[time-nuts] WWVB a different approach to d-bpsk-r (cheating)

Bob Camp lists at rtty.us
Sat Jul 14 21:53:26 UTC 2012


Hi

Well between now and midnight, you will completely loose signal at least once. It's a pretty dramatic amplitude dip as sunset gets right to the "wrong" place.

Bob

On Jul 14, 2012, at 4:56 PM, paul swed wrote:

> Bob
> Yes nights are bad for me, east coast and MSF interference.
> So it could be any number of 60 KHz crossing its just odd it lined up the
> way it did and I double confirmed that I was not doing something silly like
> using alternate triggers.
> 
> Very careful analysis does show a 1-2 us jitter and at diurnal shift I
> really expect something to change it has to.
> Regards
> Paul.
> 
> On Sat, Jul 14, 2012 at 4:32 PM, Bob Camp <lists at rtty.us> wrote:
> 
>> Hi
>> 
>> The "zero crossing" is very arbitrary. If it's correct at the transmit
>> site, it will then be off everywhere else by the speed of light / distance.
>> You will appear to be correct  once every wavelength away from Colorado
>> (roughly every 3 miles). You won't really be correct because you are
>> looking at a different zero crossing.
>> 
>> As long as you don't have sunset or sunrise between you and the
>> transmitter,  WWVB is reasonably stable. At night you will get more signal,
>> but also can have some skywave "stuff" in the mix.
>> 
>> Bob
>> 
>> On Jul 14, 2012, at 3:50 PM, paul swed wrote:
>> 
>>> OK have been doing a lot of experimenting.
>>> I was curious what is the GPS tick in relationship to wwvb. Especially
>>> since it is a reliable 1 sec marker.
>>> Using a Tbolt since everyone has one on the list. ;-) And monitoring the
>> 10
>>> us tick to the wwvb 60 Khz carrier on a scope. Amazingly and over at
>> least
>>> 2 hours now, the rising cycle of 60 Khz aligns to the 10 us Tbolt tick
>>> rising edge. Expected some form of drift.
>>> 
>>> Would not have actually thought there should be such a relationship or
>> its
>>> truly pot luck today.
>>> WWVB today is also not running bpsk.
>>> 
>>> Should such a relationship actually exist?
>>> There is a clue in a 1985 article in ham radio magazine.
>>> It went something like this. At any given instant the 60 Khz may jitter.
>>> But for every 1 sec period there will be exactly 60,000 cycles.
>>> 
>>> If it does stay aligned, then the cheating d-bpsk-r gets to be
>> interesting
>>> and very implementable.
>>> 
>>> The approach using a micro to sample a squared up 60 Khz after the Tbolt
>>> tic.
>>> Perform 2-3 1 usec samples in the leading 90 degree signal.
>>> Decide is it a 0 or 1 phase.
>>> Select a inverted or non inverted 60 Khz into the output path to
>> maintain a
>>> constant phase 60 Khz for the old recvrs.
>>> 
>>> Sure its cheating. But if this relationship is real I should be able to
>>> implement the answer very quickly as a proof point.
>>> 
>>> Have not heard if the NIST testing is completed or when the next one is.
>>> But for today all of the rcvrs are working just fine.
>>> Regards
>>> Paul
>>> WB8TSL
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>> 
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