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Re: [loopantennas] question on my first Loop antenna

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  • oene
    Just made a 5 loop and it resonates at 7.705. Maybe because it s scuare?
    Message 1 of 17 , Jun 19, 2005
      Just made a 5' loop and it resonates at 7.705.
      Maybe because it's scuare?

      john nelson schreef:

      > I have a 4' diameter loop that resonates at 7mhz and
      > it is a single turn.
      >
      > jn
      >
      > --- John <coop1776@...> wrote:
      >
      > > I am interested in building an indoor loop antenna
      > > primarily for 6-7
      > > Mhz or 41 , 49 meter band. I am new to this. I plan
      > > to make a spiral
      > > loop using about 560 ft of wire about 4 ft tall. I
      > > will connect the
      > > wire to a capacitor I got out of an old am radio,
      > > and then connect it
      > > to either the 500 Ohm connection using the same wire
      > > or connect it
      > > using coax to the 50 Ohm connection. I have a
      > > Grundig 800 receiver.
      > > I am not sure if this makes sense, any thoughts
      > > would be appreciated,
      > > thanks.
      > >
      > >
      > >
      > >
      > >
      > >
      >
      >
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    • John
      Jim, Is the big outer loop with the capacitor connected somehow to the small inner loop or is the inner loop freestanding and only connected to the coax
      Message 2 of 17 , Jun 20, 2005
        Jim,
        Is the big outer loop with the capacitor connected somehow to the
        small inner loop or is the inner loop freestanding and only connected
        to the coax connected to the receiver?

        --- In loopantennas@yahoogroups.com, Jim Dunstan <jimdunstan@r...>
        wrote:
        > At 11:47 PM 6/19/2005 +0000, you wrote:
        > >Thanks, I meant 60 ft of wire but will take your suggestion and use
        > >16 ft. Is the tuning capacitor going to help? Should it be feed
        > >straight into the receiver or thru coax?
        > >--- In loopantennas@yahoogroups.com, Jim Dunstan <jimdunstan@r...>
        > >wrote:
        >
        > Hi,
        >
        > If you feed it directly into your receiver (eg no pre-amp) you will
        need to
        > resonate the loop in order to get a strong signal. The easiest way
        to
        > couple the loop is to use a small separate coupling loop. For
        example:
        >
        > You build a support for a 4' loop (square or diamond shape is fine)
        with
        > each end of the wire terminated on either side of your tuning
        > capacitor. Then get a piece of coax the length you need to reach
        between
        > the loop and your receiver. On one end of the coax place the
        necessary
        > hardware to connect to your receiver and on the other make a
        smaller loop
        > .... say 1' in diameter. Fasten the small 1' loop inside the 4'
        loop in
        > the same plane and locate it at the inside edge opposite where you
        have the
        > tuning capacitor.
        >
        > Since your receiver runs on batteries .... locate it next to your
        loop and
        > tune it to the middle of the band of choice .... 49M. Now tune
        your
        > capacitor and you should find a point where the background noise
        rises and
        > peakes. Pick a weak signal and rotate the antenna and you should
        find a
        > position that provides a signal null. The characteristic field
        pattern of
        > the small resonant loop is 2 broad high signal directions, 180 deg
        from
        > each other and 2 sharp null positions .... also 180 deg apart.
        The normal
        > practice is to rotate the loop to minimize local noise ...
        electrical
        > interference.
        >
        > If you tune to the middle of the SW band of your choice you should
        get
        > satisfactory reception across the band. However, when you change
        bands you
        > will have to change the tuning to the middle of that band ... mark
        it and
        > it should be easy to do.
        >
        > This is one way of doing it .... you can also tune the loop with a
        remote
        > antenna tuner .... provides different problems and solutions.
        There is a
        > good site on the net for remote tuned loops made from coax. Do a
        search
        > for "Greertech" and you will find it. I use another method of
        remote
        > tuning with an antenna tuner using tv twin lead .... that is
        another story.
        >
        >
        >
        > Jim Dunstan
        > Thunder Bay, ON
      • Jim Dunstan
        ... Your second option is correct. Think of the tuned loop as if it was a hula-hoop with a tuning capacitor in series .... 3 -4 in diameter. The second loop
        Message 3 of 17 , Jun 20, 2005
          At 11:29 PM 6/20/2005 +0000, you wrote:
          Jim,
             Is the big outer loop with the capacitor connected somehow to the
          small inner loop or is the inner loop freestanding and only connected
          to the coax connected to the receiver?               

          Your second option is correct.  Think of the tuned loop as if it was a hula-hoop with a tuning capacitor in series .... 3'-4' in diameter.  The second loop is much smaller .... 8"-12" in diameter and connected to your receiver with a coax lead.  Now mount the large tuned loop to a simple frame to keep it vertical and allow simple rotation.  Then, bring the small pickup loop and mount it on the same frame inside and in the same plane as the large loop (usually close the large loop opposite the tuning capacitor.

          You should hear signals peak on your receiver when you tune the large loop through resonance.  This same system can be used to transmit as well.  If you transmit into the small loop it will couple into the tuned loop and radiate quite well.  The added considerations to make this into a transmitting arrangement would be to construct the loop from the largest diameter copper practical (eg 3/4") and use a capacitor with wide spacing to accommodate the high voltages that will be developed across it.  It is also convenient to connect the coupling loop to the transceiver via an automatic antenna tuner.

          There are simple computer programs available on line that calculate radiator diameters, capacitor size and voltage, and loop diameters.  These figures will bring you very close to a working transmitting loop.  For receiving however a loop of #14 wire with the receiving type capacitor is all you need.  A couple of lengths of 1/2" hardwood trim and a bag of electrical tie wraps and your frame and loop is up and running.



          Jim Dunstan
          Thunder Bay, ON

        • Richards
          I am interested in making a general coverage receiving loop, perhaps about 4 feet square (i.e., 4 feet on each side) and wonder how many turns of what size
          Message 4 of 17 , Jun 20, 2005
            I am interested in making a general coverage receiving loop, perhaps
            about 4 feet square (i.e., 4 feet on each side) and wonder how many
            turns of what size wire would make this a good plan. Also wondering
            whether it should direct couple or use a variable capacitor as is often
            used with medium wave band loops of this type.

            Any ideas would be really, truly, greatly appreciated.

            Best Regards. ///// Richards //////
            ========================================

            dldorrance wrote:

            >--- In loopantennas@yahoogroups.com, "John" <coop1776@y...> wrote:
            >
            >
            >>I am interested in building an indoor loop antenna primarily for
            >>6-7
            >>Mhz or 41 , 49 meter band. I am new to this. I plan to make a
            >>spiral
            >>loop using about 560 ft of wire about 4 ft tall. I will connect the
            >>wire to a capacitor I got out of an old am radio, and then connect
            >>it
            >>to either the 500 Ohm connection using the same wire or connect it
            >>using coax to the 50 Ohm connection. I have a Grundig 800 receiver.
            >> I am not sure if this makes sense, any thoughts would be
            >>appreciated,
            >>thanks.
            >>
            >>
            >
            >John, you don't need to use so much wire. You may create a circular
            >40 meter receiving loop, using a single turn loop with a diameter of 3
            >to 6 feet. 6 feet would be preferable but not necessary if you have
            >space limitations. To figure the circumference multiply the diameter
            >by 3.14 (pi). Connect both ends of the loop to a variable capacitor
            >taken from a radio (365 pf will work fine).
            >
            >How to tap the loop? For a 50 ohm connection make a smaller loop
            >whose circumference is 1/5 the circumference of the big loop. Place
            >that smaller loop inside the big loop so that both loops are in the
            >same plane and make your connection to your radio from that smaller
            >loop. You may run coax between this small "sense" loop and your
            >receiver.
            >
            >How to tune the loop? Turn the capacitor very slowly until the volume
            >jumps up. When you change frequency on your receiver you need to
            >retune the capacitor to peak the new signal. The loop described here
            >should have a bandwidth of only about 20 kHz.
            >
            >Loop direction: You will receive signals strongest off both end of
            >the loop, that is in the plane of the loop. Conversely,
            >if you find a local noise source you would like to attenuate, point
            >the loop broadside toward the noise. This is the null of the loop.
            >
            >The only difference between the loop I have described above and a
            >small transmitting loop is the size of the conductor. In the case of
            >a transmitting loop one needs to minimize. resistive losses by using
            >pipe instead of wire and by using a capacitor without a wiper (again
            >to minimize resistive losses). For receive only the resistive losses
            >are more than compensated for by the astronomical gain built into the
            >receiver.
            >
            >If you wish to delve more deeply into how to figure the parameters
            >discussed here you might want to unzip and use the calculator,
            >LOOPCALC referenced on this page:
            >http://sstv.ccone.at/downloads
            >
            >Dave WA6YSO
            >
            >
            >
            >
            >
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            >
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            >
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          • Richards
            I thought the beauty of the whole loop thing was that it could induce a current into the smaller, inner loop by magnetic inductance, and not by electrical
            Message 5 of 17 , Jun 20, 2005
              I thought the beauty of the whole loop thing was that it could induce a
              current into the smaller, inner loop by magnetic inductance, and not by
              electrical inductance, which tends to minimize or ignore certain types
              of electrical noise and or static in the environment/atmosphere. The
              inner loop fix up the magnetic field created by the current flowing in
              the outer loop, inducing a current into the inner loop which, I suppose,
              would travel in whatever direction is specified by the "Right Hand Rule."

              Parenthetically, I remember that "Right Hand Rule" saying from physics
              class nearly 30 years ago... I guess I actually learned something back
              then...

              thanks for your further feedback. Best Regards. ///// Richards //////
              ========================================

              Jim Dunstan wrote:

              > At 11:29 PM 6/20/2005 +0000, you wrote:
              > diameter. The second loop is much smaller .... 8"-12" in diameter and
              > connected to your receiver with a coax lead. Now mount the large
              > tuned loop to a simple frame to keep it vertical and allow simple
              > rotation. Then, bring the small pickup loop and mount it on the same
              > frame inside and in the same plane as the large loop (usually close
              > the large loop opposite the tuning capacitor.
              >
            • John
              Thanks for your help Jim. I love the name of your city. ... the ... connected ... was a ... diameter. The ... to your ... simple ... the small ... plane as
              Message 6 of 17 , Jun 21, 2005
                Thanks for your help Jim. I love the name of your city.
                --- In loopantennas@yahoogroups.com, Jim Dunstan <jimdunstan@r...>
                wrote:
                > At 11:29 PM 6/20/2005 +0000, you wrote:
                > >Jim,
                > > Is the big outer loop with the capacitor connected somehow to
                the
                > >small inner loop or is the inner loop freestanding and only
                connected
                > >to the coax connected to the receiver?
                >
                > Your second option is correct. Think of the tuned loop as if it
                was a
                > hula-hoop with a tuning capacitor in series .... 3'-4' in
                diameter. The
                > second loop is much smaller .... 8"-12" in diameter and connected
                to your
                > receiver with a coax lead. Now mount the large tuned loop to a
                simple
                > frame to keep it vertical and allow simple rotation. Then, bring
                the small
                > pickup loop and mount it on the same frame inside and in the same
                plane as
                > the large loop (usually close the large loop opposite the tuning
                capacitor.
                >
                > You should hear signals peak on your receiver when you tune the
                large loop
                > through resonance. This same system can be used to transmit as
                well. If
                > you transmit into the small loop it will couple into the tuned loop
                and
                > radiate quite well. The added considerations to make this into a
                > transmitting arrangement would be to construct the loop from the
                largest
                > diameter copper practical (eg 3/4") and use a capacitor with wide
                spacing
                > to accommodate the high voltages that will be developed across it.
                It is
                > also convenient to connect the coupling loop to the transceiver via
                an
                > automatic antenna tuner.
                >
                > There are simple computer programs available on line that calculate
                > radiator diameters, capacitor size and voltage, and loop
                diameters. These
                > figures will bring you very close to a working transmitting loop.
                For
                > receiving however a loop of #14 wire with the receiving type
                capacitor is
                > all you need. A couple of lengths of 1/2" hardwood trim and a bag
                of
                > electrical tie wraps and your frame and loop is up and running.
                >
                >
                >
                >
                > Jim Dunstan
                > Thunder Bay, ON
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