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source for 60 kHz loopstick antenna

Discussion in 'Electronic Basics' started by Chris Campbell, Jan 20, 2004.

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  1. I'm trying to get a radio clock to sync up with WWVB (60 kHz out of
    Colorado). In the place that I want to place the clock, I can not get
    it to sync, even at night when the signal is stronger.

    Inside the clock is a small ferrite-core loopstick antenna. I figured
    out which way the gain pattern pointed on the thing (i.e. not along
    the axis of the ferrite rod) and tried positioning the clock for
    maximum signal, but no luck.

    So now I'd like to try a better antenna. I won't have the time to
    make one myself, and I'd probably do it badly anyway. It seems that I
    should be able to buy an antenna for this fairly cheaply (thank you to
    my capitalist exploiter overlords!), but I can't find one. Ideally,
    one designed for WWVB's 60 kHz would be great, but I'll settle for
    anything really, as long as it claims to have some decent gain at 60

    This clock is going inside a building, inside two layers of cinder
    block / concrete walls, so it's possible that I just won't be able to
    get a signal in there no matter what I use. The
    external-antenna-and-a-wire-run concept is the next step, but I'd
    rather not to that unless I have to. We're moving out of that
    facility in a few months so that would be wasted labor.

    What are some sources for loopstick antennas?

    On another note, in searching this forum, someone said:

    An LF loopstick antenna wound on a 1/2 inch diameter rod is *much*
    less efficient than a 1-meter square air loop

    Assuming I have the space, am I better off trying this with a few big
    loops of wire instead of a small ferrite loopstick? What are the
    rules of thumb for comparing the two types of loop antennas?

  2. OK1SIP

    OK1SIP Guest

    Hi Chris,
    try to make a rectangular coil, about 1 ft x 1 ft, some 30 turns wound
    by a fairly thin magnet wire (#25 to #30). Bring it into resonance at
    60 kHz by a capacitor, some 8000 - 10000 pF. Place the coil
    vertically, aiming to the transmitter, and place the clock to its
    center. You do not need any mods of the clock. The signal should be
    significantly stronger.

    BR from Ivan
  3. Reg Edwards

    Reg Edwards Guest

    To design small, VLF to HF, multi-turn loop antennas, download program
    RJELOOP3 in a few seconds and run immediately.

    Sides of square, number of turns, spacing between turns, value of tuning
    capacitor, and other data.
  4. Steve Nosko

    Steve Nosko Guest

    Where are you? I'm in Illinois and just got one of the clocks. I know it
    helps you not not a bit for me to say mine sync'ed up quickly, but everybody
    says that kinda' stuff :)-)..

    Don't think there is anything to buy... Make is the only way.

    The instructions for mine say that it only listens at certain times and can
    take a few _DAYS_ to sync up. That seems strange to me...oh well.

    Ivan's passive loop is a VERY good idea - easy.

    I don't think cinder block walls will matter.

    Search for "lowfer". I wanted to actually hear WWVB and do a little SWLing
    for NDBs (300-500KHz) w/ my new IC 706 and did some snooping. A good loop
    takes a little bit of work.
  5. All you will hear is nothing, unless your detector and audio amp goes
    down to DC. The modulation rate is one bit per second, by reducing the
    carrier level by 10 dB. There is no audio modulation, because the signal
    is also a frequency standard. The only way you would hear it would be to
    mix a signal to beat against WWVB to produce a heterodyne in the radio's
    pass band.

    We now return you to our normally scheduled programming.

    Take a look at this little cutie! ;-)

    Michael A. Terrell
    Central Florida
  6. Dave Holford

    Dave Holford Guest

    I hear it fine with several different receivers provided I use either CW
    or SSB. But! I CANNOT hear it on my IC-706; it does not seem to come
    alive until somewhere between 200 and 300kHz.


  7. Try using a HP312 series Frequency Selective Voltmeter for the

    Build a 60 KHz tuned loop and look at it with a scope. You can see
    the modulation, because it is so slow. It is a CW signal with a 10 dB
    gain reduction modulation with a maximum level change of twice per
    second. (Normal and -10 dB) I built a three foot square copper loop with
    an insulator where it was mounted on a cast aluminum electrical box, and
    wound 20 turns of wire inside the 3/4" copper pipe after it was soldered
    together. I used an op amp to give some gain,. and I could watch the
    modulation. The big problem was a neighbor about a half mile away left a
    TV set on 24/7 and the horizontal oscillator drifted after the station
    went off, and the harmonics would drift right through 60 KHz. I wanted
    to use it for a frequency standard, but I couldn't do it there. I will
    try it again, some day, now that I have a couple miles of woods between
    me and Colorado. I have enough gain to get around 12V P-P at the power
    inserter. I used 75 ohm cable and "F" fittings because they were handy,
    but I would use Mini Circuits MMICs and 50 Ohm cable if I built another
    outdoor 60 KHz antenna.

    We now return you to our normally scheduled programming.

    Take a look at this little cutie! ;-)

    Michael A. Terrell
    Central Florida
  8. Dave Holford

    Dave Holford Guest

    I have no problem receiving it on a number of different Ham and General
    Coverage receivers using random wires or simple vertical whips. I also
    hear it well with an active antenna. I have not noticed any real QRM
    problems on 60kHz although there are some really strong noise sources at
    other frequencies nearby.

    45N 75W
  9. Look at the design of the front end. If it is capacitor coupled, the
    capacitive reactance is so high that it blocks anything below 200 KHz.
    In this case you can add another cap in parallel to improve the lower
    frequencies. Multiply the original by 100 or higher, and add it in
    parallel to reduce the capacitive reactance, and the attenuation. I
    built a broadband DC block for my bench at Microdyne that had five caps
    in parallel. It was flat to less that a half dB from 50 KHz to 450 MHz,
    and had a VSWR of less than 1.05 across the entire range. It was built
    to maintain a 50 ohm impedance end to end.

    If it has a transformer, the losses are too high at low frequencies. In
    that case I would build a low pass filter and pre amp, and couple it to
    the input of the mixer to see how it performs. You would have to shut it
    off to use other bands, though.

    They only signals I saw were WWVB, and that damned TV's harmonics
    drifting through 60 KHz after the station went off the air. The guy was
    only there a couple days a month, and left the TV on to make people
    think he was home.

    We now return you to our normally scheduled programming.

    Michael A. Terrell
    Central Florida
  10. Now, just so I understand you correctly, you're saying I don't
    actually connect this loop antenna to the clock? I just place the
    clock in the center of it, and the loop antenna (I guess) induces a
    stronger signal in the clock's internal antenna? Wow, I'd love that.
    As for the loop ends, I just connect them together across the cap?

    And when you say "vertically, aiming to the transmitter", you mean
    that the plane of the loop intersects with the transmitting station,
    right? That is, I don't point the *face* of the loop at the
    transmitter, I point the edge towards it. Right?

    So, anyway, I'm making an antenna. Alright :) I downloaded and
    played with Reg's program and have a configuration that might work

    Can I stack wire turns, and if not, why not? It seems that all the
    designs have the wire turns lined up next to each other like:


    and never


    Is there something about keeping each loop *exactly* the same
    circumferential length (not even 0.2% difference) that dramatically
    affects loop antenna performance? Or some other affect?

    I'd like to fill a 5mm x 5mm cross section with wire turns, which
    means stacking them.
  11. You got it.
    "Towards" is a relative direction. You may have to experiment.

    Hi Chris,

    The ultimate explanation is that if you read the instructions
    carefully, you may find they state to try on one wall, or move to
    another and try again (pretty much the same advice as that above, less
    all the wire and capacitors).

    The "synchronization" does not always happen all at once (again, this
    is undoubtedly discussed in the instructions - or used to be). You
    may spend up to a week discovering the sweet spot where the receiver
    responds. We have fielded many such questions as yours in the past,
    and I cannot recall anyone coming back after having given up (and I
    don't recall one needing an external antenna).

    Richard Clark, KB7QHC
  12. Oh, I'm sure lots of folks ask questions here about these clocks :)

    Believe me, I tried and I was very patient. I tried the clock set up
    in five different locations, which included several orthogonal
    directions, and I left it in each position for at least 24 hours, and
    probably a lot longer. I spent a month on this and I'm not
    exaggerating. It was months ago (I *did* give up :) and my memory is
    fuzzy but I know I left it up at least overnight in each position, and
    for a week or more in some locations (i.e. on the bench, pointing in
    different directions). I never got a sync indoors.

    It's just that now I'm trying again, after having given up. Thanks
    for your help and I'll try the surrounding-loop solution. Makes me
    wish I'd taken that antenna design course in EE school.
  13. Dennis

    Dennis Guest

    You, must have some phenomenal hearing......60KHz!!
  14. (60 kHz out of Colorado). ...

    From experience there are also differences in the performance
    of WWVB clock receivers of the same brand and model
    from opening the box and later from differences in aging.

    Several years ago I ordered a wristwatch and two travel clocks
    from one of then and still prominent "atomic" clock outfits.
    One of the travel clocks locked up soon (overnight? - brain cells
    fade) and the second shortly afterwards. The wristwatch
    just would not lock up - very small antenna, so I wasn't
    surprised that it would take longer. I tried leaving
    it overnight in parts of the away from PC, TV, radio, ...
    and orienting it in various ways to point it to Colorado.
    After about two weeks, when I had given up and was ready
    and call the company, I went on a trip from northern NJ
    to California. Somewhere, sometime during the trip
    it locked up. Then after returning home... nothing.
    Making a very long story short, the company _finally_
    sent me a replacement wristwatch. The new one
    locked up nearly every night for the next 2 years
    and then, after any guarantee was gone, it quit.
    It still runs, just has long since drifted off time.
    Nothing since in the last 3 years, despite the deal
    of trying to find a 60-kHz quiet place, reorienting it...

    In the meantime, the travel clocks were doing fine,
    no matter where they were left or what part of the
    country I was in. Then about 2 years ago,
    one of them quit. Again - try finding that sweet, magic spot,
    leaving it side by side with its brother, oriented
    in the same direction. Always the same result -
    one fine, one deaf.

    I have thought about building a loop antenna
    like as has been disussed here to see if I could
    get at least the deaf travel clock locking.
    Tek makes tunable AM Loop antennas where the AM radio
    sits next to the loop and they do work
    out here in rural New Jersey.
    This discussion may yet spur me
    to physical wire and solder,
    not just typing, action.

    Somewhere I did have the URL of web page
    where a fellow built a shielded loop
    with an amplifier and all. The passive design,
    using Reg's program as a start, is simpler.

    I have several of the Sam's Club US$23 atomic wall clocks
    that lock up just fine, mounted on walls facing
    every which way. The outside temperature reading
    433MHz receiver seems to be a flaky, marginal design,
    but that's a different story.

    Cheers, 73

    Ron McConnell

    N 40º 46' 57.9" W 74º 41' 21.9"

    FN20ps77GV75 per w2iol
    or FN20ps77GU46 per K2RIW
  15. Hi Chris,

    Some years ago in my Cal Lab, the antenna that I used to receive WWVL
    was a 16 foot whip. I had it connected to a specialized receiver that
    separated out the Naval Observatory's TOC which was a specifically
    shaped pulse that occurred every 17 minutes. I used this to
    synchronize my Atomic Clock to within 100nS of UTC. It was never a
    simple feat, and missing that pulse meant a delay of at least 17
    minutes (which was about how long the entire process took).

    One question that I have failed to ask the various posters that came
    here was "how do you know it hasn't synchronized?" I can imagine
    there being a gross error of seconds if not minutes (which may
    contribute their/your problem), but under one second variation is
    difficult to confirm.

    Richard Clark, KB7QHC
  16. I built a Sheilded, amplified loop for my tests, and got a decent
    signal a few miles north of Orlando, years before they built the new
    towers, and transmitter.

    As far as the oudoor thermometer, Some cordless phones on the same
    band search for an open frequency, and wipe out the sync between the
    sensor and the clock. I need a cordless phone, more than the outdoor
    temperature, so I don't worry about it.
  17. Crazy George

    Crazy George Guest

    Steve and group:

    I tuned my IC706 down there, and apparently the front end filters block
    anything that low. My Kenwood R-5000 hears the signal fine with a 100'
    random wire. The radio I would really like to try, the RCA AR-88LF, only
    goes down to 74 KHz, and I sold the old RAK? RAL? Navy monster which covers
    that range, so I have to believe the R-5000 on this one. The signal is a
    little weak mid-day, but strong the remainder of the time.

    I bought one of the cheap "atomic" wristwatches last month, and have been
    experimenting with orientation for sync. It has an indicator which shows if
    it has locked up in the last 24 hours, and the manual says it tries at 3 AM
    in whatever time zone it is set to. The wall clocks also have a lock
    indicator, and their manual says they try several times in the wee hours if
    the first try doesn't result in synchronization. But BEWARE, I have now
    observed two different instances, once each with two different clocks, that
    while indicating that resynchronization had occurred the previous evening,
    the clock indicated the time which was exactly 1 minute off, apparently due
    to a thunderstorm during the night.

    The orientation where the wristwatch synchronizes reliably is face down,
  18. [I asked this a couple days ago but it was at the tail end of a longer
    message so maybe that's why nobody replied.]

    Can I stack wire turns, and if not, why not? It seems that all the
    designs have the wire turns lined up next to each other like:


    and never


    Is there something about keeping each loop *exactly* the same
    circumferential length (not even 0.2% difference) that dramatically
    affects loop antenna performance? Or some other affect?

    I'd like to fill a 5mm x 5mm cross section around the perimeter of the
    clock with wire turns, which means stacking them.
  19. Crazy George

    Crazy George Guest


    I thought someone else would answer, but here it is: For highest Q you want
    the minimum capacitance between start and end, so what you suggest will
    work, but try to actually make the layers carefully so the outside layers
    don't collapse down to the first.

    Crazy George
    Remove N O and S P A M imbedded in return address
  20. My cordless phones work on 2.4GHz and the remote thermometers
    are on 433MHz - a frequency which is shared among many types
    of gadgets.

    I should add that there seemed to have been a redesign
    of the Sam's Club clock about a year ago. The remote
    temperature receiver seems better in new ones.
    I have 3 different brands of atomic-clocks-with-remote-thermometers
    working from one remote Sam's Club remote thermometer transmitter.

    Back to ham antennas... :)

    Cheers, 73

    Ron McConnell

    N 40º 46' 57.9" W 74º 41' 21.9"

    FN20ps77GV75 per w2iol
    FN20ps77GU46 per K2RIW

    Magnetic declination 13ºW in early 2004
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