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WWVB Time Signal Correction?

Discussion in 'Radio and Communications' started by jpanhalt, Dec 26, 2015.

  1. jpanhalt

    jpanhalt Well-Known Member Most Helpful Member

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    Here's a link that shows the WWVB code format: http://www.nist.gov/pml/div688/grp40/wwvbtimecode.cfm

    My understanding is that at point A, the signal intensity drops precisely on the second. However, there is a correction (UT1) factor included in the code.

    Assume a user has a receiver is synchronized to the WWVB signal and detects the instant of the high to low transition. Why is the error byte in the hundreds or milliseconds? My quess is that the correction is what the accumulated "leap second" would be that has not yet been taken into account. Is that correct?

    John
     
  2. JimB

    JimB Super Moderator Most Helpful Member

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    Some of these time codes make my head spin.
    A few years ago I wrote a PIC program for decoding our own time code on the 60kHz MSF transmitter.
    I got it working nicely but the coding was not very elegant in places. I digress.

    Have a look at my attachment which covers may of the worlds time tramsitters.
    Look at the Glossary and Table 21 at the end of the file.
    The UT1 correction appears to be needed due to slight errors in the earths rotation, and the leap second is there because the Earth is slowing down a bit.

    JimB
     

    Attached Files:

  3. atferrari

    atferrari Well-Known Member

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    Thanks for sharing, Jim. Do not count on LOL station; as many things in here, vanished from air. On the phone I got answers that makes me suspect that the responsible people by now, maybe ignore the service that was being provided. Reasuring. . .


    Precession and Coriolis, I guess. For the fixes taken with a sextant we applied a well tabulated correction. Sincerely, precession yes, but Coriolis was always far from intuitive to me so it became an act of faith.
     
  4. dave

    Dave New Member

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  5. jpanhalt

    jpanhalt Well-Known Member Most Helpful Member

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    Thanks, Jim.

    That was my thought too. I happen to be writing my own code (asm). I found one example online, but I think it tries to do too much (http://www.ringolake.com/pic_proj/WWVB/wwvb.html ). Presumably, a CMMR-6 equivalent receiver is in the mail to me from the UK (https://www.sparkfun.com/datasheets/Wireless/General/CMMR-6P-A2-1.pdf ). The receiver on order is described as being the same receiver, but with a COB instead of SMD device.

    I think I will just ignore the fractions of a second and stick to UTC. An RTC will be used to cover those times that WWVB can't be received. I know I can buy a cheap clock that does the same thing, but I need to keep busy on something useless.

    John
     
  6. JimB

    JimB Super Moderator Most Helpful Member

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    Our time/frequency transmissions from MSF were also on 2.5, 5, 10, 15 and 25(?) Mhz, but they were suspended years ago.
    In my younger days I adjusted may a 100kHz crystal calibrator to be zero beat with either 2.5 or 5 MHz. Happy days!
    Now I just check my super duper frequency counter against a crystal oscillator locked to the MSF on 60 kHz.
    More accurate? Yes.
    More fun? Probably not.

    JimB
     
  7. jpanhalt

    jpanhalt Well-Known Member Most Helpful Member

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    UPDATE
    My WWVB receiver arrived today from PV Electronics (brand = SYM-RFT) and it works:
    upload_2015-12-27_3-7-33.png

    The signal is inverted, and I had to wait until late to get a good signal. Here it is on a 'scope at 0228 hours:

    WWVB 0228 hours .jpg

    The biggest problem I have right now is my older TEK 210 scope puts out so much emf trash that it blanks out the WWVB signal. Had to erect all sort of shields from pastry trays to get the image. When that scope is off, my much older TEK 2235 does a great job and doesn't cause any noticeable interference, but I can't capture the screen. If it were't so fun, there are easier ways to get the correct time.

    John
     
  8. MikeMl

    MikeMl Well-Known Member Most Helpful Member

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    You might enjoy reading this.

    Clint is someone who I talk to on 7135kHz almost every Sunday morning...
     
    • Informative Informative x 2
  9. jpanhalt

    jpanhalt Well-Known Member Most Helpful Member

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    Thanks, Mike.

    I expected interference from cheap switchers, but not from a Tektronics scope several feet away. Another design using the original CMMR-6 receiver had to shield the antenna from the LCD display. Aside from the scope problem, I got pretty stable reception in my log home late at night. It was a little sporadic during the day, so I coded a simulator to facilitate coding the receiver. Once that is all done, I will fiddle with antennas and certainly refer back to the link you provide. I would like the clock to be usable in the same room I have my other electronic toys.

    John
     

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