[time-nuts] GPS USB dongle for time server

[Kasper Pedersen]

On 11/09/2010 03:07 AM, Hal Murray wrote:
> The Garmin USB 18 was much better.  Unfortunately, it wasn't as sensitive as 
> competing units and it's been replaced by the 18x which has the typical 
> horrible jitter problems.  I don't have a graph of the 18x handy, but here is 
> data from a USB 18.
>   http://www.megapathdsl.net/~hmurray/ntp/GPS18USB-off.gif
> (The Garmin USB 18/18x units don't speak NMEA, but that's just SMOP.)
>   

The 18x-lvc (rs232):

http://n1.taur.dk/permanent/hist3.png
http://n1.taur.dk/permanent/adev3.png
http://n1.taur.dk/permanent/gpst3.png

(in the last plot the y axis is seconds, not nanoseconds)

It is no timing receiver, but it suffices to drive ntpd.
Two notes: the 18x here is configured for NMEA at 115200, as
that is what the homecooked GPSDO speaks. Otherwise the
mesages pile up, moving the time message around excessively.
This unit is decapsulated and sitting indoors.

/Kasper Pedersen