[time-nuts] Time source for indoor standalone PC

James Tucker james.d.tucker at gmail.com
Sat May 18 00:34:37 UTC 2013


I agree; regular input from the outside. Here's what I do: 1) I have a
Casio wristwatch with WaveCeptor to set its time every morning, and it is
set to beep on the hour. It produces two beeps. It has never been off by
more than about 500ms against my Thunderbolt running Lady Heather. 2) I
have an Atmel demo board that can listen to ambient sound, and, within +-5
seconds of when it thinks it is on the hour, looks for the specific
frequency signature of my watch. It is uses that to align its own clock. 3)
My office is 'earth friendly', and has metalized windows, through which I
cannot RX GPS, and the network admin is *astoundingly * lazy about setting
the network time, but insists on controlling everyone's computer clock
(Windows).

JimT

Sent from *my* galaxy (Nexus).
On May 17, 2013 12:56 PM, "Chris Albertson" <albertson.chris at gmail.com>
wrote:

> My reading was that in the past he was happy to be within a few seconds but
> now wants something better.  I'm not 100% sure.  But yes a wristwatch is
> good enough for a few seconds.   Periodically the user could check his
> watch against an NTP connected computer outside the room.
>
>
> In general there are only TWO options:
> (1) Receive some kind of signal from outside be it radio or starlight
> through a glass roof but SOME kind of real-time data has to come from the
> outside or.
> (2) Physically move a calibrated clock of some kind from the outside to the
> inside.  The clock could be a wristwatch, hour glass, Rubidium atomic clock
> or whatever.   This clock would require periodic re-calibration.
>
> One question is if the OP can create his own radio signal.  Perhaps he has
> a computer connected to GPS outside the room that controls a low power
> radio that transmits IRIG time code.   We don't know what rules he has to
> operate under.    Why can't he use a long fiber optic connection to a GPS
> system?  Again we don't know what rules he has to work with.   But no
> matter what, data has to some into the room either in real time or by
> moving a clock.
>
>
> On Fri, May 17, 2013 at 9:52 AM, Bob Camp <lists at rtty.us> wrote:
>
> > Hi
> >
> > I believe the original spec on this was "accurate to a few seconds". If
> > that's still the case (I have been known to miss zigs and zags in threads
> > …) the sync requirement isn't terribly stringent. A wrist watch and some
> > care can get you to a fraction of a second.
> >
> > Bob
> >
> > On May 17, 2013, at 12:31 PM, Mark Spencer <mspencer12345 at yahoo.ca>
> wrote:
> >
> > > Hi.
> > >
> > > Re the setting issue I'd look for a solution that can be initially
> > synchronized from the 1pps pulse from a GPS receiver or other precision
> > source.
> > >
> > > If you search for prior posts from me over the last several weeks you
> > should be able to find one where I expand on this in a bit more detail.
> >  (Sorry I am on the road right now.)
> > >
> > > Regards
> > > Mark Spencer
> > >
> > > --- On Fri, 5/17/13, time-nuts-request at febo.com <
> > time-nuts-request at febo.com> wrote:
> > >
> > >
> > > From: time-nuts-request at febo.com <time-nuts-request at febo.com>
> > > Subject: time-nuts Digest, Vol 106, Issue 80
> > > To: time-nuts at febo.com
> > > Received: Friday, May 17, 2013, 9:00 AM
> > >
> > >
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> > > Today's Topics:
> > >
> > >    1. Re: Time source for indoor standalone PC (Chris Albertson)
> > >
> > >
> > > ----------------------------------------------------------------------
> > >
> > > Message: 1
> > > Date: Fri, 17 May 2013 08:43:07 -0700
> > > From: Chris Albertson <albertson.chris at gmail.com>
> > > To: Discussion of precise time and frequency measurement
> > >     <time-nuts at febo.com>
> > > Subject: Re: [time-nuts] Time source for indoor standalone PC
> > > Message-ID:
> > >     <CABbxVHs9LaeJsuP8OXspVmzi+VfHHPUbeCBwAsZgBB+BK=
> FetQ at mail.gmail.com>
> > > Content-Type: text/plain; charset=ISO-8859-1
> > >
> > > If there is no way to get radio signal into the room, then buy a
> rubidium
> > > oscillator.  Conect the Rb to a small notebook PC the run Linux or BSD
> > > Unix.  Let the Rb oscillator drive NTP and get it sync'd up outside
> your
> > > room and then  walk the Rb/NTP server into the room.    Because you are
> > > isolated you will need at least three of these systems and some people
> > > argue you need five of them.   I'd argue five is certainly better, but
> > > three is a minimum.   Then periodically you rotate one of the systems
> > > outside for calibration with GPS.
> > >
> > > Inside the room you configure the three to five servers to run in
> "Orphan
> > > Mode"  This wil allow them to develop a kind of consensus time based
> ont
> > > the set of servers that agree.  Hence the reason for having five
> servers.
> > >
> > > One real problem with a disconnected "island" is dectecting errors.
>  How
> > to
> > > know if the server is 50 or so milliseconds "off".  You can't depend on
> > > only one.
> > >
> > > The good news is theRubidium Oscilters are not expensive.  $100 Will
> get
> > > you a working unit.  And certainly PC notbook computers are dirt cheap
> if
> > > you buy older ones.
> > >
> > > The hard part here is setting the Rb units.  They need to be GPS
> > > disciplined when GPS is available and then flip over to "hold over"
> mode
> > > when GPS goes away.  with your low-precision requiremnts that should
> keep
> > > good time for over a year with GPS disconnected.   Then you take them
> > > outside and run them for a few days with GPS.   So with six servers,
> one
> > > would be outside and five inside and every two months you rotate them.
> > > This should let you run at the millisecond level and also have the
> > ability
> > > to withstand two server failures.
> > >
> > >
> > >
> > >
> > > On Thu, May 16, 2013 at 9:45 PM, Grant Waldram <grant at remobs.com.au>
> > wrote:
> > >
> > >> Hi folks. I wouldn't call myself a time nut, so this is really an
> > effort to
> > >> ask for advice from some people who know the field. My first contact
> > with
> > >> time synchronisation was looking at the instrumentation clocks for the
> > >> Woomera rocket test facility when I went out there for a few (large!)
> > hobby
> > >> rocket launches. I can't even remember the system's name but it used a
> > >> series of pulses of various lengths to give a unique time code. But, I
> > >> digress...
> > >>
> > >>
> > >>
> > >> I've not had much need for time synchronisation over the years, but in
> > >> recent years NTP has been able to get me by. Unfortunately I'm now
> faced
> > >> with a network that needs a moderately correct clock (I'm scared of
> > using
> > >> the word 'acurate' around you folks!) to the order of a few seconds or
> > so,
> > >> but with no possibility of an external internet connection (for a
> > number of
> > >> reasons). At present I'm using one PC running Windows Server as an
> SNTP
> > >> server to synchronise all of the devices, as it is the only device in
> a
> > >> physically secure location. This is inside a security-fob protected
> > room. I
> > >> can't get GPS signals in there, and the Australian radio clock network
> > was
> > >> shut down about ten years ago. Our CDMA network was turned off in
> 2008.
> > >> Right now all I can think of is GSM, and while i know it's not
> terribly
> > >> accurate it seems like it might be the easiest. It also might be that
> > I've
> > >> got tunnel vision and there's a simpler solution out there.
> > >>
> > >> I would be quite happy with some sort of dedicated GSM/NTP-server box,
> > and
> > >> there are Arduino/Raspberry Pi/Linux homebuilts for that out there,
> but
> > I
> > >> have been wondering if one of the fairly common GSM USB sticks could
> > >> somehow
> > >> be a time source to set the server clock?
> > >>
> > >>
> > >>
> > >> Regards,
> > >>
> > >>
> > >>
> > >> Grant
> > >>
> > >> _______________________________________________
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> > >>
> > >
> > >
> > >
> > > --
> > >
> > > Chris Albertson
> > > Redondo Beach, California
> > >
> > >
> > > ------------------------------
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>
>
> --
>
> Chris Albertson
> Redondo Beach, California
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