Hi, > principles. The STM32L4 series which I often use has a pretty decent > ADC: fast (5 MSPS), with about 11 good bits in differential mode, and > "proper" hardware downsampling (called the DFSDM in the manual). If the
Yes, the STM32 series also have built-in OPAmps, so one could hook up a loop or a ferrite directly to the uC without too much external components. Sampling at 160ks/s should suffice to get the phase and DCF77 is in reach as well. At this rate you have ~500-1000 processor ticks per sample which should be enough to do real time demodulation. Very nice project. Cheers Detlef Schücker "time-nuts" <[email protected]> schrieb am 22.07.2020 18:44:08: > Von: "Mark Haun" <[email protected]> > An: [email protected] > Datum: 22.07.2020 19:29 > Betreff: Re: [time-nuts] WWVB PM Time Questions > Gesendet von: "time-nuts" <[email protected]> > > Hi Ray, > > A similar project has been on my to-do list for a couple of years now > (so don't hold your breath!). It should be possible to do this using > the built-in ADC for a really nice, minimalist demonstration of SDR > principles. The STM32L4 series which I often use has a pretty decent > ADC: fast (5 MSPS), with about 11 good bits in differential mode, and > "proper" hardware downsampling (called the DFSDM in the manual). If the > noise is white it should be easy to get > 16 good bits into the > demodulator. My plan was to clock the MCU from a cheap OCXO and make it > part of the carrier tracking loop, for a simple WWVB disciplined oscillator. > > I also have some questions about the NIST document, but in general, I > think you need to assume that your receiver is already locked, in which > case you know when to expect the transitions. Getting to this point > (acquisition) is another story, but there are all sorts of > correlation-based tricks that you can use, similar to GPS code > acquisition. As others have noted, carrier phase lock can be aided by > squaring. > > My problem is that the SDR stuff is all pretty straightforward for me, > but the analog electronics leading up to the ADC are black magic. I > have a preamp circuit modeled on John Magliacane's design > (http://www.arrl.org/files/file/QEX_Next_Issue/2015/Nov-Dec_2015/ > Magliacane.pdf), > fed from a ~ 60-turn tuned loop made from old ribbon cable, but I am > having problems getting anything "reasonable" looking on the scope. I > don't know if the problem is my suburban location or if you really can't > see the signal until you get the bandwidth << 1 kHz. (I am using > RC-tuned op-amp stages so the -3 dB response is necessarily a few kHz.) > Eventually I would like a small loopstick design with a crystal filter > like the off-the-shelf clocks use, but I haven't a clue how to get > there. Maybe this project would benefit from a collaboration :) > > Regards, > Mark > > On 21-Jul-20 4:37 PM, [email protected] 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 > > > > _______________________________________________ > > time-nuts mailing list -- [email protected] > > To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time- > nuts_lists.febo.com > > and follow the instructions there. > > > > _______________________________________________ > time-nuts mailing list -- [email protected] > To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time- > nuts_lists.febo.com > and follow the instructions there. _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there.
