[time-nuts] Dephasing WWVB

Tom Van Baak tvb at LeapSecond.com
Sun Jun 29 17:09:46 EDT 2014


Paul,

Given the long evolution of the project, and the fact that even at the end, classic receivers like the hp 117A and Tracor 599 still won't work with a remodulator -- can you revisit the synchronous decoding idea I suggested?

That is, if the local receiver has a pretty good idea of UTC to begin with (via telephone, radio, smartphone, internet, GPS, etc.), plus a rough idea of the propagation delay, then you can use the published new time code format to *predict* when the 180 degree phase shifts will occur. Then using that information you simply *preemptively* invert the antenna signal polarity at the 1 Hz level.

That way any legacy code or phase receivers continue to work -- because both the 1 Hz AM subcode comes through and the 60 kHz carrier appears almost perfectly intact. The "converter" would simply sit between the unmodified antenna and the unmodified receiver.

I realize the catch-22 in this; if you don't already know the time you can't decode the time. True, and I agree this is not a desert island solution. However, the truth is more like: if you know the approximate time, then you get a NIST-traceable 60 kHz carrier. And all your old carrier tracking gear will continue to work.

For fun, under microprocessor control, you could slide it forward or back a few milliseconds to learn the actual propagation delay as a function of time of day. For extra credit, you can also put back the hourly 45 degree phase shift.

/tvb

----- Original Message ----- 
From: "paul swed" <paulswedb at gmail.com>
To: "Discussion of precise time and frequency measurement" <time-nuts at febo.com>
Sent: Sunday, June 29, 2014 12:30 PM
Subject: Re: [time-nuts] Dephasing WWVB


> The phase jumps are a killer and I assure you if a simple approach like
> limiters multipliers would work and I have done everyone of them that would
> have been the answer.
> Ya know it just can't be that hard. Guess what it actually is that hard.
> Darn, but that is the cost of learning. Nothings for free.
> There has to have been a reason that all the clever none work receivers
> went to the trouble of PLLs and such. They were pretty smart engineers.
> Regards
> Paul
> WB8TSL
> 
> 
> 
> On Sun, Jun 29, 2014 at 2:24 PM, Alex Pummer <alex at pcscons.com> wrote:
> 
>> thank you for that info, 2kHz bandwidth is a big problem for me, since a
>> very strong -- approx 20dB above the desired -- and not so stabile carrier
>> is just 700 Hz away --upward -- from the  desired 60kHz, a to narrow
>> bandwidth is also a problem since it converts  the phase modulation into
>> amplitude modulation -- the filter has to change the phase, for 180° phase
>> change it needs approx two times the Q times period time....that "trick "
>> makes the "atomic clocks"  with crystal filter also crazy., the "see" some
>> unexpected characters
>> Apropos atomic clocks, there is no usable available chip on the market
>> which would work....
>> Question, what was the goal to introduce that new modulation schema? Since
>> the new modulation scheme caused more trouble than usable  result, could it
>> happen, that it will disappear?
>> 73
>> Alex
>>
>>
>> On 6/29/2014 10:08 AM, John Reed wrote:
>>
>>> Thanks Paul.  I thought that this would be a simple project.  But, I'm
>>> seeing that random phase jump problem on every method I've tried so far.
>>>  My first attempt was a 2N2222 that would go into saturation on the plus
>>> cycle, then into a flip-flop.  I ended up with the phase problem on the 60
>>> KHz output.  Then I tried using a pulse generator into a flip-flop. Same
>>> problem.  The puzzling thing is the 120 KHz output from the 2N2222 or pulse
>>> generator look fine, but the 50 KHz output of the flip-flop is not.
>>>
>>> By the way, my 5 section synchronous filter is an LC with op-amps between
>>> each stage to bring the gain up for the squaring chip.  It has a 2 KHz -6
>>> dB bandwidth at 60 KHz.
>>>
>>> John
>>>
>>> -----Original Message----- From: paul swed
>>> Sent: Sunday, June 29, 2014 9:34 AM
>>> To: Discussion of precise time and frequency measurement
>>> Subject: Re: [time-nuts] Dephasing WWVB
>>>
>>> John welcome to time nuts. This won't be a super long post have other
>>> things to do.
>>> Search for d-psk-r and you can see a few of my exploits. Summation. "It
>>> ain't easy".
>>> It appears to be really easy unless you are far away like the east coast.
>>> Then the propagation gods enter into the picture along with the 60 KHz
>>> station in England that shows up most nights.
>>> The simplest of approaches was indeed the old doubling trick and the many
>>> flavors of it. I built most along with regenerative dividers and other
>>> trickery. Fact is it simply drops a count and that flips the phase quite
>>> annoying.
>>> I finally created two approaches. One specifically for spectracom devices
>>> essentially adding a third mixer and checking for the flip. Works but
>>> requires internal hacking of the spectracom.
>>> The other pretty much a freestanding receiever using a classic costas loop
>>> approach. All details were released to time nuts over a year ago.
>>> My next stab is more of a digital approach using the STM discovery board.
>>> Have to say I seem to get lost in some of the basics of getting all of the
>>> crazy registers set.
>>> However its value is it can run very very fast. So you can do some nice
>>> sampling.
>>> Regards
>>> Paul
>>> WB8TSL
>>>
>>>
>>> On Sat, Jun 28, 2014 at 5:38 PM, Charles Steinmetz <csteinmetz at yandex.com
>>> >
>>> wrote:
>>>
>>>  John wrote:
>>>>
>>>>  I discovered an article on the web that uses an AD835 multiplier chip to
>>>>
>>>>> square the WWVB signal *  *  *.  I built a five section synchronous
>>>>> filter
>>>>> tuned to 60 KHz to get rid of interference and its output feeds the 835
>>>>> chip.  This all works fine.  *  *  *  the 599J won't tune that high so I
>>>>> have to divide this 120 KHz frequency by 2.  *  *  *  I've tried to
>>>>> generate a pulse train from the 120 KHz signal and then use a flip-flop
>>>>> to
>>>>> divide the frequency.  This does not work well.  Apparently generating
>>>>> the
>>>>> pulse train picks up noise and I end up with a 60 KHz signal with
>>>>> fluctuating phase.  Now I'm trying to get a Miller frequency divider
>>>>> working
>>>>>
>>>>>
>>>> Why are you trying to generate pulses, rather than just squaring
>>>> (clipping) the output of the 835 in a saturated amplifier? Pulses have
>>>> less energy and therefore higher noise.  All you need is a
>>>> signal-conditioning squarer matched to the level coming out of the 835
>>>> (see
>>>> Bruce Griffith's pages at <ko4bb.com> for ideas, as well as the Wenzel
>>>> site and any number of illustrations in Experimental Methods in RF Design
>>>> -- for example, both Figures 5-46 and 4-45 show complete simple squarers
>>>> with FF dividers).  Even a CMOS gate biased to half-voltage should work
>>>> fine.  I like the NC7SZ74 Dflop for the divider.  Half of a 74HC74 works
>>>> fine, too.
>>>>
>>>> This should be the kind of thing you throw together in 15 minutes and it
>>>> works first time.
>>>>
>>>> Best regards,
>>>>
>>>> Charles
>>>>
>>>>
>>>>
>>>>
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