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

Brian Inglis Brian.Inglis at SystematicSw.ab.ca
Tue Apr 29 13:04:48 UTC 2014


On 2014-04-29 00:47, David Woolley wrote:
> On 29/04/14 03:59, Brian Inglis wrote:
>> I understand that the NBFM
>> transmitter starts with phase modulation then integrates, multiplies,
>> and filters
>> the result to the FM carrier frequency
>
> You are confusing carrier phase and audio phase.

I omitted the preemphasis because that is applied to the audio before
phase modulation of the IF, and I don't believe the 12PPMphase error
would make any difference to the audio, but may affect the IF or carrier.
  
> (FM modulation is mathematically the same as frequency modulation except
> for the frequency response of the audio.  Both direct frequency modulation
> and phase modulation can be used.  I believe NBFM is pre-emphasised such that,
> for most of the passband, it is actually more accurately described as phase
> modulation.)

ITYM FM ... PM, and the preemphasis flattens the audio spectrum to
increase the resolution of the low level high frequency voice
components and make better use of the available bandwidth.

-- 
Take care. Thanks, Brian Inglis


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