[ntp:questions] Can NTP sync within 1ms

jimp at specsol.spam.sux.com jimp at specsol.spam.sux.com
Sun Apr 27 18:59:21 UTC 2014


Rob <nomail at example.com> wrote:
> 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.

Picket fencing makes it irrelevant.

> 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.

Are you sure that figure is NOT for data communications?

Most "emergency services" have voice and data these days.

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

I don't see where that is relevant to anything here.



-- 
Jim Pennino



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