[ntp:questions] Indirect GPS time source options

William Unruh unruh at invalid.ca
Thu Mar 13 16:56:26 UTC 2014


On 2014-03-13, Olivier Drouin <ol.drouin at gmail.com> wrote:
> On Wed, Mar 12, 2014 at 3:59 PM, William Unruh <unruh at invalid.ca> wrote:
>
>> On 2014-03-12, Olivier Drouin <ol.drouin at gmail.com> wrote:
>> > Hello,
>> >       I'm located in Canada and I'm trying to find indirect GPS time
>> sources.  I like the idea of using CDMA as a time source but it seems that
>> this technology will not be around for a lot longer.
>>
>> What is an "indirect gps timing source"? How does that differ from using
>> ntp to go to a level 1 server which gets its time from gps. While cdma
>> uses accurate time, it is not really designed to deliver accurate time.
>> GPS is.
>>
>
> Well, from what I understand the cell networks are closely synchronized
> against the GPS constellation. So, synchronizing against the cellular
> network is called "indirect gps", at least according to the endrun website
> (I haven't seen this nomenclature anywhere else).

And in npt terms it would be called a  stratum 1 server. 
>
> It is different of GPS because if your WAN links are down, which can happen
> once every few years,  then, hopefully, you can still reach the cellular
> network in your neighborhood or else its the end of the world or
> something...

Or a power blackout, while the sattelites keep beeping away even if the
whole eastern seaboard is in the dark. 


And except a gps receiver is far cheaper and more accurate than a cell
timing receiver. 


>
> Also, from what I understand and please correct me if I'm wrong but
> cellular networks are indeed designed to be accurately timed because it's
> needed for the normal operations of the cell network.

Yes, but they are not designed to deliver accurate time to the rest of
the world AFAIK. 
>
>
> Thank you for your reply, best regards,
> Olivier Drouin
>
>>
>> >       For exemple, Endrun Technologies sells the Sonoma N12 which seems
>> to allow time synchronization against CDMA signal without the need for a
>> carrier subscriptions.
>> >
>>
>> And a gps receiver with PPS output is probably 1/100 the price.
>>
>> >
>> >        Is the CDMA method still available with these other cellulare
>> network technologies like HSPA or LTE? If not, do I have other options
>> beside a GPS antenna with a sky view?
>>
>> CDMA also needs an antenna with cell tower view. What's the difference?
>> (Note my gps on an east facing window through a large cedar tree works
>> just fine.)
>>
>>
>
>
> As Terje is mentioning, the cell antenna doesnt need a line of sight to a
> cell antenna, so It can be installed inside the server room and you dont
> have to deal with the maintenance problems (lots of snow around here) of a
> GPS antenna on the roof...
>
>
>
>
>> >
>> >
>> >
>> >        Thank you and best regards,
>> >        Olivier Drouin.
>>
>> _______________________________________________
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>> http://lists.ntp.org/listinfo/questions
>>
>
>
> Thank you and best regards,
> Olivier Drouin.



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