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Attempting my first successful broadband wire loop antenna project

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  • cwilliams1002002
    Hello, group. I have not written to you for such a long time simply because I have been working on a simple broadband loop antenna project. In addtion to the
    Message 1 of 2 , Apr 23, 2007
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      Hello, group.

      I have not written to you for such a long time simply because I have
      been working on a simple broadband loop antenna project. In addtion
      to the antenna, I have also attempted my latest successful
      regenerative radio receiver project to which I can attach this
      antenna.
      Basically, the broadband wire loop was made out of a 25-foot length
      of #14 AWG solid copper wire, THHN insulated, fashioned into about
      six feet each leg, an impedance matching transformer with a ratio of
      32:1 (1600 ohms primary, 50 ohms secondary), and a coaxial cable used
      for a connection to the radio via a panel mounted TV coaxial
      connector. The transformer consisted of 37 turns of #28 AWG enamelled
      copper wire on an FT-140-77 ferrite toroid for the primary and 5
      turns of #24 AWG enamelled copper wire for the secondary winding
      opposite from the primary winding. The ends of the primary winding
      were connected to the ends of the wire loop , and the ends of the
      secondary winding were connected to center tip of the connector and
      its ground lug, which is attached to the connector's threaded shell.
      An RG-59U cable is used as the feed, or lead-in to the receiver.
      Once the antenna was assembled, I hooked it up to a regenerative
      radio receiver, tuned in Radio Disney 1590, and sure enough, the
      antenna works! Its reception pattern is bidirectional (figure-8) with
      deep nulls for MW. The antenna may even cover shortwave as well as
      longwave.
      I am happy that my wire loop antenna works!

      Curtis
    • Len Warner
      ... Why did you choose such a high input impedance as 1600 ohms? I have a similar sized loop (approx. 30 feet) connected direct to my receiver and I find it
      Message 2 of 2 , May 2 1:28 PM
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        At 16:12 07/04/24, Digest Number 800 wrote:
        >1. Attempting my first successful broadband wire loop antenna project
        > Posted by: "cwilliams1002002" cwilliams1002002@... cwilliams1002002
        > Date: Mon Apr 23, 2007 2:18 pm ((PDT))
        >
        >[snip] the broadband wire loop was made out of a 25-foot length
        >of #14 AWG solid copper wire, THHN insulated, fashioned into about
        >six feet each leg, an impedance matching transformer with a ratio of
        >32:1 (1600 ohms primary, 50 ohms secondary)

        Why did you choose such a high input impedance as 1600 ohms?

        I have a similar sized loop (approx. 30 feet) connected direct to my
        receiver and I find it works better connected to the 50 ohm input
        than to the 600 ohm input. I'm not tempted to a higher impedance.

        (For your copper-tube loop, described last September, you used a
        1:9 step-UP turns ratio, or 1:81 impedance ratio, apparently into
        a 50 ohm input preamp. The loop lengths are not drastically different,
        so why such an extreme reversal in transformer ratio?)

        Since the radiation resistance of a "small" loop is tiny, its resistance
        and inductance are small, and as it isn't resonated [**], I cannot see
        a purpose in such a large "matching" impedance.

        [** Using RJELOOP3, its inductance is 10.2uH. A nomogram gives
        its reactance as 1600 ohms around 30MHz - but you won't get
        there, because its self-resonant frequency is about 20.5MHz.

        At 1590KHz, Rr=0.28 miili-ohms, Rloss=0.49 ohms and ZL=101 ohms.
        BTW, 986pF would tune it, giving a Q of 209 and an impedance of 21.2K
        at resonance and a sensitivity about -32db wrt a 1/4 wave vertical.]

        >[snip] The transformer consisted of 37 turns of #28 AWG enamelled
        >copper wire on an FT-140-77 ferrite toroid for the primary and 5
        >turns of #24 AWG enamelled copper wire for the secondary winding
        >opposite from the primary winding.

        Is this the same impedance matching transformer referred to above?

        The turns ratio is 37:5 or 7.4:1, so the impedance ratio is 54.76:1,
        which is quite a lot different to 32:1 and would result in an input
        impedance of 2738 ohms rather than your nominal 1600.

        To achieve your stated 32:1 impedance ratio the turns ratio would
        need to be approx. 5.66:1, or close to 28:5.

        Also, a ferrite has an optimum frequency range, above which it
        presents a resistive rather than reactive impedance making it
        unsuitable for inductors and transformers but excellent for RFI
        suppression. Type 77 is recommended for transformers from
        1 KHz - 2 MHz, so you might find it limiting for shortwave,
        especially as you choose to put the windings on opposite sides
        of the toroid and thus rely entirely on core flux for your coupling.

        Instead consider type 43 (.01-10 MHz) or type 61 (.2-100 MHz).

        There isn't a lower frequency limit as such, but the lower
        permeability of high-frequency ferrites demands more turns
        (perhaps impractically more turns) making a high permeability
        core more attractive where its frequency range permits.

        >[snip] tuned in Radio Disney 1590 .. the antenna works!

        To give us an idea of how impressive this feat is, please tell us
        how powerful the Radio Disney Tx is and how far from your QTH.


        Regards, LenW
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