[ntp:questions] Can NTP sync within 1ms

jimp at specsol.spam.sux.com jimp at specsol.spam.sux.com
Sun Apr 27 18:53:24 UTC 2014


Rob <nomail at example.com> wrote:
> Jochen Bern <Jochen.Bern at LINworks.de> wrote:
>> [Resend to list, rather than non-working(?) sender e-mail address]
>>
>> On -10.01.-28163 20:59, Rob wrote:
>>> We are setting up a co-channel diversity network.  That means multiple
>>> FM transmitters that are transmitting the same signal on the same
>>> frequency on different sites, where the receive areas partly overlap.
>>> 
>>> 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.
>>
>> I'm afraid I don't get it yet. You're trying to sync waveforms on the HF
>> side (~100 MHz?) instead of switching between two transmitters on the AF
>> side (couple kHz, with that much more leeway for the sync), a la
>> perfectly normal car radio with RDS AF and dual tuners, because ... ?
> 
> It is not an FM broadcast system, it is an amateur radio repeater system
> with wide area coverage.
> Similar systems are in use, or at least have been in use, in repeater
> systems used by emergency services, taxi companies, etc.
> 
> Of course it is possible to use different transmitters and find some
> way to switch the receivers.  It is also possible to use a mobile phone
> to communicate.
> 
> But amateur radio is about experimenting and self-education, and we just
> want to see if it can be done.  In fact, it already has been done by
> another group using a different system setup, and we want to see if it
> can be done this way as well.

It is all made irrelevant by a combination of channel bandwidth and the
capture effect.

http://en.wikipedia.org/wiki/Capture_effect

Unless there is a huge difference in transmission times, no one is going 
to notice unless they are somewhere where the signal strength of multiple
transmitters is roughly equal and then your major problem will be picket
fencing, not audio synchronization.


-- 
Jim Pennino



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