[time-nuts] Re: Silicom PCIe timestamping network cards
Bob kb8tq writes: > Could be. They also mention a 25 MHz clock on the card. That could > get you to a 125 MHz time base with a 8 ns resolution. Again, without > a deep dive into what they did - who knows. That is the clock-supply to the 82599 chip, but there is a boatload of PLL'ery going on such an ethernet chip. I can't remember the details, but I /think/ a 10GB ethernet runs as two independent simplex lines. If so, that 25MHz will only go to the TX side, the RX side will run at whatever frequency the other end supplies. Unless the other end is a PTP-aware switch which does clock slaving from the upstream port and ... To be honest the entire PTP and White Rabbit thing has gone ... ehh ... time-nuttery :-) -- 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@lists.febo.com To unsubscribe send an email to time-nuts-le...@lists.febo.com
[time-nuts] Re: Silicom PCIe timestamping network cards
Poul-Henning Kamp via time-nuts writes: > The timestamping counter gets its clock from the ethernet line > signals, and the counting frequency therefore depends on the ethernet > speed: > > 100 Mb/s1.5625 MHz > 1 Gb/s 15.625 MHz > 10 Gb/s 156.25 MHz > > (The 8ns timestamping mentioned must be something outside the 82599) I should probably expand on this to prevent misunderstandings: The 82599 chip will timestamp with 6.4ns resolution, and since both the frequency and the timestamp edge is derived from the ethernet signal when you time packets, there is no noise process involved, and you do get your full 6.4ns worth. I understand the "8ns" number in the datasheet for the card to refer to the PPS input and assume the extra 1.5ns to be noise in the analog domain outside the i82599 chip. -- 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@lists.febo.com To unsubscribe send an email to time-nuts-le...@lists.febo.com
[time-nuts] Re: Silicom PCIe timestamping network cards
John Miller via time-nuts writes: > I'm curious if anyone here knows much about these silicom timestamping > network interfaces? I used the i82599 ethernet chip ten years ago, to measure time in the first Adaptive Optics Real-Time Computer prototype we built for ESO's ELT telescope. I have revision 2.73 of the datasheet (930 pages), but that is probably publically available theses days in a newer revision. The timestamping counter gets its clock from the ethernet line signals, and the counting frequency therefore depends on the ethernet speed: 100 Mb/s1.5625 MHz 1 Gb/s 15.625 MHz 10 Gb/s 156.25 MHz (The 8ns timestamping mentioned must be something outside the 82599) The basic idea is that you can measure the line frequency with the PPS and timestamp PTP ethernet packets TX and RX relative to the PPS. The card is quite picky about which packets it will timestamp, in particular some of the message bytes must look "enough" like a PTP packet to be timestamped. I figured it out eventually, and Intel promised to update the data-sheet. I have not tried to use the 1PPS signal input, it was not available on the cards we used back then and we only needed relative packet timestamps. I am not sure what it would take to produce a 10G ethernet signal from a "house standard", it may not be trivial. So if you want to build a really good PTP server, yes, go for it, but it is not much use for more advanced time-nuttery. -- 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@lists.febo.com To unsubscribe send an email to time-nuts-le...@lists.febo.com
[time-nuts] Re: General discussion of PID algorithms applied to GPSDO control loops (continued 1)
Bob kb8tq writes: >>> You mean the FLL and PLL are exclusive of each other ? I guess you are >> right, but I am trying to think "outside the box" and see if there are any >> alternatives. > >You will have two people driving the car at the same time. One hits the >accelerator and the other hits the brakes at the same time. They both can’t >be active *and* feed the EFC at the same time. The practical answer is to >run each during the warmup phase that it makes sense to do so. You _can_ have hybrid steering, but you must assign "weight" to the different contributions, so that they will never oscillate. I normally have found it better to have a big switch which decides who gets to control, based on the (external) circumstances. As a general rule of thumb, FLL's only make sense if the product of the rate at which you measure phase difference, and the jitter-noise when you do, ends up way to the right and above the allan-intercept. Prof. Dave's infamous "Call NIST once a day with a modem" mode in NTPD is a good example: Forget about tracking temperature, XO drift or anything else: Just try to get the average frequency right on a timescale measured in weeks. Poul-Henning PS: When you implement your PLL: The way to void "wind-up" durign startup, is to short the integrator, until the phase error has reached its proper sign. It is surprising how hard it is to write code to spot that, compared to deciding it manually :-) -- 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@lists.febo.com -- To unsubscribe send an email to time-nuts-le...@lists.febo.com To unsubscribe, go to and follow the instructions there.
[time-nuts] Re: GPSDO Control loop autotuning
Matthias Welwarsky writes: > > My heuristic is that when you plot the histogram of the time between > > zero-crossings, you want the "bulge" on the low side of, but close to, > > the "allan-intercept" (Ie: where the OCXO and GPS allan curves cross.) > > > > If you are working with 3rd order PLLs (predicting frequency drift), > > plotting separate histograms of the duration of positive and negative > > phase inputs helps: The more they overlap, the better your drift estimate. > > That's an interesting metric, but just as well you could record the phase > error over a certain time and feed it into a linear regression solver. Not even close. That will only give the (least-square) average, you *really* want to look at the curve-shape. > give you the drift in s/s and you want it to be 0 (or, like, close). You'll > know if your PLL is coupled too loosely if you see a drift. > Or, just look at the ADEV of the phase error. If the curve is going up > instead > of down, you know something's not quite right ;) Yes, but neither way are suitable metrics as input to an autotuning PLL. -- 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@lists.febo.com -- To unsubscribe send an email to time-nuts-le...@lists.febo.com To unsubscribe, go to and follow the instructions there.
[time-nuts] Re: GPSDO Control loop autotuning
Markus Kleinhenz via time-nuts writes: > But I think i got some pointers that can put you on your path. One (always?) overlooked metric, is the frequency spectrum of the zero-crossings, of the phase difference input to the PLL. (NB: This obviously require good resolution of the phase error, including application of the "negative sawtooth" correction, otherwise the "hanging bridges" noise will swamp the signal you are looking for.) If your loop is (too) tight, the PLL will chase every wiggle in the GPS signal and your phase difference input to the PLL will change sign all the time. If your loop is (too) loose, the PLL will not follow the GPS signal as close as it should, and the phase difference will only rarely change sign, if your OCXO/Rb drifts, possibly not ever. My heuristic is that when you plot the histogram of the time between zero-crossings, you want the "bulge" on the low side of, but close to, the "allan-intercept" (Ie: where the OCXO and GPS allan curves cross.) If you are working with 3rd order PLLs (predicting frequency drift), plotting separate histograms of the duration of positive and negative phase inputs helps: The more they overlap, the better your drift estimate. I have tried my hand at the math of this phenomena, but it disappears into dark corners of math text-books, where I cannot follow its trail. Poul-Henning -- 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@lists.febo.com -- To unsubscribe send an email to time-nuts-le...@lists.febo.com To unsubscribe, go to and follow the instructions there.
[time-nuts] Re: RAGA - was Re: Re: Low Phase Noise70 10 MHz bench signal source sought
Andy Talbot writes: > I have encountered GPS active antennas that are unstable and oscillate, > especially when not mounted on a metal backing. I saw no signs of that in the original RAGA experiment, using the "remote" version of the Oncore receiver. -- 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@lists.febo.com -- To unsubscribe send an email to time-nuts-le...@lists.febo.com To unsubscribe, go to and follow the instructions there.
[time-nuts] Re: disciplning natural phenomena
Lux, Jim writes: > Can one discipline a geyser to an external source? > >a) I assume there's some data somewhere on eruption timing - sure, Old >Faithful is quite regular, sufficiently that they can say "the next >eruption will occur at" and people will gather and watch it. Last I heard, they "seeded" it by pouring some harmless household chemical (soap?) into it ? I was told that this also regularized the size of each "performance". -- 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@lists.febo.com -- To unsubscribe send an email to time-nuts-le...@lists.febo.com To unsubscribe, go to and follow the instructions there.
[time-nuts] Re: One-night experiment: empirically verifying that the west coast power grid is actually interconnected
Jeremy Elson writes: > Wow! I was not expecting the two curves to match up so well. What a beautiful > result! The effective impedances of the power grid are very low, so frequency discrepancies are almost physically impossible. If you want to see the real trouble, you need to GPS referenced high resolution phase measurements in two or more locations, and then plot the RMS of their differences. Traditionally the grid frequency has been stabilized by the inertia in the (huge!) rotors in centralized power plant's turbo generators. Solar power generation is instantaneous and contribute no inertia. Wind power has lots of small generators, but they are behind electronic "frequency converters", (AC->DC->AC conversion) which attenuates and delays the response from their generators inertia[1]. With solar and wind taking over, for instance 60% of planned new generating capacity in USA next year will be solar and batteries, "low inertia situations" have become a real worry. The UK's grid collapse a couple of years ago is the first documented case where "low inertia" was "but for" factor. The big-iron-wound-with-copper manufacturers have started hawking "inertia generators" as a solution: Huge spinning lumps of iron connected to a motor-generator. Other solutions are to mandate local battery-storage and inertia supplying control algorithems at large VE deployments. NREL has a good article called: Inertia and the Power grid: A Guide without the Spin https://www.nrel.gov/docs/fy20osti/73856.pdf Poul-Henning [1] Different control-algorithms in different wind generators on the same grid-radial could cause frequency oscillations, if the interactions are not taken into account. This mandates quite conservative control strategies, which further attenuates the "inertia contributions". [2] https://www.eia.gov/todayinenergy/detail.php?id=51518 -- 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@lists.febo.com -- To unsubscribe send an email to time-nuts-le...@lists.febo.com To unsubscribe, go to and follow the instructions there.
[time-nuts] Re: Current-day GPS timing receivers
Greg Troxel writes: > Read this paper > > > https://hamsci.org/sites/default/files/publications/2020_TAPR_DCC/N8UR_GPS_Evaluation_August2020.pdf The "multistep" jitter seen on the PPS plots is a deliberately induced high frequency jitter. The effect is to "rough up" long hanging bridges so they become oscillator wander in GPSDOs. Pretty analogous to Floyd-Steinberg dithering an image really. I have tried to implement the same basic idea with both Oncore and PRS10, by sending commands via the serial port to move the PPS pulse around but got mediocre results. -- 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@lists.febo.com -- To unsubscribe send an email to time-nuts-le...@lists.febo.com To unsubscribe, go to and follow the instructions there.
[time-nuts] Re: Is this the right way to compare the short term accuracy of two frequency counters?
Tom Van Baak writes: > To determine the noise floor of a counter it's best to use different > sources, independent in frequency and also independent in phase. That > rules out dividers or multipliers. The phase needs to "sweep" across a > wide range. A neat way to do this: Clock --+-- (ext timebase) HP3336 -> | TI-counter +--> Set the HP3336 to the same frequency as the clock source and use it to vary the relative phase of the two signals into the counter. The main advantage is that you can make many measurements at each of the 360 phase differences and thus get both avg+stddev along the curve. Any unlinearities in the HP3336 obviously mix into the resulting measurements, but as far as I can tell, it performs much better than any of my counters. That is probably not unrelated to it being built to measure "time distortion" on telephony channels frequency-stacked on coax cables :-) -- 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@lists.febo.com -- To unsubscribe send an email to time-nuts-le...@lists.febo.com To unsubscribe, go to and follow the instructions there.
[time-nuts] Re: Another reason to monitor line frequency :)
Hal Murray writes: > > The hidden background noise that can catch criminals > https://www.youtube.com/watch?v=e0elNU0iOMY > 5 1/2 minutes. Wasn't that how they proved Nixon's tapes were edited ? -- 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@lists.febo.com -- To unsubscribe send an email to time-nuts-le...@lists.febo.com To unsubscribe, go to and follow the instructions there.
[time-nuts] Re: HP105B
Magnus Danielson via time-nuts writes: > No, not for HP. Somewhere on one of the HP memory webpages there is a presentation where somebody claims the longest lived HP product is a particular microwave gadget, I seem to recall it being a directional coupler. -- 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@lists.febo.com -- To unsubscribe send an email to time-nuts-le...@lists.febo.com To unsubscribe, go to and follow the instructions there.
[time-nuts] Vectron 380 teardown
With high praise for aesthetics even: https://twitter.com/EvilMnkyzDsignz/status/1482039903995273216 -- 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@lists.febo.com -- To unsubscribe send an email to time-nuts-le...@lists.febo.com To unsubscribe, go to and follow the instructions there.
[time-nuts] Re: High precision OCXO supplier for end costomers
Bob kb8tq writes:
> My only concern here is that before one goes of and spends 5,10, or
> 20 thousand dollars on an OCXO, [...]
Bob, you are kind of missing the point here...
The entire point of Audio-Homoepathy is to spend excessive amounts
of money, so that you can brag about how rich you are, and how
super-human your refined sense of hearing is, all without wasting
any time or effort on it.
How else can there be a market for $3000 CAT-6 ethernet cables ?
It is Audio-Homoepathy, because the crucial feature is "orders of magnitude".
They do not buy a slightly expensive ethernet cable, they buy one
which cost several orders of magnitude more than what it is worth,
so that nobody can doubt that money is no issue - and thereby
make the money the only real point.
I know several people who are quite comfortable parting these
newly-rich from their money, and I cannot really fault them...
One of those companies have a business model where they hand-build
quite competent amplifiers using outrageous raw materials and hawk
them at insane prices using industry-strength flim-flam.
When I say "indystry-strength flim-flam" I mean it.
At one time they had a role of teflon foil stored next to a resarch
nuclear reactor for some weeks, so that the "neutrons could equalize
the the tension in the micro-grid structure" before it got rolled
into capacitors with a gold foil with similar super-natural properties.
Often the invariably "very serious buyer" will persuade them, in
return for a stiff compensation, to never build any more, and refuse
to ever talk abut it, so he can (also) brag about having the only
one ever made, and make up some flim-flam about why that is so
("... but that reactor is closed now, and the guy who knew how to
reorient the rolls is dead.")
Then they rinse & repeat, this time with capacitors wound by virgins
from some tropical island or whatever.
The fact that the socalled "NFT" market has negatively impacted the
"high end audio" market recently tells you everything you need to
know about both of them.
So the question we are really being asked here, is what which
OCXO can be flim-flam'ed the most, when it becomes another dose
of audio-homoepathy.
Poul-Henning
--
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.
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[time-nuts] Re: PICDIV stability (was: Crystal oscillator for a begginer)
Attila Kinali writes: > Oh.. and if anyone is going to build a DIY oven for some instruments, a > 55x35x30cm > styrofoam box with 2cm wall thickness, suspended in air has a thermal > resistance of > approximately 3K/W. But beware that proper seating of the lid is quite > critical as > that alone can drop the thermal resistance by a factor of 3 (guess how I > know). Sorry for repeating myself about this: If you want a good thermally stable enclosure, pick and old freezer or fridge, leave it unplugged, add as many bricks as you can for thermal mass and get on with the fun stuff... They come in all sizes, have well designed door closing mechanisms and can often be had for free, when a working compressor is not needed. If you need active temperature control, get somebody with the proper kit to suck the gas out, and run water through the nice plumbing already installed. -- 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@lists.febo.com -- To unsubscribe send an email to time-nuts-le...@lists.febo.com To unsubscribe, go to and follow the instructions there.
[time-nuts] Re: PICDIV stability
The PIC controllers have gone through a large number of iterations and mask-shrinks over the years and your mileage may vary. -- 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@lists.febo.com -- To unsubscribe send an email to time-nuts-le...@lists.febo.com To unsubscribe, go to and follow the instructions there.
[time-nuts] Re: Where do people get the time?
Hal Murray writes: > Are people sensitive to the sound being early? There has been quite a lot of research on that, but I have not followed it for many years. The overall situation is that if the sound arrives before the visual event the brain gets quite confused, but it can arrive and up to a surprising large delay, the brain just handles it. -- 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@lists.febo.com -- To unsubscribe send an email to time-nuts-le...@lists.febo.com To unsubscribe, go to and follow the instructions there.
[time-nuts] Re: Derivation of time from celestial sight
Lux, Jim writes: >On 12/27/21 12:18 PM, Brent wrote: >> My understanding (and I could be wrong) is that one could derive 'stellar' >> time from a start sight/fix on polaris or another well tracked celestial >> object. I was once told that early editions of Bowditch provided the >> process (for the moon I was told) although one of the relatively old >> edition's that I have doesn't provide it. You want a bright star as close to your latitudes Zenith as possible, to get maximum apperant transit velocity. Polaris would be a spectacular bad choice as it barely moves at all. >Occultation of stars by the Moon provides a "universal" time source >(assuming you can see the Moon and stars). Interesting history search term: "Latitude observatory". -- 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@lists.febo.com -- To unsubscribe send an email to time-nuts-le...@lists.febo.com To unsubscribe, go to and follow the instructions there.
[time-nuts] Re: Where do people get the time?
Attila Kinali writes: > Not only did the US switch to > digital cellphone systems about half a decade after Europe, Dont just blame the telco's, both FCC, DOJ (on behalf of FBI) and in particular NSA, exhibited olympic-class foot-dragging to keep the air analog. -- 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@lists.febo.com -- To unsubscribe send an email to time-nuts-le...@lists.febo.com To unsubscribe, go to and follow the instructions there.
[time-nuts] Re: Why do have OCXO a Vref output? (was: help reviving Trimble UCCM-LPS GPSDO)
Being also a bit of a volt-nut, I played a bit with the Vref output from some of my OCXO's and must sadly report that they were not spectacular, seen from a volt-nut perspective. In at least once case, an admittedly pretty old OCXO design, the voltage reference was not located in the most well-regulated part of the oven and the chosen chip had pretty bad tempco at the elevated temperature. -- 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@lists.febo.com -- To unsubscribe send an email to time-nuts-le...@lists.febo.com To unsubscribe, go to and follow the instructions there.
[time-nuts] Re: PPS latency? User vs kernel mode
Andrew Kalman writes: > in a cooperative RTOS, the only latency is the MCU's own interrupt handling > mechanism. Which, as I explained earlier in the thread, is increasingly rubbish on any high-end platform these days because it is gone "soft" and become a message-passing phenomena across several clock domains etc. -- 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@lists.febo.com -- To unsubscribe send an email to time-nuts-le...@lists.febo.com To unsubscribe, go to and follow the instructions there.
[time-nuts] Re: PPS latency? User vs kernel mode
Javier Herrero writes: > - To implement a counter in the FPGA for use as the Linux clock source, > instead of the ARM timer > - Implement harware timestamping on the PPS, and generate the interrupt > (and since I was there, I use an external clock source for the counter > like the GPSO that gives also the PPS signal, instead of the usually > crappy XO that drives the Zynq clocks) > - And then have a lot of fun convincing the kernel to use the FPGA > counter as clock source, and converting raw PPS timestamp times to wall > clock in the kernel, to be able to give a good timestamp value to ntp/chrony In FreeBSD you get all that for free: https://papers.freebsd.org/2002/phk-timecounters.files/timecounter.pdf -- 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@lists.febo.com -- To unsubscribe send an email to time-nuts-le...@lists.febo.com To unsubscribe, go to and follow the instructions there.
[time-nuts] Re: PPS latency? User vs kernel mode
Interrupts are no longer hardware phenomena, but bus transactions which must lay claim to one or more busses, send a formatted message which is received by some kind of "interrupt prioritizer" which again, may or may not send another message on another kind of bus to the instruction sequencer in one or more CPU cores. Both of these message transmissions will very likely involve clock-domain-crossings. The good news is the per-interrupt overhead is lower, thanks to interrupts being 'gently woven into' the instruction stream, instead of hitting it with a sledgehammer. But the latency and jitter is literally all over the place... Fortunately a lot of "counter-module" hardware can be used to hardware-timestamp signals, even if the design does not exactly support it. For instance, the code I wrote for the Soekris 4501 uses two hardware counters: The first one, free-running, is the "timecounter" which the system clock is based on. The second one starts counting at the same rate as the first when the PPS signal comes in. By the time the CPU comes around to read both counters, it subtracts the second from the first, to figure out what time the hardware signal happened. -- 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@lists.febo.com -- To unsubscribe send an email to time-nuts-le...@lists.febo.com To unsubscribe, go to and follow the instructions there.
[time-nuts] Re: Oncore UT+ EEPROM -
k1...@att.net writes: > I have an Oncore UT+ for a project and found that it works fine after > updating the almanac and getting a 3D fix but it never stores my location > coordinates in its EEPROM. Each time I power up it shows all zeroes in Lat, > Lon, Alt for about an hour or so until it finds satellites. With Lady > Heather I tried entering my coordinates and this leads to faster tracking. > Is this normal Oncore UT+ behavior? Any advice other than a battery backup. As far as I know, the EEPROM (Flash?) is only used for code. The almanac and other changing info is in battery-backed NOVRAM. -- 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@lists.febo.com -- To unsubscribe send an email to time-nuts-le...@lists.febo.com To unsubscribe, go to and follow the instructions there.
[time-nuts] Re: Project Great
Hal Murray writes: > > j...@luxfamily.com said: > > And a lot ofsources may have a low flat spot in the curve, but it > > eventually trends up. Except for primary standards like Cs beam. > > What's magic about "primary standard" or "Cs beam" that keeps the ADEV from > trending up? Primarily (no pun intended) that there are no (relevant) mechanisms of frequency drift. Cesium beam standards measure free-flying atoms which means the only relevant external influence is the black-body radiation, which is constant, thanks to the thermostatic ovens. Rubidium standards measure atoms which are confined in a glass-bulb, which means they literally bounce of the walls all the time. The resonance we measure is not the real one, but one affected by the doppler-shift of the atoms speed, ie: velocity without sign, in the direction of interrogation. This also broadens the resonance. I belive the primary source of drift in Rb's are adsorption and absorption of Rb molecules onto and into the glass itself. This causes a drop of gas pressure, which changes the collision dynamics for the remaining Rb gas, which affects their velocity distribution, which again moves the "appearant resonance" we measure. One of the things which set the 5065A apart from "telecom" Rb's is that there is a side-reservoir which is cooled with a TEC to stabilize the gas pressure and thus velocity. If you put your Rb atoms in a fountain instead, they work as well, or even slightly better than Cs atoms. -- 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@lists.febo.com -- To unsubscribe send an email to time-nuts-le...@lists.febo.com To unsubscribe, go to and follow the instructions there.
[time-nuts] Re: measuring multiple gps modules
folkert writes: > I thought I understood just enough from electronics to be able to these > kind of experiments but apparently not (3 damaged rpi's and gps > modules). For a long time I used a HP1301 with relay boards to do stuff like that, worked a treat, althought it soaked up a lot of power. -- 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@lists.febo.com -- To unsubscribe send an email to time-nuts-le...@lists.febo.com To unsubscribe, go to and follow the instructions there.
[time-nuts] Re: function generator
Jeremy Elson writes: > [...] I plugged an RbXO into the DG1022Z and simply asked the > DG1022Z to divide it down to a 1pps signal. That is, I configured it to > create a pulse with a small duty cycle and 1hz frequency using the external > clock as a reference. To my surprise, it introduces a small but > measurable error of one part in 1E11 in the dividing-down. You can read the > full story of this in my post from earlier this year: When you feed such instruments an external clock, you often have to change one or more calibration constants for the internal (OC)XO's offset to zero. Another problem is that if you use the square wave output of a DDS based generator, they often produce the square from the sine output of the DDS chip with a schmitt-trigger, which causes lousy jitter. -- 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@lists.febo.com -- To unsubscribe send an email to time-nuts-le...@lists.febo.com To unsubscribe, go to and follow the instructions there.
[time-nuts] Re: FS740 Thoughts?
Bob kb8tq writes: > The 'filter' in the PRS-10 is not really set up for a GPS sort of signal. It is particularly bad at handling GPS's because of the "hanging bridge" phenomena, and the better the GPS, the worse the result... I tried injecting the "negative sawtooth" via the serial port to my PRS10 but firmware features/bugs prevented that. The offset could only be changed permanently in the saved configuration, you could not change the running value on a second to second basis. -- 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@lists.febo.com -- To unsubscribe send an email to time-nuts-le...@lists.febo.com To unsubscribe, go to and follow the instructions there.
[time-nuts] Re: FS740 Thoughts?
Dana Whitlow writes: > You did not really answer the basic question: "Does the 2.5 Hz > (or 5 Hz if applicable) C-field reversal cause the 2-sec bump in > the ADEV plot for the PRS-10?". I cannot answer that question as stated. My PRS10 died years ago, all I can say is that when I commissioned it, I disabled the MS because it improved things. > BTW, some radio hams are involved with microwave and even > MMW communications between mobile stations, [...] In any mobile application, or other application where the magnetic field is not nearly contant (for instance behind a steel door in a outdoor base-station cabinet, I would absolutely keep MS on. But for a time-nut installation, where the location is fixed, temperature controlled and, I would assume, due consideration is given to also keep the magnetic field from slamming around, I suggest MS be disabled. But it's a really trivial experiment to perform, so do it, measure and decide what is right for you. -- 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@lists.febo.com -- To unsubscribe send an email to time-nuts-le...@lists.febo.com To unsubscribe, go to and follow the instructions there.
[time-nuts] Re: FS740 Thoughts?
Matt Huszagh writes: > "Poul-Henning Kamp" writes: > > > The PRS-10 switches the polarity of the C-field solenoid at 5Hz to > > cancel out varying external magnetic fields. > > > > If that is not a concern for you, for instance because you use it > > in a stationary application, it can be disabled with the "MS0" command. > > > > It's all in the manual. > > How does the 5Hz switching relate to the 2s hump in the ADEV plot? The manual says: "[...]the current in the coil is switched at a 5 Hz rate." You can either read that as: "There are five positive and five negative periods every second" or "The sign changes five times per second" It is not entirely obvious which reading is the correct one. When I experimented with it ages ago, I concluded the latter fit my data best, but that was a pretty early firmware version, with quite a number of variances from the manual. If your ambient magnetic field is stable, and it should be for time-nuts purposes, modulating the hyperfine transition is a bad idea, no matter the frequency. -- 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@lists.febo.com -- To unsubscribe send an email to time-nuts-le...@lists.febo.com To unsubscribe, go to and follow the instructions there.
[time-nuts] Re: FS740 Thoughts?
Dana Whitlow writes: > But if you can stand the ADEV hump around 2 sec, the PRS-10 is delightful. The PRS-10 switches the polarity of the C-field solenoid at 5Hz to cancel out varying external magnetic fields. If that is not a concern for you, for instance because you use it in a stationary application, it can be disabled with the "MS0" command. It's all in the manual. -- 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@lists.febo.com -- To unsubscribe send an email to time-nuts-le...@lists.febo.com To unsubscribe, go to and follow the instructions there.
[time-nuts] Re: GPS D (i.e. gpsd) roll over bug..Oct 24th
Björn writes: > The L1 C/A was optimised many decades ago. The first GPS receiver to use the L1 C/A code took up four full racks and required to very alert persons to operate. There is a picture of it in one of the many "History of GPS" presentations given by the principals of the programme. -- 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@lists.febo.com -- To unsubscribe send an email to time-nuts-le...@lists.febo.com To unsubscribe, go to and follow the instructions there.
[time-nuts] Re: When did computer clocks get so bad?
Alec Teal writes: > So you suspect/expect around the time frequency changes started > happening, clocks became crap? Well, it gets complicated fast there, but yes, that's pretty much where the shit inescapably hit the fan. Previous to that, most CPU's were clocked with a small PLL chip which multiplied a 14.318MHz X-tal to whatever was needed. "Not good, not terrible" is probably a fair summary. But there are two different things at work here: On one hand the choice of Xtals: To keep the jitter on the multiplied clock low, the Xtal had to be better and better. (This is something the "extreme overclocking" people totally fail to consider when doing their high-school physics experiments.) But on the other hand, the CPU architecture must offer /something/ to the kernel to keep time with, and that's what Intel utterly fiasco'ed because of their windows focus. The entire ACPI-solves-that, ACPI-without-gliches-solves-that, reading-ACPI-is-faster-now saga was just sheer incompetence. But the ACPI running at 14.318 MHz is inadequate for most modern kernels in the first place, and that gets us into the TSC-counts-cycles, TSC-counts-cycles-without-overflow-issues, TSC-counts-cycles-onlyfor-this-core, TSC-pretends-the-core-is- always-running-at-the-same-speed saga, which was also caused by Intels idiocy. Admittedly, there are good and sane explanations why this is a hard problem to solve, but competent people solved in in other architectures decades before Intel botched it. -- 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@lists.febo.com -- To unsubscribe send an email to time-nuts-le...@lists.febo.com To unsubscribe, go to and follow the instructions there.
[time-nuts] Re: When did computer clocks get so bad?
Alec Teal writes: > My theory is that super cheap crappy quartz clocks are now used in > things which can be reasonably expected to be online most of the time, There are multiple answers to your question. The funny one is: When they set fire to a prototype motherboard at Intel Architecture Labs. Unfortunately that is not my story to tell. But for the PC-ecosystem, that really is the answer: When Intel had to start modulating clock-frequency in order to not set things on fire. Their execution was far from stellar, because they had their eyes only on Windows, which for all intents and purposes had no timekeeping worth anything at the time. By now they have it relatively under control, and due to the very steep PLL multipliers high end kit actually have comparatively good XTALS in order to keep the jitter within spec. For the Internet of Shit segment, the answer is it was never any good to begin with. Since these embedded chips generally are incredibly robust with respect to timing, the xtal on the BOM is the cheapest that will meet spec. The one saving grace is external high-speed interfaces like USB-3 and 10G ethernet: You need good-ish xtals before it even works. -- 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@lists.febo.com -- To unsubscribe send an email to time-nuts-le...@lists.febo.com To unsubscribe, go to and follow the instructions there.
[time-nuts] Re: constructing a moon base
Bob kb8tq writes: > Road building and graders sort of implies moving large amounts of “stuff” > onto the lunar surface. While a “road to nowhere” on earth might happen, > I’d bet you only build one on the moon to connect inhabited installations > to other full blown (inhabited or not) sites of some sort. It's funny how peoples thinking about this is still firmly cast in a 1950'ies NASA/science-fiction mindset. People really do not grasp how much work robots can do. One place I really see this is when people look at my lawnmower robot and go "There's no /way/ that can handle 5000 m² of lawn..." But the thing is: If a human did it on a garden-tractor once a week, we'd want it done quickly, so lots of power, wide cutting board and so on. But the robot has 168 times as much time[1] for the same job, so it does not even need one percent of the power of the garden-tractor, in particular because it does not have to lug 100 kg of human & associated creature-comforts around. If we need a road on the moon, we will launch robots and let them get on with the job, and they'll be done way ahead of when we arrive, probably not even leaving us a few really largish boulders to blow up. In other words: The grader on the moon will at most be a meter wide. Poul-Henning [1] The quoted capacity for lawn-mower robots is for 24hx7d, but in general you should not let it work while dark, for the sake of the other inhabitants in your lawn: Porcupines etc. -- 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@lists.febo.com -- To unsubscribe send an email to time-nuts-le...@lists.febo.com To unsubscribe, go to and follow the instructions there.
[time-nuts] Re: constructing a moon base
Chris Howard writes: > No GPS probably means cesium on the road grader? There are perfectly good optical gyros for that kind of job, most expensive planes already have them, and space qualifying them is not going to be that different from their current qualifications. Random press-release: https://investor.emcore.com/news-releases/news-release-details/emcore-awarded-41-million-supplemental-contract-raytheon That said, colonizing any planet, it would make a lot of sense to install some kind of high frequency hyberbolic transmitter coverage with a bidirectional data-channel, as a safety-of-life capability for time, position, alerts, space-weather etc. -- 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@lists.febo.com -- To unsubscribe send an email to time-nuts-le...@lists.febo.com To unsubscribe, go to and follow the instructions there.
[time-nuts] Re: Death of a Capacitor
Gerhard Hoffmann writes: > Where it really counts is in the low Hz region, when even costly 1uF > show barely any effect. Do not overlook that electrolytics are variable capacitors, depending on pretty much anything and therefore may increase noise in the up-to-around-a-Hz domain. Plastic film capacitors of releavant size do exist, for instance Kemet's C44U series, but they are obviously huge and expensive. -- 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@lists.febo.com -- To unsubscribe send an email to time-nuts-le...@lists.febo.com To unsubscribe, go to and follow the instructions there.
[time-nuts] Re: ammonia, cesium, masers, etc.
Bob kb8tq writes: >I think it’s safe to say that the interaction between the ammonia and whatever >the >structure is made of will be exciting on a number of levels. Corrosion is only >the first >item on a very long list …. Just stick with a single metal and keep water away, and you should be fine, with the footnote that amonia tends to disassociate and the hydrogen goes into or through metals. The simplest solution might be a dielectric-lined waveguide. That may indeed have been what they did, because those were a hot field of research around the same time, largely drive by AT projection that they would need to install a cross-continental 2" wave-guide using carrier frequencies up to 100 GHz to keep up with traffic. -- 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@lists.febo.com -- To unsubscribe send an email to time-nuts-le...@lists.febo.com To unsubscribe, go to and follow the instructions there.
[time-nuts] Re: ammonia, cesium, masers, etc.
Dana Whitlow writes: > My dad worked in the absorption air conditioning field using ammonia and > water, > and he once told me that ammonia-water was hell on aluminum copper points, or > even aluminum tubing that had impurities in the form of tiny copper flakes in > it. An aluminum-copper volta-cell developers just shy of one volt, so no surprise there... -- 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@lists.febo.com -- To unsubscribe send an email to time-nuts-le...@lists.febo.com To unsubscribe, go to and follow the instructions there.
[time-nuts] Re: ammonia, cesium, masers, etc.
paul swed writes: > Though honestly bending 23 GHz waveguide might be tricky. Or simply leave it > straight after all it Amatuer grade. I seem to recall that there was about 10-ish meter coiled up in the one on the famous old picture. That might be a bit unwieldy. On the other hand, that was probably not waveguide as much as just plain copper-tubing ? > Lastly they discussed an Amonia maser. Never knew. Wonder if it actually > vented amonia slowly. Sort of sounds that way. I would suspect the main problem with an amonia maser is that the Amonia disassociates and the hydrogen leaks out though the metal ? -- 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@lists.febo.com -- To unsubscribe send an email to time-nuts-le...@lists.febo.com To unsubscribe, go to and follow the instructions there.
[time-nuts] Re: in-ground clock room
Gilles Clement writes: > Magnetic levitation, dampening external vibrations ? By theselves magnetic fields are just really good springs. To get any kind of dampening you either need to add a dash-pot (=shock-absorber) as a dissipative device or you need to modulate the magnitic field to emulate the same result. I'm told the latter is much harder than it sounds. -- 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@lists.febo.com -- To unsubscribe send an email to time-nuts-le...@lists.febo.com To unsubscribe, go to and follow the instructions there.
[time-nuts] Re: in-ground clock room
Bill Beam writes: > >Bill's idea of a 0C water bath also sounds kind of cool and perhaps it might > be attainable with a double or triple stacked pettier cooler [...] There are excellent and cheap, widely available cabinets for this kind of experiment: Buy a fridge or a freezer and dont plug it in. If you want to, you can use the plumbing to run your own cooleant. -- 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@lists.febo.com -- To unsubscribe send an email to time-nuts-le...@lists.febo.com To unsubscribe, go to and follow the instructions there.
[time-nuts] Re: in-ground clock room
Hendrik writes: > go to ebay and get a cheap geophone. [...] I did that prior to building our house, because we built about 60m from the main rail-road through Denmark, and I needed vibration data to design of the house. There are a number of footnotes about geophones, the primary one being that they have a resonance frequency in the 4-7 Hz range and therefore provide no usable information below that. The second is that it is anyones guess what their sensitivity is, in particular if you buy it on eBay from somebody who found it lying in a field after percussive oil-exploration, so buy more than one. The good news is that it is easy to calibrated a geophone for absolute response using common T kit. I feed the geophone directly into a TI ADS1282 evaluation board, that ADC is built specifically for geophones and it works great. It is now bolted to the foundation of our house, and here is a recent plot: http://phk.freebsd.dk/misc/_.18856.pdf The 50 & 100 Hz lines are electical noise. The vertical red impulses at night are typical of passing trains, around 5Z construction work on the rails started. See if you can guess when they used the huge vibration compactor :-/ I have no data from any other building to compare with, and we did succeed in building a very quiet house: You really have to pay attention to hear the train-traffic. Amongst the many faint domestic signals I can identify in these plots are our ground-circuit heat-pump, the "GenVex" ventilation, the cooling in my lab, the fans in my Dell-server, the freezer, the washer, the dryer, and the occational good "rocking-through" on the Rauna-Njord speakers. I've tried playing the recordings back through head-phones, but none of those signals were audible. The vibration compactor on the other hand... -- 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@lists.febo.com -- To unsubscribe send an email to time-nuts-le...@lists.febo.com To unsubscribe, go to and follow the instructions there.
[time-nuts] Re: in-ground clock room
Tom Van Baak writes: >For scale, assume the room is 1 meter × 1 meter × 2 meters deep. So >that's vastly smaller than digging a basement, but much larger than >drilling a 8 inch round pipe. Digging down gives some natural isolation >and temperature regulation. A couple tons of concrete gives high >stability vertical walls for the pendulum clocks. I researched this extensively before we built a house 5 years ago. Look at the plot on page 37 in this paper: https://www.researchgate.net/publication/279526204_Temperatur_og_temperaturgradienter_ved_og_under_jordoverfladen_i_relation_til_lithologi It shows that in Denmark the yearly temperature variations in penetrates to a depth of 15 meters, and that even at 10 meters depth, you can expect the swing to be several Kelvin in any year. I did find handwaving which said tree-cover reduced the swing by "a lot" but no measurements to substantiate it. In the end I concluded that I could do better in the comfort of my lab. You should try to find similar data for your local climate and geology, before you pour too much money into a hole in the ground. -- 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@lists.febo.com -- To unsubscribe send an email to time-nuts-le...@lists.febo.com To unsubscribe, go to and follow the instructions there.
[time-nuts] Re: thermodynamics of time keeping
Lewis Masters writes: > They found that an ideal clock — one that ticks with perfect periodicity — > would burn an infinite amount of energy and produce infinite entropy, which > isn’t possible. Thus, the accuracy of clocks is fundamentally limited. I cant say that in any way surprises me, because you intuitively converge onat the same conclusion from the directions of quantum mechanics and information theory. -- 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@lists.febo.com -- To unsubscribe send an email to time-nuts-le...@lists.febo.com To unsubscribe, go to and follow the instructions there.
[time-nuts] Re: thermodynamics of time keeping
Dana Whitlow writes: > Perhaps the author is trying to include Schmitt triggers to sort of emulate > mechanical escapements. > I've occasionally used the things (Schmitt triggers) to help square up > sinewaves, but never in a case > where I was concerned about stability or jitter. > > BTW, how do three inverters constitute a Schmitt trigger? I dont think the important thing is the Schmitt Trigger, but rather the square wave. But putting multiple '04 inverters in sequence was a well known method to shapen flanks, and I have always understood that as the reason for using three in the xtal clock generator setup. -- 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@lists.febo.com -- To unsubscribe send an email to time-nuts-le...@lists.febo.com To unsubscribe, go to and follow the instructions there.
[time-nuts] Re: thermodynamics of time keeping
Richard Karlquist writes: > He lost me when he started talking about quartz clocks utilizing > > Schmidtt triggers. Never heard of that before and I'm going on > > 50 years of designing oscillators. I bet you just forgot about it: The classical 3-TTL-inverter clock-generator was used almost everywhere, including in quite a number of HP products. -- 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@lists.febo.com -- To unsubscribe send an email to time-nuts-le...@lists.febo.com To unsubscribe, go to and follow the instructions there.
[time-nuts] Re: Query about List and about 10 MHz Distro
David I. Emery writes: > On Sun, Aug 29, 2021 at 10:43:51AM -0400, paul swed wrote: > Not completely clear what the common > mode Z of the things is at 10 MHz... Twisted pair is 135 Ohm. -- 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@lists.febo.com -- To unsubscribe send an email to time-nuts-le...@lists.febo.com To unsubscribe, go to and follow the instructions there.
[time-nuts] Re: uncertainty/SNR of IQ measurements
Lux, Jim writes: >I'm looking for a simplified treatment of the uncertainty of I/Q >measurements. Say you've got some input signal with a given SNR and you >run it into a I/Q demodulator - you get a series of I and Q measurements >(which might, later, be turned into mag and phase). > >[...] > >I'm looking for a sort of not super quantitative and analytical >treatment that I can point folks to. Good luck with that :-) Some of the noise processes will be along the "vector" and distributed between I & Q components depending on the phase, while other noise processes affect the components individually. To make matters worse, both kinds of noise processes may depend on the phase, usually because of cross-talk and/or insufficient isolation. Low-resolution ADC's are a particular nasty problem, because they add +/-1 count jitter independent of the phase, and that causes very large arctangent errors. Counterintuitive as it may sound, it is easier to process the bits from ADC's where the low two bits are pure noise, than ADC's where all bits are good... -- 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@lists.febo.com -- To unsubscribe send an email to time-nuts-le...@lists.febo.com To unsubscribe, go to and follow the instructions there.
[time-nuts] Re: Isotemp OCXO question
Robert DiRosario writes: > I really wish NIST didn't add the BPSK modulation to WWVB. Increasing > the transmitter power would have been a lot better, but I'm sure that > would have cost a lot more then just changing the modulation. One does not simply increase the transmitter power at 60kHz. The WWVB antennas are essentially capacitors against ground, around 15nF, and they operate at voltages somewhere in the 30-50kV range. -- 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@lists.febo.com -- To unsubscribe send an email to time-nuts-le...@lists.febo.com To unsubscribe, go to and follow the instructions there.
[time-nuts] Re: GPSDO Software & Performance
Pluess, Tobias writes: > However in the other plot "gpsdo-outliers" we can see that there are huge > outliers in the phase error. At these times, we had huge thunderstorms here > in Switzerland at my place and I believe that the GPS signal quality was so > bad at these times that the GPS time pulse did not work reliably. (what > other reasons could there be for these 1PPS timing outliers?) Thunderstorms, in particular in regions with high ground resistance (= mountains) causes electrostatic fields which can cause trouble. One of the lesser known kinds of this trouble is induced voltages in high impedance CMOS inputs. Therefore: make sure that all unused CMOS pins are either tied to something with a suitably low resistance. On microcontrollers one can configure unused pins as outputs and drive them low. > Obviously, the "magic" of a GPSDO control algorithm is in the filtering of > these outliers! so far, my control code (src/cntl.c on Github) does not > seem to filter these outliers good enough In general median filters are probably the most robust way to deal with outliers, but if you do them the naiive way, they cause a usually unacceptable time-delay. When the outliers are less than half of samples, and always wrong, running the median filter in "gate mode" works well. Since the output from the median filter only defines a "gate" which input signals must pass, it causes no time-delay in the control loop. Something like: NMEDIAN = 300 GATE = 1e-3 median_filter = [None] def new_measurement(x): median = sorted(median_filter)[len(median_filter)//2] if median is None or median - GATE < x < median + GATE: ok_measurement(x) if len(median_filter) >= NMEDIAN: median_filter.pop(0) median_filter.append(x) This will reliably discard any sample which are more than 1e-3 from the median of the previous 300 samples. If the outliers are sometimes true, ie, where step-changes are to be expected and sensibly handled, median filters are not so swell and Kalman filters may be indicated. -- 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@lists.febo.com -- To unsubscribe send an email to time-nuts-le...@lists.febo.com To unsubscribe, go to and follow the instructions there.
[time-nuts] Re: LH "No usable sats"
Lux, Jim writes: > GPS orbit inclination is 55 degrees. If you plot the ground track, it > just touches 55N and 55S (i.e. there are times during the orbit when the > satellite is directly overhead the latitude = inclination), so you'd > have to be north (or south) of 55, to have an actual hole to the north. I live at 55N and I very much have a "hole to the north": http://phk.freebsd.dk/raga/sneak/fig1.png That also means I live in one of the two circles where the lattiude DOP is worst on the entire planet :-/ North of this circle, one can pick up sats on the far side of the hole. South of it, the hole occupies a smaller angle of azimuth. -- 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@lists.febo.com -- To unsubscribe send an email to time-nuts-le...@lists.febo.com To unsubscribe, go to and follow the instructions there.
[time-nuts] Re: HP 5372A opt. 040 FFT
Magnus Danielson writes: > You have EPROM-images of the normal FW? Yes, I have the following: 05372-80032-a7u16 05372-80033-a7u17 05372-80034-a7u18 05372-80035-a7u19 05372-80036-a7u52 05372-80037-a7u53 05372-80038-a7u54 05372-80039-a7u55 05373-80012-a7u16.bin 05373-80013-a7u17.bin 05373-80014-a7u18.bin 05373-80015-a7u19.bin 05373-80016-a7u52.bin 05373-80017-a7u53.bin 05373-80018-a7u54.bin 05373-80019-a7u55.bin The plan was to find out if one could simply plunk the 5373 FW in a 5372 but the current shortage of round tuits seems to continue unabated. If anybody feels like spelunking this firmware, I have the first iteration of a disassembly using https://github.com/bsdphk/PyReveng3 I can share. -- 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@lists.febo.com -- To unsubscribe send an email to time-nuts-le...@lists.febo.com To unsubscribe, go to and follow the instructions there.
[time-nuts] Re: HP 5372A opt. 040 FFT
Magnus Danielson writes: >I have a HP5372A with option 040. > >I would assume it's just another EPROM on the CPU board and a DIP-switch >setting to tell it's installed. > >I do not recall that I've seen an installation description of it, but it >should be fairly easy to identify which EPROM it should be. I strongly suspect that the 5372 has a command called "MREAD" to read a memory location, but I have not spent the time to reverse-engineer the command-parsing code enough to know how to invoke it. -- 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@lists.febo.com -- To unsubscribe send an email to time-nuts-le...@lists.febo.com To unsubscribe, go to and follow the instructions there.
[time-nuts] Re: Help ID'ing Frequency Standard
Magne Mæhre writes: > On 6/6/21 4:22 PM, John Ackermann N8UR wrote: > > Looking through the junk box I came upon a metal box labeled: > > > > Frequency Standard > > 05110-6014 > > Series 330 > > This eBay listing lists it as a 1 MHz HP frequency standard HP 5110 was the driver HP's first "cash-register" synthesizer. According to the HP5110A manual: 05110-6014 is "A2 Frequency Standard" And: 05110-6081 is "A3 Crystal Filter" https://bama.edebris.com/manuals/hp/5110a/ -- 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@lists.febo.com -- To unsubscribe send an email to time-nuts-le...@lists.febo.com To unsubscribe, go to and follow the instructions there.
[time-nuts] Re: PCTEL Timing Antenna with integrated GPS Receiver?
paul swed writes: > I have used some pctel antennas and they have been very good over the > years. (Very good = works). The model number at least gives you a hint if > RS 422 or 232. But if you can't find any further detail you are stuck with > one option. If you can figure out how to power it, it is pretty trivial to see if the data stream is single-ended (RS232) or differential (RS422) -- 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@lists.febo.com -- To unsubscribe send an email to time-nuts-le...@lists.febo.com To unsubscribe, go to and follow the instructions there.
[time-nuts] Re: PCTEL Timing Antenna with integrated GPS Receiver?
Mike Ingle writes: > Hi, in reading between the lines, are you saying that in practice, the > tempco of twisted pair is worse than the tempco of coax? I seriously doubt it. The change in coppers conductivity will not make that kind of difference in propagation time until the cables are measured in kilometers. I suspect the tempco comes from the RS-422 linedriver chip in the antenna or possibly from ceramic capacitors used to control its slew-rate. -- 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@lists.febo.com -- To unsubscribe send an email to time-nuts-le...@lists.febo.com To unsubscribe, go to and follow the instructions there.
[time-nuts] Re: PCTEL Timing Antenna with integrated GPS Receiver?
Douglas Baker writes: > I am trying to figure what the advantage is for an antenna with the > built-in GPS receiver is. On reason is that the running the twisted pairs through standard preinstalled lightning protection barriers is trivial, whereas certifying and finding space for a suitable lightning barrier for coax is a lot of work. Another advantage is that you can reuse existing cabling in rented buildings, instead of paying sometimes unbeliveable amounts to run your coax to the roof. (One of the main reasons Telecome Cesiums are still a thing, is that they often are much cheaper than renting space for a GPS antenna on the roof and cabled down to your kit in the basement.) However, one downside is that the PPS signals may suffer from tempco on the order of 1 µs/K. -- 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@lists.febo.com -- To unsubscribe send an email to time-nuts-le...@lists.febo.com To unsubscribe, go to and follow the instructions there.
[time-nuts] Re: Austron 2110 Electroluminescent Backlight Replacement
Ed Palmer writes: > It's easy to find replacement backlight panels, but are there any > physical or electrical issues that would cause problems? Not really. The contrast-adjustment may need tweaking, but otherwise it is plug -- 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@lists.febo.com -- To unsubscribe send an email to time-nuts-le...@lists.febo.com To unsubscribe, go to and follow the instructions there.
[time-nuts] Re: The amazing $5 timestamper, part 2: discovering a bug in my signal generator
Pluess, Tobias writes: > In my very first GPSDO I built, I used a STM32F303. This one had a quite > bad PLL stability, the frequency was varying over time in a sawtooth like > manner for some reason. It's called "spread-spectrum" and is done deliberately to game the EMI criteria for various certifications. By sweeping the frequency through a range, the peak energy of any one frequency, as averaged over a second, drops correspondingly. In many cases you can actually disable it, but you may have to punk the manufacturer quite hard to find out what bit to set or clear. -- 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@lists.febo.com -- To unsubscribe send an email to time-nuts-le...@lists.febo.com To unsubscribe, go to and follow the instructions there.
[time-nuts] Where leap-seconds went ?
Polar Drift in the 1990s Explained by Terrestrial Water Storage Changes: https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2020GL092114 -- 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@lists.febo.com -- To unsubscribe send an email to time-nuts-le...@lists.febo.com To unsubscribe, go to and follow the instructions there.
[time-nuts] Re: RE - before time was invented (Jan Boutsen)
Rex writes: > png = an image file format > php = a sort of more secure, advanced html (web page format) Actually "PHP" = "Perl for HomePages" and far more dangerous than html. -- 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@lists.febo.com -- To unsubscribe send an email to time-nuts-le...@lists.febo.com To unsubscribe, go to and follow the instructions there.
[time-nuts] Re: PN measurement thesis published
Detlef Schuecker via time-nuts writes: > German is a gorgeous language, I can assure ;)) Some time ago I asked one of my german friends what the german word was for "a wife who keeps talking to her husband long time after he left the room" ? After a moments pause he said "Christina" and burst into laughter :-) -- 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@lists.febo.com -- To unsubscribe send an email to time-nuts-le...@lists.febo.com To unsubscribe, go to and follow the instructions there.
[time-nuts] Re: Voltage Regulator
Shawn writes: > Question 2: Should I just replace the fan with a 24V unit and put a 10- > 20 ohm resistor inline to lower the speed? (probably the better choice > but I'd love to hear your suggestions.) I would replace the fan and see if I could get one with PWM control input ? -- 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@lists.febo.com -- To unsubscribe send an email to time-nuts-le...@lists.febo.com To unsubscribe, go to and follow the instructions there.
[time-nuts] Re: Sparkfun lists SA.35m
Dana Whitlow writes: > I knew about the use of the VCSEL, but I'd bet a good dinner that it's not a > Rubidium laser! I dont see anybody claiming that ? It is a laser interrogated rubidum frequency standard. The crucial part of the "Theory of Operation" is: The MAC is a passive atomic clock, incorporating the interrogation technique of Coher- ent Population Trapping (CPT) and operating upon the D1 optical resonance of atomic 87Rb to control the frequency […] The laser is mounted on a Thermal-Electric Cooler (TEC) for precise temperature control and is modulated by the microwave synthesizer at half the hyperfine frequency to produce sidebands in the laser spectrum. […] But more relevant: The product is EOL with last ship date of 20210420 -- 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@lists.febo.com -- To unsubscribe send an email to time-nuts-le...@lists.febo.com To unsubscribe, go to and follow the instructions there.
[time-nuts] Sparkfun lists SA.35m
I know it's not a particular outstanding atomic clock, but I was still surprised to see that Sparkfun lists the SA.35m for $1995... https://www.sparkfun.com/products/14830 Not in stock though... -- 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@lists.febo.com -- To unsubscribe send an email to time-nuts-le...@lists.febo.com To unsubscribe, go to and follow the instructions there.
[time-nuts] Re: Best frequency to start for GHz synth ?
Lux, Jim writes: >SAW devices were all the rage in the 80s for signal processing. Also certain CPUs: Some of the DEC Alpha's had a SAW oscillator next to the CPU chip to get a sufficiently pure clock-signal. They had a tempco from hell and were nearly impossible to wrangle with NTP. -- 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@lists.febo.com -- To unsubscribe send an email to time-nuts-le...@lists.febo.com To unsubscribe, go to and follow the instructions there.
[time-nuts] Re: Best frequency to start for GHz synth ?
>If you were going insane on a fountain, you likely would go with one of the >sapphire whispering gallery devices as the start of your chain. A good one >will blow a quartz crystal based part away …. That reminds me: I think the first quartz-crystal at Bell Labs was ring-shaped, do you know if that used a whispering gallery vibration mode ? -- 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@lists.febo.com -- To unsubscribe send an email to time-nuts-le...@lists.febo.com To unsubscribe, go to and follow the instructions there.
[time-nuts] Best frequency to start for GHz synth ?
Somewhat related to the discussion about GPSDO's I have a basic question: It used to be that 5MHz was the "hot spot" for crystals on the parameters we care about as time-nuts. Have advances in X-tal science changed that ? To make it a concrete question: If tasked with designing a Cs/Rb beam/fountain/whatever today, would one still start the synthesizer-chain at 5 MHz or would a higher frequency give better results ? -- 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@lists.febo.com -- To unsubscribe send an email to time-nuts-le...@lists.febo.com To unsubscribe, go to and follow the instructions there.
[time-nuts] Re: NPR: Researchers Are One Step Closer To Redefining The Second
Magnus Danielson writes: > A number of different approaches to new SI definition of Hz (was second) > was put forward, by among others me, and that range from a single > species to actually use a ensemble of species. The later would have a > benefit in using the advancement of several species and allow a larger > range of clock realizations. In one of his lectures Feynmann mentions that the energy levels of hydrogen have been calculated to 15 or 16 digits "from first principles". As far as I can figure out, that must have happened in the 1970'ies, which means it was probably done on one of Seymour Cray's designs. Hydrogen is obviously "the easy one", but even if the calculation scales to the power of four on the number of particles in the atom, we should still be well inside current super-computing capacities. Do you know if anybody has considered that as way to nail the frequencies ? -- 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@lists.febo.com -- To unsubscribe send an email to time-nuts-le...@lists.febo.com To unsubscribe, go to and follow the instructions there.
[time-nuts] Re: Water in connectors
Ole Petter Ronningen writes: > I am trying to chase down a 2-3-4 ns/day "anomaly" in a gpsdo I am working > on - it could be temperature sensitivity in the antenna (cheap patch > jobbie), [...] My first suspect would be temperature-sensitivity of the antenna & preamp. -- 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@lists.febo.com -- To unsubscribe send an email to time-nuts-le...@lists.febo.com To unsubscribe, go to and follow the instructions there.
[time-nuts] Re: Primary frequency standard
Lux, Jim writes: > Would a sundial (or zenith meridian crossing sensor) be a primary > standard for measurement of a solar day? Using Corbys "desert island" criteria, I think the answer is "yes(footnote)". Imagine you wake up, teleported to a different planet, about which you know nothing. First you need to establish the orientation of the planets rotational axis, because your sundials'gnomon' must be aligned parallel to it. You can do this by measuring the minimal and maximal noon elevation of the appearant sun over approx 60% of the planets "year". As a side effect you get a pretty good idea how long a "year" is in "days". Note that unlike this planet, there is no guarantee that these two numbers "mesh" well, or even which is the longer time interval[1]. Next you need to partition the scale in however many "hours" you want, but that is simply an invariant exercise of constructive geometry. So I think the answer is yes. However, the footnote is that your sundial is only primary on that particular latitude, and it is debatable if it is even that, if the planets rotation has any chaotic or higher order components, such as nutation and all that stuff. [1] See for instance Venus: A venus-day = 243 earth-days, but a venus-year = 225 earth-days. -- 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@lists.febo.com -- To unsubscribe send an email to time-nuts-le...@lists.febo.com To unsubscribe, go to and follow the instructions there.
[time-nuts] Re: Primary frequency standard
cdel...@juno.com writes: > In reference to: > > "It would be cool to say one has a "primary standard", So, I think > we should be careful with the term, it's get thrown around too lightly." > > Any of the hobby grade used Cesium standards is actually a Primary > frequency standard as it does meet the definition of: > > A frequency source that meets national standards for accuracy and > operates without the need for calibration against an external standard. That is the definition I was referring to, but as Magnus said, other sectors uses the term "primary" differently. -- 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@lists.febo.com -- To unsubscribe send an email to time-nuts-le...@lists.febo.com To unsubscribe, go to and follow the instructions there.
[time-nuts] Re: Long term ADEV of 5071
Attila Kinali writes: > Does someone of those who own a 5071 have long-term ADEV data? > I'm looking for multi-year data. While there are plenty of ADEV > plots online, most of them stop at 1Ms or even at 100ks. As I understand it, cesium beams are considered "primary" standards because once the ADEV hits the floor, it stays down there ? -- 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@lists.febo.com -- To unsubscribe send an email to time-nuts-le...@lists.febo.com To unsubscribe, go to and follow the instructions there.
[time-nuts] Re: Complex PLL
Detlef Schuecker via time-nuts writes: > Now I have to get rid of the atan, cos and sin functions. Just because you have complex frequencies does not mean you have to use both dimensions if you dont want to :-) Here is how I did it when I worked on Dave Mills' LORAN-C receiver: Step 1: Stop the rotation. Calculate deltavector from previous sample, figure out direction of rotation, output counteracting error signal roughly proportional to the delta vector length. Step 2: Bring angle < +/- PI/4 Look at the coordinates, output error signal to bring error signal "home". if you are not in a hurry, simply output a constant error term and detect when the vector rotate into +/- PI/4. Step 3: Sin(x) ~= x Use one of the coordinates as scalar input to the PI. -- 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@lists.febo.com -- To unsubscribe send an email to time-nuts-le...@lists.febo.com To unsubscribe, go to and follow the instructions there.
Re: [time-nuts] AN/URQ13 reference AT cut crystal? ==> Crystal Robot
Bob kb8tq writes: > Even if you went with a different material, moving any of the specs listed > above by 10X would be pretty amazing. That was the answer I expected :-) What about geometry ? Would things like whispering gallery improve things if we found a reasonable way to produce them ? -- 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@lists.febo.com To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there.
Re: [time-nuts] AN/URQ13 reference AT cut crystal? ==> Crystal Robot
Bob kb8tq writes: > > What properties would you program a quartz-crystal-prototyping robot > > to search for ? > > You very much want to (eventually) know about perturbations over > temperature for a given resonator design at a specific frequency. That > tends to be the 'gotcha' on a new cut. Running 100% of the production > through a 150C sweep at 1C per minute is *not* going to make the > production people (or the customer) happy. Yes, but that's once you have found a promising cut. I was asking: What would a promising cut be in the first place ? What properties could it have or be free from, that would make it relevant, as opposed to join the the hundreds of already "parked" cuts you mention ? > More Q is always nice. > Better ADEV never hurts > Lower aging is popular > Flat(er) temperature curves are attractive to an OCXO or TCXO designer So you only see incremental improvements, there are no unfound "philosophers stone" properties we think are there but havn't been able to locate yet ? -- 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@lists.febo.com To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there.
Re: [time-nuts] AN/URQ13 reference AT cut crystal?
Magnus Danielson writes: > Exactly which double-angle cut's they did before SC remains to be found. If somebody knows a crystallographer and is willing to sacrifice a unit, that is something which could be found out... -- 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@lists.febo.com To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there.
Re: [time-nuts] AN/URQ13 reference AT cut crystal?
Bob kb8tq writes: > Turning an “idea” into a production capable part involves making many > batches of test samples. Think in the thousands of batches and hundreds > of parts in each batch. You have a “search” process at the blank chopping > level. You also have a search at the resonator fabrication level. Getting the > chopping part right is only a small part of the whole process…. I realize this used to be a manual process, but today I would expect that you could automate a lot, of not most of it, if you wanted to ? It would still be a lot of work, and very expensive, but like biochemist trying out hundred of thousand compounds from their "libraries", robots really lower the cost. The real question must therefore be, if anybody reasonably expects there to be any superior "new" cuts to find in the first place ? What properties would you program a quartz-crystal-prototyping robot to search for ? Which parameter(s) of current crystal-cuts are "their weak point" ? -- 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@lists.febo.com To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there.
Re: [time-nuts] Daft idea with the National Grid
John Moran, Scawby Design writes: > "If you happen to own something like a steel mill running electric > > furnaces or an aluminum refinery, so you can manipulate the load..." > > Sometime in the late '80s, my first decent sized computer system came on line > [...] We had the same problem when we installed the largest non-university UNIX computer in Denmark in the late 1980'ies. In our case it was our heavy-weight receptionist getting into the antique lift, heading for the canteen on the top floor. -- 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@lists.febo.com To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there.
Re: [time-nuts] Daft idea with the National Grid
Hal Murray writes: > I'd expect an ADEV type pattern. For long tau, the wander in the system will > dominate. We have lots of long term data so should be able to plot that part > of the graph. I did that some years ago: The Nordic grid bottomed out around 1e-10, with a frequency error less than 2e-11 measured over 45 years. > How much energy is in the rotating turbine and generator? That should > provide > a lower limit on the time constant of the control loop. Answer A: Surprisningly much (do the math on 50 tons of iron, 1m diameter at 3000 or 3600 RPM) Answer B: Not enough to keep modern grids stable (Google term: "Low inertia conditions") -- 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@lists.febo.com To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there.
Re: [time-nuts] Daft idea with the National Grid
Lux, Jim writes: > If you happen to own something like a steel mill running electric > furnaces or an aluminum refinery, so you can manipulate the load... More scary: Several independent studies have shown that even relatively moderate bot-nets in the hands of somebody who knows the math of grid stability would mean no grid stability. -- 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@lists.febo.com To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there.
Re: [time-nuts] Daft idea with the National Grid
Andy Talbot writes: > Not sure what the time constant of the grid control is, but for* small > signals* I doubt it can be faster than a few minutes. There are generally spaking two time constants, the physical and the human. The physical time constants are probably best understood as water in a bucket: If you kick it, complex ripples happen but eventually die out. The timeconstant is generally order of five or ten cycles, unless you make a short, those are much faster. Mechanisms: Huge lumps of rotating iron, lots of switch-mode equipment (including solar, wind mills and HVDC converters), magnetic hysteresis in really big transformers, Maxwells/Telegraphers equations on long cables. Unless the grid is on the verge of collapsing, the human time constant is around 15 minutes. Mechanism: People making mostly financial decisions. As for your experiment, unless you use a psedurandom pattern, you stand no chance of detecting a pattern. I expect you may be able to show a bigger effect than you hypothesize because the grid is not that "stiff". Unless your house is right next to a big plant, there are five to ten transformers between you and the power producer, and all of those "delay" the phase in response to increasing load. Your primary singal will therefore be phase-shift rather than frequency- shift, which means your switching will have to be slow enough that you can measure the difference between them. PS: If you get friendly with people at grid control, they will send you a copy of a pile of laplace equations from hell, which they use to model the grid, and you can start by plugging your experiment into them. It wont be pretty. -- 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@lists.febo.com To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there.
Re: [time-nuts] Raspberry Pi 4 oscillator replacement
Trent Piepho writes: > On Thu, Feb 4, 2021 at 4:09 PM Hal Murray wrote: > I've not seen one where the input clock frequency had much of a range. > It might be 24-26 MHz, but never 10 - 52 MHz. Usually if you read very closely, you will find a wide range is OK but a footnote to the effect that they only warrant USB will work at the following specific frequencies. -- 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@lists.febo.com To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there.
Re: [time-nuts] Raspberry Pi 4 oscillator replacement
Hal Murray writes: > > p...@phk.freebsd.dk said: > > I dont know if the datasheet for the Rpi4 is available to check what the > > requirements are, but you should probably expect to need some kind of PLL > > chip to deliver a clean 54 MHz on the RPi4, locked to your external > > frequency. > > Plan B would be to avoid the 10=>54 PLL chip by reprogramming the software > that sets up the internal PLLs to run off 10 MHz rather than 54MHz. That may > not be possible. It depends on how the clocking inside the ARM chip is setup. One of the big problems with the RPi family is that only a skeleton datasheet has been made available - because: Qualcom magic sauce recipe or similar verbiage.. I've heard a lot of gripes about precisely the clock circuits being underdocumented, but I have deliberately stayed well clear of the details. -- 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@lists.febo.com To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there.
Re: [time-nuts] Raspberry Pi 4 oscillator replacement
Avamander writes: > I was wondering if anyone here has replaced the 54 MHz oscillator on the > Raspberry Pi 4 with a GNSS-disciplined rubidium standard? An overkill > upgrade, but is technically doable? What hardware would it take in addition > to a GNSS-disciplined rubidium standard and a Pi 4? This trick has gotten a lot harder over the decades. Higher and higher PLL ratios in the chips means they demand more of their clock signal. I dont know if the datasheet for the Rpi4 is available to check what the requirements are, but you should probably expect to need some kind of PLL chip to deliver a clean 54 MHz on the RPi4, locked to your external frequency. -- 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@lists.febo.com To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there.
[time-nuts] Cheap 5370B on german fleabay
In case any timenuts in EU still do not have one... -- 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@lists.febo.com To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there.
Re: [time-nuts] ISS NTP operation problems.
Hal Murray writes:
> There is a huff-puff filter, I think it's optional.
I think it is more likely that the median-filter is causing trouble.
If you let the poll-rate ramp all the way up to 1024 seconds, the
median filter can get "stuck" for almost an hour before it notices
that something is horribly wrong[1].
These days there are almost no circumstances under which you should not
clamp your poll-rate to one minute "server bla maxpoll 6"
On a strange path like the ISS, I would clamp it to the minimum
16 seconds ('maxpoll 4').
When the backbone of the ARPAnet was 56kbit/s, being able to ramp
up to 1024 seconds poll rate made sense. It never makes sense now.
Poul-Henning
[1] The median filter should be automatically disabled and the most
recent sample used, if the samples in the shift register are
mononotonic or spread too much. That's another change I never
managed to "sell" to Dave Mills.
--
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.
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Re: [time-nuts] ISS NTP operation problems.
Hal Murray writes: > NTP likes symmetric delays. That's strictly speaking to true: NTP *assumes* symmetric delays. If your path is not symmetric, you can a time offset of half the asymmetry. If your path is stable you can calibrate that out with a temporary reference or something. If you path is not stable, or you flip between different servers with different delays and/or assymetries, your time will not be stable. -- 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@lists.febo.com To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there.
Re: [time-nuts] ISS NTP operation problems.
Steven Sommars writes: > There is a ~600-700 msec RTT between the ground NTP servers and the ISS NTP > server. How stable is that ? Is there a lot of sample-to-sample jitter ? Have they clamped the poll-rate on the S2 ? -- 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@lists.febo.com To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there.
Re: [time-nuts] x86 CPU Timekeeping and clock generation
Tom Van Baak writes: >If you do your kernel timekeeping in integers and modulus arithmetic you >are essentially doing cycle counting and the kernel will keep perfect >time relative to the external oscillator. So that should be the goal. >Not e-6, not e-9, not e-10, but perfect cycle counting. Consider this a >strong plea for someone in both BSD- and Linux- land to pull that off. But not all of us have masers Tom :-) Problem is, you still need fractions when NTP tells you that the X-tal is 7.1PPM off frequency. When I did timecounters, I tried a couple of things of the sort you suggest, but when I benchmarked it, a single brutal 64 bit multiply with a 32bit shift invariably ran faster, had more predictable latency, worked with any frequency the hardware happened to have and did NTP's bidding: http://phk.freebsd.dk/pubs/timecounter.pdf -- 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@lists.febo.com To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there.
Re: [time-nuts] 20th year of time nuts mailing list
Magnus Danielson writes: So what does an analog synthesizer's allan deviation look like ? :-) -- 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@lists.febo.com To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there.
Re: [time-nuts] 20th year of time nuts mailing list
Tom Van Baak writes: > One reason I've been looking forward to 2021 is that it's now officially > the 20th year of the time nuts mailing list. ...and twenty years feeling part of a community, rather than like an utter goof-ball, for caring about nanoseconds :-) I also think it is fair to say that our community being already up and running, made a lot of other peoples lives easier, once the rest of the world caught up with precision timing. Stay safe! Poul-Henning -- 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@lists.febo.com To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there.
Re: [time-nuts] TECs in cooling below ambient
Bob kb8tq writes: > I think you will find that things work out a whole lot better if you target > something > just above room temp. If your room runs 22 +/- 3 C , a set point of 27C > likely results > in better operation than 17C. This decision should be based on expected abnormal situations. If your ambient might reach 35-40°C when cooling fails, running lower than ambient will cope, running higher than ambient will not. If your ambient might drop to -20°C when the heating fails or the lid is opened, then running higher than ambient is the robust thing to do. And as others have said: If you run lower than ambient, you have to plan for condensation. Bidirectional TEC setups need special attention: You have to take into account the 3:1 efficiency difference between heating:cooling, and only seldom, and then gently, switch direction, in order to reduce thermal stress in the TEC element. A sound bidirectional design use an inner oven to keep the payload temperature constant, and use a more coarse outer TEC loop only to keep the oven's operating conditions inside a narrow window. That way the TEC can operate with a suitably slow time-constant. -- 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@lists.febo.com To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there.
Re: [time-nuts] DHS Resilient PNT Conformance Framework
Magnus Danielson writes: > In the end, if this takes off, what it does is that it creates a market > for devices to meet these requirements. [...] Sorry Magnus but I don't belive a word of it. This is simply a clever ploy from your side, to get tons of perfectly fine GPSDO's dumped cheaply onto eBay because "they no longer comply with government regulations" :-) Merry X-mas, and stay safe everybody! Poul-Henning -- 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@lists.febo.com To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there.
Re: [time-nuts] DHS Resilient PNT Conformance Framework
Bob kb8tq writes: > I have seen cases of “goes away until power cycled”. I have not seen any > cases of > “goes away forever” other than the obvious ( = feed it an insane almanac > that prevents > if from ever locking up ). Even with that said, I have not seen an example ot > that sort of > thing living through a hard reset … ( which isn’t quite the same thing as a > power cycle ). I have: An corrupt alamanac in NV storage contained something which made a particular GPS receiver divide by zero, shit its pants and wedge during startup. The post mortem report said that the alamanac passed the "technical consistency checks", by which I suppose they mean the Hamming code, but it still caused a divide by zero. This incident is the reasons why GPS receivers in some critical applications are not allowed to have NV storage for "operational purposes" and get the almanac downloaded from the attached systems at startup. -- 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@lists.febo.com To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there.
Re: [time-nuts] Congratulations to David Allan
Richard (Rick) Karlquist writes: > If I had thought about it, I would have assumed > David made fellow decades ago. He was already > a legend around the HP Precision Frequency section > when I started at HP 40 years ago. Maybe he was > just too modest and didn't do enough self > promotion. Anyway, I'm happy that the powers > that be finally corrected this situation. Maybe the finally recognized his revision of General Relativity ? http://www.allanstime.com/UnifiedFieldTheory/gravity.htm -- 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@lists.febo.com To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there.
Re: [time-nuts] HP 5065 Rb update
Dana Whitlow writes: > Would it be feasible to add a smaller winding around the outside of > the existing C-field winding, and drive it from something other than > the crude rheostat circuit? That would be on the outside of the mu-metal screen and therefore a really bad idea. -- 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@lists.febo.com To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there.
Re: [time-nuts] HP 5065 Rb update
paul swed writes: > Bob by the way did move the unit around no effect. That only shows if the surroundings contribute with a magnetic field, it does not tell you if the mu-metal shield around the physics package has been magnetized. I would still try to change the polarity of the C-field current. -- 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@lists.febo.com To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there.
