[ntp:questions] Can NTP sync within 12us for NBFM

Brian Inglis Brian.Inglis at SystematicSw.ab.ca
Tue Apr 29 02:59:24 UTC 2014


On 2014-04-28 13:20, William Unruh wrote:
> On 2014-04-28, Rob <nomail at example.com> wrote:
>> William Unruh <unruh at invalid.ca> wrote:
>>>> All in all it is funny to read all the "that cannot be done"-like comments
>>>> by several persons on a ntp newsgroup while systems like this have been in
>>>> use since the seventies, and in fact have already been build by amateurs
>>>> and are in operation today.  So I prefer to go by the experience of
>>>> the people who built those networks, rather than the armchair experts.
>>>
>>> Not, "it cannnot be done", but "it is silly to try". I simply have a
>>> really really hard time figuring out why you want to do that.
>>
>> You apparently are not familiar with the radio amateur hobby.
>>
>> Most people have a hard time figuring out why you would want to construct
>> a repeater to talk to someone else driving around in a car, when you
>> could simply dial his number on the mobile phone.
>
> That was not what I had trouble figuring out.
>
>>
>>> If it really is 12us I would be really interested in knowing why. I
>>> might even learn something.
>>
>> I already said that I was suprised about this as well, but I have heard
>> it from two different persons who had not been working together and
>> it was explicitly asked if if would not be 12ms instead of 12us.
>
> And they did not explain themselves!?

Speculatively and IANA RE (asking in the hope that an RE or Time Nuts mailing list
member of this group may provide the correct answer) I understand that the NBFM
transmitter starts with phase modulation then integrates, multiplies, and filters
the result to the FM carrier frequency, could a phase error more than 12us/s (PPM)
possibly generate either a significant signal distortion, and/or unwanted harmonics
within the filter passband?
-- 
Take care. Thanks, Brian Inglis


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