Haven't looked into this in depth but sub-nanosecond sync for systems up to 10km apart is interesting since 10km is about 33 light microseconds. There is some trickery going on.
It's totally possible to achieve synchronization better than light transmission time. For the purposes of synchronization, the speed of light delay, and any other delay are indistinguishable, and need not be distinguished.
The gravity well time dilation is about 3.5 nanoseconds per meter per year near the surface of the earth. (time changes rate with altitude in a gravity well)
Sub-nanosecond synchronization is getting into the relativity is measurable realm.
Haven't looked into this in depth but sub-nanosecond sync for systems up to 10km apart is interesting since 10km is about 33 light microseconds. There is some trickery going on.
Yes, it uses phased locked loops and measures phase difference between the master clock and the local clock.
It's totally possible to achieve synchronization better than light transmission time. For the purposes of synchronization, the speed of light delay, and any other delay are indistinguishable, and need not be distinguished.
The gravity well time dilation is about 3.5 nanoseconds per meter per year near the surface of the earth. (time changes rate with altitude in a gravity well)
Sub-nanosecond synchronization is getting into the relativity is measurable realm.
Two-way time transfer measures the round-trip propagation time. As a result, it's not directly relevant to the accuracy.