[time-nuts] Phase modulation detection/NIST plan

[J. Forster]

There is not an infinity of good sync words. A typical good sync word has
a high positive autocorrelation when synced, sloping downwards
monotonically.

Thus the cross-correlation of the received word with a locally stored
reference can be used to steer the loop using a small dither and a lock-in
technique.

-John

================



> Hi
>
> The gotcha is that they may change the sync word based on test data. They
> may also tweak other vague points in the spec based on the troubles they
> run into in their tests or with their silicon.
>
> Bob
>
> On Jul 8, 2012, at 8:07 PM, Magnus Danielson wrote:
>
>> On 07/09/2012 12:46 AM, paul wrote:
>>>
>>> Peter indeed there could be
>>> But it should not need to be decoded to undo the psk.
>>> Plus documentation lacks some of the details I think to actually do it.
>>> But that would be a significant project since the formats not been
>>> settled completely yet.
>>
>> I have looked at the PTTI 2011 paper (wwvb.pdf) and much of a format is
>> being shown. Has anyone established the 14 bit sync-word and verified
>> the format? It seems that aligning up with the normal AM broadcast
>> should be possible.
>>
>> Can someone record it as it has been reduced to say 2 kHz and analyze
>> the produced audio file? Recoding with 48 kHz sampling rate should allow
>> almost trivial 2 kHz I-Q demodulation to illustrate phase swaps.
>>
>> Cheers,
>> Magnus
>>
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