[time-nuts] WWVB PM Time Questions

[paul swed]

Hi Ray
Paul here and there is also a Rodger that may help.
How to address your questions at 10 pm.
With BPSK you can always lock on the wrong half. So after you lock the
local oscillator you then look for the sync signal pattern at the top of
the minute. The pattern is correct or inverted. You then know what to do.
Flip the local oscillator or invert the data. Either will get you the
correct stream data. Then its fun time decoding it.

With respect to the sample point John Lowe is correct. During the start of
the the AM signal drops about 20 DB intentionally as the second marker. So
if you sample in the 100 ms window the signal is weak. Sampling later
towards the end of the second gives the best signal strength.
With respect to the KD2BD design it works but there is a bad catch. The
oscillator he controlled is not available. I have tried to map other high
grade oscillators in and been unsuccessful. (But thats just me) Using a
GPSDO and slipping the phase with a HP 3336 generator. I can very nicely
align the carrier and it works quite well. But thats a complex radio to
build.

The STM32 (Bluepill) is a very good idea. Hmmm I wonder if that is why I
have one just over to my right. Its given me a heck of a time. Just trying
to get the bootloader going and then the simple blink program. I have not
worked on it in a bit as other things have cropped up.
Regards
Paul.

On Tue, Jul 21, 2020 at 8:47 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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