[ntp:questions] Local time sources

unruh unruh at wormhole.physics.ubc.ca
Tue May 11 15:10:50 UTC 2010

On 2010-05-11, David J Taylor <david-taylor at blueyonder.co.uk.invalid> wrote:
> "Jaap Winius" <> wrote in message 
> news:4be85b0e$0$6761$e4fe514c at dreader14.news.xs4all.nl...
> []
>> Okay, I think this answers my question. I've been running a Garmin GPS 
>> 18
>> LVC for a few years now...
>>   http://www.rjsystems.nl/en/2100-ntpd-garmin-gps-18-lvc-gpsd.php
>> What this page does not say is that my configuration also includes a
>> DFC77 receiver. This long-wave radio time signal receiver is an order of
>> magnitude less precise than the GPS receiver, but it has already proved
>> its value several times in terms of redundancy: twice when the GPS fell
>> from the skylight following a suction-cup failure, and once when gpsd
>> failed to function properly after an update. That's great, but the point
>> is that there's not much else to it.
>> Thanks,
>> Jaap
> Indeed, having that backup has been worthwhile for you.
> I do like your Web page, and added a pointer to it from mine - I made a 
> FreeBSD write-up here:
>   http://www.satsignal.eu/ntp/FreeBSD-GPS-PPS.htm
> When I bought my second GPS 18 LVC I got the X version (GPS 18x LVC) which 
> is a lot more sensitive and allows better indoor operation - you may like 
> to add that to your page where you say the GPS 18 LVC is now obsolete.

Yes. Also note that chrony also now (1.24 version) allows use of gpsd to synchronize your
clock with the Garmin ( and also does not have the problem you mention
with ntpd that if it freeruns too long, it may not resynchronize-- it
will and do so far faster than ntpd does.)

It is hard to imagine that the suction cup could fail and you not notice
it with the gps mounted where it is. I'm afraid my family would shoot
me. I run the cable out a basement window and the gps is mounted on the
front iron rails of the house using its magnetic mount. It sees about
1/4 of the southern sky (tall trees on the street ahead of it, house
behind it), but that seems to be enough.  

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