[ntp:questions] Indirect GPS time source options

Brian Inglis Brian.Inglis at SystematicSw.ab.ca
Fri Mar 14 05:45:08 UTC 2014

On 2014-03-13 11:52, Olivier Drouin wrote:
> Thank you Greg, Jochen, William,
>                                 Great answers.
>                                 Diversity is really what I'm looking for and
> I dont really need microsecond accuracy.
>                                 CDMA seemed to be the most 'convenient' way
> to add diversity without a need for a working WAN link and/or line of sight
> view to the sky.
>                                 Also, I already know that I get good cell
> signal from inside the server room.
>                                 The thing with CDMA is that it looks like
> it'll not be around for many years and I haven't seen any equipement for
> 4g, hspa, LTE, etc...
>                                 For your information, I think I can get away
> with a 10K budget but I need to be absolutely sure It'll work beforehand.
>                                 I'll talk with the facility owner and do
> some tests with handheld GPS so I can verify what kind of signal I can get
> (and where). I'm a bit worried because I dont have roof access whenver I
> want and I dont know how the antenna will behave with the snow we get
> around here (quebec city).
>                                 Ill also verify if I can synthonize the CHU
> radio frequency inside the server room if I can get my hand on a scanner.

To test CHU reception you need a SW receiver to tune 3330, 7850, and 14670 kHz
- 1kHz tones of different durations are broadcast every second except second 29
of each minute, data from seconds 31 to 39 ending at each half second, and
voice is broadcast from seconds 50 to 59: see time signals at
http://www.nrc-cnrc.gc.ca/eng/services/time/short_wave.html and data format at

To use CHU, you need a SW receiver, possibly an external antenna, Bell 103 300 bps
8-N-2 compatible modem, an async serial UART port that will read it, and a system
running NTP.

For testing GPS, you could use any smart device with GPS, such as recent iP* or
Android players, phones, or tablets, and a monitor app that shows satellite
counts and visibility.

To use GPS, you need a Sirf receiver module, like a Garmin 18x LVC, or uBlox NEO/
LEA-6T/M8F, ideally mounted inside a south facing roof space without steel,
or window with no buildings in the way, or else an external active GPS antenna
rated for -40C-+40C mounted above snow and obstruction level, hooked to an async
serial UART port, on a system running NTP. See David Taylor's various devices,
systems, and releases at http://www.satsignal.eu/ntp/.

There are also a number of vendors who will sell you commercial GPS gear with
antennas, and consultancies who will buy, install, and set it up for you.

All OEM timing receivers typically perform much better than hand held devices,
and the gold standard seems to be the Trimble Thunderbolt, available locally
from Novotech in Pointe Claire near Montreal.

Take care. Thanks, Brian Inglis

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