[time-nuts] WWVB PM Time Questions

Thu Jul 30 19:42:21 UTC 2020

Its done in a cheap small custom chip. (Though whats in the chips
complicated and is a SDR)
Its the Everset ES100 or 110 as I recall. Look for that and you will get
some very nice insight.
Unfortunately the direct bits aren't accessible only the output messages.
You can but that chip on a board for $66 with two loopstick antennas.
Kind of goes back to the goal of your interest.
Time or maybe locking a oscillator.
Regards
Paul.

On Thu, Jul 30, 2020 at 3:26 PM <rcbuck at 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. 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 <paulswedb at gmail.com>
> Date: Thu, July 30, 2020 10:39 am
> To: Discussion of precise time and frequency measurement
> <time-nuts at lists.febo.com>
> Cc: rcbuck at 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 <paulswedb at 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 <phk at phk.freebsd.dk>
> wrote:
>
> --------
>  rcbuck at 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
>  phk at 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.
>
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