[ntp:questions] Best NMEA sentence

Neil Green ncguk at hotmail.co.uk
Sun Feb 21 17:23:42 UTC 2016

On 20 Feb 2016, at 9:52 pm, Hal Murray <hmurray at megapathdsl.net> wrote:

> Do you have a specific brand/model in mind?  (or chip set?)

Currently a SkyTraq Venus 6. My previous experiments with a Trimble Copernicus II using TSIP proved fruitless (I know the Copernicus II will output NMEA sentences but I’ve been struggling to get coverage with it lately).

> Simple answer is use GPRMC.  Turn off the others if you can.

I always do. I’ve always vacillated between GPRMC, GPGGA and GPZDA, but I’ll stick to RMC from now on.

> GPGGA doesn't include the date.  That might make a difference when booting after power loss if your clock battery is dead.  GPZDA doesn't include a valid status marker.
> The other consideration is that the length of some sentences changes depending on how many satellites are visible and working.  If the cluster of sentences starts at the same offset each second and the one you pick is after one that changes the length, the offset will vary by the length and baud rate.  So pick one that is early in the cluster.

A supplementary question: when searching for ways to make an NTP server better, I find FreeBSD recommended a lot, but only FreeBSD 8 or earlier. Is, say, Debian Linux now on a par with FreeBSD 10.2 in terms of low latencies and so forth or is FreeBSD still favoured?

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