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WTF with my computer clock?

Discussion in 'Electronic Repair' started by root, Aug 11, 2009.

  1. Sylvia Else

    Sylvia Else Guest

    Certainly, no one in their right mind would deliberately reverse the
    interlace ordering - the result is unwatchable.

    Sylvia.
     
  2. Sylvia Else

    Sylvia Else Guest

    Here in Australia I got documentary proof that a station was
    deliberately running late. See

    http://groups.google.com/group/aus.tv/browse_frm/thread/703f398d4e875bc6/a1a580334e9ff9f2

    I had recorded that channel that evening, on a PC that has its clock
    synchronized to an accurate clock, and the times given in that schedule
    were to within one second of when the material was actually broadcast.

    They just weren't the times that had been advertised.

    Sylvia.
     
  3. Sylvia Else

    Sylvia Else Guest

    Much as I'd like to be able to support the view that the BBC's standards
    are falling, I have to advise that I was already being frustrated by the
    BBC's apparent inability to keep to its published schedules back in the
    early 1980s. This is nothing new.

    Australia's counterpart, the government funded ABC which also doesn't
    carry advertisements, is also apparently unable, or unwilling, to
    broadcast things when they say they will.

    I suspect that, as with the commercial stations, it's deliberate. I'm
    just less than clear what the motivation would be for a non-commercial
    station.

    Sylvia.
     
  4. Well, duh; that was kinda my point.

    So I take it you don't disagree with what I said, or have nothing else
    to add?
     
  5. So that kinda begs the question of why computer mfrs. can't (or won't)
    include clocks that are at *least* as accurate as a Timex, no? Wouldn't
    a computah be a more compelling reason for a more accurate clock? (I
    know, $$$ bottom line, right?)
    Of course, it would be nice to know one's computer would maintain
    accurate time even if, god forbid, it was somehow disconnected from The
    Network ...
     
  6. I don't care about zero. One minute a month is plenty accurate enough
    for me.
    You're admonishing me not to use NIST? Why?

    After all, they offer this service to me. See
    http://tf.nist.gov/service/its.htm:

    The NIST Internet Time Service (ITS) allows users to synchronize
    computer clocks via the Internet. The time information provided by
    the service is directly traceable to UTC(NIST). The service responds
    to time requests from any Internet client in several formats
    including the DAYTIME, TIME, and NTP protocols.

    So why shouldn't I use them?

    Keep in mind that I use this service *at most* 3 or 4 times a *year*.
     
  7. David, it depends upon how you use it. If you use Windows' or MacOS's
    automatic time sync or *NIX's NTPDATE, you only access it occasionaly.
    Windows and Mac access it once a week, NTPDATE does it whenever it is invoked,
    usually when you boot your computer.

    If you are runnin *NIX NTP deamon (including MacOS's) or a third party Windows
    time sync program, your computer is in frequent contact with the time server.
    In that case, it would be a good idea not to use those servers as they are
    heavily loaded down.

    For once in a week sync of one computer, you can use just about any server
    without worry about it being overloaded or adding any additional load.

    If you have multiple computers networked together, that is a different story.

    Geoff.
     
  8. Sylvia Else

    Sylvia Else Guest

    In the UK, or in London at least, the mains frequency was maintained
    with a very accurate long term average, so that synchronous mains clocks
    just stayed correct.

    Sometimes, after short power cuts, the frequency was increased to bring
    such clocks back to the correct time. Which was actually a bit of a
    nuiscance for us - we had clocks that weren't self starting (a
    reflection of the rareness of power outages in those days), so after a
    power cut, we'd set the clocks correctly and start them, only to find
    them gaining.

    It seems a backward step that now, forty or so years later, household
    wall clocks are less accurate than they were back then.

    Sylvia.
     
  9. It's a very simple system that is well documented. It's simple and slow
    enough that anyone used to pulling apart data streams would be able to
    decode it with a Z80 derived embedded processor, the ARM chips in dead iPods,
    WiFi routers, etc would be "overkill".

    Here in Jerusalem, we don't receive the signals of WWVB, or the German
    or UK equivalents here. Someone about 50 miles north and out of the
    mountains has a clock that syncs, but he never told me which station it
    uses (he may not know), or how often it syncs. This lead me to research
    how one would do the opposite, devise a local transmitter with an
    ethernet port on one end for NTP sync and a 60kHz transmitter to sync a
    clock on the other.

    I gave up due to lack of a suitable design for the transmitter, no receiver
    and a lack of funds to obtain them. You probably could do it out of one
    of the Linux based routers, and blink one of the status LED's to generate
    the 50/60kHz signal.

    I know by now you must be thinking "why would anyone even think of such
    a thing", but a discussion a few months ago about resurecting a Heathkit
    Most Accurate Clock, got me going. I think I also read a posting that the
    WWVB signals were being phased out.

    Geoff.
     
  10. That's sort of what I was thinking of. Get the time from NTP, generate
    a fresh time code signal, which would not be accurate enough for someone who
    wanted truely accurate time code, but to keep a clock that displays to the
    minute, or even to the second on time, it would be good enough.

    As for the transmitter, how much power do you need to transmit a signal from
    a time code generator to a receiver next to it, connected via a coax cable?

    A microwatt? A milliwatt?
    It depends. A cheap router, such as the Linksys WRTG-54L (note the L at the
    end it's the enhanced model that runs Linux) would do it. It sells new for
    not much money, will be obosolete as the 802.11N routers come into general
    useage, has an ARM processor, two ethernet interfaces (one connected to a
    4 port hub), a WiFi radio and a bunch of status LEDs. The advantage of it
    is that there are several alternate Linux packages for it and you can easily
    compile your own programs, build your own "flash" (firmware image) and load it.

    There are also distributions for other routers, I recently bought a $30 EDIMAX
    wired router that had a distribution for it.
    If it is directly connected to the input of the receiver, it needs no
    license.
    I also expect there are none. Around here the noise level is so high that
    they would never hear it until I got into the "real antenna" type system.
    A microwatt with true isotropic radiator antenna (a short wire) would not
    leave my apartment, let alone go anywhere. But if it is connected directly,
    then it is a moot point.

    I was thinking of something simple, such as flashing the LED at 60kHz, and
    wrapping a pickup loop around it. That's about the same power level and
    frequency of a TV remote control and no one from the MOC has come and
    complained about any of the ones I have. I'm talking about the RF leakage
    from it, not the optical signal.
    Not here. I have never heard them here, nor have I heard CHU (yes, I know it
    moved), any of the European stations, etc. I'm not talking about a cheap
    portable shortwave, I'm talking about a Kenwood R-5000 with a 75 foot random
    wire, or other equally as sensitive ham receivers either with a 20m resonant
    dipole or 1/4 wave vertical, or a 40m resonant dipole.

    I'm not actually familar with the clock in question, the discussion (I think
    it was on this newsgroup) focused on them using WWVB (VLF) radios.
    I'll agree with that.

    Geoff.
     
  11. They will shut it down eventually because of the cost. NTP servers cost
    almost nothing, GPS is "free" because there are no incremental costs for
    providing the time signals.

    Eventually someone will figure out that a 75kW transmitter has both a
    significant expense and a large "carbon footprint".

    The upgrade was thought to be needed because of a satellite time system
    that was dropped due to GPS was thought to be unable to fit the needs of
    the common user. Now GPS units are almost throw away "toys", being used in
    almost every cell phone, and for all sorts of SATNAV devices.

    Geoff.
     
  12. You are confusing the hardware clock and software clock in a computer.

    The hardware clock is crystal controlled. It is used at boot time to set
    the software clock.

    The software clock is incremented by the lowest priority interupts, which
    causes it to wander off.

    There are various schemes to sync it with the hardware clock, but without
    an external source, e.g. NTP, the don't work very well as hardware clocks
    are not very accurate.

    Geoff.
     
  13. So I wonder if the lowly SX28, one of my favorite little machines to
    program (a PIC-like li'l guy) is an exception to this seeming rule?

    I ask because, looking at the specs for this CPU, it has some
    configuration bits (marked IRCTRIM0-2) that trim the internal RC
    oscillator frequency, supposedly in steps of about 3%, up to a maximum
    of +/- 8% (yeah, I know, doesn't add up, but whatever). Is this what you
    would call a "tunable oscillator"?
    So presumably what I just described is a varactor built into the SX28.
     
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