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Re: Newbie question: pick-off loop design

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  • tenorman1952
    ... One turn is just fine. It can be the same size as the main loop, or smaller, inside of the main loop. Paul - AE5JU
    Message 1 of 5 , Apr 6, 2013
      --- In loopantennas@yahoogroups.com, "dfq98" <dfq98@...> wrote:
      >
      > Hi folks,
      > I made tunable loop antennas about 34 yrs ago and again this month for DX-ing, the first time for coupling to a small radio with built-in ferrite loop, and this time for a receiver that has antenna terminals.
      >
      > The small 11" square loop I've made this time is made from two loops of 6-conductor telephone cable, with the internal wires daisy-chained to make the equivalent of 12 loops, and tuned with a 700 pF variable capacitor. It has very sharp nulls and sharp tuning over about 1510-1400 kHz or so.
      > So: on to my question. I've coupled this to the radio using a single turn of wire nestled between the two telephone cables (total width about 0.3"), but I have been unable to find any design criteria for how to optimize this second loop. I.e. is there a formula to estimate the optimal number of turns, position relative to the tuned loop, and radio parameters? None of the loop calculators that I've seen include such details.
      > Thanks in advance!
      >

      One turn is just fine. It can be the same size as the main loop, or smaller, inside of the main loop.

      Paul - AE5JU
    • tenorman1952
      ... Also, I ve connected the sense loop aka pickup loop to the radio with coax, 300 ohm twinlead, and simple twisted pair of 22 ga hookup wire. I can t
      Message 2 of 5 , Apr 6, 2013
        --- In loopantennas@yahoogroups.com, "dfq98" <dfq98@...> wrote:
        >
        > Hi folks,
        > I made tunable loop antennas about 34 yrs ago and again this month for DX-ing, the first time for coupling to a small radio with built-in ferrite loop, and this time for a receiver that has antenna terminals.
        >
        > The small 11" square loop I've made this time is made from two loops of 6-conductor telephone cable, with the internal wires daisy-chained to make the equivalent of 12 loops, and tuned with a 700 pF variable capacitor. It has very sharp nulls and sharp tuning over about 1510-1400 kHz or so.
        > So: on to my question. I've coupled this to the radio using a single turn of wire nestled between the two telephone cables (total width about 0.3"), but I have been unable to find any design criteria for how to optimize this second loop. I.e. is there a formula to estimate the optimal number of turns, position relative to the tuned loop, and radio parameters? None of the loop calculators that I've seen include such details.
        > Thanks in advance!
        >

        Also, I've connected the "sense loop" aka "pickup loop" to the radio with coax, 300 ohm twinlead, and simple twisted pair of 22 ga hookup wire. I can't tell the difference with any of these three.

        Paul - AE5JU
      • dldorrance
        Message 3 of 5 , Apr 6, 2013
          <Also, I've connected the "sense loop" aka "pickup loop" to the radio with coax,300 ohm twinlead, and simple twisted pair of 22 ga hookup wire. I can't tell the difference with any of these three>

          That's because your receiver is much less sensitive to mismatched impedance than a transmitter.
          >
        • Jerry Flanders
          FYI, Cat-5 cable also makes a good cheap transmission line. Either pair of the 4 pairs there is about 200 ohms balanced, two pairs paralleled is 100, all 4
          Message 4 of 5 , Apr 6, 2013
            FYI, Cat-5 cable also makes a good cheap transmission line. Either
            pair of the 4 pairs there is about 200 ohms balanced, two pairs
            paralleled is 100, all 4 pairs paralleled is about 50. Observe
            polarity at both ends.

            I use it to carry component HDTV sigs around my house.

            Good to above 100 MHz, IIRC.

            Jerry W4UK

            At 10:57 AM 4/6/2013, you wrote:
            ><Also, I've connected the "sense loop" aka "pickup loop" to the
            >radio with coax,300 ohm twinlead, and simple twisted pair of 22 ga
            >hookup wire. I can't tell the difference with any of these three>
            >
            >That's because your receiver is much less sensitive to mismatched
            >impedance than a transmitter.
            > >
          • tenorman1952
            ... What does a transmitter have to do with it? It is a receiving loop. The impedance mismatch has no discernable effect. All three methods work well. Paul -
            Message 5 of 5 , Apr 7, 2013
              --- In loopantennas@yahoogroups.com, "dldorrance" <dldorrance@...> wrote:
              >
              > <Also, I've connected the "sense loop" aka "pickup loop" to the radio with coax,300 ohm twinlead, and simple twisted pair of 22 ga hookup wire. I can't tell the difference with any of these three>
              >
              > That's because your receiver is much less sensitive to mismatched impedance than a transmitter.
              > >
              >

              What does a transmitter have to do with it? It is a receiving loop.

              The impedance mismatch has no discernable effect. All three methods work well.

              Paul - AE5JU
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