[time-nuts] : L1 GPS timing signal(s) into local time on computer(s)

Chris Albertson albertson.chris at gmail.com
Tue Aug 21 16:48:50 UTC 2012

On Tue, Aug 21, 2012 at 9:35 AM, Sarah White <kuzetsa at gmail.com> wrote:

> Thanks Chris.
> I always appreciate clear explanations. I'm assuming that the "fixed
> location" requirement is important to note for purposes of compensating
> for any dopler shift, as well as the distance the signal must first
> travel before being decoded.
> ... I would presume that the fixed location used for above calculations
> would be relative to the position of the antenna? I read somewhere that
> even compensating for the length of the antenna cabling is important?
> Yes, the GPS' site survey measure the antenna location.   And it will not
be exactly right unless you measure the cable length.

Yes.  the cable length delay is close to the speed of light or aboutone
nanosecond per foot.  Actually there is a correction called "velocity
factor" that a given cable will have.  All this is in the Trimble user
manual and I'm sure the UMs for other GPSes.  There is delay in the serial
cable and in any "glue" logic chps and in the PPS distibution amp.    To
push the state of the art you have to carefully model all of this.  For
normal use you may not have to except if you have really long cables.

Chris Albertson
Redondo Beach, California

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