[time-nuts] : L1 GPS timing signal(s) into local time on computer(s)
kuzetsa at gmail.com
Tue Aug 21 16:53:03 UTC 2012
Wow. Okay. The user manual actual considers this cable delay to be worth
I can see why the trimble thunderbolt is a favorite among time nuts <3
On 8/21/2012 12:48 PM, Chris Albertson wrote:
> 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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