[ntp:questions] Can NTP sync within 1ms

Rob nomail at example.com
Sun Apr 27 18:42:10 UTC 2014

jimp at specsol.spam.sux.com <jimp at specsol.spam.sux.com> wrote:
> Rob <nomail at example.com> wrote:
>> jimp at specsol.spam.sux.com <jimp at specsol.spam.sux.com> wrote:
>>>> The listeners should enjoy a smooth reception while driving around.
>>>> So of course there should be no time lag between the modulation signals
>>>> of the different transmitters.  Experts in the field tell us we should
>>>> be within 12us.
>>> Unless I fat fingered the calculator, that means the difference in distance
>>> between transmitters relative to the receiver can be no more than 3.6 km.
>>> 300 meters per microsecond; it is the law...
>> The goal is not to have 12us difference in arrival time, but to be
>> within 12us for transmission time.
> What good does that do you?
> And regarding "smooth reception while driving around", have you ever heard
> of multipath or the capture effect?

Well, smooth reception must be explained as "communication is possible",
not with the HIFI quality expected from a broadcast station.

What I mean is that you can drive around and receive the signal all over
the place, even when you drive out of range of one transmitter into the
range of the next.  It works perfectly when the capture effect results
in reception of one transmitter, and in the area where two transmitters
are equal in strength it requires suitable synchronization to still have
good communication.

I did not come up with the 12us figure, I would have guessed it a bit
higher.  The figure comes from different experts in the field.  The
people that designed and deployed such systems in the world of emergency
services etc.

We can now try it in amateur radio because the advances in technology
have made things like GPSDOs and fast network connections affordable.

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