Hi
> On Jul 30, 2020, at 3:01 PM, rcb...@atcelectronics.com wrote: > > So the $64 million dollar question is this. How do the La Crosse > distributors sell the ULTRATOMIC clock for $35-$40. That means La > Crosse's manufacturing cost is probably around $15-$20. Building a > million clocks would get the cost down, but still..... I'm sure there > are a lot of transistors in their IC to handle all the phase tracking > and time decoding. It is obvious they don't have a vcTCXO in the clock > so they must be doing everything in software. Since they have no interest in extracting the carrier phase for timing, there is no real need for a fancy oscillator …… Their definition of “precision” and the TimeNut definition are pretty far apart. Bob > Or maybe the IC is a > combination micro and FPGA. Any ideas how they would approach that? > > If you read the online reviews of the clock they are about 99% positive. > A lot of reviews say their clocks based on the AM modulation method > would not sync but the phase modulation ones always work. > > Ray, > AB7HE > > -------- Original Message -------- > Subject: Re: [time-nuts] WWVB PM Time Questions > From: paul swed <paulsw...@gmail.com> > Date: Thu, July 30, 2020 10:39 am > To: Discussion of precise time and frequency measurement > <time-nuts@lists.febo.com> > Cc: rcb...@atcelectronics.com > > Well John perhaps there is some interest in your receiver. I see the > vcTCXO is down by 5 devices from yesterday. Make that 6 now. For anyone > else usps is cheapest at $4.99. > Regards > Paul > > > On Thu, Jul 30, 2020 at 10:29 AM paul swed <paulsw...@gmail.com> wrote: > > Hello to the group. > Poul has done some very fine work and you can learn a lot from him. > But several comments that will help. Its easy to create all kinds of > solutions that look for phase shifts. I spent quite a bit of time doing > that. But the nasty reality is without accounting for the noise, signal > fades, and delay shifts they generally fail. Or work for short periods > of times. > Simplistically if you have a 1 second image of the incoming signal its > easy to see the phase shift. > With respect to zero crossings it works really poorly. Thats why on > Loran C they were very clear the slice point was as I recall 30% up the > envelope. > > > Humor on the d-psk-r. The new unit does not have an output that contains > the phase shifts of wwvb. The units intention is to remove all phase > shifts so that all old style phase tracking receivers and clocks work. > They all do. Have 7 of them. > So to experiment with Johns fine KB2DB receiver I need the raw phase > flipping wwvb signal. > I have built his receiver and now that there is an answer to the TCXO > issue I need a raw feed. Chuckle. When I built the new unit I really > debated adding that BNC. Hindsight is always really clear. > Best regards > Paul > WB8TSL > > > > > On Thu, Jul 30, 2020 at 4:48 AM Poul-Henning Kamp <p...@phk.freebsd.dk> > wrote: > > -------- > rcb...@atcelectronics.com writes: >> Paul, >> "The new de-psk-r I built has no raw wwvb outputs." What do you mean > by >> raw? >> >> I have been thinking about how the phase shift could be detected in >> software instead of hardware. Could something like this maybe work: > > Back when I played with VLF, I did this on DCF77/Rugby etc. > > In my case I used a 12 bit 1MSPS ADC, and (exponentially) averaged > the RF signal into per-station circular buffer, this is very cheap > and fast to do in an interrupt handler. > > In your main code you can demodulate that buffer to DC by multiplying > and summing with precomputed sin&cos tables. > > That gives you baseband I & Q from which you can trivially calculate > phase and amplitude. > > You can make the buffer as short or long as you want, I did the > trivial thing and made it a full second long: > > http://phk.freebsd.dk/loran-c/CW/ > > The trick to that is that you can recover many stations from the > same circular buffer, by using different sin&cos tables. All the > above plots came out of the same single 1sec buffer snapshot. > > This obviously works for any buffer length which is a full number > of carrier cycles for all the stations you are interested in, in > principle you can recover all stations on N*kHz, N << 500 from from > a single 1000 sample buffer at 1MSPS. > > The advantage of using a 1second buffer was that I could extract > what the stations thought was top of the second from their modulation. > > (I actually calculated my position based on DCF77, Rugby, HBG, > France Inter and the strange 200/3 kHz station in Moscow, the result > I got was about half a kilometer wrong.) > > To recover the per-second modulation you simply need to shorten the > buffer so it resolves the modulation, which probably means no longer > than 1/20 second for WWVB, but 1/100, if you have the S/N for it, > is much easier in terms of signal analysis code. > > An alternative strategy, which I used for DCF77 phase recovery, is > to detect the duration of the AM pulse and pick one of two 1-second > long buffers based on that. > > And you don't need much CPU power at all, I did Loran-C time/freq > on a Analog Devices Aduc7206: > > http://phk.freebsd.dk/AducLoran/ > > And that included a graphical display, (watch the animation.gif :-) > > -- > Poul-Henning Kamp | UNIX since Zilog Zeus 3.20 > p...@freebsd.org | TCP/IP since RFC 956 > FreeBSD committer | BSD since 4.3-tahoe > Never attribute to malice what can adequately be explained by > incompetence. > > _______________________________________________ > time-nuts mailing list -- time-nuts@lists.febo.com > To unsubscribe, go to > http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com > and follow the instructions there. > > _______________________________________________ > time-nuts mailing list -- time-nuts@lists.febo.com > To unsubscribe, go to > http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com > and follow the instructions there. _______________________________________________ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there.