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Re: Shortwave Loop Antenna Construction

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  • gmcjetpilot
    That is a nice LOOP kit and it is for MW or for AM radio broadcast, not SW. Yea you can copy that very easy, make an X frame with 2 sides, wrap some wire
    Message 1 of 10 , Jul 1, 2008
      That is a nice LOOP kit and it is for MW or for AM radio broadcast,
      not SW.

      Yea you can copy that very easy, make an X frame with 2' sides, wrap
      some wire (magnet, insulated, almost any really) around it to a AIR
      Capacitor and you have a tunable passive loop. Here is a GOOD BASIC
      LOOP LINK:

      http://www.mindspring.com/~loop_antenna/

      You can copy his design exactly. The kit you talk of saves you from
      scrounging for all the parts. There are not that many parts, but if
      you don't have it you have to get it. THE DESIGN IS 100 YEARS OLD, no
      state secret.

      You can make an untuned LOOP with out the capacitor. I just made one
      out of a 1' x 1' pizza box and about 22' of wire, no capacitor. It
      works well for my needs, to bring in a few near by AM stations. The
      radio in question has no internal loop or loop-stick so I needed
      something. It probably came with an untuned loop, no doubt that I
      lost. Here is a link to the ultimate AM antenna and a pic of one I
      built like it (I went 5 turns because I had the wire):

      http://members.cox.net/rwagoner/columns/am_antenna.html

      Here is my last post of thread on this antenna with pictures:
      http://groups.yahoo.com/group/loopantennas/message/5333


      HOW DOES IT (tuned passive loops) WORK. The best explanation is a
      swinging pendulum held in you hand. For a given weight hanging off a
      string of given length, if you move your hand back and forth at a
      certain rate (frequency) the weight at the end will react in a given
      way. If you get the rate of hand moving back and forth just right
      (for the string length & weight) it will swing wide (resonance). If
      you move your hand back and forth faster or slower, the pendulum will
      not move as vigorously or with regular movement. If you increase or
      decrease the weight or length of string, it will react differently to
      different freq of hand movement. SO WHAT DOES THAT HAVE TO DO WITH A
      LOOP. Well the input or hand movement is the radio signal
      (frequency). The string length is the length of the loop, and the
      weight is the CAPACITOR! If you get the length of loop (number of
      wraps around a frame of X circumference) and capacitor (weight at end
      of string) just right for a given radio freq (hand movement) you get
      the most resonance.

      If you google LOOP antenna you will find web links for calculating
      the range of "resonance" for a given loop, size, number of turns and
      capacitor (capacitance) range.

      The kit in question, if you varnish it and take your time will be
      nice to look at and listen to. Like all passive loops, you have to
      aim them and tune them. Of course you can make your own for cheaper.
      The most expensive part is the air capacitor which is about $15-$20.

      Cheers George

      --- In loopantennas@yahoogroups.com, "Adam E." <gccradioscience@...>
      wrote:
      >
      >
      > That sounds pretty hard, oops, my mistake, I got the wrong one.
      Ok
      > let me explain, there is a shortwave loop antenna that I want to
      plan
      > on building soon a company called MTM Scientific made and they sell
      it
      > as a kit and I wanted to learn more about how to build one with
      > readably available parts . I saw this kit and I thought it would
      be
      > fun to build since there is a frame and wire and other parts and
      > pieces. If not possible I guess I will have to buy this kit soon.
      I
      > am still considering getting myself a copy of the JJ Carrs Loop
      > Antenna Handbook for me to study when I am bored. Thanks for the
      > help, its really appreciated.
      >
      > link: http://www.mtmscientific.com/swloop.html
      >
      > Adam E.
      > Virginia Beach VA
      >
      > SWL Radios: Grundig YB-400PE, G5, Mini 300, S-350DL, FR-200. Radio
      > Shack DX-380, 390, 392, 398. RY-611 and CF-1888
      >
      >
      >
      >
      >
      >
      > --- In loopantennas@yahoogroups.com, Chris Trask <christrask@>
      wrote:
      > >
      > > >
      > > > >
      > > > > > Sorry but there is no link there except a Spanish forum that
      > does not
      > > > > > have any instructions in building a SW loop antenna. If
      > anyone else
      > > > > > can help that would be greatly appreciated thanks.
      > > > > >
      > > > > >
      > > > > > Adam E.
      > > > >
      > > > > Adam; I agree with Jim. What do you want to build? ... untuned
      > passive
      > > > > loop? active loop? tuned passive loop? resonant cut
      loop/folded
      > > > > dipole?
      > > >
      > > >
      > > > Tuned passive loop for to hang around by the window.
      > > >
      > >
      > > A wideband tuned passive loop will be very difficult to
      > implement as the impedance of the loop will vary significantly. For
      > instance, a 1 meter diameter loop consisting of 1 turn of 1/4"
      > diameter copper tubing will have a resistance of about 0.5 ohms at
      > 4MHz, 10 ohms at 12MHz, and then increases to 420 ohms at 15MHz.
      It's
      > parallel resonance is around 17.9MHz. With a 4:1 BalUn transformer,
      > such an antenna can be easily used for the 25M SWBC band without an
      > amplifier.
      > >
      > > I went through months of building and testing loops of
      various
      > diamters, turns, and conductor diameters for my 2-part series on
      > active loops in the Jul/Aug and Sep/Oct 2003 issues of QEX.
      > >
      > >
      > >
      > >
      > >
      > > Chris
      > >
      > > ,----------------------. High Performance Mixers and
      > > / What's all this \ Amplifiers for RF Communications
      > > / extinct stuff, anyhow? /
      > > \ _______,--------------' Chris Trask / N7ZWY
      > > _ |/ Principal Engineer
      > > oo\ Sonoran Radio Research
      > > (__)\ _ P.O. Box 25240
      > > \ \ .' `. Tempe, Arizona 85285-5240
      > > \ \ / \
      > > \ '" \ IEEE Senior Member #40274515
      > > . ( ) \
      > > '-| )__| :. \ Email: christrask@
      > > | | | | \ '.
      http://www.home.earthlink.net/~christrask
      > > c__; c__; '-..'>.__
      > >
      > > Graphics by Loek Frederiks
      > >
      >
    • tenorman1952
      ... He s referring to this loop at MTM Scientific: http://www.mtmscientific.com/swloop.html No, actually that loop is for SW. It is a 1 turn loop with a
      Message 2 of 10 , Jul 2, 2008
        --- In loopantennas@yahoogroups.com, "gmcjetpilot" <gmcjetpilot@...>
        wrote:
        >
        > That is a nice LOOP kit and it is for MW or for AM radio broadcast,
        > not SW.


        He's referring to this loop at MTM Scientific:

        http://www.mtmscientific.com/swloop.html

        No, actually that loop is for SW. It is a 1 turn loop with a 9.5-365
        pf variable cap. If your run 1 turn loops of various reasonable
        sizes through the calculators online, including Bruce Carter's, they
        will fall in the SW range.

        http://www.mindspring.com/~loop_antenna/umr_emc_calc.htm

        Using that calculator, 1 turn, 36" sides, gives 3.8 mhz - 23.6 mhz.

        With 1 turn, 30" sides, it gives 4.2 mhz - 27.2 mhz.

        If 1 turn, 24" sides, it gives 4.8 mhz -29.8 mhz.

        MTM scientific has a 15 turn tuned loop, 17" sides, that covers the
        MW/AM band:

        http://www.mtmscientific.com/loop.html

        I have photos of my MTM AM loop in the Photos section in the Loop
        Kits folder.

        Paul C.
        tenorman1952
      • Bill McGraw
        Hal S. said, 4. Twist the wire ends together approximately 2 turns per inch (I made a change here. On the base, I installed a two-wire terminal so I could
        Message 3 of 10 , Jul 3, 2008
          Hal S. said, "4. Twist the wire ends together approximately 2 turns per inch
          (I made a change here. On the base, I installed a two-wire terminal so I
          could easily connect a different length lead wire. I connected the ends of
          the wire from the loop to the terminal block and then connected a shielded
          wire to the terminal block to act as a lead-in. The ground (shield) lead
          connects to the ground terminal of the radio, the center wire connects to
          the "external AM antenna" terminal of the radio. You may have to experiment
          with your own radio to find what works best)."

          Hal,
          1. Do I understand you twist the antenna loop ends together?
          2. What is "approximately 2 turns per inch?"
          3. What is the "two-wire terminal" and how do you fashion two wires if the
          antenna ends are twisted together?
          4. What kind of terminal block do you describe?
          5. What kind of shielded wire do you use for the terminal block?
          6. Once built, is there any kind of tuning, V-cap or does the radio receiver
          need to be in close proximity?

          William W."Bill" McGraw
          "Somewhere South of Chicago"
          Greenville, MS 38701
        • gandalfg8@aol.com
          In a message dated 03/07/2008 08:57:48 GMT Daylight Time, mcgr3799@bellsouth.net writes: Hal S. said, 4. Twist the wire ends together approximately 2 turns
          Message 4 of 10 , Jul 3, 2008
            In a message dated 03/07/2008 08:57:48 GMT Daylight Time,
            mcgr3799@... writes:

            Hal S. said, "4. Twist the wire ends together approximately 2 turns per
            inch.........

            Hal,
            1. Do I understand you twist the antenna loop ends together?
            2. What is "approximately 2 turns per inch?"

            ---------------------------

            Hi Bill

            I'm not sure what the original reference was, so don't have any details of
            this particular loop and can't comment on any of the other questions, but this
            won't mean twist together in the sense of a tight twist just to join right at
            the very end.

            The implication seems to me that you should expect to have some wire "ends",
            let's say each two feet long just for example, presumably after constructing
            the loop, and it's these you're supposed to twist together along their
            length so you end up with a twisted pair of wires.
            Approximately two turns per inch will mean just that, as you twist it
            together allow approx two turns every inch of wire, ie don't twist it too tight.

            Not knowing the original source, I can't say exactly what you're supposed to
            with it after that nor if these "ends" are from a main loop or coupling loop,
            but would guess that could be the connection to your radio:-)

            regards

            Nigel
            GM8PZR
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