[time-nuts] WWVB PM Time Questions

[Dana Whitlow]

Try looking up the "Costas Loop" and the "frequency doubling loop".  They
should
give you some ideas of how to generate a stable local reference.

Dana


On Tue, Jul 21, 2020 at 7:47 PM <rcbuck at atcelectronics.com> wrote:

> I want to decode the WWVB time information using the BPSK information
> that is broadcast. I will use a STM32 to do the actual decoding of the
> bit stream. This is just an exercise in "can I do it?" as I know I can
> buy clocks for $30 that use the BPSK method. At one time you could buy
> an IC that output the data stream but I believe there is nothing
> currently available to do that.
>
> I read the document "Enhanced WWVB Broadcast Format" by John Lowe from
> NIST. One thing that is confusing to me is this paragraph: "Although the
> phase representing the information in each symbol is shown to be
> available before the amplitude in it transitions from VH to VL, it is
> recommended that receivers extract it only from the high amplitude
> portion of the symbol. This is not only because of the higher power
> there, allowing for more robust phase demodulation, but also because the
> low amplitude portion may be used in the future for additional (higher
> rate) phase modulation."
>
> How would you detect the phase had changed if you don't detect it when
> it changes at 100 msec after the carrier level drops? After the signal
> reverses phase wouldn't any reference you are using then be in lock with
> the current phase of the signal after it has changed?
>
> Or would you use a locally generated 60 kHz ultra stable signal as the
> phase reference? If so, how would you keep your local source locked to
> the 0 degree phase signal of WWVB and have it ignore the 180 degree
> phase shift?
>
> I have done a lot of searching and reading from various sources. But I
> haven't really found a good explanation of the hardware that would be
> used to detect the phase changes. Is there a block diagram somewhere
> that would illustrate the steps needed to detect the change during the
> high power portion of the WWVB signal?
>
> I am going to put together a 60 kHz amplifier using a couple of
> FET/transistors and a couple of high speed opamps. Then I can observe
> the signal on my scope. Using the output of the amp I can then try to
> figure out the best way to detect the phase changes. I can use my AWG to
> supply the local 60 kHz signal source.
>
> I have found two articles that give me some ideas. One is the Nov/Dec
> QEX article by John, KD2BD and the other is an article titled WWV
> de-PSK-r by Paul, WB8TSL. Paul is a member of this list.
>
> Can someone make other suggestions that will get me pointed in the
> correct direction?
>
> Thanks,
> Ray, AB7HE
>
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