David I. Emery skrev:
Most network broadcast distribution is via satellite, and satellites move around in their box in the sky so any time or frequency derived from satellite downlinked signals is subject to Doppler shifts over the course of a day as the satellite completes its figure eight pattern in the sky (most operational birds are slightly inclined, thus the figure 8 - none are dead nuts on the equator and in perfectly circular orbits). This means that no network timing from a satellite signal is stable by precise metric standards... even if the uplink signal is right on.What all this means in practice is that there is no longer anyprecise broadcast TV signal that can be depended on as really accurate.
You are correct, until the time when an ATSC network is operated in Single Frequency Network (SFN) mode, in which case the transmitter signals is coordinated with the aid of GPS receivers. The ATSC SFN specs is in a separate document. As I recalled it when I fast read it a few years back was that it seemed like they had made a few thought errors which caused overspecing but still possible.
Cheers, Magnus _______________________________________________ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
