EEVblog Electronics Community Forum
General => General Technical Chat => Topic started by: hamster_nz on September 15, 2016, 04:35:21 am
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It's just become obvious to me the that pulse per second output on a GPS module are only indirectly tied to the satellites 'transmitting' a time reference signal.
When the pin waggles based on a prediction made by the GPS module of when a satellite that is over 20,000 kms way and moving at 14,000km/hr will start transmitting a new time stamp - and 20,000kms is about 67 light-millisecond away!
Pretty miraculous.
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And if you want to know just how far you can push this, take a look on the time nuts mailing list archives.
That PPS signal could well be locked to some exceptionally accurate Caesium atomic clocks which are monitored and adjusted to ridiculous levels of accuracy.
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Something else I just discovered is that the Space Vehicles are in semi-synchronous orbit, completing two orbits every 24 hours.
Before I really looked in to it I was thinking that they would be way closer, 1000 km or so but now realise that it wouldn't make sense. Drag and geographic features would destroy accuracy.
And the TX power levels as very much lower than I thought... l can't find the numbers, but I remember it being around 50W - So that is 50W to covers the whole earth, and a tiny bit of that hits our GPS antennas is enough.