[time-nuts] NPL Time & Frequency Club Meeting
NPL (National Physical Laboratory) Time & Frequency Club hold their next meeting on 14th September at NPL Teddington. The meeting is free to all, but you need to register. Please see www.npl.co.uk/time/club for more details, and a registration form. Rob Kimberley ___ time-nuts mailing list time-nuts@febo.com https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
[time-nuts] British Horological Institute
Again, for UK readers, unless you are holidaying in our hot and sunny country (don't worry it never lasts!), the British Horological Institute at Upton Hall is opening its doors to the public on 28th-30th July for its annual Clock & Watch Show. For those of you who like the mechanical versions of time keeping it is a lovely place to visit. Lots to see, and always guaranteed to be a good day out. www.bhi.co.uk for more information. Rob Kimberley ___ time-nuts mailing list time-nuts@febo.com https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
[time-nuts] MSF 60KHz Transmission
Updated details on the MSF transmission in the UK can be found at www.npl.co.uk/time/msf/ It provides information on the signal coverage expected from the new Anthorn site (starts transmitting April '07) and some recent FAQs. Rob Kimberley [EMAIL PROTECTED] Skype: robkimberley Just a thought. Human activities contribute slightly to greenhouse gas concentrations through farming, manufacturing, power generation, and transportation. However, these emissions are so dwarfed in comparison to emissions from natural sources we can do nothing about, that even the most costly efforts to limit human emissions would have a very small-- perhaps undetectable-- effect on global climate. This e-mail has also been checked for viruses but it is your responsibility to conduct your own virus checks on all parts of it. ___ time-nuts mailing list time-nuts@febo.com https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
[time-nuts] Dithering vs. locking all the clocks to the OCXO?
Hi All, Earlier, I explained that my application require very good relative stability between various GPSDOs. A rough estimate of my requirements is: -Baselines of 100s of meters to 10s of kilometres. -Sub-nanosecond relative stability (this I forgot to mention earlier - thanks to TvB for reminding me). -Time scales of maybe 100s of seconds to 10s of minutes. -The lower limit on my stability requirement is maybe the 200ps of jitter that the FPGA will add to the processed data. My question is this: At this stage I'm not sure what all the various causes are for the error in the 1PPS output of a GPS receiver. (I sure I will find the answer to this in all that references TvB and Magnus gave me). However, a quick guess would be the delay caused by atmospheric effects (I don't think thermal noise would play a big role since the antenna is looking straight up) Also, there will be errors higher up in the food chain, such as changes in satellite orbits etc. I guess these errors are fairly systematic. Lower down in the food chain, I presume the M12+T adds further errors to the signal (viz. the antenna, LNA, TCXO jitter, etc). I presume these errors would be on faster time scales, smaller and much more stochastic in nature. If the resolution of my phase comparator is about 100ps, and keeping in mind that I want relative stability, wouldn't it make sense to lock the M12+T's on-board TCXO to the OCXO (probably not straight forward to do)? I realise that one would lose the advantage of any dithering effect which would quickly average any zero mean effect. I guess this will depend on the nature of the errors introduced due to clock jitter: Is it Gaussian and zero mean? I guess one will have to investigate what happens at down-conversion to IF etc. And, that ultimately it will depend on the size and nature of noise caused by the TCXO. If one could closely follow the drifts in atmospheric effects (which would be the same for short baselines) one will have very good relative stability. Regards, Stephan ___ time-nuts mailing list time-nuts@febo.com https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
Re: [time-nuts] Linear Interpolator
Hi Ulrich, Thanks for the useful link. Regards, Stephan. -Original Message- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of Ulrich Bangert Sent: 01 July 2006 05:39 PM To: 'Discussion of precise time and frequency measurement' Subject: Re: [time-nuts] Linear Interpolator Hi Stephan, a lot of excellent scientifical reading is availabale on the net about that topic. My personal #1 reference is "A Jitter Characterization Sytem Using a Component-Invariant Vernier Delay Line" by Antonio H. Chan. There are other companies to sell ready to go ps resolution stuff but not at the prices of ACAM. Regards Ulrich > -Ursprüngliche Nachricht- > Von: [EMAIL PROTECTED] > [mailto:[EMAIL PROTECTED] Im Auftrag von Stephan Sandenbergh > Gesendet: Freitag, 30. Juni 2006 14:02 > An: 'Discussion of precise time and frequency measurement' > Betreff: Re: [time-nuts] Linear Interpolator > > > Hi Ulrich, > > Thanks for the tip. And, also many thanks to Magnus for > introducing me to the concept of Time-to-Digital conversion. > It is a brilliant and yet so simple technique. (Until > yesterday, I blissfully believed that a fast clocking counter > was one's best bet.) > > Accordingly, I did a bit of research on the topic: > > Google took me to a lot of interesting sites (as Tom van Baak > noted). However, I found only one company, Acam (which is the > one you also pointed out), that sell these things inside an IC. > > I also read the article posted earlier by Tom van Baak > (Thanks Tom! This is indeed a very comprehensive article.) It > turns out that you can implement a very elegant linear > interpolator using a digital delay line inside a FPGA. It is > called the Vernier technique. From the article I understand > that resolutions of between 10s and 100s of picoseconds have > been achieved for various designs. > > Has anyone else used this Vernier technique with delay lines? > I seems pretty neat to me. > > It means my hardware doesn't need to change. A software > update will do the > trick :) > > Regards, > > Stephan. > > PS: Thanks Ulrich for the link to your M12+T results. I was > looking all over the place for these results for a long time now. > > > > ___ > time-nuts mailing list > time-nuts@febo.com > https://www.febo.com/cgi-> bin/mailman/listinfo/time-nuts > ___ time-nuts mailing list time-nuts@febo.com https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts ___ time-nuts mailing list time-nuts@febo.com https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
Re: [time-nuts] Dithering vs. locking all the clocks to the OCXO?
From: "Stephan Sandenbergh" <[EMAIL PROTECTED]> Subject: [time-nuts] Dithering vs. locking all the clocks to the OCXO? Date: Tue, 4 Jul 2006 14:49:19 +0200 Message-ID: <[EMAIL PROTECTED]> > Hi All, > > Earlier, I explained that my application require very good relative > stability between various GPSDOs. > > A rough estimate of my requirements is: > > -Baselines of 100s of meters to 10s of kilometres. > > -Sub-nanosecond relative stability (this I forgot to mention earlier - > thanks to TvB for reminding me). > -Time scales of maybe 100s of seconds to 10s of minutes. > > -The lower limit on my stability requirement is maybe the 200ps of jitter > that the FPGA will add to the processed data. > > My question is this: > > At this stage I'm not sure what all the various causes are for the error in > the 1PPS output of a GPS receiver. (I sure I will find the answer to this in > all that references TvB and Magnus gave me). > > However, a quick guess would be the delay caused by atmospheric effects (I > don't think thermal noise would play a big role since the antenna is looking > straight up) Also, there will be errors higher up in the food chain, such as > changes in satellite orbits etc. I guess these errors are fairly systematic. Actually no, not so much as you might expect. Your receivers are *close* to each other in GPS terms, you will certainly experience what is referred to as GPS common view. The receivers will experience almost identical shifts due to atmospheric effects since they are so close to each other. You will most definitly have the same satelites overhead, except where local foilage prohibits the view of a certain satelite. > Lower down in the food chain, I presume the M12+T adds further errors to the > signal (viz. the antenna, LNA, TCXO jitter, etc). I presume these errors > would be on faster time scales, smaller and much more stochastic in nature. You should be looking at making sure you have a fairly unobstructed view of the sky and minimal of ground-reflections. A good antenna could reduce dependence on reflections. BG made some similar comments privately as we met during the weekend, and I agree. > If the resolution of my phase comparator is about 100ps, and keeping in mind > that I want relative stability, wouldn't it make sense to lock the M12+T's > on-board TCXO to the OCXO (probably not straight forward to do)? Infact, BG and I is going to engange in such an experiement, we both had been playing around with that thought. The details vary depending on which particular receiver one has, both chipset and software plays a factor. I do infact have a suitable GPS receiver board here in my hand (thanks to BG!). > I realise that one would lose the advantage of any dithering effect which > would quickly average any zero mean effect. Dithering effect is what you use if you can't do better. It is one of several methods. If you have better single-shot resolution you will directly lower the measurement noise-floor and averaging will just work with you. > I guess this will depend on the nature of the errors introduced due to clock > jitter: Is it Gaussian and zero mean? Yes and no. Yes, there is a large white and Gaussian noise in there, no, it is not all Gaussian and as you go down in frequency (i.e. up in time - tau) you will experience non-Gaussian noises too. However, most of that should come from the GPS system and not the local clocks, really depends on the clocks and PLL bandwidth, a topic which have been discussed lately. > I guess one will have to investigate what happens at down-conversion to IF > etc. And, that ultimately it will depend on the size and nature of noise > caused by the TCXO. Indeed. A good TCXO is needed anyway, low noise is crutial since high noise will effectively lower the selectivity of the receiver. > If one could closely follow the drifts in atmospheric effects (which would > be the same for short baselines) one will have very good relative stability. Indeed. Cheers, Magnus ___ time-nuts mailing list time-nuts@febo.com https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
Re: [time-nuts] Dithering vs. locking all the clocks to the OCXO?
Are these permanent installations or portable? If portable, how quickly do they need to lock up to within sub-nanoseconds? In a permanent (or semi-permanent) installation, it's hard to beat GPS-steered cesium, with a loop-tau of DAYS to eliminate all the GPS jitter, ionosphere effects, etc. -RL Robert Lutwak, Senior Scientist Symmetricom - Technology Realization Center 34 Tozer Rd. Beverly, MA 01915 (978) 232-1461 Voice [EMAIL PROTECTED] (Business) (978) 927-4099 FAX [EMAIL PROTECTED] (Personal) (339) 927-7896 Mobile - Original Message - From: "Stephan Sandenbergh" <[EMAIL PROTECTED]> To: Sent: Tuesday, July 04, 2006 8:49 AM Subject: [time-nuts] Dithering vs. locking all the clocks to the OCXO? > Hi All, > > Earlier, I explained that my application require very good relative > stability between various GPSDOs. > > A rough estimate of my requirements is: > > -Baselines of 100s of meters to 10s of kilometres. > > -Sub-nanosecond relative stability (this I forgot to mention earlier - > thanks to TvB for reminding me). > -Time scales of maybe 100s of seconds to 10s of minutes. > > -The lower limit on my stability requirement is maybe the 200ps of jitter > that the FPGA will add to the processed data. > > My question is this: > > At this stage I'm not sure what all the various causes are for the error > in > the 1PPS output of a GPS receiver. (I sure I will find the answer to this > in > all that references TvB and Magnus gave me). > > However, a quick guess would be the delay caused by atmospheric effects (I > don't think thermal noise would play a big role since the antenna is > looking > straight up) Also, there will be errors higher up in the food chain, such > as > changes in satellite orbits etc. I guess these errors are fairly > systematic. > Lower down in the food chain, I presume the M12+T adds further errors to > the > signal (viz. the antenna, LNA, TCXO jitter, etc). I presume these errors > would be on faster time scales, smaller and much more stochastic in > nature. > > If the resolution of my phase comparator is about 100ps, and keeping in > mind > that I want relative stability, wouldn't it make sense to lock the M12+T's > on-board TCXO to the OCXO (probably not straight forward to do)? I realise > that one would lose the advantage of any dithering effect which would > quickly average any zero mean effect. I guess this will depend on the > nature > of the errors introduced due to clock jitter: Is it Gaussian and zero > mean? > I guess one will have to investigate what happens at down-conversion to IF > etc. And, that ultimately it will depend on the size and nature of noise > caused by the TCXO. > > If one could closely follow the drifts in atmospheric effects (which would > be the same for short baselines) one will have very good relative > stability. > > Regards, > > Stephan > > > > ___ > time-nuts mailing list > time-nuts@febo.com > https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts ___ time-nuts mailing list time-nuts@febo.com https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
Re: [time-nuts] Dithering vs. locking all the clocks to the OCXO?
From: "Robert Lutwak" <[EMAIL PROTECTED]> Subject: Re: [time-nuts] Dithering vs. locking all the clocks to the OCXO? Date: Tue, 4 Jul 2006 10:34:01 -0400 Message-ID: <[EMAIL PROTECTED]> > Are these permanent installations or portable? If portable, how quickly do > they need to lock up to within sub-nanoseconds? > > In a permanent (or semi-permanent) installation, it's hard to beat > GPS-steered cesium, with a loop-tau of DAYS to eliminate all the GPS jitter, > ionosphere effects, etc. Actually, for these distances, pulling some fibre and do two-way time transfer should not be too hard. Acheiving sub-nanosecond relative timing should not at all be unfeasable but should rather be consider fairly easy. Cheers, Magnus ___ time-nuts mailing list time-nuts@febo.com https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
Re: [time-nuts] NPL Time & Frequency Club Meeting
Rob, It happens I will be in the UK that week, but I am not sure my 6 year old daughter would be welcome! I have bookmarked the site and will keep a watch on it because it may be that a future trip could coincide with a meeting, thanks for the post. John At 03:35 AM 7/4/2006, you wrote: >NPL (National Physical Laboratory) Time & Frequency Club hold their next >meeting on 14th September at NPL Teddington. The meeting is free to all, but >you need to register. Please see www.npl.co.uk/time/club for more details, >and a registration form. > >Rob Kimberley > > > >___ >time-nuts mailing list >time-nuts@febo.com >https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts ___ time-nuts mailing list time-nuts@febo.com https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
Re: [time-nuts] NPL Time & Frequency Club Meeting
John, NPL is right next door to Bushy Park http://www.royalparks.gov.uk/parks/bushy_park/ . Hampton Court Palace and River Thames are close by. I'm sure your family could find a lot to amuse themselves if you visited NPL. If you look at the enlarged map on the link provided, NPL is situated adjacent to Queens Road and Bushy House at top of map. Rob -Original Message- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of John Day Sent: 04 July 2006 15:59 To: Discussion of precise time and frequency measurement Subject: Re: [time-nuts] NPL Time & Frequency Club Meeting Rob, It happens I will be in the UK that week, but I am not sure my 6 year old daughter would be welcome! I have bookmarked the site and will keep a watch on it because it may be that a future trip could coincide with a meeting, thanks for the post. John At 03:35 AM 7/4/2006, you wrote: >NPL (National Physical Laboratory) Time & Frequency Club hold their >next meeting on 14th September at NPL Teddington. The meeting is free >to all, but you need to register. Please see www.npl.co.uk/time/club >for more details, and a registration form. > >Rob Kimberley > > > >___ >time-nuts mailing list >time-nuts@febo.com >https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts ___ time-nuts mailing list time-nuts@febo.com https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts ___ time-nuts mailing list time-nuts@febo.com https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
[time-nuts] questions on uncompensated crystal oscillators
Hello, Please excuse the fact that this is not what we all consider precise frequency. I am selecting crystals to use for a medium to high volume application. The basic criterion are: - used with a VLSI inverter based oscillator with 3.3 V supply, but somewhat high impedance output. - frequency: 27.000 MHz fundamental within 40 (or so) ppm over temperature including 7 to 10 years of aging. - HC49S case - no production line trimming - low cost After looking at the design issues, I wonder if some of you haven't faced similar designs and have some suggestions regarding the following issues: - Is there a free (or inexpensive) spice that works well simulating crystal oscillators? (I did see the submissions to this email list last September on LTSpice.) (I have tried using the SIMetrix Intro package, and it generally seems to produce good results, but I found it's awkward or impossible to measure frequency to lots of precision (taking an FFT helps), and some results regarding oscillator frequency shifts as a result of small delay changes in the inverter seemed questionable to me.) - Are there some good papers dealing with the practical aspects of: - transforming the Q limiting element of the design from a series R to a parallel R - Rs vs. ESR - exceeding the correlation drive level of a crystal - measuring the drive level & calculating the maximum drive level - negative R and oscillator startup margin - consumer video color subcarrier tolerance - Do you have any suggested suppliers for crystals with the following specifications: - HC49S - 27.000 MHz - 10 ppm tolerance - 10 ppm stability - 18 pF load - trim sensitivity less than 15 ppm/pF - 7 (or better yet 10) year aging less than 10 ppm - drive level up to 1 mW (may not need to be this high if the ESR is < 30 ohms or I better understand our maximum inverter output voltage) If someone is interested in providing comments on the app note I'm working on, that would also be appreciated. Thanks Stan Searing ___ time-nuts mailing list time-nuts@febo.com https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
Re: [time-nuts] Dithering vs. locking all the clocks to the OCXO?
> However, a quick guess would be the delay caused by atmospheric effects (I > don't think thermal noise would play a big role since the antenna is looking > straight up). Seems to me that thermal noise depends only on the resistive impedance of the antenna and input circuit. See Johnson noise. Orientation of the antenna would affect reception of external noise radiation. Don't think cosmic background radiation is a problem for the usual GPS ground antenna. What causes the "atmospheric effects"? I'd expect radiation to slow down a bit as it passes through water. Are there heat effects as well? Does the density of the atmosphere change enough to make a 10E-10 second delay possible? If so, it seems there would be non-negligible changes due to turbulence over a kilometer or so. I have two each HP 58532A antenna, 58535A distribution amplifier, and Z3801A receiver connected to a laptop running a common (not HP) program that provides receiver status reports. The antennae are mounted 4 feet apart on a sturdy pole (6 inch plastic pipe). There are nearby trees above the pole. One has to live with one's mate when it comes to unnatural things that are visible from the street. I ran it for a while and got diverted to other matters, but I remember seeing relative variations in altitude and position. A Racal-Dana 1992 counter set for phase angle showed a constantly increasing phase difference between the receivers, with readings taken hours apart. I have not automated data collection yet. Is this setup able to quantify atmospheric effects or are there too many system errors? Regards, Bill Hawkins ___ time-nuts mailing list time-nuts@febo.com https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
[time-nuts] Hello Christopher Re topic 1. EROS -750- OVCXO
Hello Christopher The company that did make the OVCXO changed name But are still making the Crystal Oscillator you have, that is also used in the TrueTime GPS-DC Receiver Try the web page and on there you have the contact details http://www.electrodynamics.com/index.php Its hard to open unit, best use a small micro blow torch, I did with mine, but looking on the construction I later decided to look for a replacement unit. Track printed on rubber and surface mount with plenty of black glue ! I have been told the Units are approximately $900 to make one off's ! yes quite an expensive unit. One inputs are +12 V and the other is + 5 V from my Truetime GPS-DC unit that I have Best Regards Philip Davies, Altrincham, in Cheshire UK... Today's Topics: 1. ERC EROS-750 OVCXO? (Christopher Hoover) 2. NPL Time & Frequency Club Meeting (Rob Kimberley) 3. British Horological Institute (Rob Kimberley) 4. MSF 60KHz Transmission (Rob Kimberley) 5. Re: Linear Interpolator (Stephan Sandenbergh) 6. Dithering vs. locking all the clocks to the OCXO? (Stephan Sandenbergh) 7. Re: Dithering vs. locking all the clocks to the OCXO? (Magnus Danielson) 8. Re: Dithering vs. locking all the clocks to the OCXO? (Robert Lutwak) ___ time-nuts mailing list time-nuts@febo.com https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
Re: [time-nuts] Dithering vs. locking all the clocks to the OCXO?
On Tue, July 4, 2006 19:18, Bill Hawkins said: > What causes the "atmospheric effects"? I'd expect radiation to > slow down a bit as it passes through water. Are there heat > effects as well? Does the density of the atmosphere change > enough to make a 10E-10 second delay possible? If so, it > seems there would be non-negligible changes due to turbulence > over a kilometer or so. Largest error source for single freq receivers are ionospheric errors, because of time varying TEC. (The very same effect that makes some radiowaves sometimes circle the globe.) The next important error source is the trophosphere, where water vapor content delays the signal somewhat unpredictable. -- Björn ___ time-nuts mailing list time-nuts@febo.com https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
Re: [time-nuts] questions on uncompensated crystal oscillators
> The basic criterion are: > - used with a VLSI inverter based oscillator with >3.3 V supply, but somewhat high impedance output. An inverter is not specified for oscillator duty. It cannot be analyzed for this application on SPICE. It will never be a high precision oscillator circuit. (10 ppm is "high precision" when it comes to using inverters). If you care about performance, use a transistor to make the oscillator and use the inverter to convert the sine wave to logic levels. If you "cannot" use a transistor, relax your specs about an order of magnitude. Rick Karlquist ___ time-nuts mailing list time-nuts@febo.com https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
Re: [time-nuts] Dithering vs. locking all the clocks to the OCXO?
>On 7/4/06, Magnus Danielson <[EMAIL PROTECTED]> wrote: >Actually, for these distances, pulling some fibre and do two-way time transfer >should not be too hard. Acheiving sub-nanosecond relative timing should not at >all be unfeasable but should rather be consider fairly easy. Do you mean easy for fibre or for a GPSDO? Regards, Stephan. ___ time-nuts mailing list time-nuts@febo.com https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
Re: [time-nuts] questions on uncompensated crystal oscillators
In a message dated 7/4/2006 09:52:33 Pacific Daylight Time, [EMAIL PROTECTED] writes: Hello, Please excuse the fact that this is not what we all consider precise frequency. I am selecting crystals to use for a medium to high volume application. The basic criterion are: - used with a VLSI inverter based oscillator with 3.3 V supply, but somewhat high impedance output. - frequency: 27.000 MHz fundamental within 40 (or so) ppm over temperature including 7 to 10 years of aging. - HC49S case - no production line trimming - low cost After looking at the design issues, I wonder if some of you haven't faced similar designs and have some suggestions regarding the following issues: Hi Stan, I have designed a circuit that does exactly this, and published it in EDN. See page 92 for the article: _http://www.edn.com/contents/images/112703di.pdf_ (http://www.edn.com/contents/images/112703di.pdf) It's a VCXO 27/32MHz reference for a Video Decoder. You can delete the Varicaps if you don't need it to be adjustable. BTW: The crystals and inverter used in the design are quite good, the circuit generates less than 3ps jitter (measured on a Wavecrest SIA-3000) - jitter is really what counts in digital timing for video etc. Some caveats to watch out for: * for NTSC you can have up to about +-840Hz deviation and still be within limits. * Don't overdrive your crystal (see manufacturers spec) otherwise it can age too fast, and get damaged. Typically, use about 100uW or so. Measure the current into the crystal using a fast AC current probe * Make sure you have enough gain to guarantee startup (the circuit should work with at least 3x series resistance as will be used in production). This will mostly depend on the crystal ESR (should be as low as possible), while still not overstressing the crystal * 10ppm crystals are very(!) expensive, rather use trimming during production testing by removing/adding load cap options. This allows you to use a cheaper crystal (with a higher ppm rating), and spend more money on lower thermal susceptability specs. Hope this helps, bye, Said ___ time-nuts mailing list time-nuts@febo.com https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
