[ntp:questions] Too much offset from GPS?

Unruh unruh-spam at physics.ubc.ca
Tue Mar 11 15:18:55 UTC 2008

Steve Kostecke <kostecke at ntp.org> writes:

>On 2008-03-11, chowalit.lab Chowalit Lab Linux <chowalit.lab at gmail.com> wrote:

>> So It's wrong on my GPS (GPSmap60).

>The problem with the GPSMAP 60 is that it is the wrong type of GPS
>receiver for an application which needs highly stable time.

>There are two types of GPS receivers: mapping and timing.

>The key difference between these two type of receivers is that the
>timing receivers provide a Pulse Per Second (PPS) output which is
>typically aligned to within 1 microsecond (0.000001 sec) of UTC time.
>Higher quality timing receivers may be capable of closer (e.g.
>nanosecond) alignment.

>Both types of receivers are able to emit NMEA sentences via a serial or
>USB interface. These NMEA sentences are emitted when the receiver is
>not busy doing other things such as processing satellite data, updating
>the display, etc., and can occur at _any_ _time_ during second they are
>valid for. Time sources utilizing only NMEA sentences are not suitable
>for a Stratum 1 time server.

>It is up to you to decide if the GPSMAP 60 is good enough for your

>The USD249.99 GPSMAP 60 is a mapping receiver.

>The USD74.50 GPS18 LVC is a timing receiver.

68.50 You are quoting the USB which is useless for timing.



MAKE SURE you get the LVC, not the PC or USB version. Only the LVC is useful
for timing. 

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