Hi Bob,

The use of the PIC for WWVB carrier/data detection was only ever
intended for use with a visual clock, thus uncertainty (e.g. lag, delay
or whatever you want to call it) was par for the course in the
implementation that I described.

On 8/7/2015 3:51 AM, time-nuts-request@febo.com wrote:

Neil, as for the link below, unfortunately that's not it.  The project
in question used the PIC's A/D converter to directly process the
signal.  This would rule out the PIC16F84 used in the link, below, as
that has no A/D capability.  I've looked some more and have still been
unable to find it:  I'm sure that it's on the Wayback Machine somewhere,
but things can be tricky to find if you don't already have a URL!

I did see a mention of a "Tayloe" detector (or "QSD" - Quadrature
Sampling Detector) that might also be used to advantage in a project
like this.  As with A/D converters, they, too may be undersampled with
reasonable effect - Some of the readily-available SDR receiver kits do
this -  so it should be very practical to do something like the following:

• Produce an audio/sine wave DDS in software using the PWM hardware in
  the processor (PIC, Arduino) at 4x the desired frequency using outboard
  low-pass filtering.
• Slice it using the processor's onboard comparator or an outboard: Many
  PICs have comparators with outputs that may be made external.
• Apply this sliced signal to a divide-by-four system or counter to
  produce the quadrature signal, or use the interrupt from the comparator
  have the processor produce a count on a pair of pins for a multi-channel
  analog switch.
• Use a QSD (a.k.a. Tayloe) to yield "baseband" at/around DC.
• Apply said baseband quadrature output to a pair of A/D inputs.  If the
  A/D's are sampled in quick succession compared to the detection
  bandwidth, reasonable balance could be maintained.

Again, the QSD could be operated at a fraction of the desired frequency
using undersampling techniques provided that the input was adequately
bandpass-filtered - but this would seem like overkill since
undersampling using the A/D converter could accomplish practically the
same thing and the quadrature channels (or Costas) be done in software.

Taking a different approach, one could feed the sine output (at audio
frequencies) to a plain-old 4046 VCO/PLL and multiply the audio
frequency to 4x the receive frequency (240 kHz for WWVB, 310 kHz for
DCF77, etc.) and then produce the quadrature clocks for a direct
conversion at-frequency, the advantage being that there would need not
be any particular bandpass filtering in front of the QSD - just standard
low-pass filtering - to produce the baseband/quadrature outputs.  The
phase/jitter incurred by the squaring/frequency multiplication would be
largely irrelevant in the long-term detection windows involved.

An audio-frequency DDS synthesizer with 32 bit accumulator resolution is
very easy to produce in software and with microHertz tuning resolution,
very fine phase control may be achieved in the long term:  I've used
PIC-based audio DDS generators referenced from stabilized oscillators to
produce references to synthesize VHF frequencies as well as discipline
VHF/UHF oscillators with excellent results - with special steps taken to
mitigate phase modulation issues - so such should be practical at 60 kHz
with trivial hardware.  (See links below for information on using audio
DDS techniques with respect to VHF oscillators.)

What would produce delay/uncertainty would be the necessary lowpass
filtering on the output of the QSD needed to limit the detection
bandwidth, but some of this could be mitigated with multiple windowed
detectors (in software), stable analog components and appropriate
characterization of the circuits involved.

It is probably fair to say that given the limited detection bandwidth
and, more importantly, the rather limited processing resources of a
low-end processor one will never quite achieve the same timing accuracy
that one might get with long-term correlation techniques to determine
the phase reversal of the original carrier down to the half-cycle -
minus propagational uncertainties, of course!

(One would have to be nuts to want to do all of this, but that's half of
the name of this group!)

73,

Clint
KA7OEI

References for using PIC-generated DDS audio signals as references for
VHF oscillators:

• http://www.ka7oei.com/wxsat.html
• http://utaharc.org/rptr/synchronous_62.html - using the same DDS
  techniques to discipline VCXOs.

On 8/7/2015 4:30 PM, Clint Turner wrote:

Thank You for your explanation, I had thought of this as well, but I do
not know enough to implement this.

Looking at the WWVB chips that were available, what might it take to
make a discrete version of those designs ??

Thanks

HI

Discrete as in resistors and transistors or discrete as in “stuff plus an MCU”?

Bob

I looked at the site its the typical cmall board with everything on it.
Saves you the trouble of doing that very fine soldering.
No antenna.
Regards
Paul
WB8TSL

On Sat, Aug 8, 2015 at 1:16 PM, Bob Camp kb8tq@n1k.org wrote:

Hi

Like it or not, the world is going to BGA’s. Even the “fine pitch” leaded stuff
is slowly going away. You might or might not like soldering a fine pitch IC.
Doing a BGA at home - sorry, not for me. I doubt it’s on the “fun list” for
anybody else either. We had better all get used to the idea that a part on a
board is the “smallest unit of construction” for this or that project.

Thankfully the fine people far over the ocean seem to be able to put a part
on a board for less money than I can buy the raw part. They as a group also seem to
deliver a working (though maybe a bit messy) part every time I’ve got this or
that. Hook a couple boards up and poof instant project. Even mounted to a
board the stuff is still tiny. Unless you are doing a “wearable” project it’ll be
plenty small enough.

Go for the board, it’s the way you do a prototype these days !! That’s every bit as true
at work as it is at home ….

Bob

On 8/8/2015 11:16 AM, Bob Camp wrote:

To be clear(er):

This data sheet is one of a few receivers from a few vendors:
http://www.datasheetcatalog.com/datasheets_pdf/U/4/2/2/U4221B.shtml

Looking at the data sheet link shows the internals of the receiver chip.

This chip outputs the serial stream of the WWVB pwm data.

From there any MCU can decode that stream via bit-bang.

Hi

Ok, that’s a 20 year old IC. When it talks about doing WWVB, it’s talking about
the AM modulation format. It’s not talking about the new phase modulation approach.
These are the chips that probably will disappear completely once the chips for the newer format
show up.

Bob

Hi Don,

About the U4221B -- that TEMIC series was widely used in WWVB receivers 15 to 20 years ago. The problem for many hobbyists today is that these very nice chips have long since been out of production. Note the May '96 date on the datasheet.

I figure there minimal low-volume demand -- just not enough WWVB hobbyists in the world. And for high-volume -- companies like Sony, Seiko, Casio, and Junghans typically roll their own chips, one where they can fully integrate the receiver into the single IC that does everything else: clock, calendar, display, subcode decode, motor control, power management (solar charge).

WWVB RCC (radio controlled clocks) and watches have evolved -- many companies now offer "multi-band" clocks that automatically handle all the world-wide LF broadcasts (WWVB,JJY40/60,MSF,DCF77). This further lowers the market demand for a WWVB-only plain receiver IC.

Under my http://leapsecond.com/pages/sony-wwvb/ page is a full set of vintage Temic datasheets:

http://leapsecond.com/pages/sony-wwvb/U4221B-96.pdf
http://leapsecond.com/pages/sony-wwvb/U4223B-97.pdf
http://leapsecond.com/pages/sony-wwvb/U4224B-98.pdf
http://leapsecond.com/pages/sony-wwvb/T4225B-96.pdf
http://leapsecond.com/pages/sony-wwvb/U4226B-98.pdf
http://leapsecond.com/pages/sony-wwvb/

And lastly, this old Temic time code document is a must-read for anyone playing with RC clocks:

http://leapsecond.com/pages/sony-wwvb/timeco-97.pdf

/tvb

Hi

Maybe a little more on “why demodulate the phase mod?”.

1. The signal to noise of the recovered data stream will be significantly
   better with the phase mod data. The NIST paper is correct about that.
   That alone makes it a neat thing.

2. The interference rejection of the phase mod approach is better. This
   is a bigger deal in some parts of the country than others. Night time MSF rejection
   is not easy here in the Northeast ...

3. You need to demodulate (to some degree) the phase mod to implement
   a “frequency reference” receiver. All the fine old ones no longer work directly
   with the current WWVB signal.

4. There is more information in the phase mod signal than in the AM modulation
   data stream. It would be fun / useful  to have access to that data.

5. The last crop of precision receivers came out several decades ago. There
   are a lot of things you could try today that simply did not make (economic) sense
   back then. Propagation prediction based on location, season, and time of day would be
   pretty high up on that list.

6. A whole lot has happened in the world of amateur SDR that could apply to this sort
   of receiver. This is at the “cheap and slow” end of the world. That makes applying
   a digital radio a whole lot easier than at microwaves.

7. A lot of us grew up with phase comparison (either WWVB or Loran-C) as
   a method of calibrating / evaluating frequency standards. It’s a technique that
   is know to work. It may not be of interest to the word at large. It is of interest
   to a number of people here on the list.

8. You might learn something by building a receiver like this. Can you detect
   the phase transitions to X,XXX us or to XX.X ns? who knows. Can you better
   catch cycle slips with the help of the phase mod? Again, unknown until the
   receiver is up and running.

9. GPSDO’s are an outgrowth of the original WWVB ( or more generaly VLF)
   disciplined standards. We (or at least I) now have piles of these GPSDO things
   taking up room in the front hall. They are getting pretty cheap. Using some of
   what has been learned in that arena (and some of the hardware) to improve a
   WWVB approach is a real possibility.

10. Since GPSDO’s are all over the place. You can use one as a reference
    for a lot of the development of a WWVB device. We don’t all have to move into
    Tom’s basement and “borrow” the H-Maser signal in order to get one going.

Bottom line it’s a “basement compatible” project. It’s not massively expensive. It
does not require “nutty” levels of instrumentation. You can go as far as you desire
towards the full list of bells and whistles. Compared to other “Time Nut” grade projects
it’s towards the simple end of the list. (Consider that home built H-Masers, DIY Rb’s,
Ion clocks, and Cs fountains have been suggested in the past). It’s a lot of work and
by no means trivial to do. I’d say it’s worth trying.

Bob