[ntp:questions] best gps receiver for time synchronization
unruh-spam at physics.ubc.ca
Tue Mar 10 17:16:43 UTC 2009
Martin Burnicki <martin.burnicki at meinberg.de> writes:
>David Woolley wrote:
>> Unruh wrote:
>>> No. That is what GPS does for you. It determines your postion, then uses
>>> that to determine the time delay from the sattelite to your receiver.
>> Actually, it is the other way round. It uses the differences in the
>> time delays to solve for the position (and the actual time delays).
Actaully they solve for the position and the time delay all at once.
But if the receiver knows its position, it only needs one sattelite to
determine the time, and it uses the position to determine the delay.
>Right. However, it computes the position of the *antenna*. So if you
>receiver is connected via a long antenna cable you have to compensate the
>signal delay on the cable. This can not be done automatically by the GPS
Agreed. On the other hand, 300m is 1usec and most computers are completely
incapable of discipling the clock to that accuracy ( interrupt latencies,
etc) If you actually have a system which could do better than that, then
antenna delay is important. As may proper cable termination so the signal
bouncing back and forth along the cable does not mess up the timing.
>For examples, for our GPS receivers the antenna can be installed up to 300
>meters away from the receiver, and you can configure the antenna cable
>length in the receiver to compensate that delay.
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