Re: [time-nuts] Holdover, RTC for Pi as NTP GPS source

tpie...@gmail.com said: > Forget about accurate time from the RTC's registers. The slowness and > variably in I2C is quite poor and most of them don't even have sub-second > resolution when read or written. If your RTC has a PPS output, you can read the registers to get the coarse time, then w

Re: [time-nuts] Holdover, RTC for Pi as NTP GPS source

Some of the DS chips have a square wave input that can be fed from a GPS PPS and the RTC will discipline itself. It can also produce a PPS when the GPS stops. The question is, is NTP's holdover on the system clock better than NTP disciplining the system clock with an RTC PPS. I'd guess not. For

Re: [time-nuts] Oscillators and Ovens

On 11/1/17 1:38 PM, Hal Murray wrote: In general, OCXOs have crystals with high Q -> low phase noise, especially compared to a TCXO, which *can't* have high Q, or the temperature compensation circuit can't do it's work. I don't understand that. Why can't I build a high Q TCXO? I don't nee

[time-nuts] Trimble UCCM weird behaviour

That looks like the device is defective. I'd see if the seller will replace it. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.

Re: [time-nuts] Designing an embedded precision GPS time

On 11/1/17 12:13 PM, Adrian Godwin wrote: How do those compare with vectron's part : ? https://www.vectron.com/products/ocxo/mx-503.htm That part is interesting, but the phase noise (-124 dBc @ 100 Hz) isn't particularly impressive compared to a middle of the road OCXO (-155dBc at 100Hz)

Re: [time-nuts] Oscillators and Ovens

Hi As mentioned in Rick’s post, it’s not really Q, it’s the motional capacitance that is the issue. Even if you resonate out C0, you still have to deal with Cm. The only practical high Q designs for crystals are very low Cm resonators. Yes, if you could do a design that had Rm of 0.1 ohms it c

Re: [time-nuts] Oscillators and Ovens

On 11/1/2017 3:44 PM, Dana Whitlow wrote: Bob, This discussion is getting really interesting. In thinking about the crystal Q versus tuning range conundrum, two (presumably-overlapping) concerns come to mind: 1. The motional parameters of a high-Q crystal are such that the external network

Re: [time-nuts] Oscillators and Ovens

Bob, This discussion is getting really interesting. In thinking about the crystal Q versus tuning range conundrum, two (presumably-overlapping) concerns come to mind: 1. The motional parameters of a high-Q crystal are such that the external network needed to pull it very far would be wholly

Re: [time-nuts] Holdover, RTC for Pi as NTP GPS source

On Wed, Nov 1, 2017 at 7:21 PM, MLewis wrote: > > And the DS3231 has: > - a 32K output, and > - an Active-Low-Interrupt/SQW output that can be set to PPS. > It's unclear to me how to sync the DS3231 PPS to the GPS PPS, or if that > can be done. > > > The DS3231 has an 8 bit register that will cha

Re: [time-nuts] Holdover, RTC for Pi as NTP GPS source

Hi The normal NTP kernel does a pretty good job in “flywheel” mode. For modest outages, it’s quite adequate. Bob > On Nov 1, 2017, at 7:21 PM, MLewis wrote: > > Is this a workable or worthwhile strategy?: > - RTC providing date & time to second to system on boot > - RTC frequency output driv

Re: [time-nuts] HP 5335A Question

Hi The gate time on a 5335 can be set via GPIB. It can be set to some *very* long gates (well past 100 seconds). When you do this, the data reported on GPIB does “stretch” to cover the added digits. The problem is that there are internal register overflows. The designers did not anticipate needi

Re: [time-nuts] Holdover, RTC for Pi as NTP GPS source

Is this a workable or worthwhile strategy?: - RTC providing date & time to second to system on boot - RTC frequency output driving a counter/divider to produce PPS - GPS module providing UTC PPS - GPS module's secondary PPS disciplining the RTC-counter-divider PPS by resetting the RTC's counter/d

Re: [time-nuts] Holdover, RTC for Pi as NTP GPS source

For this apparatus, a lepton is a lepton is a lepton. If the standard model is complete/correct and neutrinos are massless, they can be ignored as a potential threat to our project. They'll just zip through on their way to wherever. The likelihood of a particle interaction is so minute that we can

Re: [time-nuts] Designing an embedded precision GPS time

Regarding spread spectrum issues: You might be lucky to find (or have) SSCG implementation that is reasonably stable. I suspect most are - because it is easy to generate hershey kiss spectrum based on SM, LUT or some sort of multi-level LFSRs. I don't know what this means - these are some ran

[time-nuts] HP 5335A Question

I have an HP 5335A and I am measuring the output of a Suzler 2.5. I >have a GPSDO 10 MHz input into the back of the 5335A. >There is mention in the manual that the counter can display 11 or 12 >digits (in addition to the two Exponent digits). I presently have it >displaying nine digits. >Does

Re: [time-nuts] Room temperature control (was: Holdover, RTC for Pi as NTP GPS source)

You would be amazed by the effectiveness of installing a small fan, mounted parallel to the wall, to create a slow whirlpool circulation in the room. Just a 10 w computer fan. If the air velocity is below 0.3 m/s it is hardly perceptible. That takes about 30 seconds to get around the room. The r

Re: [time-nuts] Oscillators and Ovens

Hi A high Q crystal by design is very difficult to tune. Putting it in a circuit that will swing it far enough to compensate it degrades the Q. In addition, thermal noise will come into the compensation circuit (even if it is noise free) and degrade things. Bob > On Nov 1, 2017, at 4:38 PM,

Re: [time-nuts] Designing an embedded precision GPS time

Hi > On Nov 1, 2017, at 1:11 PM, tn...@joshreply.com wrote: > >> While crystal curves are indeed cubic, there are higher order terms in >> the curve. The “why” is something people get to write papers on. If you >> are trying to compensate to tight specs, you will see all sorts of >> stuff. It

Re: [time-nuts] Holdover, RTC for Pi as NTP GPS source

Super-lumious or non-speeding neutrinos? Cheers, Magnus On 11/01/2017 04:30 PM, William H. Fite wrote: Oh crap, I forgot about neutrinos. On Wednesday, November 1, 2017, William H. Fite > wrote: Inside a three-meter thick sphere of lead and mu-metal, pressure

Re: [time-nuts] Holdover, RTC for Pi as NTP GPS source

That sloppy temperaturestabilization??? Also, we would need to care about the lead-poisoning of the mu-metal and the needed re-alignment... ehm... ah well. Cheers, Magnus On 11/01/2017 04:29 PM, William H. Fite wrote: Inside a three-meter thick sphere of lead and mu-metal, pressure pulled do

Re: [time-nuts] Designing an embedded precision GPS time

> On Nov 01, 2017, at 05:39, Attila Kinali wrote: > > 6-10µs is the interrupt latency of linux on ARM SoC. I guess, to get > below that you'd have to tweak the kernel a bit. Which should not > be that difficult. Definitly simpler than writing your own IP and NTP > stack from scratch. Just tweak

Re: [time-nuts] Holdover, RTC for Pi as NTP GPS source

This GPS/Pi server, with possibly a second copy, are intended to be the sole NTP sources for a local network. No going out to the internet. My intent was to discipline the RTC, so it's current when needed. If I had to do a cold boot without GPS available, I'd want the RTC to be current. I had

Re: [time-nuts] Holdover, RTC for Pi as NTP GPS source

>> How are you planning on making ntp use the RTC as a secondary >> time source? I don't see that as a supported refclk driver. > hadn't got there yet likely using NTPsec, as the codebase is available if a > driver or generic driver won't work The PPS driver expects the pulse to be on the seco

Re: [time-nuts] Oscillators and Ovens

On Wed, November 1, 2017 3:38 pm, Hal Murray wrote: > >> In general, OCXOs have crystals with high Q -> low phase noise, >> especially >> compared to a TCXO, which *can't* have high Q, or the temperature >> compensation circuit can't do it's work. > > I don't understand that. Why can't I build a

Re: [time-nuts] Holdover, RTC for Pi as NTP GPS source

On Wed, November 1, 2017 3:17 pm, MLewis wrote: > hadn't got there yet Your RTC is not likely to be tightly synchronized to NTP time, so there is a high probability that trying to use RTC as a secondary time source will actually make the system worse than just riding through using the NTP estimate

Re: [time-nuts] Oscillators and Ovens

> In general, OCXOs have crystals with high Q -> low phase noise, especially > compared to a TCXO, which *can't* have high Q, or the temperature > compensation circuit can't do it's work. I don't understand that. Why can't I build a high Q TCXO? I don't need to change the compensation very

Re: [time-nuts] Holdover, RTC for Pi as NTP GPS source

hadn't got there yet likely using NTPsec, as the codebase is available if a driver or generic driver won't work https://docs.ntpsec.org/latest/driver_howto.html On 01/11/2017 12:38 PM, Chris Caudle wrote: On Tue, October 31, 2017 9:27 pm, MLewis wrote: I'm intending to add a "precision" (well

[time-nuts] Designing an embedded precision GPS time

Trying to further compensate a TCXO can be a losing proposition. Your control loop and the TCXO's control loop can easily get their panties all twisted in a wad. You are probably better off compensating a plain XO... which yields a TCXO that you can actually manipulate to your hearts conten

Re: [time-nuts] Designing an embedded precision GPS time

tn...@joshreply.com said: > I am trying to build the most accurate fee running, low power time base I can. > I am trying to beat existing products like the Dallas DS3231 and Micro > Crystal RV-8803-C7-32.768kHz-3PPM-TA-QC, which use (I think) a similar > strategy. I’m hoping I can beat them by

Re: [time-nuts] Room temperature control (was: Holdover, RTC for Pi as NTP GPS source)

In message <20171101190841.366058d77e544d256b862...@kinali.ch>, Attila Kinali w rites: >The best we can do today is to have a well insulated room (no windows >with whith unknown power flows) and measure the temperature at a few >strategically choosen points. Then control the heat influx a

Re: [time-nuts] Room temperature control (was: Holdover, RTC for Pi as NTP GPS source)

I remember visiting the metrology lab in HP Palo Alto (Glen Whatshisname) when I worked for them in the early 70s. There was a set of toggle switches on the wall; for every person inside, one switch was turned on. I don't know how well it worked but apparently, well enough for 1970s-vintage metrolo

Re: [time-nuts] Designing an embedded precision GPS time

How do those compare with vectron's part : ? https://www.vectron.com/products/ocxo/mx-503.htm There's also this patent. http://www.google.sr/patents/US20020005765 I don't really know if that's valid - it seems to propose something similar to the numerically-compensated oscillator in my rather

Re: [time-nuts] Holdover, RTC for Pi as NTP GPS source

Tbolt is a good oneBert Kehren Sent from my Galaxy Tab® A Original message From: David J Taylor via time-nuts Date: 11/1/17 12:07 PM (GMT-05:00) To: time-nuts@febo.com Subject: Re: [time-nuts] Holdover, RTC for Pi as NTP GPS source From: Mark Sims I have an analytical bal

Re: [time-nuts] Oscillators and Ovens

On 11/1/17 10:59 AM, Attila Kinali wrote: Hi Jim, On Wed, 1 Nov 2017 06:17:31 -0700 jimlux wrote: That's why I wish they'd sell OCXOs, cheap, without the oven. Or maybe look for regular XO (no TC). Those might have a more "pure" (read lower order) freq vs temp characteristic. It feels lik

Re: [time-nuts] Designing an embedded precision GPS time

Hoi Leo, On Wed, 1 Nov 2017 15:35:46 + Leo Bodnar wrote: > > From: Attila Kinali > > What you should do is basically system identification and adaptive control. > > Thanks for your advice, Attila, I am going to google this tonight. This is > exciting! Before you dive into sys-id and ad

[time-nuts] Room temperature control (was: Holdover, RTC for Pi as NTP GPS source)

On Wed, 1 Nov 2017 15:37:38 +0100 Magnus Danielson wrote: > Silly people > want a relative comfortable temperature and well, building A/C is > typically bang/bang regulated so you get what you paid for. My short stint in the HVAC business taught me, that it's surprisingly difficult to stabili

[time-nuts] Oscillators and Ovens (was: Designing an embedded precision GPS time)

Hi Jim, On Wed, 1 Nov 2017 06:17:31 -0700 jimlux wrote: > That's why I wish they'd sell OCXOs, cheap, without the oven. Or maybe > look for regular XO (no TC). Those might have a more "pure" (read lower > order) freq vs temp characteristic. It feels like I have asked this before, but I cann

Re: [time-nuts] Holdover, RTC for Pi as NTP GPS source

From: David C. Partridge ? RasPi-4? Not released until 2019 AFAIK ... I have RasPi-3 === My Raspberry Pi #1 and Raspberry Pi #4. See: http://www.satsignal.eu/mrtg/performance_ntp.php Cheers, David -- SatSignal Software - Quality software written to your requirements Web

Re: [time-nuts] Designing an embedded precision GPS time

>While crystal curves are indeed cubic, there are higher order terms in >the curve. The “why” is something people get to write papers on. If you >are trying to compensate to tight specs, you will see all sorts of >stuff. It is not at all uncommon to see >9th order curves residual curves. >Indee

Re: [time-nuts] Holdover, RTC for Pi as NTP GPS source

? RasPi-4? Not released until 2019 AFAIK ... I have RasPi-3 -Original Message- From: time-nuts [mailto:time-nuts-boun...@febo.com] On Behalf Of David J Taylor via time-nuts Sent: 01 November 2017 16:08 To: time-nuts@febo.com Subject: Re: [time-nuts] Holdover, RTC for Pi as NTP GPS source

Re: [time-nuts] Holdover, RTC for Pi as NTP GPS source

From: Mark Sims I have an analytical balance that reads down to micrograms. The weigh chamber is surrounded by three layers of IR absorbing glass so that radiated body heat does not induce convection currents in the air. I worked on a balance that had nanogram resolution (mostly wishful th

[time-nuts] Holdover, RTC for Pi as NTP GPS source

I have an analytical balance that reads down to micrograms. The weigh chamber is surrounded by three layers of IR absorbing glass so that radiated body heat does not induce convection currents in the air. I worked on a balance that had nanogram resolution (mostly wishful thinking in that spe

Re: [time-nuts] Designing an embedded precision GPS time

> From: Attila Kinali > What you should do is basically system identification and adaptive control. Thanks for your advice, Attila, I am going to google this tonight. This is exciting! Leo ___ time-nuts mailing list -- time-nuts@febo.com To unsubscr

Re: [time-nuts] Holdover, RTC for Pi as NTP GPS source

Oh crap, I forgot about neutrinos. On Wednesday, November 1, 2017, William H. Fite wrote: > Inside a three-meter thick sphere of lead and mu-metal, pressure pulled > down to .01 mTorr , temperature regulated to .001 degree C, > operating in total darkness and absolute silence, aligned wi

Re: [time-nuts] Designing an embedded precision GPS time

Antenna is a Tallysman TW4722. I'll try a different antenna later. If nothing else, right now I've got regular dropouts for failsafe testing... But I feel a better solution is a reliable holdover capability, which I should have anyway for failsafe. Thanks, Michael On 01/11/2017 10:22 AM,

Re: [time-nuts] Holdover, RTC for Pi as NTP GPS source

Inside a three-meter thick sphere of lead and mu-metal, pressure pulled down to .01 mTorr , temperature regulated to .001 degree C, operating in total darkness and absolute silence, aligned with the galactic axis of rotation, and situated 20 light years from the nearest star. That should s

Re: [time-nuts] Designing an embedded precision GPS time

One can minimize temperature change which affects things like regulated voltages, CMOS transition points for those converting sine to TTL with gates, etc. in addition to the oscillators. The November issue of Nuts and Volts Magazine has an article on an Arduino based PID controller which might i

Re: [time-nuts] Holdover, RTC for Pi as NTP GPS source

Hi, On 11/01/2017 04:03 PM, jimlux wrote: On 11/1/17 7:37 AM, Magnus Danielson wrote: Hi,  Silly people want a relative comfortable temperature and well, building A/C is typically bang/bang regulated so you get what you paid for. wouldn't a true time-nut be in a basically isothermal cav

Re: [time-nuts] Holdover, RTC for Pi as NTP GPS source

Surely he'd want to be in an isolating suit to avoid introducing a nasty warm body into his nice stable cave ? On Wed, Nov 1, 2017 at 3:03 PM, jimlux wrote: > On 11/1/17 7:37 AM, Magnus Danielson wrote: > >> Hi, >> >> Silly people > >> want a relative comfortable temperature and well, building

Re: [time-nuts] Holdover, RTC for Pi as NTP GPS source

On 11/1/17 7:37 AM, Magnus Danielson wrote: Hi, Silly people want a relative comfortable temperature and well, building A/C is typically bang/bang regulated so you get what you paid for. wouldn't a true time-nut be in a basically isothermal cave at 10C far underground, and just follow

Re: [time-nuts] Holdover, RTC for Pi as NTP GPS source

Hi, This is also true for labs. One NMI lab I visited had issues with their 5071As and H-maser clocks. It took some time to correlate it, but it turned out to correlate with the florescent lamps in the lab and people walking in and out. Changing these lamps to milder labs removed that disturb

Re: [time-nuts] Designing an embedded precision GPS time

Hi Ok, local RF interference sounds like a significant part of the problem. I would suggest that swapping antennas might make sense. Not all “super interference rejecting” antennas are created equal. Bob > On Nov 1, 2017, at 9:55 AM, MLewis wrote: > > I wish. > > It's using GLO and GPS now

Re: [time-nuts] Designing an embedded precision GPS time

I wish. It's using GLO and GPS now, yet gets reception dropouts. That's why I'm hoping to eventually get the firmware update that will add GAL to the mix. I had anticipated reception issues, which is why I went with the M8T for its sensitivity, multi-constellation and it's a timing module so

Re: [time-nuts] Designing an embedded precision GPS time

Hi > On Nov 1, 2017, at 9:17 AM, jimlux wrote: > > On 11/1/17 6:01 AM, Bob kb8tq wrote: >> Hi >> Unfortunately not all TCXO’s are created equal. It depends a bit on the >> original intended use. I’d bet it also depends a bit on the original target >> price. Perturbations (frequency jumps) over

Re: [time-nuts] Designing an embedded precision GPS time

On 11/1/17 6:01 AM, Bob kb8tq wrote: Hi Unfortunately not all TCXO’s are created equal. It depends a bit on the original intended use. I’d bet it also depends a bit on the original target price. Perturbations (frequency jumps) over temperature are one “feature” that might be present. Hysteresis

Re: [time-nuts] Holdover, RTC for Pi as NTP GPS source

Hi > On Nov 1, 2017, at 12:14 AM, MLewis wrote: > > (I suspect this is drifting from the original thread too much, so new subject) > > Temperature ranges from 65F to 78F, with the potential for drafts, but is > more typically 76F. The gotcha in a real environment often involves people. They

Re: [time-nuts] Designing an embedded precision GPS time

Hi > On Oct 31, 2017, at 11:33 PM, Leo Bodnar wrote: > >> From: Bob kb8tq >> Working all this back into a holdover spec in an unknown temperature >> environment is not at all easy. >> Bob > > > This is true, it is too easy to multiply figures from the datasheet and then > start believing in

Re: [time-nuts] Designing an embedded precision GPS time

Hi Unfortunately not all TCXO’s are created equal. It depends a bit on the original intended use. I’d bet it also depends a bit on the original target price. Perturbations (frequency jumps) over temperature are one “feature” that might be present. Hysteresis at half the temperature spec is anoth

Re: [time-nuts] Designing an embedded precision GPS time

Hi For NTP levels of accuracy Glonas is quite fine. Combining that with GPS should get you a pretty good “time source” even under your extreme conditions. Bob > On Oct 31, 2017, at 11:14 PM, MLewis wrote: > > I'm stuck with a near ground level antenna site (~16" above grade?), with > half a s

Re: [time-nuts] Designing an embedded precision GPS time

On Tue, 31 Oct 2017 22:13:01 -0700 Denny Page wrote: > Depends upon the results you are trying to achieve. Using Linux pretty > much guarantees that your server clock will be off by 6-10us, with > substantial variance. Even with a good nic that supports hardware > timestamping, the variance will

Re: [time-nuts] Designing an embedded precision GPS time

On Wed, 1 Nov 2017 04:06:06 + Leo Bodnar wrote: > > From: Attila Kinali > > Basically, all you have to do is use an SBC that runs linux and has > > a GPIO with an interrupt to act as a PPS input. Attach a GPS receiver > > and you are almost done. The cheapest option are probably the i.MX233

[time-nuts] Trimble UCCM weird behaviour

Hi, I recently bought a Trimble UCCM from ebay and it shows a rather strange behaviour. Beside the unit having a low sensitivity (the LEA-5 I have considers satellites having a good C/N0 where the trimble cannot even track them) it does not seem to properly lock. Periodically it steers the DAC out