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devel / comp.protocols.time.ntp / Re: gpsd no PPS output - Solved

SubjectAuthor
* gpsd no PPS outputJim Pennino
+* Re: gpsd no PPS outputchris
|+* Re: gpsd no PPS outputWilliam Unruh
||`* Re: gpsd no PPS outputJim Pennino
|| `* Re: gpsd no PPS outputWilliam Unruh
||  `- Re: gpsd no PPS outputJim Pennino
|`* Re: gpsd no PPS outputJim Pennino
| `* Re: gpsd no PPS outputchris
|  +* Re: gpsd no PPS outputchris
|  |`- Re: gpsd no PPS outputJim Pennino
|  +* Re: gpsd no PPS outputWilliam Unruh
|  |+- Re: gpsd no PPS outputchris
|  |`- Re: gpsd no PPS outputDavid Woolley
|  `* Re: gpsd no PPS outputJim Pennino
|   +* Re: gpsd no PPS outputWilliam Unruh
|   |`* Re: gpsd no PPS outputJim Pennino
|   | `* Re: gpsd no PPS outputchris
|   |  +* Re: gpsd no PPS outputchris
|   |  |`- Re: gpsd no PPS outputJim Pennino
|   |  `* Re: gpsd no PPS outputJim Pennino
|   |   `* Re: gpsd no PPS outputWilliam Unruh
|   |    `* Re: gpsd no PPS outputJim Pennino
|   |     `* Re: gpsd no PPS outputchris
|   |      `* Re: gpsd no PPS outputJim Pennino
|   |       `* Re: gpsd no PPS outputchris
|   |        `* Re: gpsd no PPS outputJim Pennino
|   |         `* Re: gpsd no PPS outputchris
|   |          `* Re: gpsd no PPS outputJim Pennino
|   |           `* Re: gpsd no PPS outputWilliam Unruh
|   |            `* Re: gpsd no PPS outputJim Pennino
|   |             `* Re: gpsd no PPS outputWilliam Unruh
|   |              `- Re: gpsd no PPS outputJim Pennino
|   `* Re: gpsd no PPS outputchris
|    +* Re: gpsd no PPS outputJim Pennino
|    |`* Re: gpsd no PPS outputchris
|    | `* Re: gpsd no PPS outputJim Pennino
|    |  `* Re: gpsd no PPS outputchris
|    |   `- Re: gpsd no PPS outputJim Pennino
|    `* Re: gpsd no PPS outputDavid Woolley
|     `- Re: gpsd no PPS outputchris
+* Re: gpsd no PPS outputMiroslav Lichvar
|`* Re: gpsd no PPS outputJim Pennino
| `* Re: gpsd no PPS outputMiroslav Lichvar
|  `- Re: gpsd no PPS outputJim Pennino
`* Re: gpsd no PPS output - SolvedJim Pennino
 +* Re: gpsd no PPS output - SolvedWilliam Unruh
 |`* Re: gpsd no PPS output - SolvedJim Pennino
 | `* Re: gpsd no PPS output - SolvedWilliam Unruh
 |  `* Re: gpsd no PPS output - SolvedJim Pennino
 |   +* Re: gpsd no PPS output - SolvedWilliam Unruh
 |   |`- Re: gpsd no PPS output - SolvedJim Pennino
 |   `- Re: gpsd no PPS output - Solvedchris
 `* Re: gpsd no PPS output - SolvedMiroslav Lichvar
  +* Re: gpsd no PPS output - Solvedchris
  |`* Re: gpsd no PPS output - SolvedJim Pennino
  | `* Re: gpsd no PPS output - Solvedchris
  |  `* Re: gpsd no PPS output - SolvedJim Pennino
  |   `* Re: gpsd no PPS output - SolvedWilliam Unruh
  |    `- Re: gpsd no PPS output - SolvedJim Pennino
  `* Re: gpsd no PPS output - SolvedJim Pennino
   `* Re: gpsd no PPS output - SolvedDavid Taylor
    +* Re: gpsd no PPS output - SolvedTerje Mathisen
    |`* Re: gpsd no PPS output - SolvedJim Pennino
    | +* Re: gpsd no PPS output - Solvedchris
    | |+* Re: gpsd no PPS output - SolvedDavid Woolley
    | ||+* Re: gpsd no PPS output - SolvedJim Pennino
    | |||`* Re: gpsd no PPS output - SolvedDavid Woolley
    | ||| `* Re: gpsd no PPS output - SolvedJim Pennino
    | |||  +* Re: gpsd no PPS output - SolvedWilliam Unruh
    | |||  |`* Re: gpsd no PPS output - SolvedJim Pennino
    | |||  | `* Re: gpsd no PPS output - SolvedWilliam Unruh
    | |||  |  `* Re: gpsd no PPS output - SolvedJim Pennino
    | |||  |   +* Re: gpsd no PPS output - SolvedWilliam Unruh
    | |||  |   |`- Re: gpsd no PPS output - SolvedJim Pennino
    | |||  |   `* Re: gpsd no PPS output - Solvedchris
    | |||  |    `* Re: gpsd no PPS output - SolvedJim Pennino
    | |||  |     `* Re: gpsd no PPS output - SolvedDavid Woolley
    | |||  |      `- Re: gpsd no PPS output - SolvedJim Pennino
    | |||  `- Re: gpsd no PPS output - SolvedDavid Woolley
    | ||`* Re: gpsd no PPS output - Solvedchris
    | || +* Re: gpsd no PPS output - SolvedWilliam Unruh
    | || |`- Re: gpsd no PPS output - Solvedchris
    | || +* Re: gpsd no PPS output - SolvedJim Pennino
    | || |+* Re: gpsd no PPS output - SolvedDavid Woolley
    | || ||`* Re: gpsd no PPS output - SolvedJim Pennino
    | || || `* Re: gpsd no PPS output - Solvedchris
    | || ||  +* Re: gpsd no PPS output - SolvedJim Pennino
    | || ||  |`* Re: gpsd no PPS output - Solvedchris
    | || ||  | `* Re: gpsd no PPS output - SolvedJim Pennino
    | || ||  |  +* Re: gpsd no PPS output - Solvedchris
    | || ||  |  |`* Re: gpsd no PPS output - SolvedJim Pennino
    | || ||  |  | `* Re: gpsd no PPS output - Solvedchris
    | || ||  |  |  `* Re: gpsd no PPS output - SolvedJim Pennino
    | || ||  |  |   +* Re: gpsd no PPS output - Solvedchris
    | || ||  |  |   |+* Re: gpsd no PPS output - Solvedchris
    | || ||  |  |   ||`- Re: gpsd no PPS output - SolvedJim Pennino
    | || ||  |  |   |`- Re: gpsd no PPS output - SolvedJim Pennino
    | || ||  |  |   `* Re: gpsd no PPS output - SolvedTerje Mathisen
    | || ||  |  |    `* Re: gpsd no PPS output - SolvedJim Pennino
    | || ||  |  |     `* Re: gpsd no PPS output - SolvedTerje Mathisen
    | || ||  |  |      +* Re: gpsd no PPS output - SolvedJim Pennino
    | || ||  |  |      `* Re: gpsd no PPS output - SolvedDavid Woolley
    | || ||  |  `* Re: gpsd no PPS output - SolvedDavid Woolley
    | || ||  `* Re: gpsd no PPS output - SolvedTerje Mathisen
    | || |`* Re: gpsd no PPS output - SolvedTerje Mathisen
    | || `- Re: gpsd no PPS output - SolvedDavid Woolley
    | |`* Re: gpsd no PPS output - SolvedJim Pennino
    | `* Re: gpsd no PPS output - SolvedTerje Mathisen
    `- Re: gpsd no PPS output - SolvedJim Pennino

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Re: gpsd no PPS output - Solved

<laioth-kdi4.ln1@gonzo.specsol.net>

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https://www.rocksolidbbs.com/devel/article-flat.php?id=223&group=comp.protocols.time.ntp#223

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From: jimp@gonzo.specsol.net (Jim Pennino)
Newsgroups: comp.protocols.time.ntp
Subject: Re: gpsd no PPS output - Solved
Date: Tue, 3 Aug 2021 12:34:15 -0700
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 by: Jim Pennino - Tue, 3 Aug 2021 19:34 UTC

Terje Mathisen <terje.mathisen@tmsw.no> wrote:
> chris wrote:
>> On 08/03/21 15:15, Jim Pennino wrote:
>>> David Woolley<david@ex.djwhome.demon.invalid>  wrote:
>>>> On 03/08/2021 00:37, Jim Pennino wrote:
>>>>> PPS has no information. The purpose of PPS is to provide a reference
>>>>> that is as close to 1 Hz, i.e. an elapsed time of 1 second, as
>>>>> possible.
>>>>>
>>>>
>>>> PPS provides information on where within the cycle the true UTC second
>>>> transition most probably lies.  You pretty much acknowledge that later
>>>> in your description.
>>>
>>> Nope.
>>>
>>> In fact if one were to build a highly stable oscillator totally
>>> independent of GPS, it would still work as a PPS signal.
>>>
>>> If you think otherwise, please provide the GPS specification.
>>>
>>
>> It may generate a pps signal if divided down, but it would not
>> be synchronised to UTC or anything else. Only a gps 1 pps
>> can provide that signal, or another clock locked to UTC.
>>
>> I should stop digging mate, ever more ridiculous...
>
> A PPS signal without some additional signal (serial or otherwise) which
> names/numbers the seconds will be dropped very quickly by ntpd.
>
> I.e. even if those pulses are delivered by an HP atomic clock, they are
> worthless without the secondary info.
>
> Terje

That is the basis for gpsd, i.e. simplifying ntpd setup and getting it
right.

With gpsd the newbie user is relieved from having to select which clock
driver to use, whether their version of ntpd is new enough such that the
..20 is atomized or not, knowing the difference between .20 and .22, etc.

Re: gpsd no PPS output - Solved

<fqjoth-u2j4.ln1@gonzo.specsol.net>

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https://www.rocksolidbbs.com/devel/article-flat.php?id=225&group=comp.protocols.time.ntp#225

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From: jimp@gonzo.specsol.net (Jim Pennino)
Newsgroups: comp.protocols.time.ntp
Subject: Re: gpsd no PPS output - Solved
Date: Tue, 3 Aug 2021 12:59:45 -0700
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 by: Jim Pennino - Tue, 3 Aug 2021 19:59 UTC

Miroslav Lichvar <mlichvar@redhat.com> wrote:
> On 2021-08-03, Jim Pennino <jimp@gonzo.specsol.net> wrote:
>> It is still my position, and will be until someone comes up with a GPS
>> specification that says otherwise, that the only specification for the
>> GPS PPS signal is interval accuracy, i.e. that it is 1 Hz +/- some
>> specification.
>
> Maybe this will help https://www.usno.navy.mil/USNO/time/gps/gps-info
>
> GPS SYSTEM TIME
> GPS system time is given by its Composite Clock (CC). The CC or "paper"
> clock consists of all operational Monitor Station and satellite
> frequency standards. GPS system time, in turn, is referenced to the
> Master Clock (MC) at the USNO and steered to UTC(USNO) from which system
> time will not deviate by more than one microsecond. The exact difference
> is contained in the navigation message in the form of two constants, A0
> and A1, giving the time difference and rate of system time against
> UTC(USNO,MC). UTC(USNO) itself is kept very close to the international
> benchmark UTC as maintained by the BIPM, and the exact difference, USNO
> vs. BIPM is available in near real time.

Well, actually no, as it says nothing about how the PPS signal is
generated.

I thought the current standard for system time was less than or equal to
40 nanoseconds from USNO to a 95% probability.

Re: gpsd no PPS output - Solved

<mfjoth-u2j4.ln1@gonzo.specsol.net>

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https://www.rocksolidbbs.com/devel/article-flat.php?id=226&group=comp.protocols.time.ntp#226

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From: jimp@gonzo.specsol.net (Jim Pennino)
Newsgroups: comp.protocols.time.ntp
Subject: Re: gpsd no PPS output - Solved
Date: Tue, 3 Aug 2021 12:54:00 -0700
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 by: Jim Pennino - Tue, 3 Aug 2021 19:54 UTC

Terje Mathisen <terje.mathisen@tmsw.no> wrote:
> Jim Pennino wrote:
>> It also seems the ntpd algorithms fall apart if you have multiple high
>> accuracy reference clocks attached. I doubt any of the designers ever
>> envisioned the day would come when someone could afford more than one as
>> at that time such things would set you back many tens of thousands of
>> dollars.
>
> Rather the opposite, this is how we compare various PPS devices, i.e. by
> setting 'prefer' on one of them and comparing how the others behave
> relative to this, then optionally swtich the prefer around and retry.

Try it with two identical sources and I think you will find that without
a prefer, ntpd gets rather confused rather quickly.

Which means if you actually do this, you MUST use prefer for it to work
properly. AFAIK, that is not documented.

> Good refclocks, like the original Oncore UT+ allow you to both offset
> the PPS signal from the top of the second (to avoid any extra interrupt
> latency due to multiple events firing at the same time), and to
> determine the sawtooth error, which is the +/-50 ns you get when the PPS
> signal is generated from the 10 MHz reference: The serial protocol
> includes information about how far off the current pulse is/will be.
>>
>> Now they cost less than $50.
>>
>> This is irrelevant as if you have a high accuracy reference clock, you
>> only need one and ntpd will sort itself out just fine.
>>
> ntpd is designed to handle _many_ sources and (with the pool)
> automatically settle on a near-optimal set of up to 10 sources.

True, but if you do have a high accuracy reference clock, you do not
need any other sources other than if in the unlikely failure of your
device there would be serious consequences.

>
> Terje
>

Re: gpsd no PPS output - Solved

<sedqh5$amb$1@gioia.aioe.org>

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https://www.rocksolidbbs.com/devel/article-flat.php?id=233&group=comp.protocols.time.ntp#233

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From: terje.mathisen@tmsw.no (Terje Mathisen)
Newsgroups: comp.protocols.time.ntp
Subject: Re: gpsd no PPS output - Solved
Date: Wed, 4 Aug 2021 12:35:16 +0200
Organization: Aioe.org NNTP Server
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 by: Terje Mathisen - Wed, 4 Aug 2021 10:35 UTC

Jim Pennino wrote:
> chris <chris-nospam@tridac.net> wrote:
>> You really are beyond help, but how do you think gsm cell handover, or
>> high frequency stock trading works ?. Are you even curious about how
>> things like that work and make some effort to find out ?.
>>
>> The thing about gps time and pps is that you can have a gps rx in London
>> and one on NY and both pps will be in sync to within 10's
>> of nS typically. How amazing is that ?. nS accuracy just about
>> anywhere on the planet where you can see satellites.
>>
>> Do your own homework and stop being so lazy :-)...
>
> Yet again, nothing but arm waving.
>
> You have claimed the GPS PPS pulse is synced to UTC.
>
> I say it is not and the GPS PPS pulse is only specified as an interval.

Jim, now you are just being a troll:

Yes, we all know that UTC is a paper clock, determined a month behind
after collecting data from the (order of magnitude) 100+ atomic clocks
in many national laboratories.

This means that nobody can claim to know "This is the exact PPS
instant", only that statistical data for their local reference clocks
(like USNO whoch provides the baseline for GPS) show that they have been
consistently within single-digit ns of the consensus/paper calculated value.

However, for our purposes, USNO used to have an original goal of being
within (afair) 25 ns of the UTC paper clock, and to keep each GPS sat
within another 25 (or so) ns of UTC(USNO), with a total max offset of
~45 ns.

In reality they are doing far better these days, so we can safely claim
GPS time to be within 10 ns of UTC, simply because they have
consistently been so for a decade or two.

In order to provide 3m positional accuracy, we get a relative timing
accuracy of better than 10 ns, i.e. all the visible sats needs to agree
what TAI(GPS) is within a ns or two.

Similarly, starting with the timing GPS receiver: Since it knows where
it is (either statically or due to long-term averaging) with sub-meter
precision, it will only introduce time errors in the same ballpark, i.e.
a couple of ns.

The end of all this is that we can all safely claim that a working
GPS-based PPS source will be in the 5-50 ns (RMS) range of true TAI/UTC.

If you need beter than this then you need your own atomic clock and
long-term comparisons with your friendly neigborhood national lab.

Terje

--
- <Terje.Mathisen at tmsw.no>
"almost all programming can be viewed as an exercise in caching"

Re: gpsd no PPS output - Solved

<e2nqth-ov66.ln1@gonzo.specsol.net>

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From: jimp@gonzo.specsol.net (Jim Pennino)
Newsgroups: comp.protocols.time.ntp
Subject: Re: gpsd no PPS output - Solved
Date: Wed, 4 Aug 2021 08:07:28 -0700
Organization: A noiseless patient Spider
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 by: Jim Pennino - Wed, 4 Aug 2021 15:07 UTC

Terje Mathisen <terje.mathisen@tmsw.no> wrote:
> Jim Pennino wrote:
>> chris <chris-nospam@tridac.net> wrote:
>>> You really are beyond help, but how do you think gsm cell handover, or
>>> high frequency stock trading works ?. Are you even curious about how
>>> things like that work and make some effort to find out ?.
>>>
>>> The thing about gps time and pps is that you can have a gps rx in London
>>> and one on NY and both pps will be in sync to within 10's
>>> of nS typically. How amazing is that ?. nS accuracy just about
>>> anywhere on the planet where you can see satellites.
>>>
>>> Do your own homework and stop being so lazy :-)...
>>
>> Yet again, nothing but arm waving.
>>
>> You have claimed the GPS PPS pulse is synced to UTC.
>>
>> I say it is not and the GPS PPS pulse is only specified as an interval.
>
> Jim, now you are just being a troll:
>
> Yes, we all know that UTC is a paper clock, determined a month behind
> after collecting data from the (order of magnitude) 100+ atomic clocks
> in many national laboratories.
>
> This means that nobody can claim to know "This is the exact PPS
> instant", only that statistical data for their local reference clocks
> (like USNO whoch provides the baseline for GPS) show that they have been
> consistently within single-digit ns of the consensus/paper calculated value.
>
> However, for our purposes, USNO used to have an original goal of being
> within (afair) 25 ns of the UTC paper clock, and to keep each GPS sat
> within another 25 (or so) ns of UTC(USNO), with a total max offset of
> ~45 ns.
>
> In reality they are doing far better these days, so we can safely claim
> GPS time to be within 10 ns of UTC, simply because they have
> consistently been so for a decade or two.
>
> In order to provide 3m positional accuracy, we get a relative timing
> accuracy of better than 10 ns, i.e. all the visible sats needs to agree
> what TAI(GPS) is within a ns or two.
>
> Similarly, starting with the timing GPS receiver: Since it knows where
> it is (either statically or due to long-term averaging) with sub-meter
> precision, it will only introduce time errors in the same ballpark, i.e.
> a couple of ns.
>
> The end of all this is that we can all safely claim that a working
> GPS-based PPS source will be in the 5-50 ns (RMS) range of true TAI/UTC.
>
> If you need beter than this then you need your own atomic clock and
> long-term comparisons with your friendly neigborhood national lab.
>
> Terje
Yeah, I know all that, but nowhere do you address the actual issue.

Addressing the actual issue would require citing the GPS specification
that says how PPS is generated and it's specified accuracy.

Quoting observed things is interesting but not a specification.

Re: gpsd no PPS output - Solved

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From: terje.mathisen@tmsw.no (Terje Mathisen)
Newsgroups: comp.protocols.time.ntp
Subject: Re: gpsd no PPS output - Solved
Date: Wed, 4 Aug 2021 18:59:26 +0200
Organization: Aioe.org NNTP Server
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 by: Terje Mathisen - Wed, 4 Aug 2021 16:59 UTC

Jim Pennino wrote:
> Terje Mathisen <terje.mathisen@tmsw.no> wrote:
[big snip]
>> Similarly, starting with the timing GPS receiver: Since it knows where
>> it is (either statically or due to long-term averaging) with sub-meter
>> precision, it will only introduce time errors in the same ballpark, i.e.
>> a couple of ns.
>>
>> The end of all this is that we can all safely claim that a working
>> GPS-based PPS source will be in the 5-50 ns (RMS) range of true TAI/UTC.
>>
>> If you need beter than this then you need your own atomic clock and
>> long-term comparisons with your friendly neigborhood national lab.
>>
>> Terje
>
> Yeah, I know all that, but nowhere do you address the actual issue.
>
> Addressing the actual issue would require citing the GPS specification
> that says how PPS is generated and it's specified accuracy.
>
> Quoting observed things is interesting but not a specification.
>
GPS never talks about PPS, that is simply not a part of what a
position/timing constellation needs to care about.

A PPS signal is always locally generated, for most (all?) those I have
read the specifications, this PPS signal is generated by the GPS
receiver chipset using a local 10 MHz oscillator, so that the PPS signal
is a pulse that rises on the edge which it has calculated will be the
closest to the true UTC/TAI second start.

With this approach we automatically get a standard deviation of 25-50 ns
from UTC(USNO), even if the average is perfectly centered around the
true second tick.

As you have alluded to multiple times, GPS time which is very close to
UTC(USNO) introduces two more sources of jitter, i.e. the USNO to GPS
sat time transfer and the UTC to UTC(USNO) delta, but in the current
worl we are living in, UTC(GPS) is effectively the only real source for
time sync in global use.

Terje

--
- <Terje.Mathisen at tmsw.no>
"almost all programming can be viewed as an exercise in caching"

Re: gpsd no PPS output - Solved

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From: jimp@gonzo.specsol.net (Jim Pennino)
Newsgroups: comp.protocols.time.ntp
Subject: Re: gpsd no PPS output - Solved
Date: Wed, 4 Aug 2021 10:39:48 -0700
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 by: Jim Pennino - Wed, 4 Aug 2021 17:39 UTC

Terje Mathisen <terje.mathisen@tmsw.no> wrote:
> Jim Pennino wrote:
>> Terje Mathisen <terje.mathisen@tmsw.no> wrote:
> [big snip]
>>> Similarly, starting with the timing GPS receiver: Since it knows where
>>> it is (either statically or due to long-term averaging) with sub-meter
>>> precision, it will only introduce time errors in the same ballpark, i.e.
>>> a couple of ns.
>>>
>>> The end of all this is that we can all safely claim that a working
>>> GPS-based PPS source will be in the 5-50 ns (RMS) range of true TAI/UTC.
>>>
>>> If you need beter than this then you need your own atomic clock and
>>> long-term comparisons with your friendly neigborhood national lab.
>>>
>>> Terje
>>
>> Yeah, I know all that, but nowhere do you address the actual issue.
>>
>> Addressing the actual issue would require citing the GPS specification
>> that says how PPS is generated and it's specified accuracy.
>>
>> Quoting observed things is interesting but not a specification.
>>
> GPS never talks about PPS, that is simply not a part of what a
> position/timing constellation needs to care about.
>
> A PPS signal is always locally generated, for most (all?) those I have
> read the specifications, this PPS signal is generated by the GPS
> receiver chipset using a local 10 MHz oscillator, so that the PPS signal
> is a pulse that rises on the edge which it has calculated will be the
> closest to the true UTC/TAI second start.
>
> With this approach we automatically get a standard deviation of 25-50 ns
> from UTC(USNO), even if the average is perfectly centered around the
> true second tick.
>
> As you have alluded to multiple times, GPS time which is very close to
> UTC(USNO) introduces two more sources of jitter, i.e. the USNO to GPS
> sat time transfer and the UTC to UTC(USNO) delta, but in the current
> worl we are living in, UTC(GPS) is effectively the only real source for
> time sync in global use.
>
> Terje

So you are saying every GPS receiver has a 10 MHz oscillator ergo the
accuracy of the PPS output signal is totally dependent on the accuracy
of the internal oscillator, ignoring what one MAY externally add?

If so, you have validated my contention that GPS does NOT specify PPS
syncronization to UTC, but rather it is totally up to whoever designed
the receiver.

Re: gpsd no PPS output - Solved

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From: david@ex.djwhome.demon.invalid (David Woolley)
Newsgroups: comp.protocols.time.ntp
Subject: Re: gpsd no PPS output - Solved
Date: Wed, 4 Aug 2021 22:17:00 +0100
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 by: David Woolley - Wed, 4 Aug 2021 21:17 UTC

On 04/08/2021 17:59, Terje Mathisen wrote:

> using a local 10 MHz oscillator

I can't see why a GPS receiver would need a 10MHz oscillator. The
chipping rates are 1.023Mhz, and 10.023MHz, and I would expect a
multiple of one of those

Re: gpsd no PPS output - Solved

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From: chris-nospam@tridac.net (chris)
Newsgroups: comp.protocols.time.ntp
Subject: Re: gpsd no PPS output - Solved
Date: Wed, 04 Aug 2021 22:47:19 +0100
Organization: Aioe.org NNTP Server
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 by: chris - Wed, 4 Aug 2021 21:47 UTC

On 08/04/21 22:17, David Woolley wrote:
> On 04/08/2021 17:59, Terje Mathisen wrote:
>
>> using a local 10 MHz oscillator
>
> I can't see why a GPS receiver would need a 10MHz oscillator. The
> chipping rates are 1.023Mhz, and 10.023MHz, and I would expect a
> multiple of one of those

A gps receiver may use a 10MHz oscillator, if it's primarily aimed at
the gps do market, eg: a frequency standard application to drive
test equipment, as 10MHz tends to be the industry standard these days
for such applications. All the telco gps d0 boxes i've seen have both
pps and 10MHz outputs, but also various timing signals to suit T1 and
E1 telco framing specs. Many amateurs and professionals use a
gps do as primary frequency standards, as their outputs are directly
traceable to nationals standards and UTC. That is, almost caesium
accuracy and stability at a small fraction of the cost. Have a caesium
standard here, only gets powered ip occasionally, but the offset
between that and a typical 10MHz gps do is almost unmeasureable.

Have a look at the time-nuts mailing list for more info. Time and
frequency are an interest area here, but not so obsessive as some on
that list. Some good open source software there as well, for
characterising standards...

Re: gpsd no PPS output - Solved

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From: jimp@gonzo.specsol.net (Jim Pennino)
Newsgroups: comp.protocols.time.ntp
Subject: Re: gpsd no PPS output - Solved
Date: Wed, 4 Aug 2021 14:56:39 -0700
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 by: Jim Pennino - Wed, 4 Aug 2021 21:56 UTC

David Woolley <david@ex.djwhome.demon.invalid> wrote:
> On 04/08/2021 17:59, Terje Mathisen wrote:
>
>> using a local 10 MHz oscillator
>
> I can't see why a GPS receiver would need a 10MHz oscillator. The
> chipping rates are 1.023Mhz, and 10.023MHz, and I would expect a
> multiple of one of those

Why?

PLL tech is a bit better than it was in 1971 when I first used one.

Re: gpsd no PPS output - Solved

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From: unruh@invalid.ca (William Unruh)
Newsgroups: comp.protocols.time.ntp
Subject: Re: gpsd no PPS output - Solved
Date: Thu, 5 Aug 2021 00:07:43 -0000 (UTC)
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 by: William Unruh - Thu, 5 Aug 2021 00:07 UTC

On 2021-08-04, Jim Pennino <jimp@gonzo.specsol.net> wrote:
> Terje Mathisen <terje.mathisen@tmsw.no> wrote:
>> Jim Pennino wrote:
>>> Terje Mathisen <terje.mathisen@tmsw.no> wrote:
>> [big snip]
>>>> Similarly, starting with the timing GPS receiver: Since it knows where
>>>> it is (either statically or due to long-term averaging) with sub-meter
>>>> precision, it will only introduce time errors in the same ballpark, i.e.
>>>> a couple of ns.
>>>>
>>>> The end of all this is that we can all safely claim that a working
>>>> GPS-based PPS source will be in the 5-50 ns (RMS) range of true TAI/UTC.
>>>>
>>>> If you need beter than this then you need your own atomic clock and
>>>> long-term comparisons with your friendly neigborhood national lab.
>>>>
>>>> Terje
>>>
>>> Yeah, I know all that, but nowhere do you address the actual issue.
>>>
>>> Addressing the actual issue would require citing the GPS specification
>>> that says how PPS is generated and it's specified accuracy.
>>>
>>> Quoting observed things is interesting but not a specification.
>>>
>> GPS never talks about PPS, that is simply not a part of what a
>> position/timing constellation needs to care about.
>>
>> A PPS signal is always locally generated, for most (all?) those I have
>> read the specifications, this PPS signal is generated by the GPS
>> receiver chipset using a local 10 MHz oscillator, so that the PPS signal
>> is a pulse that rises on the edge which it has calculated will be the
>> closest to the true UTC/TAI second start.
>>
>> With this approach we automatically get a standard deviation of 25-50 ns
>> from UTC(USNO), even if the average is perfectly centered around the
>> true second tick.
>>
>> As you have alluded to multiple times, GPS time which is very close to
>> UTC(USNO) introduces two more sources of jitter, i.e. the USNO to GPS
>> sat time transfer and the UTC to UTC(USNO) delta, but in the current
>> worl we are living in, UTC(GPS) is effectively the only real source for
>> time sync in global use.
>>
>> Terje
>
> So you are saying every GPS receiver has a 10 MHz oscillator ergo the
> accuracy of the PPS output signal is totally dependent on the accuracy
> of the internal oscillator, ignoring what one MAY externally add?

No. He is saying that the gps picks the edge of 10MHz signal that is
closest to GPS time. That does not depend on the accuracy of the 10MHz.
Sometime the gps signal may pick the edge that is 997 cycles away from
the lastone, sometimes the 998, sometimes the 1001 -- whichever is
closest. The GPS sattelites send down a time signal. The PPS tends to
ramp up in a sawtooth.and when it gets to 50 flips to the next one. A
good timing gps will figure out what its 10MHz is with respect to GPS
time and send down a correction so you can, after the fact correct for
the sawtooth offset.
>
> If so, you have validated my contention that GPS does NOT specify PPS
> syncronization to UTC, but rather it is totally up to whoever designed
> the receiver.

You did not read what he said.
>
>

Re: gpsd no PPS output - Solved

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From: jimp@gonzo.specsol.net (Jim Pennino)
Newsgroups: comp.protocols.time.ntp
Subject: Re: gpsd no PPS output - Solved
Date: Wed, 4 Aug 2021 17:57:39 -0700
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 by: Jim Pennino - Thu, 5 Aug 2021 00:57 UTC

William Unruh <unruh@invalid.ca> wrote:
> On 2021-08-04, Jim Pennino <jimp@gonzo.specsol.net> wrote:
>> Terje Mathisen <terje.mathisen@tmsw.no> wrote:
>>> Jim Pennino wrote:
>>>> Terje Mathisen <terje.mathisen@tmsw.no> wrote:
>>> [big snip]
>>>>> Similarly, starting with the timing GPS receiver: Since it knows where
>>>>> it is (either statically or due to long-term averaging) with sub-meter
>>>>> precision, it will only introduce time errors in the same ballpark, i.e.
>>>>> a couple of ns.
>>>>>
>>>>> The end of all this is that we can all safely claim that a working
>>>>> GPS-based PPS source will be in the 5-50 ns (RMS) range of true TAI/UTC.
>>>>>
>>>>> If you need beter than this then you need your own atomic clock and
>>>>> long-term comparisons with your friendly neigborhood national lab.
>>>>>
>>>>> Terje
>>>>
>>>> Yeah, I know all that, but nowhere do you address the actual issue.
>>>>
>>>> Addressing the actual issue would require citing the GPS specification
>>>> that says how PPS is generated and it's specified accuracy.
>>>>
>>>> Quoting observed things is interesting but not a specification.
>>>>
>>> GPS never talks about PPS, that is simply not a part of what a
>>> position/timing constellation needs to care about.
>>>
>>> A PPS signal is always locally generated, for most (all?) those I have
>>> read the specifications, this PPS signal is generated by the GPS
>>> receiver chipset using a local 10 MHz oscillator, so that the PPS signal
>>> is a pulse that rises on the edge which it has calculated will be the
>>> closest to the true UTC/TAI second start.
>>>
>>> With this approach we automatically get a standard deviation of 25-50 ns
>>> from UTC(USNO), even if the average is perfectly centered around the
>>> true second tick.
>>>
>>> As you have alluded to multiple times, GPS time which is very close to
>>> UTC(USNO) introduces two more sources of jitter, i.e. the USNO to GPS
>>> sat time transfer and the UTC to UTC(USNO) delta, but in the current
>>> worl we are living in, UTC(GPS) is effectively the only real source for
>>> time sync in global use.
>>>
>>> Terje
>>
>> So you are saying every GPS receiver has a 10 MHz oscillator ergo the
>> accuracy of the PPS output signal is totally dependent on the accuracy
>> of the internal oscillator, ignoring what one MAY externally add?
>
> No. He is saying that the gps picks the edge of 10MHz signal that is
> closest to GPS time. That does not depend on the accuracy of the 10MHz.
> Sometime the gps signal may pick the edge that is 997 cycles away from
> the lastone, sometimes the 998, sometimes the 1001 -- whichever is
> closest. The GPS sattelites send down a time signal. The PPS tends to
> ramp up in a sawtooth.and when it gets to 50 flips to the next one. A
> good timing gps will figure out what its 10MHz is with respect to GPS
> time and send down a correction so you can, after the fact correct for
> the sawtooth offset.
>>
>> If so, you have validated my contention that GPS does NOT specify PPS
>> syncronization to UTC, but rather it is totally up to whoever designed
>> the receiver.
>
> You did not read what he said.

Yes, I read it but apparently you did not.

"this PPS signal is generated by the GPS receiver chipset" is what he
said.

I presume where you wrote "A good timing gps will" you meant to say
"timing GPS receiver" but have problems with what you meant by "and
send down a correction" other than maybe "and output a correction".

The line "The PPS tends to ramp up in a sawtooth" is baffling as PPS is
a digital signal and is either low or high.

Perhaps you meant something like "The PPS dectector or generator ramps".

In regards to the line "Sometime the gps signal may pick the edge",
please explain how a signal can pick anything.

Perhaps you meant something like "Sometimes the GPS receiver time
processing circuitry may pick".

Re: gpsd no PPS output - Solved

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From: chris-nospam@tridac.net (chris)
Newsgroups: comp.protocols.time.ntp
Subject: Re: gpsd no PPS output - Solved
Date: Thu, 05 Aug 2021 11:45:28 +0100
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 by: chris - Thu, 5 Aug 2021 10:45 UTC

On 08/04/21 22:17, David Woolley wrote:
> On 04/08/2021 17:59, Terje Mathisen wrote:
>
>> using a local 10 MHz oscillator
>
> I can't see why a GPS receiver would need a 10MHz oscillator. The
> chipping rates are 1.023Mhz, and 10.023MHz, and I would expect a
> multiple of one of those

Just to disambiguate the comments about 10MHz. While the gps receiver
module will have an internal oscillator to suit the design, that
oscillator is not normally available external to the module. What the
gps receiver does provide, is a 1pps signal traceable to UTC and it is
to that, that an external high stability 10 MHz or other frequency
oscillator may be phase locked to.

There all kinds of applications for gps capabilities, with navigation
being just one...

Re: gpsd no PPS output - Solved

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From: david@ex.djwhome.demon.invalid (David Woolley)
Newsgroups: comp.protocols.time.ntp
Subject: Re: gpsd no PPS output - Solved
Date: Thu, 5 Aug 2021 12:00:09 +0100
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 by: David Woolley - Thu, 5 Aug 2021 11:00 UTC

On 04/08/2021 22:56, Jim Pennino wrote:
>> I can't see why a GPS receiver would need a 10MHz oscillator. The
>> chipping rates are 1.023Mhz, and 10.023MHz, and I would expect a
>> multiple of one of those
> Why?
>
> PLL tech is a bit better than it was in 1971 when I first used one.
>
>

Do you mean frequency synthesizer tech?

It does seem that the internal crystal frequency is somewhat arbitrary,
because the real working frequencies are generated by synthesizers. I
found products using 26MHz, as well as 10MHz for their primary oscillators.

Re: gpsd no PPS output - Solved

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From: jimp@gonzo.specsol.net (Jim Pennino)
Newsgroups: comp.protocols.time.ntp
Subject: Re: gpsd no PPS output - Solved
Date: Thu, 5 Aug 2021 08:02:01 -0700
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 by: Jim Pennino - Thu, 5 Aug 2021 15:02 UTC

David Woolley <david@ex.djwhome.demon.invalid> wrote:
> On 04/08/2021 22:56, Jim Pennino wrote:
>>> I can't see why a GPS receiver would need a 10MHz oscillator. The
>>> chipping rates are 1.023Mhz, and 10.023MHz, and I would expect a
>>> multiple of one of those
>> Why?
>>
>> PLL tech is a bit better than it was in 1971 when I first used one.
>>
>>
>
> Do you mean frequency synthesizer tech?

If you want to be very general about it, but few if any frequency
synthesizers, as opposed to waveform generators, use anything other
than PLL tecnology.

That does not mean they use NE565 analog IC technology from 1970, but
rather they implement the PLL equations in hardware in some manner, such
as the use of fractional-N and computational based PLL devices.

> It does seem that the internal crystal frequency is somewhat arbitrary,
> because the real working frequencies are generated by synthesizers. I
> found products using 26MHz, as well as 10MHz for their primary oscillators.

Why would it be other than arbitrary?

GPS receivers are not part of the GPS specifications, as ONE other
person has noted.

The GPS system specifications are for the ground segment, i.e. command and
control, and the space segment, i.e. the satellites, and that is it.

The specifications define the radio signals from the satellites, i.e.
the carrier frequency(s), the modulation method(s) used, and the data
streams therein.

Everything else is up to the end user to design equipment to utilize
those radio signals in a manner totally up to the equipment designer.

Nowhere in the GPS specifications is PPS mentioned.

Along with the specifications is a set of what amounts to white papers
describing various things that can be done using the GPS system.

Among those papers is one directed at metrologists who have interest in
time and frequency measurement.

The latest revision I can find is from 1996, so it is sometimes a
somewhat quaint read in 2021, but goes into a lot of detail about doing
such things as generating precise frequency standards traceable to GPS
accuracies. Most of that detail is in the form of equations with some
generalized algorithms.

Again, it is up to the equipment designer how to implement those things.

As a 1 Hz signal, i.e. PPS, is something commonly used by metrologists,
it is in there that generating a PPS is discussed along with generating
other common frequencies used in metrology.

So, in what today we call a gps, there are at least three separate
devices, a radio receiver to obtain the the GPS data, a device to
generate PPS, and a device to convert GPS data to NMEA sentences.

BTW, NMEA stands for National Marine Electronics Association. Guess why
commercial GPS devices output data in a marine standard format.

In circa 1996 those three devices would likely be in three 19 inch rack
mount boxes containing mostly discrete components.

Today everything is fabricated on chip sets.

In regards to PPS alignment with UTC, since it is up to the equiment
maker, it will be whatever the equipment maker decides it will be.

Re: gpsd no PPS output - Solved

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From: jimp@gonzo.specsol.net (Jim Pennino)
Newsgroups: comp.protocols.time.ntp
Subject: Re: gpsd no PPS output - Solved
Date: Thu, 5 Aug 2021 08:06:37 -0700
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 by: Jim Pennino - Thu, 5 Aug 2021 15:06 UTC

chris <chris-nospam@tridac.net> wrote:
> On 08/04/21 22:17, David Woolley wrote:
>> On 04/08/2021 17:59, Terje Mathisen wrote:
>>
>>> using a local 10 MHz oscillator
>>
>> I can't see why a GPS receiver would need a 10MHz oscillator. The
>> chipping rates are 1.023Mhz, and 10.023MHz, and I would expect a
>> multiple of one of those
>
> Just to disambiguate the comments about 10MHz. While the gps receiver
> module will have an internal oscillator to suit the design, that
> oscillator is not normally available external to the module. What the
> gps receiver does provide, is a 1pps signal traceable to UTC and it is
> to that, that an external high stability 10 MHz or other frequency
> oscillator may be phase locked to.

No, the receiver does not provide a PPS signal unless you are calling
the entire gps device a receiver, which contains three separate devices,
i.e a radio receiver, a time standard (PPS) generator, and a NMEA
sentence generator.

> There all kinds of applications for gps capabilities, with navigation
> being just one...

No shit, Captain Obvious?

Re: gpsd no PPS output - Solved

<seh1bn$r60$1@gioia.aioe.org>

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From: terje.mathisen@tmsw.no (Terje Mathisen)
Newsgroups: comp.protocols.time.ntp
Subject: Re: gpsd no PPS output - Solved
Date: Thu, 5 Aug 2021 17:50:16 +0200
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 by: Terje Mathisen - Thu, 5 Aug 2021 15:50 UTC

Jim Pennino wrote:
> David Woolley <david@ex.djwhome.demon.invalid> wrote:
> So, in what today we call a gps, there are at least three separate
> devices, a radio receiver to obtain the the GPS data, a device to
> generate PPS, and a device to convert GPS data to NMEA sentences.

Except that in a modern chipset as used in a cell phone, all of those
functions, plus wifi and possibly even more, is a single chip.
>
> BTW, NMEA stands for National Marine Electronics Association. Guess why
> commercial GPS devices output data in a marine standard format.
>
> In circa 1996 those three devices would likely be in three 19 inch rack
> mount boxes containing mostly discrete components.

Your timing is off by a substantial number of years: Garmin sold
(portable) GPSs for $105M already in 1995, I have track logs which are
older than this.

https://en.wikipedia.org/wiki/Garmin#Handheld_GPS

> Today everything is fabricated on chip sets.
>
> In regards to PPS alignment with UTC, since it is up to the equiment
> maker, it will be whatever the equipment maker decides it will be.

Yes, and when the time nuts compare the PPS signal from those cheap
boards, against proper atomic reference clocks, like the sub-80 dollar
SURE which was popular about 8-10 years ago, they found about 25 ns RMS
offset.

Terje

--
- <Terje.Mathisen at tmsw.no>
"almost all programming can be viewed as an exercise in caching"

Re: gpsd no PPS output - Solved

<seh3uv$5if$1@gioia.aioe.org>

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From: chris-nospam@tridac.net (chris)
Newsgroups: comp.protocols.time.ntp
Subject: Re: gpsd no PPS output - Solved
Date: Thu, 05 Aug 2021 17:34:38 +0100
Organization: Aioe.org NNTP Server
Message-ID: <seh3uv$5if$1@gioia.aioe.org>
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 by: chris - Thu, 5 Aug 2021 16:34 UTC

On 08/05/21 16:06, Jim Pennino wrote:
> chris<chris-nospam@tridac.net> wrote:
>> On 08/04/21 22:17, David Woolley wrote:
>>> On 04/08/2021 17:59, Terje Mathisen wrote:
>>>
>>>> using a local 10 MHz oscillator
>>>
>>> I can't see why a GPS receiver would need a 10MHz oscillator. The
>>> chipping rates are 1.023Mhz, and 10.023MHz, and I would expect a
>>> multiple of one of those
>>
>> Just to disambiguate the comments about 10MHz. While the gps receiver
>> module will have an internal oscillator to suit the design, that
>> oscillator is not normally available external to the module. What the
>> gps receiver does provide, is a 1pps signal traceable to UTC and it is
>> to that, that an external high stability 10 MHz or other frequency
>> oscillator may be phase locked to.
>
> No, the receiver does not provide a PPS signal unless you are calling
> the entire gps device a receiver, which contains three separate devices,
> i.e a radio receiver, a time standard (PPS) generator, and a NMEA
> sentence generator.

I said gps receiver module, which most familiar with the technology
would take to mean the sort of thing you can buy for a few $ on Ebay,
but I guess with have to make allowances. So, enlighten us, just
how do the pps and nmea sentances appear on output pins ?. Some
sort of black magic perhaps ?...

>
>> There all kinds of applications for gps capabilities, with navigation
>> being just one...
>
> No shit, Captain Obvious?
>

Nurse !!!. Has Doreen not not been taking her meds today ?.

>

Re: gpsd no PPS output - Solved

<2ihtth-38h8.ln1@gonzo.specsol.net>

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From: jimp@gonzo.specsol.net (Jim Pennino)
Newsgroups: comp.protocols.time.ntp
Subject: Re: gpsd no PPS output - Solved
Date: Thu, 5 Aug 2021 09:51:48 -0700
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 by: Jim Pennino - Thu, 5 Aug 2021 16:51 UTC

Terje Mathisen <terje.mathisen@tmsw.no> wrote:
> Jim Pennino wrote:
>> David Woolley <david@ex.djwhome.demon.invalid> wrote:
>> So, in what today we call a gps, there are at least three separate
>> devices, a radio receiver to obtain the the GPS data, a device to
>> generate PPS, and a device to convert GPS data to NMEA sentences.
>
> Except that in a modern chipset as used in a cell phone, all of those
> functions, plus wifi and possibly even more, is a single chip.

I believe I said something like that in the next to last sentence which
you quoted below.

>> BTW, NMEA stands for National Marine Electronics Association. Guess why
>> commercial GPS devices output data in a marine standard format.
>>
>> In circa 1996 those three devices would likely be in three 19 inch rack
>> mount boxes containing mostly discrete components.
>
> Your timing is off by a substantial number of years: Garmin sold
> (portable) GPSs for $105M already in 1995, I have track logs which are
> older than this.
>
> https://en.wikipedia.org/wiki/Garmin#Handheld_GPS

Yes, but without PPS.

As for portabale, while in the Army I worked on a "portable" system who's
command and control part alone was mounted on 5 truck pulled trailers.

The first GPS chipsets were circa 2004 so anything GPS related HAD to be
built with discrete components, e.g. PLL IC's with associate components.

>> Today everything is fabricated on chip sets.
>>
>> In regards to PPS alignment with UTC, since it is up to the equiment
>> maker, it will be whatever the equipment maker decides it will be.
>
> Yes, and when the time nuts compare the PPS signal from those cheap
> boards, against proper atomic reference clocks, like the sub-80 dollar
> SURE which was popular about 8-10 years ago, they found about 25 ns RMS
> offset.
>
> Terje

Which is not as good as can be theoretically obtained.

The reality is that "time nuts" are an insignificant market for GPS
chipset makers and are inconsequential to them. They make chip sets
for a mass market and not to make David L. Mills happy.

Mximizing market share and profit margin are important so makers will
make things with that in mind, e.g. will optimize things and add
features, such as WAAS, that will do so.

As an example, most of the GNSS chipsets (I don't think anyone is actually
making GPS chipsets anymore) I have seen output their data via an I2C bus
because given the VAST number of types of I2C chipsets that exist, it
becomes trivial for the end maker to integrate GNSS chipsets with end
product, be it an aviation navigator, cell phone, or whatever.

If increasing the accuracy of PPS will increase their profit margin, it
will happen, but right now it appears that the PPS accuracy is a function
of what the fabrication technology happens to do rather than a design
specification.

Which means PPS accuracy will improve automatically as fabrication
technology improves.

Re: gpsd no PPS output - Solved

<j1itth-38h8.ln1@gonzo.specsol.net>

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From: jimp@gonzo.specsol.net (Jim Pennino)
Newsgroups: comp.protocols.time.ntp
Subject: Re: gpsd no PPS output - Solved
Date: Thu, 5 Aug 2021 10:00:05 -0700
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 by: Jim Pennino - Thu, 5 Aug 2021 17:00 UTC

chris <chris-nospam@tridac.net> wrote:
> On 08/05/21 16:06, Jim Pennino wrote:
>> chris<chris-nospam@tridac.net> wrote:
>>> On 08/04/21 22:17, David Woolley wrote:
>>>> On 04/08/2021 17:59, Terje Mathisen wrote:
>>>>
>>>>> using a local 10 MHz oscillator
>>>>
>>>> I can't see why a GPS receiver would need a 10MHz oscillator. The
>>>> chipping rates are 1.023Mhz, and 10.023MHz, and I would expect a
>>>> multiple of one of those
>>>
>>> Just to disambiguate the comments about 10MHz. While the gps receiver
>>> module will have an internal oscillator to suit the design, that
>>> oscillator is not normally available external to the module. What the
>>> gps receiver does provide, is a 1pps signal traceable to UTC and it is
>>> to that, that an external high stability 10 MHz or other frequency
>>> oscillator may be phase locked to.
>>
>> No, the receiver does not provide a PPS signal unless you are calling
>> the entire gps device a receiver, which contains three separate devices,
>> i.e a radio receiver, a time standard (PPS) generator, and a NMEA
>> sentence generator.
>
> I said gps receiver module, which most familiar with the technology
> would take to mean the sort of thing you can buy for a few $ on Ebay,
> but I guess with have to make allowances. So, enlighten us, just
> how do the pps and nmea sentances appear on output pins ?. Some
> sort of black magic perhaps ?...

Your question is answered at some length in another post.

I am not going to repost it just for you.

This is a technical discussion group, not a marketing group, and as such
precision in language and the lack of arm waving matters.

The phrase "gps receiver module" is ambiguous in a discussion of GPS
technology in 2021 absent a definition of what you mean.

Re: gpsd no PPS output - Solved

<seh623$16o1$1@gioia.aioe.org>

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From: chris-nospam@tridac.net (chris)
Newsgroups: comp.protocols.time.ntp
Subject: Re: gpsd no PPS output - Solved
Date: Thu, 05 Aug 2021 18:10:27 +0100
Organization: Aioe.org NNTP Server
Message-ID: <seh623$16o1$1@gioia.aioe.org>
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 by: chris - Thu, 5 Aug 2021 17:10 UTC

On 08/05/21 18:00, Jim Pennino wrote:
> chris<chris-nospam@tridac.net> wrote:
>> On 08/05/21 16:06, Jim Pennino wrote:
>>> chris<chris-nospam@tridac.net> wrote:
>>>> On 08/04/21 22:17, David Woolley wrote:
>>>>> On 04/08/2021 17:59, Terje Mathisen wrote:
>>>>>
>>>>>> using a local 10 MHz oscillator
>>>>>
>>>>> I can't see why a GPS receiver would need a 10MHz oscillator. The
>>>>> chipping rates are 1.023Mhz, and 10.023MHz, and I would expect a
>>>>> multiple of one of those
>>>>
>>>> Just to disambiguate the comments about 10MHz. While the gps receiver
>>>> module will have an internal oscillator to suit the design, that
>>>> oscillator is not normally available external to the module. What the
>>>> gps receiver does provide, is a 1pps signal traceable to UTC and it is
>>>> to that, that an external high stability 10 MHz or other frequency
>>>> oscillator may be phase locked to.
>>>
>>> No, the receiver does not provide a PPS signal unless you are calling
>>> the entire gps device a receiver, which contains three separate devices,
>>> i.e a radio receiver, a time standard (PPS) generator, and a NMEA
>>> sentence generator.
>>
>> I said gps receiver module, which most familiar with the technology
>> would take to mean the sort of thing you can buy for a few $ on Ebay,
>> but I guess with have to make allowances. So, enlighten us, just
>> how do the pps and nmea sentances appear on output pins ?. Some
>> sort of black magic perhaps ?...
>
> Your question is answered at some length in another post.
>
> I am not going to repost it just for you.
>
> This is a technical discussion group, not a marketing group, and as such
> precision in language and the lack of arm waving matters.
>
> The phrase "gps receiver module" is ambiguous in a discussion of GPS
> technology in 2021 absent a definition of what you mean.
>

You talk about arm waving, but the fact is, you don't know, don't
understand and are too lazy to make the effort to find out...

Re: gpsd no PPS output - Solved

<slrnsgo7a1.3fo.theise@panix2.panix.com>

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From: theise@panix.com (Ted Heise)
Newsgroups: comp.protocols.time.ntp
Subject: Re: gpsd no PPS output - Solved
Date: Thu, 5 Aug 2021 17:17:52 -0000 (UTC)
Organization: My own, such as it is
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 by: Ted Heise - Thu, 5 Aug 2021 17:17 UTC

On Thu, 5 Aug 2021 17:50:16 +0200,
Terje Mathisen <terje.mathisen@tmsw.no> wrote:
> Jim Pennino wrote:
> > David Woolley <david@ex.djwhome.demon.invalid> wrote: So, in
> > what today we call a gps, there are at least three separate
> > devices, a radio receiver to obtain the the GPS data, a device
> > to generate PPS, and a device to convert GPS data to NMEA
> > sentences.
>
> Except that in a modern chipset as used in a cell phone, all of
> those functions, plus wifi and possibly even more, is a single
> chip.
> >
> > BTW, NMEA stands for National Marine Electronics Association.
> > Guess why commercial GPS devices output data in a marine
> > standard format.
> >
> > In circa 1996 those three devices would likely be in three 19
> > inch rack mount boxes containing mostly discrete components.
>
> Your timing is off by a substantial number of years: Garmin
> sold (portable) GPSs for $105M already in 1995, I have track
> logs which are older than this.
>
> https://en.wikipedia.org/wiki/Garmin#Handheld_GPS

I for one have been fascinated by this discussion. I ran my own
linux server (Slackware) for the better part of two decades, and
spent quite a lot of time getting ntp up and running to my
satisfaction.

The Garmin page reminds me I have an old etrex Vista HCx sitting
in a closet at home. I don't suppose there's any way to hack it
into use as a GPS clock? Guessing it may not even generate a PPS
signal, let alone have any way to get it out of the unit.

It was a terrific device for its time. It rode on the handlebars
of my bike for tracking speed, mileage, and routes.

--
Ted Heise <theise@panix.com> West Lafayette, IN, USA

Re: gpsd no PPS output - Solved

<ahjtth-fvi8.ln1@gonzo.specsol.net>

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From: jimp@gonzo.specsol.net (Jim Pennino)
Newsgroups: comp.protocols.time.ntp
Subject: Re: gpsd no PPS output - Solved
Date: Thu, 5 Aug 2021 10:25:32 -0700
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 by: Jim Pennino - Thu, 5 Aug 2021 17:25 UTC

chris <chris-nospam@tridac.net> wrote:
> On 08/05/21 18:00, Jim Pennino wrote:
>> chris<chris-nospam@tridac.net> wrote:
>>> On 08/05/21 16:06, Jim Pennino wrote:
>>>> chris<chris-nospam@tridac.net> wrote:
>>>>> On 08/04/21 22:17, David Woolley wrote:
>>>>>> On 04/08/2021 17:59, Terje Mathisen wrote:
>>>>>>
>>>>>>> using a local 10 MHz oscillator
>>>>>>
>>>>>> I can't see why a GPS receiver would need a 10MHz oscillator. The
>>>>>> chipping rates are 1.023Mhz, and 10.023MHz, and I would expect a
>>>>>> multiple of one of those
>>>>>
>>>>> Just to disambiguate the comments about 10MHz. While the gps receiver
>>>>> module will have an internal oscillator to suit the design, that
>>>>> oscillator is not normally available external to the module. What the
>>>>> gps receiver does provide, is a 1pps signal traceable to UTC and it is
>>>>> to that, that an external high stability 10 MHz or other frequency
>>>>> oscillator may be phase locked to.
>>>>
>>>> No, the receiver does not provide a PPS signal unless you are calling
>>>> the entire gps device a receiver, which contains three separate devices,
>>>> i.e a radio receiver, a time standard (PPS) generator, and a NMEA
>>>> sentence generator.
>>>
>>> I said gps receiver module, which most familiar with the technology
>>> would take to mean the sort of thing you can buy for a few $ on Ebay,
>>> but I guess with have to make allowances. So, enlighten us, just
>>> how do the pps and nmea sentances appear on output pins ?. Some
>>> sort of black magic perhaps ?...
>>
>> Your question is answered at some length in another post.
>>
>> I am not going to repost it just for you.
>>
>> This is a technical discussion group, not a marketing group, and as such
>> precision in language and the lack of arm waving matters.
>>
>> The phrase "gps receiver module" is ambiguous in a discussion of GPS
>> technology in 2021 absent a definition of what you mean.
>>
>
> You talk about arm waving, but the fact is, you don't know, don't
> understand and are too lazy to make the effort to find out...
Your questions are answered at some length in another post.

Go look it up.

I am not going to repost it just for you nor is it my job to alleviate
your abysmal ignorance or tutor you in technical writting.

Re: gpsd no PPS output - Solved

<irltth-92l8.ln1@gonzo.specsol.net>

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https://www.rocksolidbbs.com/devel/article-flat.php?id=256&group=comp.protocols.time.ntp#256

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From: jimp@gonzo.specsol.net (Jim Pennino)
Newsgroups: comp.protocols.time.ntp
Subject: Re: gpsd no PPS output - Solved
Date: Thu, 5 Aug 2021 11:05:08 -0700
Organization: A noiseless patient Spider
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 by: Jim Pennino - Thu, 5 Aug 2021 18:05 UTC

Ted Heise <theise@panix.com> wrote:
> On Thu, 5 Aug 2021 17:50:16 +0200,
> Terje Mathisen <terje.mathisen@tmsw.no> wrote:
>> Jim Pennino wrote:
>> > David Woolley <david@ex.djwhome.demon.invalid> wrote: So, in
>> > what today we call a gps, there are at least three separate
>> > devices, a radio receiver to obtain the the GPS data, a device
>> > to generate PPS, and a device to convert GPS data to NMEA
>> > sentences.
>>
>> Except that in a modern chipset as used in a cell phone, all of
>> those functions, plus wifi and possibly even more, is a single
>> chip.
>> >
>> > BTW, NMEA stands for National Marine Electronics Association.
>> > Guess why commercial GPS devices output data in a marine
>> > standard format.
>> >
>> > In circa 1996 those three devices would likely be in three 19
>> > inch rack mount boxes containing mostly discrete components.
>>
>> Your timing is off by a substantial number of years: Garmin
>> sold (portable) GPSs for $105M already in 1995, I have track
>> logs which are older than this.
>>
>> https://en.wikipedia.org/wiki/Garmin#Handheld_GPS
>
> I for one have been fascinated by this discussion. I ran my own
> linux server (Slackware) for the better part of two decades, and
> spent quite a lot of time getting ntp up and running to my
> satisfaction.
>
> The Garmin page reminds me I have an old etrex Vista HCx sitting
> in a closet at home. I don't suppose there's any way to hack it
> into use as a GPS clock? Guessing it may not even generate a PPS
> signal, let alone have any way to get it out of the unit.
>
> It was a terrific device for its time. It rode on the handlebars
> of my bike for tracking speed, mileage, and routes.

I doubt it even has a PPS signal anywhere as a general purpose
navigation device would have no need for it. If it outputs serial NMEA
sentences, which I would doubt, you could use it without PPS assuming
that an NTP accuracy in the millseconds is good enough for you.

Assuming you want to use something Linux PC based, then your options
are for minimal investment:

Finding something old on ebay or in a surplus store.

A DYI project using inexpensive board sets. This will cost in the $50
range and requires soldering, building cables, etc.

A Commercial Off The Shelf device you can just plug in. The cheapest
COTS devices I have found that provide both NMEA sentences and PPS are
about $180 new on ebay. They also contain a disciplined oven crystal
oscillator with both 10 MHz and 1 PPS singnals on BNC connectors. These
are handy if you also do RF or test equipment stuff.

There does not seem to be any current market for simple GPS receiver
devices with a serial output and PPS. There is a huge market for USB
GPS, actually GNSS, devices and if NTP accuracy in the millseconds is
good enough for you, they cost about $15 on amazon. Look for the VK-162
G-Mouse available from several vendors.

If you have a SBC such as a Arduino or Raspberry Pi, you have LOTS of
cheap options for building a NTP server.

And finally, if you have more money than common sense and want to be the
envy of your geek friends, you can get a new rubidium standard box on ebay
for about $800 complete with NMEA and PPS on a DB-9 connector and 10 MHz
and PPS on BNC's.

Re: gpsd no PPS output - Solved

<sehb5g$1vbs$1@gioia.aioe.org>

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https://www.rocksolidbbs.com/devel/article-flat.php?id=257&group=comp.protocols.time.ntp#257

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From: terje.mathisen@tmsw.no (Terje Mathisen)
Newsgroups: comp.protocols.time.ntp
Subject: Re: gpsd no PPS output - Solved
Date: Thu, 5 Aug 2021 20:37:37 +0200
Organization: Aioe.org NNTP Server
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 by: Terje Mathisen - Thu, 5 Aug 2021 18:37 UTC

Jim Pennino wrote:
> Ted Heise <theise@panix.com> wrote:
>> On Thu, 5 Aug 2021 17:50:16 +0200,
>> Terje Mathisen <terje.mathisen@tmsw.no> wrote:
>>> Jim Pennino wrote:
>>>> David Woolley <david@ex.djwhome.demon.invalid> wrote: So, in
>>>> what today we call a gps, there are at least three separate
>>>> devices, a radio receiver to obtain the the GPS data, a device
>>>> to generate PPS, and a device to convert GPS data to NMEA
>>>> sentences.
>>>
>>> Except that in a modern chipset as used in a cell phone, all of
>>> those functions, plus wifi and possibly even more, is a single
>>> chip.
>>>>
>>>> BTW, NMEA stands for National Marine Electronics Association.
>>>> Guess why commercial GPS devices output data in a marine
>>>> standard format.
>>>>
>>>> In circa 1996 those three devices would likely be in three 19
>>>> inch rack mount boxes containing mostly discrete components.
>>>
>>> Your timing is off by a substantial number of years: Garmin
>>> sold (portable) GPSs for $105M already in 1995, I have track
>>> logs which are older than this.
>>>
>>> https://en.wikipedia.org/wiki/Garmin#Handheld_GPS
>>
>> I for one have been fascinated by this discussion. I ran my own
>> linux server (Slackware) for the better part of two decades, and
>> spent quite a lot of time getting ntp up and running to my
>> satisfaction.
>>
>> The Garmin page reminds me I have an old etrex Vista HCx sitting
>> in a closet at home. I don't suppose there's any way to hack it
>> into use as a GPS clock? Guessing it may not even generate a PPS
>> signal, let alone have any way to get it out of the unit.
>>
>> It was a terrific device for its time. It rode on the handlebars
>> of my bike for tracking speed, mileage, and routes.
>
> I doubt it even has a PPS signal anywhere as a general purpose
> navigation device would have no need for it. If it outputs serial NMEA
> sentences, which I would doubt, you could use it without PPS assuming
> that an NTP accuracy in the millseconds is good enough for you.

The etrex was a late relative to the Garmin GPS II, II+, III etc, the
very first devices Garmin made used a two -channel receiver which they
had to multiplex across the tracked channels, but then they very early
made their own 12-channel chipset which was used all over the their many
offerings.

One of those was the model 18 (afair), a puck antenna/receiver which had
a serial interface, and which included a PPS signal (although at TTL
levels, but that usually worked as is, otherwise the needed RS232
buffering chip was dirt cheap to add.

I used both this and the Motorola Oncore UT+ as the sole internal
reference for a multi-national corporation with 70-80K employees and
offices and/or factories in 130 countries.

>
> Assuming you want to use something Linux PC based, then your options
> are for minimal investment:
>
> Finding something old on ebay or in a surplus store.
>
> A DYI project using inexpensive board sets. This will cost in the $50
> range and requires soldering, building cables, etc.

Right, except it is in fact easy to get even lower these days.
>
> A Commercial Off The Shelf device you can just plug in. The cheapest
> COTS devices I have found that provide both NMEA sentences and PPS are
> about $180 new on ebay. They also contain a disciplined oven crystal

Almost certainly not: OCXOs were almost completely replaced by TCXOs due
to both faster startup times and much lower power usage, while getting
more or less exactly the same performance.

Have this changed back over the last 5+ years?

> oscillator with both 10 MHz and 1 PPS singnals on BNC connectors. These
> are handy if you also do RF or test equipment stuff.
>
> There does not seem to be any current market for simple GPS receiver
> devices with a serial output and PPS. There is a huge market for USB
> GPS, actually GNSS, devices and if NTP accuracy in the millseconds is
> good enough for you, they cost about $15 on amazon. Look for the VK-162
> G-Mouse available from several vendors.
>
> If you have a SBC such as a Arduino or Raspberry Pi, you have LOTS of
> cheap options for building a NTP server.
>
> And finally, if you have more money than common sense and want to be the
> envy of your geek friends, you can get a new rubidium standard box on ebay
> for about $800 complete with NMEA and PPS on a DB-9 connector and 10 MHz
> and PPS on BNC's.

What's funny is that you can in fact do far better even using USB, if
you use the same type of protocol as some of the early (non-GPS)
reference clocks did, i.e. a two-way protocol where the computer would
tell the reference clock what it thought the current time was, while the
receiver measured the round-trip delay, and then sent back a timestamp
adjusted to be as close as possible when the computer read it.

On RS232 this allowed sub-ms, with USB3 speeds you should be able to get
into the low microseconds range.

Terje

--
- <Terje.Mathisen at tmsw.no>
"almost all programming can be viewed as an exercise in caching"

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