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atomically correct time

Discussion in 'Electronic Design' started by eli, Aug 5, 2005.

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  1. eli

    eli Guest

    I was wanting to design a clock that updated by both
    -the atomic clock radio signal
    -cell phone towers

    this is because the atomic clock signal sometimes is hard to get so I
    figured that cellphone towers are more reliable

    does anyone have any suggestions
     
  2. Why not use a GPS receiver and get it the same way the cell sites get time?
     
  3. The clocks only update once a day. Realistically since they are crystal
    controlled even if they can't update for a few days, the average person
    will never notice. Clocks go out of time because they aren't set exactly
    right (ie they use the wrong "standard" to set them to, or they are sluggish
    in pressing the button), and because over a very long time the inaccuracy of
    the crystal (or the AC line if they use that for the timebase) is off and
    the accumulated error adds up. But you are hardly likely to notice
    that a clock is off until it has been long enough since it was
    set, or in the case of the "atomic clocks" since it last sync'ed up.

    Michael
     
  4. night dalits

    night dalits Guest

    they sell the electronic clock that works on wwb at 10mhz atomic clock at
    woodcraft stores cheap to build atomic wood clocks,
     
  5. artie

    artie Guest

    Cheap:

    www.klockit.com -- wwvb synchronized clock movements (from about $10).

    Not so cheap:

    search eBay for Z3801A -- a GPS disciplined 10 MHz time base (clock
    hands extra, around $400, and that's what cell sites used to use)
     
  6. Ben Bradley

    Ben Bradley Guest

    I at first thought the subject was "Anatomically correct time."
    Surely that's no reflection of what's on my mind...

    Alternatively (or along with other suggestions), you could use a
    more precise oscillator that will keep you closer to the actual time
    when your receiver isn't getting a good enough signal. Check out the
    DS32kHz, IIRC it's good to within seconds a year.
    Even worse than a temporary signal fade, perhaps someday society
    will break down and all these signals will be gone, then how will
    anyone know what time it is?

    Well, here's a solution. Go to http://leapsecond.com/ and scroll
    down to and click on the fourth picture, the "Most Accurate
    Wristwatch." No doubt there is an Agilent distributor standing by to
    take your order.
     
  7. What are you talking about the power line being wrong? Short term it
    may be off but long term it's right on. SO- build a clock that uses the
    power company as a time base and then add a WWVB of GPS receiver to
    set/verify your time. Galleon has a WWVB receiver, antenna and RS-232
    interface to your computer for about $60. See
    http://tf.nist.gov/stations/wwvbtimecode.htm
    for the data format from the receiver. If I read it correctly, it's a
    continuous update, not just once per day.

    For a cheapy frequency reference, the color subcarrier from a network
    TV station should be really close to 3579545 Hz. FCC requires them to
    be +/- 10 Hz but they're usually much closer than that.

    GG
     
  8. dave

    dave Guest

    I think the idea is to get the clock signal and send it to a primairy
    device and the idea is to have it accurate.

    I think it is an aproaching the problem from 2 different angles
     
  9. Paul Burke

    Paul Burke Guest

    Why did I read this as 'anatomically correct time'? Like Hubert in Sir
    Henry at Rawlinson's End:

    "In his adolescence, during the long summers of yesterday, he would
    throw himself naked onto the lawns in a northerly direction parallel to
    the earthly axis. And with a bluey roman clockface tattoo'd about his
    private parts, think about Jean Harlow very hard and - from the shadow
    cast -tell the time with remarkable accuracy. "Look! No hands!" In
    winter he tried with birthday candles stuck in the end but he was hours
    slow and the drips hurt. Later, Henry told him to 'put a sock' on the
    sundial bit."

    <http://homepages.tesco.net/sansun/Rawlinson End Book.htm>

    Paul Burke
     
  10. No, for some reason the same thought crossed my mind.

    Michael
     
  11. Jim Thompson

    Jim Thompson Guest

    Me too ;-)

    ...Jim Thompson
     
  12. Jim Yanik

    Jim Yanik Guest

    Note that NTSC standard TV signals are due to go off the air in 2006,IIRC.
    Due to the forced move to HDTV.
     
  13. Jim Thompson

    Jim Thompson Guest

    Nonsense. It's DTV not HDTV and...

    "The change to digital TV is triggered no sooner than the end of 2006,
    but only when 85% of U.S. homes can receive a digital television
    picture. Apparently that doesn't mean 'are capable of receiving the
    signal,' but rather 'have the equipment to view a digital television
    signal.'

    I find it difficult to imagine digital TV market penetration being
    anywhere close to 85% less than <two> years from today."

    I have SEVEN NTSC sets in the house.

    I receive signal via Cox Cable.

    Unless Cox Cable can provide me with a signal that the new sets can
    tune WITHOUT A SET-TOP BOX, there is no way I will switch.

    But I could probably just cease TV altogether. For instance my office
    TV is always tuned to Fox News and my back is to it, so radio would
    suffice.

    In the evening we generally just watch a movie from our collection of
    nearly 300 DVD's.

    ...Jim Thompson
     
  14. On Fri, 05 Aug 2005 04:16:20 GMT, in sci.electronics.design Ben

    snip
    If that happens, a sundial will be all that is required, and a
    knowledge of when to plant crops


    martin
     
  15. Does anyone still receive terrestrial analog TV signals over the air?

    I wonder where the subcarrier frequency is generated for the NTSC
    signals we get out of the coax (which are converted from digital, it
    looks like). Anyone know? I'm guessing it's in the distribution
    boxes.


    Best regards,
    Spehro Pefhany
     
  16. Rich Grise

    Rich Grise Guest

    Yup. I've even built a little Yagi for channel 56. :)

    Thanks,
    Rich
     
  17. What's so interesting about channel 56?

    Back in the 70s we had a channel 79 (now channel 57 broadcast
    frequency) which showed racy movies every Friday night. People bought
    directional UHF antennas just to get them (they didn't really have
    much of a broadcast antenna either at the time). Now the signal from
    the world's tallest free-standing structure is powerful, but the
    movies are long gone.


    Best regards,
    Spehro Pefhany
     
  18. Jim Thompson

    Jim Thompson Guest

    On Fri, 05 Aug 2005 13:49:51 -0400, Spehro Pefhany

    [snip]
    What do you think those towers on Phoenix South Mountain are for ?:)


    ...Jim Thompson
     

  19. Most tv stations use a framestore at the transmitter site to remove
    switching glitches and regenerate the sync with a 4* colorburst crystal,
    like the cheap ones used on computer boards. There is no oven or
    temperature control, and most stations don't have an in house frequency
    standard to tweak the circuit after it is at normal operating
    temperature. Add changes in temperature due to time of day, heat load
    on the air conditioning and how the cold air is distributed in the
    control room its a crap shoot. I had to try to sync to framestore
    systems for a telethon using multiple studios for a telethon once. It
    took both engineers over four hours to get them locked and to less than
    one degree of phase error.

    All of the hard work only worked for a couple days before it had to be
    adjusted again. We were forced to use two different models which made
    it worse, but I doubt that station will try it again.

    I may have the schematic of a framestore in my collection. if I run
    into it anytime soon I will scan that page and post it to ABSE.

    --
    Link to my "Computers for disabled Veterans" project website deleted
    after threats were telephoned to my church.

    Michael A. Terrell
    Central Florida
     
  20. Rich Grise

    Rich Grise Guest

    It's a local indy that shows nostalgic shows like "Magnum PI" and
    "Columbo." And there's one that's not so old, "Becker", although
    I'm seeing rerun reruns already. ;-)
    Yeah, now to get free porno, you have to use USENET. ;-P

    Cheers!
    Rich
     
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