[ntp:questions] NMEA ref.clock better than my ISP's timeserver?

David J Taylor david-taylor at blueyonder.not-this-part.nor-this.co.uk.invalid
Thu Jun 11 10:29:55 UTC 2009

David Lord wrote:
> Late last night I got round to connecting the Garmin GPS18x-LVC and
> just after midnight it stepped from around 60s to 0.5ms and 8 hours
> later is between -74us and +62us. The module is in south facing
> upstairs window in same location I failed to get anything useful
> from the Globalsat BR304. Now I need to make a 30m extender cable to
> get the signals downstairs to back of house to connect to servers.
> David

Good news, David.  Sensitive little pill-box, isn't it?

One suggestion might be wireless - could you get a very atom-based small 
PC or even a wireless router to accept the GPS signal and serve NTP over 
the WLAN?  Cable would be nicer and my preference.  With Dave Hart's new 
PPS support it /should/ be possible to send just the PPS signal around 
(two wires), and use that to refine an Internet-derived time.  I might be 
inclined to go for a screened cable if you need a 30m run, but thin 3-core 
mains cable /might/ suffice.  The RS-232 I used to use was very tolerant 
of cabling, but it probably had higher signal levels and robustness than 
the GPS 18x LVC.


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