[time-nuts] Time source for indoor standalone PC

Fri May 17 12:52:02 EDT 2013

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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>    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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