[time-nuts] WWVB PM Time Questions

[rcbuck at atcelectronics.com]

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