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Simple 60 Khz Transmitter Design?

Discussion in 'Electronic Design' started by [email protected], Feb 2, 2008.

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  1. Guest

    I'd like to be able to update my watches with the NIST atomic time
    broadcast, which unfortunately we don't have here in Australia. I've
    looked at the format of the broadcast and think it should all be quite
    achievable except the actual RF, which I have no experience in. I
    would like to know if anyone experienced with transmitter design is
    out there and can confirm for me if this simple idea might work.

    To my way of thinking 60 Khz is extremely low frequency, so I was
    thinking of just using a 555 timer (wired for 50% duty cycle), with
    the output hooked through a capacitor (to make it AC) and a coil (to
    make it more sine-waveish) to a short length of wire for an antenna.
    Would that constitute a transmitter?

    Sean
     
  2. Cool idea. Let us know how you make it work. I can see myself resetting
    all the clocks in my neighborhood a couple of hours off.

    --
    Joe Leikhim K4SAT
    "The RFI-EMI-GUY"©

    "Treason doth never prosper: what's the reason?
    For if it prosper, none dare call it treason."

    "Follow The Money" ;-P
     
  3. Leon

    Leon Guest

    Doing that would be illegal in most countries.

    Leon
     
  4. Tim Wescott

    Tim Wescott Guest

    Make the coil big, leave off the short length of wire, and put your stuff
    inside the coil to adjust the time.

    Then turn the power way down to avoid interfering with whatever Oz uses
    60kHz for.

    --
    Tim Wescott
    Control systems and communications consulting
    http://www.wescottdesign.com

    Need to learn how to apply control theory in your embedded system?
    "Applied Control Theory for Embedded Systems" by Tim Wescott
    Elsevier/Newnes, http://www.wescottdesign.com/actfes/actfes.html
     
  5. It might work however the coverage area will be very small.
    Generate the signal by a microcontroller and use a push - pull pair of
    MOSFETs as the power stage.
    The biggest problem with the VLF is the transmitting antenna. The efficient
    antenna has to be several kilometers in size. Alternatively, you can use the
    frame antenna, however even if you pump hundreds of watts on it the range
    will be only about 20...30 meters or so.

    Vladimir Vassilevsky
    DSP and Mixed Signal Consultant
    www.abvolt.com
     
  6. I have wind up pendulum clocks that are more accurate than your
    'reference'. You do know the carrier frequency is _extremely_
    accurate.

    http://tf.nist.gov/stations/wwvb.htm

    http://www.timeanddate.com/worldclock/results.html?query=sydney

    GG
     
  7. mike

    mike Guest

    Ok, think about it...
    How accurate does the RECEIVER oscillator have to be to make NIST work?
    IF the time code is encoded accurately, you won't be off by more than
    the oscillator peroid, which is plenty good for setting a watch.

    But I agree that you should not transmit on this frequency. I don't
    want anyone setting MY clock.
     
  8. Ecnerwal

    Ecnerwal Guest

    Which is ideal, since it would constitute an unlicensed transmitter, and
    the Australian authorities are probably no more fond of that than
    anybody else's government. In point of fact, I'd suggest setting up an
    old microwave oven carcass (or other metal box) with the transmitter and
    watches placed inside, and only powering it up for a brief period to set
    the watches. Hardly needs efficiency or power.
     
  9. MooseFET

    MooseFET Guest

    Partial post just to see if Google is working today:

    Go down to a lower frequency for better results.
     
  10. MooseFET

    MooseFET Guest

    It appears that google is working.

    On Feb 2, 3:27 pm, wrote:
    [...]
    It is likely against the law.

    so I was
    I suggest that you make it crystal controlled. A LM555 has too much
    drift.
     
  11. Guest

    Thanks all for the input. My understanding is what I am doing is legal
    in Australia, as long as I don't exceed the maximum EIRP for LIPDs in
    this frequency range. With my current plans I don't think that is
    possible. I want to use simple components I have available to me and I
    am familiar with. The frequency must be 60Khz, and I would worry
    placing the watch into a big inductive loop might damage the watch/
    receiver.

    I think I'll put the oscillator together on a proto board and see what
    comes of it. Another thought, is more voltage better for transmission?
    I could hook up the 555's output to the secondary winding of a
    transformer and hook one side of the primary to ground and the other
    to my antenna. Maybe a mains transformer would be no good, but one
    from a switch-mode power supply might be? Or maybe an audio
    transformer?

    Sean
     
  12. This is how to drive a current loop at 60kHz:

    60kHz generator - amplifier --low volt lightbulb - capacitor -- L-
    |
    ) 1 or more turns around the room
    |
    ///
    The lightbulb forms a constant current source, you need to figure C and L
    so the L + Lloop, together with C, is in resonance.
    Use a high voltage C, there will be huge voltages.

    A good audio amp IC will do for the amplifier.

    I have used this (with license) for translation systems in conference halls.
    I think you will need a license in most places.
    Something like 10 W should be enough.
     
  13. Guest

    The COTS are designed for 60KHz. You can't change the frequency.

    I wonder if the original poster tried to listen to 60KHz on a radio.
    The signal might be there, but too weak to drive something COTS. If
    that is the case, maybe a repeater of sorts would work. The signal
    itself is very low bandwidth. In the states, it is no problem to pick
    it up on a radio, especially with a CW filter and loop antenna.

    Most of these atomic clocks have puny antennas. I have a Sony alarm
    clock that has the NIST built in. The antenna is nearly the size of a
    computer mouse. How the watches work is beyond me.
     
  14. donald

    donald Guest

    Has anyone told the OP that you can not transmit a square wave from a
    555 type device.

    Yes you can add all the Ls and Cs you want, but it still will not do as
    the OP thinks he can.

    The 60Khz transmitter at WWVB in Colorado has all the info he may need
    to get the idea that his building a "little toy" transmitter will not work.

    If the OP has not done his homework yet, here is the link he needs:
    http://tf.nist.gov/stations/wwvb.htm

    Good luck, I am glad he's not in my part of the world. (Colorado)

    donald
     
  15. donald

    donald Guest

  16. John G

    John G Guest

    I hope before you (and a lot of members of this NG) waste any more
    "time" on this problem you realise 2 things.

    1. a 555 timer is less acurate than a klepsydra and certainly less
    accurate than a 1925 long case pendulum clock I have in my lounge room.

    2. There is a whole lot of data embedded in the 60khz signal that you
    cannot generate without first owning an atomic clock to establish the
    time.

    John G.
     
  17. Martin Brown

    Martin Brown Guest

    In message
    A loop is probably the easiest way of coupling the watch to the
    transmitter without radiating nuisance signals to all and sundry.

    Your biggest problem will be hitting the required 60kHz carrier
    frequency accurately enough for the high Q clock receiver to even
    notice. .
    You do realise that you have to modulate the carrier with the
    appropriate time code data for this to work. And if you have to do that
    then you may as well use a PIC with a 6MHz or 12Mhz quartz xtal (about
    $1) and divide that down . At least then you can get the carrier wave
    exactly on frequency spec and concentrate on modulating it.

    Cheap hobbyist PIC kits might even come with all the bits for $10-20.

    A 555 will drift like hell compared with what the receiver needs.

    I doubt it is legal to jam 60kHz signals even in Australia, but so long
    as you keep the power low there is enough space that no-one will notice.
    Place the bits you want to tweak close to your transmitter and use the
    lowest power needed to do what you want.

    Regards,
     
  18. mike

    mike Guest

    You're overthinking this. If I understand the project, it's to set a
    watch...not recreate WWVB.

    Some of us think it might be fun to do the
    experiment with someone else actually building it.
    And probably more accurate than the spray can of cheese whiz in my
    fridge...and about as relevant.

    The 555 is the carrier. All it has to do is stay in the bandpass of
    the receiver. So, the real question is, "what are the receiver
    requirements for carrier accuracy and stability?" I'm betting that the
    $19 WWVB atomic clock hanging on my wall has a pretty sloppy receiver.

    While I'm at it, let's ask one more relevant question...
    WHEN does the watch update itself. I'm just guessing that the power
    consumption of the WWVB receiver might be orders of magnitude greater
    than the power consumption of the part that goes tick-tock.
    That suggests that the receiver might be OFF most of the time.
    Won't help to have a synchronization setup that's not near
    when the watch is listening. And what if it can't find a signal?
    Does it retry? How often? Does it ever give up and quit trying
    altogether? Battery drain may go through the roof. Or it may just
    stop trying to synchronize.
    Knowledge of the update algorithm might be critical here.
    Most of us DO have access to an atomic clock. It's called GPS. For the
    rest of you, the time clock in your computer, synchronized to a time server,
    is plenty accurate to set a watch...my watch anyway...

    The whole project is silly. If you've got a wrist watch that cost over
    $9.99 and needs to be set more than once a year, it's broke. Take it
    back. If you need action on a schedule that accurate, you need
    something more reliable than a human with an accurate watch
    to orchestrate it.

    But who among us has never delighted in a project that others
    thought a waste of time?

    mike
     
  19. Guest

    The MSF (UK) radio-controlled clock that I disassembled contained a
    crystal used as the filter in the receiver, so it probably has a
    receiver bandwidth of only a couple of Hz. You wil need a crystal-
    controlled transmitter. Probably the easiest way is to use a
    microcontroller with an appropriate crystal (e.g. 6MHz ? 24MHz etc.)
    and then configure one of the counters inside the microcontroller to
    act as a divider. The micro could also generate the time code
    modulation. A coil of wire would be the most effective antenna,
    ideally with a capacitor across it so that it resonates at the right
    frequency.

    The clock that I disassembled also contained a 32768Hz watch crystal
    which was used for the time-keeping most of the time. At the end of
    each hour it would turn on the radio receiver and wait until it
    received a time code with correct parity and then it would set the
    time and turn off the receiver. Unfortunately, when receiving pure
    interference it would have a 50% chance of receiving correct parity,
    at which point it would set the time to some nonsensical time like
    34:81, because they did not think to check whether the hours were less
    than 24 or the minutes less than 60.

    Whether or not building the proposed trnasmitter would be legal where
    you are, it is unlikely to be noticed amongst all of the BPL hash, and
    so as long as you don't go telling people about it, probably noone
    will care. If you were to build the whole arrangement inside a metal
    box with your watch, then that would quite likely be legal, and so for
    the purpose of this discussion that is what I will assume you did.

    I met an engineer who (whilst a student) built a time code transmitter
    so configured that it would make all of the clocks at his university
    run roughly backwards, to the amusement of all.

    Chris
     
  20. Joseph2k

    Joseph2k Guest

    No, we are not. You are refusing to understand.

    See chrisgj198's post. If the bit pattern does not make some
    sense and have good parity, then the clock will not set.

    The same data is also encoded in the WWV and WWVH
    transmissions at 5 MHz, 10 MHz, and 20 MHz. I consider
    it more reasonable for a watch to use one of those signals.
     
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