[ntp:questions] Shared PPS source/Multiple PPS sources

Paul tik-tok at bodosom.net
Sat Feb 7 00:28:52 UTC 2015


On Fri, Feb 6, 2015 at 3:17 PM, <walter.preuninger at gmail.com> wrote:

> Ok, so these questions might be off the wall.
>

Yes.


>
> Is there any reason why I could not share the PPS output of say, my u-blox
> 7 GPS module on multiple computers?


 Of course you can.  However the correct way to do this is with a
distribution amplifier and it would be cheaper to buy another GPS.

Would it be good or bad to peer these 2 systems with each other?
>

It depends.  What are you trying to do?


>
> On the opposite end of the spectrum, would it be reasonable to have a PPS
> output from said module on a computer, with a second PPS (from another GPS
> module) on that same computer?
>

It depends on why you would do it.  Again what are you trying to do?


> The Chronodot/DS323X chips have 1 Hz sqaure wave output and they have +/-
> 2ppm. It seems that the ATOM clock driver could be used, but would it be
> better to write a driver specifically for this chip?
>

RTC parts are not intended for hold-over input into NTP.  Unless you've
lost network access you'd do better to use a remote system.


>
> And a side question: Is it the GPS module that calculates when the PPS
> goes active?


If by calculate you mean determine then yes the PPS source (typically but
not exclusively a GPS in the NTP community) completely determines when the
PPS signal is active but I suspect you have a different question in mind.


> Is this signal compensated for the time it takes the signal from the sats
> in the module, or on the SV?
>

I've decided I have no idea what this question means.


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