[ntp:questions] Indirect GPS time source options

Olivier Drouin ol.drouin at gmail.com
Thu Mar 13 14:29:10 UTC 2014

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).

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

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.

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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Thank you and best regards,
Olivier Drouin.

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