[time-nuts] Time source for indoor standalone PC

Fri May 17 17:23:28 UTC 2013

Even something as simple as a Chronodot will hold to a few seconds a year.
 Make something out of an ocxo and you can beat that.  You just need to
transfer time in from some outside source once a year or so to synchronize
it.  Make your gizmo output GPS time sentences and most NTP implementations
should be able to read it.

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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