy; Thomas Knox Thomas Knox From: namic...@gmail.com Date: Wed, 14 Jan 2015 07:00:09 +1100 To: time-nuts@febo.com CC: namic...@gmail.com Subject: Re: [time-nuts] Current state of optical clocks and the definition of the second THe stability /accuracy of lasers is entirely dependent on the cavity length. Materials used are usually invar or silica, so you are no better off than with a quartz crystals. They are just a resonant cavity. cheers, Neville Michie ___ 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] New algorithm, better ADEV
Hi
Ok, now that’s looking a lot more like a counter and the normal counter
residuals. The slope isn’t quite 1/tau, but it’s pretty close to that. Very
nice.
One question:
One side of the counter is running on the FE5650. What is the other side of the
counter running on? Are the reference and input the same in this case?
Bob
On Jan 14, 2015, at 10:55 AM, Li Ang lll...@gmail.com wrote:
Hi
Just now, I changed the way to calculate frequency and get a better
ADEV chart.
http://www.qsl.net/b/bi7lnq/freqcntv4/test/20150114/0114.gif
http://www.qsl.net/b/bi7lnq/freqcntv4/test/20150114/newway.tim
http://www.qsl.net/b/bi7lnq/freqcntv4/test/20150114/oldway.tim
Thanks to John Miles's reply in the thread about ADEV.
If you feed in frequency samples, it will convert them to phase-difference
samples internally, so the
program itself doesn't really care. The use of frequency data has a few
drawbacks such as less accurate
ADEV plots due to the counter's dead time between readings, but it's the
easiest way to get started and is
perfectly usable for many purposes.
Old way:
//reset counter every second to avoid the overflow issue
while (1) {
reset_fpga_counter();
trigger_and_read_cnt(refA, sigA);
delay_1s();
trigger_and_read_cnt(refB, sigB);
Freq = Calc_freq(refB - refA, sigB - sigA);
}
New way:
//The counter keeps running. The software takes care of the overflow issue.
No dead time.
trigger_and_read_cnt(ref_prev, sig_prev);
while (1) {
delay_1s();
trigger_and_read_cnt(ref_curr, sig_curr);
ref_delta = (ref_curr ref_prev) ? (ref_curr - ref_prev) : (0x
- ref_prev + ref_curr);
sig_delta = (sig_curr sig_prev) ? (sig_curr - sig_prev) : (0x
- sig_prev + sig_curr);
Freq = CalcFreq(ref_delta, sig_delta);
ref_prev = ref_curr;
sig_prev = sig_curr;
}
BTW: I've put the counter into a box.
http://www.qsl.net/b/bi7lnq/freqcntv4/pic/20150114_212857.jpg
more pictures: http://www.qsl.net/b/bi7lnq/freqcntv4/pic/
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Re: [time-nuts] Current state of optical clocks and the definition of the second
Hi More or less by definition: AM noise has the sidebands in phase, PM noise has the sidebands out of phase. PM adds to no envelope power, AM adds to the envelope power. If you have purely random noise, half of the power is AM, half is PM by this approach. If you have what is effectively a SDR (high speed ADC(s), decimators, cross correlation …) doing your phase noise measurement, figuring out sidebands and phase is part of the process. With an old style single mixer approach, you switch your operating point on the mixer. Bob On Jan 14, 2015, at 2:19 PM, Mike Feher mfe...@eozinc.com wrote: At those low levels, how does one differentiate between phase or AM noise? Thanks Regards - Mike Mike B. Feher, EOZ Inc. 89 Arnold Blvd. Howell, NJ, 07731 732-886-5960 office 908-902-3831 cell -Original Message- From: time-nuts [mailto:time-nuts-boun...@febo.com] On Behalf Of Bruce Griffiths Sent: Wednesday, January 14, 2015 1:22 AM To: Discussion of precise time and frequency measurement Subject: Re: [time-nuts] Current state of optical clocks and the definition of the second Although the phase noise when using optical combs to generate Rf signals is low there is no mention of the am noise. Bruce ___ 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] L1 and L2 frequencies
Hi Martyn: On each frequency there are a couple or more different codes. The Civilian Acess (C/A) code on the L1 frequency is all public information and so is the most commonly used. But there are classified codes that have a much higher bit rate and allow for more accurate position, time and velocity measurements. Tom mentioned that there are civilian GPS receivers that make use of the L2 frequency, but they do that my using what's called carrier phase (that's to say they do not make use of the classified code). This is mainly used in surveying applications where, by recording a lot of data and post processing, you can get a very precise location. When two frequencies are used there's a possibility of removing an error related to the total electron count in the path of the signal. The new F5 frequency allows for doing that, but as far as I know none of the commercial GPS receivers make use of it yet. http://www.prc68.com/I/DAGR.shtml#GPSs Mail_Attachment -- Have Fun, Brooke Clarke http://www.PRC68.com http://www.end2partygovernment.com/2012Issues.html http://www.prc68.com/I/DietNutrition.html Martyn Smith wrote: Hello, I have some questions on GPS and GNSS. Do all the civilian GPS receivers only operate on the L1 frequency? Are there any GPS frequency standards out there that use L1 and L2 and that can be purchased by non-military customers? I am playing with the new Lea-M8T receiver. How do I know what satellites are GPS, GLONASS, Galileo etc. From my understanding GLONASS have different SV numbers but not 100% sure. Any help appreciated. Regards Martyn ___ 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] New algorithm, better ADEV
Just now, I changed the way to calculate frequency and get a better ADEV chart. http://www.qsl.net/b/bi7lnq/freqcntv4/test/20150114/0114.gif Looking good! Nice example of a white PM noise floor, just like a 'real' HP counter. Let it run for a few days and see how the environmental sensitivity looks. BTW: I've put the counter into a box. http://www.qsl.net/b/bi7lnq/freqcntv4/pic/20150114_212857.jpg more pictures: http://www.qsl.net/b/bi7lnq/freqcntv4/pic/ Those small SPI LCDs are really neat, especially for the price. I just used one the other day to replace a 1 CRT in a receiver panadaptor. -- john, KE5FX Miles Design LLC ___ 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] New algorithm, better ADEV
Hi
Just now, I changed the way to calculate frequency and get a better
ADEV chart.
http://www.qsl.net/b/bi7lnq/freqcntv4/test/20150114/0114.gif
http://www.qsl.net/b/bi7lnq/freqcntv4/test/20150114/newway.tim
http://www.qsl.net/b/bi7lnq/freqcntv4/test/20150114/oldway.tim
Thanks to John Miles's reply in the thread about ADEV.
If you feed in frequency samples, it will convert them to phase-difference
samples internally, so the
program itself doesn't really care. The use of frequency data has a few
drawbacks such as less accurate
ADEV plots due to the counter's dead time between readings, but it's the
easiest way to get started and is
perfectly usable for many purposes.
Old way:
//reset counter every second to avoid the overflow issue
while (1) {
reset_fpga_counter();
trigger_and_read_cnt(refA, sigA);
delay_1s();
trigger_and_read_cnt(refB, sigB);
Freq = Calc_freq(refB - refA, sigB - sigA);
}
New way:
//The counter keeps running. The software takes care of the overflow issue.
No dead time.
trigger_and_read_cnt(ref_prev, sig_prev);
while (1) {
delay_1s();
trigger_and_read_cnt(ref_curr, sig_curr);
ref_delta = (ref_curr ref_prev) ? (ref_curr - ref_prev) : (0x
- ref_prev + ref_curr);
sig_delta = (sig_curr sig_prev) ? (sig_curr - sig_prev) : (0x
- sig_prev + sig_curr);
Freq = CalcFreq(ref_delta, sig_delta);
ref_prev = ref_curr;
sig_prev = sig_curr;
}
BTW: I've put the counter into a box.
http://www.qsl.net/b/bi7lnq/freqcntv4/pic/20150114_212857.jpg
more pictures: http://www.qsl.net/b/bi7lnq/freqcntv4/pic/
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Re: [time-nuts] L1 and L2 frequencies
Hello, I have some questions on GPS and GNSS. Do all the civilian GPS receivers only operate on the L1 frequency? Are there any GPS frequency standards out there that use L1 and L2 and that can be purchased by non-military customers? I am playing with the new Lea-M8T receiver. How do I know what satellites are GPS, GLONASS, Galileo etc. From my understanding GLONASS have different SV numbers but not 100% sure. Any help appreciated. Regards Martyn ___ 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] L1 and L2 frequencies
I have some questions on GPS and GNSS. Note GNSS is the generic word for any satellite based navigation system. GPS is one of GNSS so you don't actually need to say GPS *and* GNSS. Do all the civilian GPS receivers only operate on the L1 frequency? No. All the cheap ones do, though. Are there any GPS frequency standards out there that use L1 and L2 and that can be purchased by non-military customers? Yes. Almost all high-end survey receivers are L1 and L2. Check the web. There are hundreds to choose from. I am playing with the new Lea-M8T receiver. How do I know what satellites are GPS, GLONASS, Galileo etc. See appendix B Satellite Numbering of your u-blox M8 Receiver Description manual. From my understanding GLONASS have different SV numbers but not 100% sure. Each GNSS system has its own internal numbering scheme, but a multi-GNSS receiver has to disambiguate among them with their own scheme. Again, see the wonderful table on page 272. Any help appreciated. Regards Martyn /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] New algorithm, better ADEV
Hi Li Ang, You're making good progress. Thanks for the update and the photos. I am impressed with both the project and the way you are documenting and sharing the progress on the qsl.net web site. The new algorithm is good. Yes, the whole idea of a timestamping counter is that you start it once and then let it run indefinitely, checking on the deltas only as much as you need to prevent counter aliasing. One correction -- when you compute deltas using two's compliment integer variables there is no need for a special-case overflow check. This is a common misunderstanding by non-assembly programmers. So, instead of your: ref_delta = (ref_curr ref_prev) ? (ref_curr - ref_prev) : (0x - ref_prev + ref_curr); sig_delta = (sig_curr sig_prev) ? (sig_curr - sig_prev) : (0x - sig_prev + sig_curr); Just use: ref_delta = ref_curr - ref_prev; sig_delta = sig_curr - sig_prev; Not only is it much simpler but it also works in every case (your code would fail whenever curr equals prev). Here's a test program in case you don't believe me: http://leapsecond.com/tools/wrap1.c /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
Bonjour Magnus, Many thanks for your very long and detailed answer. I've read quickly bu will go deeper tonight. Here are the results of today experiments... which are not giving anything valuable... I still don't understand the results I get :-/ With the PM6654C, I've put the HP GPSDO on the standard input, the 1 PPS on channel A and the 10 MHz from the DUT (GPSDO as well) on channel B. This gives something in the range of 2E-9 which looks like the counter resolution, right ? The gating takes 4s and the Time A-B displays a value like 64 E-6 Now if I downmix the channel B to 5 kHz (LO is a DDS Standford Reseach generator), I have a sinus with lower amplitude and no squarer in my hand at the moment to shape the signal. Anyway, I do the same operation and I get on the display two more digits like xx.xx E-6 but the ADEC is in the range of E-7 I do not understand at all this fact. Even if the slew rate is not great, I was expecting an improvement. Note that the values displayed are always changing quite a lot between two samples. For instance with the 5 KHz channel B signal, I can read first sample at 27.11E-6, in the next one is 31.22E-6... which sounds huge, right ? I've then found an HP5370A and tried the same operation. Unfortunately the 5 kHz output is too low for the HP5370A sensitivity. I need an amplifier or sqauerer here but had no time to build on today. Si I could not get anything valuable with the HP5370A at the moment... Stephane -Message d'origine- De : time-nuts [mailto:time-nuts-boun...@febo.com] De la part de Magnus Danielson Envoyé : mercredi 14 janvier 2015 08:04 À : time-nuts@febo.com Cc : mag...@rubidium.se Objet : Re: [time-nuts] question Alan deviation measured with Timelab and counters Bonjour Stéphane, On 01/14/2015 02:16 AM, Stéphane Rey wrote: Hi Magnus, For some reason I've missed this message and the one from Jim until now ! This answers many of the questions I had. For my defense, I've 3000 messages since the last 3 months on the list !!! ah, yes, I'd like to get even better than 1E-12. 1E-14 would be perfect but my best standards for now are a HP GPSDO and an Effratrom FRK Rb which both are around 1E-12 'only'. I may have to invest in something better if prices are acceptable. I guess I won't be able to measure beyond the standard itself. The method you describes gives tau=2E-9 ? This is more or less what I could get with the frequency measurement (even a bit lower). So what is the benefit of the time interval measurement here against the frequency measurement ? I've been sloppy with the scaling factor, so there is a fixed scaling factor for the noise that the single-shot resolution produces, and that would be a measurement limit that if everything else is ideal would dominate. This quantization noise is sqrt(1/12) or about 0.289 if I remember correctly, so that is the scale-factor. It will also have a 1/tau slope. So that is how you can expect this noise to behave, it will look like white phase noise, but isn't, it is highly systematic noise, and if you play nicely with it, you can measure below it. However, doing so is non-trivial. I have one counter that does that. The good old HP5328A with the Option 040-series of boards will introduce noise to the counting 100 MHz oscillator such that averaging gets you down towards 10 ps rather than 10 ns resolution in TI mode. However, it does not help you to get nice frequency or stability measures. I've not taken the time to detail-analyse the ADEV scaling factor thought, I should do that, but it follows the general formula of ADEV(tau) = k*t_res/tau where t_res is the single-shot resolution and k is a constant. There is more to this, as counters can show up non-linearities of several sorts, and that the trigger conditions of the input has been optimized, which can be slew-rate limited for many counters and conditions. So, anyway, there is a bit of hand-waving in there, but I thought it was better to get you to get the basic trend there first, and then we can discuss the detailed numbers, as theory is one thing and achieved number can be quite a different one. As for frequency and time-interval measurements, if properly done, they can be used interchangeably without much impact. Realize that frequency and time-interval measurements will both be based on time-interval measurements as the core observation inside the counter, so the single-shot resolution limit applies to them both. However, subtle details lies in how the counter works and there is ways that the frequency precision can be lost. A good counter is the SR620, but the way it does the frequency measure, you need to calibrate the internal delay to make it on the mark measure. Using it in time-interval mode and you can eliminate that offset, because the start and stop measure of your signal under test is done with the same channel, with essentially the same delay both trigger-times.
Re: [time-nuts] Sources for Mission Time Clock
On Sun, Jan 11, 2015 at 10:10 PM, Wayne Holder wayne.hol...@gmail.com wrote: But, 7 segment just doesn't quite capture that retro feel, IMO. I know precisely what you are saying and I get the feel. Nixie clocks seem so much cooler than seven-segment LED clocks. (And vacuum fluorescent just seems cheesy. Go figure.) So early '60s is retro but late '60s is not. From my view 50 years down the road that seems just ... humorous. Seems like a BBB driving a good-sized 1080P display (both are cheap) would be a good platform to do something like this. You can make it count or display anything you want. Since the linux distro in the BBB has NTP installed already, it should be able to keep reasonably accurate time from a human PoV. Hmm, I am going to want a display like that for my video wall. -- Brian Lloyd 706 Flightline Drive Spring Branch, TX 78070 br...@lloyd.aero +1.210.802-8FLY (1.210.802-8359) ___ 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 John, I hadn't noticed before you were here as well ;-) Thanks for answering. So I do understand I can use Timelab in frequency difference even if my counter sends data in TI in nanoseconds. Great. Ah and thanks for the manual link. I didn't remember this was in the manual of the Timepod Will investigate further today -Message d'origine- De : time-nuts [mailto:time-nuts-boun...@febo.com] De la part de John Miles Envoyé : mercredi 14 janvier 2015 07:26 À : 'Discussion of precise time and frequency measurement' Objet : Re: [time-nuts] question Alan deviation measured with Timelab and counters - Can I use Frequency difference mode from Timelab to monitor time intervals ? If no is there a way to use the time interval measurement from the counter with Timelab to plot ADEV ? If you feed in frequency samples, it will convert them to phase-difference samples internally, so the program itself doesn't really care. The use of frequency data has a few drawbacks such as less accurate ADEV plots due to the counter's dead time between readings, but it's the easiest way to get started and is perfectly usable for many purposes. In general you should avoid letting the counter do any averaging. Except in very specific circumstances, any apparent improvement in ADEV measurement floor will be illusory. There are exceptions, but this isn't something you want to mess with until you're very comfortable with the rest of the measurement process. Your counter's true ADEV measurement floor at t=1s should be assumed to be close to its single-shot resolution specification (e.g., 100 ps = about 1E-10). - In case the principle of plotting ADEV from Time Interval, what is the interpretation of the result ? The ADEV shows the relative stability between the two GPSDO... So, practically what does it bring ? And how to use this method if I want to characterize a device ? An ADEV graph shows frequency stability statistics at different intervals, ranging from the rate at which the readings are returned from the counter (tau zero, at the left end of the plot) to a maximum interval that's related to how long you let the measurement run. It's much too deep a subject to go into in an email; see http://www.ke5fx.com/stability.htm for more pointers. Again, TimeLab always plots ADEV from time interval/phase data, even if you give it frequency readings. ADEV is fundamentally a frequency stability metric, but it can be computed identically from either TI or frequency samples (assuming zero dead time). - stupid question on Timelab. If I let Timelab in Auto to select the period between two samples (correctly detected), the time scale of the graph is wrong. For instance, a 3h plot stops at 2000s (0.5h)... Here again, I miss something but what ? The TimeLab manual, for one thing. :) Hit the books (specifically http://www.miles.io/TimePod_5330A_user_manual.pdf , page 31). -- john, KE5FX Miles Design LLC ___ 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. --- L'absence de virus dans ce courrier électronique a été vérifiée par le logiciel antivirus Avast. http://www.avast.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] Current state of optical clocks and the definition of the second
On 01/13/2015 11:41 AM, Attila Kinali wrote: On Mon, 12 Jan 2015 20:09:45 + Gregory Maxwell gmaxw...@gmail.com wrote: On Mon, Jan 12, 2015 at 12:34 PM, Attila Kinali att...@kinali.ch wrote: Seems that the state of the art in stabilized lasers has improved a lot lately, e.g. there are commercial available 1550nm devices which have a =3Hz line-width: http://stablelasers.com/products.html (well on a short term basis, the medium term performance is not so impressive) Laser stabilization, especially for quantum metrology is still an actively researched field. Current state of the art is IIRC 0.3Hz linewidth (sorry, cannot find the reference at the moment). Mid- and long term stability depends highly on the reference used. Current research is fucused mainly on special, low vibration structures made out of low expansion glass or silicon. And these cavities are usually put into a temperature controlled chamber in vacuum. Well, guess what I found standing around in a lab with an optical comb? :) With optical line-widths in sub-Hz range and optical combs you have a nice way of comparing the frequency of that free-running and un-steerable but stable oscillator. However, as you mix it down the noise of the optical comb will dominate, but you can know which multiple of the optical comb and offset it is. Considering the rarity and extreme cost of H-masers, or just really exceptional quarts oscillators; might it be the case that optical LOs start looking interesting for applications which just need stability (or being steered by other sources; e.g. GPSDL)? Well, an 8607 costs more than a Rb-standard. Yes, the 8607 has lower close in phase noise and up to several 1000s it rivals the Rb, but handling it is much more difficult than handling an Rb. Also, if you want to buy one of those exceptionally low noise/high stable 8607's (those that go down into the 10^-14 range) you'd have to sell your car. But, if you buy a H-maser from SpectraTime, you get a 8607 for free ;-) That is also the only way to get the 8607 now, as Oscilloquartz is closing down that business. There used to be quite some literature on how to build low noise quartz oscillators. Most of those books are out of print today. With two notable exceptions: Discrete Oscillator Design: Linear, Nonlinear, Transient, and Noise Domains by Randall Rhea, 2010 and Understanding Quartz Crystals and Oscillators, by Ramon Cerda, 2014 I had a look at the book by Rhea, it looks quite well written and contains a lot of real world information, but is a bit weak on the more theoretical part (description of oscillation, noise sources,...) and thus on the on the why things are done that way. I didn't had the chance to buy Cerdas book yet. An interesting book in that context is Enrico Rubiolas book on phase-noise, which among other things goes into explain the Leeson model of oscillators and it's real life design aspects. The UFFC has some of the older books online. You need to be registered to access them, though. There is also a lot of knowledge on quartz crystalls hidden in old papers, but going trough them is some serious work. On the topic of opto-electronic oscillators, those are technologically nice, but they are rather bulky. That's why they are mostly used in research projects for atomic clocks. Also getting them to do low phase noise is not that easy, and unlike quartz oscillators, there is not much literature about that. It's a serious bulk of glas in there, but the laser-technology as well as temperature-stabilization of it isn't rocket science, (They can be down-converted to microwave frequencies using an optical comb; a mode-locked laser whos pulses are phase locked to an incoming beam.) That is actually the current trend. There was a paper by NIST last year on downconverting the beat frequency of an optical comb down to RF using a frequency divider chain. They managed to get noise measures that rival that of a good quartz oscillator at 5MHz. Ie at higher frequencies, it is actually better than what a quartz oscillator can deliver. (for some reason i have not archived that paper and google fails me) The NIST TF archive is where you should go. Nice folks doing that work. Certainly just the local oscillator is _closer_ to something a time-nut might experiment with than a complete optical atomic standard (if still not quite in reach). Well, building a CPT based Rb vapor cell frequency standard should be feasible. Yes, it's not a primary standard, but should do the job for most :-) From what i've read, using one of the MOT cells like those of Sachser Laser [1] one might even be able to build a primary standard. But my understanding of MOT is relatively weak and i cannot say how difficult it actually would be. But it would be definitly a fun project to try :-) Building a MOT setup is relatively easy know, I have not yet seen it go sub 100.000 USD, but it seems like modern setups could do that if you let it.
Re: [time-nuts] Current state of optical clocks and the definition of the second
Although the phase noise when using optical combs to generate Rf signals is low there is no mention of the am noise. Bruce On Tuesday, January 13, 2015 02:49:33 PM Tom Knox wrote: I think the key to this concept is an optical comb filter. Archita Hati of the Phase Noise measurement Group at NIST has been researching ultra low phase noise 5MHz references using an optical standard and comb filter as well as extensive RF components to down converting to the desired frequency. In experiments I believe she has achieved phase noise better then -154db @ 1Hz offset. It does appear to be the future but currently is far to large and complex for most if any practical use. I believe this link is the paper by Archita Hati I referred addressing State-of-the-Art RF Signal Generation From Optical Frequency Division. http://tf.boulder.nist.gov/general/pdf/2646.pdf Enjoy; Thomas Knox Thomas Knox From: namic...@gmail.com Date: Wed, 14 Jan 2015 07:00:09 +1100 To: time-nuts@febo.com CC: namic...@gmail.com Subject: Re: [time-nuts] Current state of optical clocks and the definition of the second THe stability /accuracy of lasers is entirely dependent on the cavity length. Materials used are usually invar or silica, so you are no better off than with a quartz crystals. They are just a resonant cavity. cheers, Neville Michie ___ 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] Current state of optical clocks and the definition of the second
Dr David Kirkby Managing Director Kirkby Microwave Ltd Registered office: Stokes Hall Lodge, Burnham Rd, Chelmsford, Essex, CM3 6DT, United Kingdom Registered in England and Wales as company number 08914892 http://www.kirkbymicrowave.co.uk/ Tel 07910 441670 / +44 7910 441670 (0900-2100 GMT) On 13 Jan 2015 20:39, Neville Michie namic...@gmail.com wrote: THe stability /accuracy of lasers is entirely dependent on the cavity length. Materials used are usually invar or silica, so you are no better off than with a quartz crystals. They are just a resonant cavity. cheers, Neville Michie I do realise that thermal stability is important. The pulsed titanium sapphire laser I used during my PhD took about 8 hours to become stable, and that had a lump of invar in it which was probably about 1.2 m long and 120 mm in diameter. But to say that the stability/accuracy depends entirely on the cavity length is a gross simplification. Someone posted a link to some information on getting narrow linewidths from cheap semiconductor lasers with something as simple as a piece of glass in front. That does nothing to stabilise the cavity length. There's a free webiminar on the 29th Jan at 1300 PST with the title Laser Test of RIN, Linewidth and Optical Noise Parameters. http://www.microwavejournal.com/events/1310-laser-test-of-rin-linewidth-and-optical-noise-parameters Dave. ___ 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] Lucent KS-24361/Z3810A : problem with Z3812A/REF 0 unit power up--RESOLVED!
Hello all, I contacted the eBay seller and he sent me an exchange REF 0 module. I swapped it in and it powered right up. Now there is a single green LED (ON) illuminated on the REF 0 module and a single yellow led (STBY) illuminated on the REF 1 module, so I'm pretty sure that all is well. Thanks to everyone on this list for all of the helpful suggestions. I also want to give the highest praise to the eBay seller, who stood behind his product and very quickly made it right for me! Regards, Stan ___ 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
Bonjour Stéphane, On 01/14/2015 02:16 AM, Stéphane Rey wrote: Hi Magnus, For some reason I've missed this message and the one from Jim until now ! This answers many of the questions I had. For my defense, I've 3000 messages since the last 3 months on the list !!! ah, yes, I'd like to get even better than 1E-12. 1E-14 would be perfect but my best standards for now are a HP GPSDO and an Effratrom FRK Rb which both are around 1E-12 'only'. I may have to invest in something better if prices are acceptable. I guess I won't be able to measure beyond the standard itself. The method you describes gives tau=2E-9 ? This is more or less what I could get with the frequency measurement (even a bit lower). So what is the benefit of the time interval measurement here against the frequency measurement ? I've been sloppy with the scaling factor, so there is a fixed scaling factor for the noise that the single-shot resolution produces, and that would be a measurement limit that if everything else is ideal would dominate. This quantization noise is sqrt(1/12) or about 0.289 if I remember correctly, so that is the scale-factor. It will also have a 1/tau slope. So that is how you can expect this noise to behave, it will look like white phase noise, but isn't, it is highly systematic noise, and if you play nicely with it, you can measure below it. However, doing so is non-trivial. I have one counter that does that. The good old HP5328A with the Option 040-series of boards will introduce noise to the counting 100 MHz oscillator such that averaging gets you down towards 10 ps rather than 10 ns resolution in TI mode. However, it does not help you to get nice frequency or stability measures. I've not taken the time to detail-analyse the ADEV scaling factor thought, I should do that, but it follows the general formula of ADEV(tau) = k*t_res/tau where t_res is the single-shot resolution and k is a constant. There is more to this, as counters can show up non-linearities of several sorts, and that the trigger conditions of the input has been optimized, which can be slew-rate limited for many counters and conditions. So, anyway, there is a bit of hand-waving in there, but I thought it was better to get you to get the basic trend there first, and then we can discuss the detailed numbers, as theory is one thing and achieved number can be quite a different one. As for frequency and time-interval measurements, if properly done, they can be used interchangeably without much impact. Realize that frequency and time-interval measurements will both be based on time-interval measurements as the core observation inside the counter, so the single-shot resolution limit applies to them both. However, subtle details lies in how the counter works and there is ways that the frequency precision can be lost. A good counter is the SR620, but the way it does the frequency measure, you need to calibrate the internal delay to make it on the mark measure. Using it in time-interval mode and you can eliminate that offset, because the start and stop measure of your signal under test is done with the same channel, with essentially the same delay both trigger-times. Another subtle detail is that when you make frequency measurements, you arm your counter, the start channel triggers, you wait the time you have programmed as the measurement time before you arm the stop channel, and then it triggers, after which you then read out your coarse counter of cycles, the interpolator states for the start and stop channels and well, the count of the time-base (which should be known), you calculate the frequency and output and well, once you cleared the bench from that measure you then arm the counter core of the next measurement. The time from the stop event to the following start event is called the dead-time. This dead-time is a period when the signal is not being observed. The actual time between the measures (time between the start events) and the length of the measures (time between the start and stop events) will not be the same, this will create a measurement bias in the ADEV. If you can establish the length of the dead-time you can compensate the measures. Very very few people do this these days, part of it is ignorance, part of it is why bother when you can use any of a number of techniques that avoid the dead-time altogether. Being able to measure frequency does not easily convert into making quality ADEV measures. Also, another danger of using frequency measures is that many modern counters use one of several techniques to improve the frequency measurement resolution by using things like linear regression. This behaves as a narrow-band filter, and the ADEV measures for white noise depend on the bandwidth of the system, and well, very very few measurements is annotated with their bandwidth, so traceable ADEV measurements will not be done there, and this pre-filtering effect bandwidth
Re: [time-nuts] FOSDEM 2015 has a time-track
Hi, On 01/13/2015 11:48 AM, Attila Kinali wrote: On Tue, 13 Jan 2015 01:57:56 -0800 Tom Van Baak t...@leapsecond.com wrote: I was told some of the time slots of https://fosdem.org/2015/schedule/track/ time/ might be tentative Well, it's FOSDEM. It's not a professionally organised conference. And as presentations often take longer than their time slot, the schedule tends to shift around quite a bit. but we'll all get together after the last talk, whenever it is. So far everyone I've heard from has the evening open. Time nuts -- if you're within a couple hundred km of Brussels it should be worth it -- Sunday, 2015-02-01. If you are new to FOSDEM, don't miss the social event on friday evening. Who knows, Tom's beard mignt not be the only one to show up. :) Good to know that Fridays session might be worth getting to. Thanks for the heads up Attila. 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.
