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Some loop antenna ideas

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  • Jim Dunstan
    Hello all, I think of the oddest things while walking the dog. To illustrate this, tonight I was thinking of antenna theory and loop antennas in particular.
    Message 1 of 12 , Nov 3, 2005
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      Hello all,

      I think of the oddest things while walking the dog. To illustrate this,
      tonight I was thinking of antenna theory and loop antennas in
      particular. I read somewhere that the production of electromagnetic waves
      (radiation) is literally a function of the generation and combination of a
      magnetic field and an electric field (the function of an antenna). It is
      important to understand that the radiation is not a sum of the 2 fields, it
      is the product. Thus a Mag. F. of 4 x Elec. F. of 1 = Radiation of 4 and
      a situation where the Mag. F. of 1 x Elec. F. of 4 = Radiation of 4
      !!! Exactly the same.

      The EFFECTIVENESS of the antenna is a result of maximizing the EFFECTIVE
      magnetic field and the EFFECTIVE electric field of the antenna either of
      which will do the job equally well. What I mean by an EFFECTIVE field is
      that it is arranged so it can contribute to radiation. A coil inserted in
      series with a wire antenna creates an inductance allowing the antenna to be
      shortened. The magnetic field within the coil creates an inductive
      reactance but it does not add to the effective magnetic field of the
      wire. In fact it subtracts from the effective magnetic field of the wire
      (antenna) as the wire must be shortened to maintain the overall inductive
      reactance (required for resonance). Conversely a capacitor can be added to
      an antenna (as in a loop for example) in order to tune it to
      resonance. The electric field (between the plates) does not contribute to
      the effective electrical field of the loop and in fact allows the loop to
      be reduced in size (while maintaining resonance) thus reducing the
      effective electrical field.

      Lets get back to practical loop configurations for both receiving and
      transmitting. I'm thinking of small loops of approximately 1/10 of a
      wavelength or less. Let's say a transmitting loop for 40M (7Mhz) that is
      approximately 4 Ft. in dia. It will be necessary to tune the loop to
      resonance by introducing a rather large external capacitor. The electrical
      field created between the plates will be quite intense and the voltage
      across the plates will rise to high values .... requiring substantial
      spacing between them. The tuning capacitor will tune the loop to resonance
      but it will not create an electric field that contributes to radiation.

      So how are the effective electrical and magnetic fields created in this
      loop? The effective magnetic field is a result of the electric current that
      flows around the loop and the effective electric field is a result of the
      differential voltage around the loop. The loop has self capacitance. This
      differential voltage in combination with the self capacitance of the loop
      creates the electric field. The combination of these highly interrelated
      fields creates the electromagnetic radiation.

      Having thought through this I ask myself how do I maximize the effective
      magnetic and electrical fields of this 4' loop?

      The magnetic field is a function of the current in the loop which in turn
      is a function of the conductivity of the loop at 7 Mhz. I understand that
      conductivity is a function of the material used (eg aluminium is good,
      copper is better) and surface area (due to skin effect). Metal strap of 1"
      width represents a surface of 1" x 2 = 2 (both sides) and a 1" pipe
      represents a surface of 3.14 (pi) So the pipe has it in terms of
      electrical conduction (and rigidity).

      Now of what is the electrical field a function? Well certainly it is a
      function of the self capacitance of the loop and the voltage
      differential. The voltage differential is a function of the current flow
      (interrelated to the magnetic field but out of phase, by what, 90 degrees
      ??). What is the self capacitance related to? I would think the surface
      area of the inside of the loop. Am I right? If this is true how can we
      increase the self capacitance of the loop (and maintain the required
      conductivity). If we increase the electric field component by 10% we
      increase the radiation by 10% as well since radiation is product of the
      magnetic and electrical fields.

      What if we constructed the loop of strap instead of tubular material would
      that substantially increase the self capacitance of the loop? Fixed
      capacitors use flat plates not curved plates. What about tacking a 3" or
      4" wide strip of mesh around the inside of the loop? Would that
      substantially increase the self capacitance of the loop?

      If it is possible to substantially increase the self capacitance of the
      loop what would be the effect on feed point impedance, radiation pattern,
      near effect of metal objects, effect of aperture size or capture area (I'm
      not sure of the correct terminology), etc..

      Food for thought









      Jim Dunstan
      Thunder Bay, ON
    • Ken Javor
      I don t think you are on the right track. If a radiating element is electrically short, it radiates either a predominantly electric or magnetic field,
      Message 2 of 12 , Nov 3, 2005
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        I don't think you are on the right track. If a radiating element is
        electrically short, it radiates either a predominantly electric or magnetic
        field, depending on whether it is a whip or a loop. An electrically short
        whip looks like a small capacitance that is a very high impedance. Adding
        inductance in series with that capacitor decreases the high impedance
        allowing more current to flow, hence better radiation efficiency. Likewise,
        an electrically short loop used at HF and above is an inductive load that
        will present a high impedance which can be decreased by a series capacitor,
        again allowing more current to flow. You don't really need to have a deep
        understanding of electromagnetics to get a feel for this, simply look at the
        limiting cases. A short rod is close to an open circuit. Driving it from
        50 or 75 Ohms places a potential on it but no current. That means no power
        is flowing into the whip. If no power is flowing into the whip, then no
        power can flow out in the form of a radiated field (conservation of energy).
        The more current (power) you can get into the radiating element, the more
        power in the field, and the better the transmitter.

        From: Jim Dunstan <jimdunstan@...>
        Reply-To: loopantennas@yahoogroups.com
        Date: Thu, 03 Nov 2005 20:14:32 -0500
        To: loopantennas@yahoogroups.com
        Subject: [loopantennas] Some loop antenna ideas



        Hello all,

        I think of the oddest things while walking the dog. To illustrate this,
        tonight I was thinking of antenna theory and loop antennas in
        particular. I read somewhere that the production of electromagnetic waves
        (radiation) is literally a function of the generation and combination of a
        magnetic field and an electric field (the function of an antenna). It is
        important to understand that the radiation is not a sum of the 2 fields, it
        is the product. Thus a Mag. F. of 4 x Elec. F. of 1 = Radiation of 4 and
        a situation where the Mag. F. of 1 x Elec. F. of 4 = Radiation of 4
        !!! Exactly the same.

        The EFFECTIVENESS of the antenna is a result of maximizing the EFFECTIVE
        magnetic field and the EFFECTIVE electric field of the antenna either of
        which will do the job equally well. What I mean by an EFFECTIVE field is
        that it is arranged so it can contribute to radiation. A coil inserted in
        series with a wire antenna creates an inductance allowing the antenna to be
        shortened. The magnetic field within the coil creates an inductive
        reactance but it does not add to the effective magnetic field of the
        wire. In fact it subtracts from the effective magnetic field of the wire
        (antenna) as the wire must be shortened to maintain the overall inductive
        reactance (required for resonance). Conversely a capacitor can be added to
        an antenna (as in a loop for example) in order to tune it to
        resonance. The electric field (between the plates) does not contribute to
        the effective electrical field of the loop and in fact allows the loop to
        be reduced in size (while maintaining resonance) thus reducing the
        effective electrical field.

        Lets get back to practical loop configurations for both receiving and
        transmitting. I'm thinking of small loops of approximately 1/10 of a
        wavelength or less. Let's say a transmitting loop for 40M (7Mhz) that is
        approximately 4 Ft. in dia. It will be necessary to tune the loop to
        resonance by introducing a rather large external capacitor. The electrical
        field created between the plates will be quite intense and the voltage
        across the plates will rise to high values .... requiring substantial
        spacing between them. The tuning capacitor will tune the loop to resonance
        but it will not create an electric field that contributes to radiation.

        So how are the effective electrical and magnetic fields created in this
        loop? The effective magnetic field is a result of the electric current that
        flows around the loop and the effective electric field is a result of the
        differential voltage around the loop. The loop has self capacitance. This
        differential voltage in combination with the self capacitance of the loop
        creates the electric field. The combination of these highly interrelated
        fields creates the electromagnetic radiation.

        Having thought through this I ask myself how do I maximize the effective
        magnetic and electrical fields of this 4' loop?

        The magnetic field is a function of the current in the loop which in turn
        is a function of the conductivity of the loop at 7 Mhz. I understand that
        conductivity is a function of the material used (eg aluminium is good,
        copper is better) and surface area (due to skin effect). Metal strap of 1"
        width represents a surface of 1" x 2 = 2 (both sides) and a 1" pipe
        represents a surface of 3.14 (pi) So the pipe has it in terms of
        electrical conduction (and rigidity).

        Now of what is the electrical field a function? Well certainly it is a
        function of the self capacitance of the loop and the voltage
        differential. The voltage differential is a function of the current flow
        (interrelated to the magnetic field but out of phase, by what, 90 degrees
        ??). What is the self capacitance related to? I would think the surface
        area of the inside of the loop. Am I right? If this is true how can we
        increase the self capacitance of the loop (and maintain the required
        conductivity). If we increase the electric field component by 10% we
        increase the radiation by 10% as well since radiation is product of the
        magnetic and electrical fields.

        What if we constructed the loop of strap instead of tubular material would
        that substantially increase the self capacitance of the loop? Fixed
        capacitors use flat plates not curved plates. What about tacking a 3" or
        4" wide strip of mesh around the inside of the loop? Would that
        substantially increase the self capacitance of the loop?

        If it is possible to substantially increase the self capacitance of the
        loop what would be the effect on feed point impedance, radiation pattern,
        near effect of metal objects, effect of aperture size or capture area (I'm
        not sure of the correct terminology), etc..

        Food for thought









        Jim Dunstan
        Thunder Bay, ON




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      • Jim Dunstan
        ... I m not sure what my track was let alone if it was the right one hi. So let me see .... what you are saying above is that an electrically short whip
        Message 3 of 12 , Nov 4, 2005
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          At 09:08 PM 11/3/2005 -0600, you wrote:
          >I don't think you are on the right track. If a radiating element is
          >electrically short, it radiates either a predominantly electric or magnetic
          >field, depending on whether it is a whip or a loop.

          I'm not sure what my track was let alone if it was the right one hi. So
          let me see .... what you are saying above is that an electrically short
          whip creates (radiates) an electromagnetic field that is predominantly
          electric and an electrically short loop radiates an electromagnetic field
          that is predominantly magnetic. Okay I'll buy that.

          > An electrically short
          >whip looks like a small capacitance that is a very high impedance. Adding
          >inductance in series with that capacitor decreases the high impedance
          >allowing more current to flow, hence better radiation efficiency. Likewise,
          >an electrically short loop used at HF and above is an inductive load that
          >will present a high impedance which can be decreased by a series capacitor,
          >again allowing more current to flow. You don't really need to have a deep
          >understanding of electromagnetics to get a feel for this, simply look at the
          >limiting cases.

          One thing for sure, I don't have a deep understanding of electromagnetics
          hi. I'm getting a feel for what you are saying. You are saying a loop of
          short electrical length say 4' diameter (12.5") represents an inductive
          load (say at 7Mhz) and a high impedance. By placing a capacitor in the
          loop it will it will decrease the impedance and allow more current to
          flow. I assume this effect will maximize when the capacitive reactance
          matches the inductive reactance (resonance).

          Okay I fully agree. Now lets say we feed some power into this loop (lets
          leave coupling the power aside), there will be a radiated electromagnetic
          field that you say (and I agree) will be predominately magnetic. Once we
          have reached resonance the only way we can increase the magnetic field
          (increase the current in the loop) is to improve the conductivity of the
          loop (at 7MHZ) by selecting the best materials in the construction of the
          loop. I am sure you will agree that such a loop constructed of #12 wire
          would radiate a smaller field than one constructed of 1" copper pipe. The
          loop constructed of copper pipe will conduct more current (input power and
          resonance kept at a constant) than the wire and will have a stronger
          magnetic field and thus create a stronger electromagnetic field (radiation).

          Since the formula for radiation is magnetic F. x electrical field
          increasing the magnetic field 10% (by careful construction) will increase
          radiation 10%. Since the electric field is interrelated to the magnetic
          field increasing the current flow will also increase the electric field
          .... but the increase will be predominately magnetic. I ask is there a way
          to increase the electric field in this loop .... that is in relation to the
          magnetic field.

          I am not talking about violating the law of conservation of energy .... I
          am just asking is it possible to construct this loop in such a way that
          significantly affects the ratio of magnetic field to electrical field ....
          and if it is possible how will that affect the characteristics of the antenna?

          Any ideas?

          By the way, I asked my dog and all she does is wag her tail hi.
        • Ken Javor
          As far as I know, you can t do anything to a loop of a given size to increase the electric field output in its immediate vicinity. As you move away from the
          Message 4 of 12 , Nov 4, 2005
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            As far as I know, you can't do anything to a loop of a given size to
            increase the electric field output in its immediate vicinity. As you move
            away from the loop the field impedance (E/H) will increase from the loop
            impedance itself to the impedance of free space, which is 377 Ohms.
            However, I normally work with very small loops whose reactive impedance is a
            few Ohms. That wouldn't be the case for a four foot loop at 7 MHz. The
            rule is that in the quasi-static field (very close to the radiating element)
            the field impedance mirrors the impedance of the radiating element, and the
            farther away you are the closer the field impedance will be to 377 Ohms.
            For a small loop the field starts out magnetic (lower than 377 Ohms) and
            becomes more electric. For a short whip, the field starts out electric
            (higher than 377 Ohms) and becomes more magnetic as you move away.

            From: Jim Dunstan <jimdunstan@...>
            Reply-To: loopantennas@yahoogroups.com
            Date: Fri, 04 Nov 2005 08:23:59 -0500
            To: loopantennas@yahoogroups.com
            Subject: Re: [loopantennas] Some loop antenna ideas


            At 09:08 PM 11/3/2005 -0600, you wrote:
            >I don't think you are on the right track. If a radiating element is
            >electrically short, it radiates either a predominantly electric or magnetic
            >field, depending on whether it is a whip or a loop.

            I'm not sure what my track was let alone if it was the right one hi. So
            let me see .... what you are saying above is that an electrically short
            whip creates (radiates) an electromagnetic field that is predominantly
            electric and an electrically short loop radiates an electromagnetic field
            that is predominantly magnetic. Okay I'll buy that.

            > An electrically short
            >whip looks like a small capacitance that is a very high impedance. Adding
            >inductance in series with that capacitor decreases the high impedance
            >allowing more current to flow, hence better radiation efficiency. Likewise,
            >an electrically short loop used at HF and above is an inductive load that
            >will present a high impedance which can be decreased by a series capacitor,
            >again allowing more current to flow. You don't really need to have a deep
            >understanding of electromagnetics to get a feel for this, simply look at the
            >limiting cases.

            One thing for sure, I don't have a deep understanding of electromagnetics
            hi. I'm getting a feel for what you are saying. You are saying a loop of
            short electrical length say 4' diameter (12.5") represents an inductive
            load (say at 7Mhz) and a high impedance. By placing a capacitor in the
            loop it will it will decrease the impedance and allow more current to
            flow. I assume this effect will maximize when the capacitive reactance
            matches the inductive reactance (resonance).

            Okay I fully agree. Now lets say we feed some power into this loop (lets
            leave coupling the power aside), there will be a radiated electromagnetic
            field that you say (and I agree) will be predominately magnetic. Once we
            have reached resonance the only way we can increase the magnetic field
            (increase the current in the loop) is to improve the conductivity of the
            loop (at 7MHZ) by selecting the best materials in the construction of the
            loop. I am sure you will agree that such a loop constructed of #12 wire
            would radiate a smaller field than one constructed of 1" copper pipe. The
            loop constructed of copper pipe will conduct more current (input power and
            resonance kept at a constant) than the wire and will have a stronger
            magnetic field and thus create a stronger electromagnetic field (radiation).

            Since the formula for radiation is magnetic F. x electrical field
            increasing the magnetic field 10% (by careful construction) will increase
            radiation 10%. Since the electric field is interrelated to the magnetic
            field increasing the current flow will also increase the electric field
            .... but the increase will be predominately magnetic. I ask is there a way
            to increase the electric field in this loop .... that is in relation to the
            magnetic field.

            I am not talking about violating the law of conservation of energy .... I
            am just asking is it possible to construct this loop in such a way that
            significantly affects the ratio of magnetic field to electrical field ....
            and if it is possible how will that affect the characteristics of the
            antenna?

            Any ideas?

            By the way, I asked my dog and all she does is wag her tail hi.




            If you've got links, post them in the Links section!
            http://groups.yahoo.com/group/loopantennas/links

            For uploading images, I prefer the Files section since Photos only allows
            everyone (except the uploader and moderators) to see a max of 300x400.
            http://groups.yahoo.com/group/loopantennas/files

            Put them in the appropriate folder, or create one.





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            " on the web.

            To unsubscribe from this group, send an email to:
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          • Jim Dunstan
            ... You can t increase the electric field of a loop antenna. What your saying is that no matter how you construct a loop the electric field will be exactly
            Message 5 of 12 , Nov 4, 2005
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              At 08:34 AM 11/4/2005 -0600, you wrote:
              >As far as I know, you can't do anything to a loop of a given size to
              >increase the electric field output in its immediate vicinity.

              You can't increase the electric field of a loop antenna. What your saying
              is that no matter how you construct a loop the electric field will be
              exactly the same ... eg whether it is #12 wire or 3'" diameter pipe. Hmmm.


              > As you move
              >away from the loop the field impedance (E/H) will increase from the loop
              >impedance itself to the impedance of free space, which is 377 Ohms.

              Lets leave impedance aside for the moment and not confuse the issue. I
              assume E means electric field and H means magnetic field .... if not, what
              do they mean? As far as I know every antenna that radiates by definition
              has an E and H field. These fields by definition do no by themselves
              radiate beyond the antenna. however when they come into contact with each
              other they create a new field, an electromagnetic field that leaves the
              antenna (radiates). A magnetic field does not radiate, an electric field
              does not radiate, but an electromagnetic field does.

              The radiated electromagnetic field is a product of the two
              fields. Therefore it is legitimate to ponder how each of the 2 fields is
              created and controlled as any design feature that can increase either of
              the 2 fields will have a direct effect on the radiated electromagnetic field.

              I don't mean to be contrary but I'm looking for some ideas that might
              contribute to increasing the electric field of a loop as well as the
              magnetic field of a loop. The same question could be asked of a vertical
              or dipole antenna .... but since this is a loop group I am limiting to loop
              antennas.


              >However, I normally work with very small loops whose reactive impedance is a
              >few Ohms. That wouldn't be the case for a four foot loop at 7 MHz. The
              >rule is that in the quasi-static field (very close to the radiating element)
              >the field impedance mirrors the impedance of the radiating element, and the
              >farther away you are the closer the field impedance will be to 377 Ohms.
              >For a small loop the field starts out magnetic (lower than 377 Ohms) and
              >becomes more electric. For a short whip, the field starts out electric
              >(higher than 377 Ohms) and becomes more magnetic as you move away.


              Here I am confused, I am not sure about "quasi-static field" let alone it's
              impedance? Does this mean a field that doesn't radiate? eg not an
              electromagnetic field? It is very interesting what you say (leaving
              impedance out of the discussion); that a radiated field (electromagnetic)
              from a small loop starts out as a predominately magnetic and becomes
              predominately (at least more) electric .... while a short whip radiates an
              electromagnetic field that is primarily electric and becomes more magnetic
              as it moves away from the antenna.

              I think what you are saying in the examples above is that the ratio of
              magnetic to electric component in the electromagnetic field radiated from
              the antenna changes as it moves away from the antenna. However the ratio
              may change as the electromagnetic field moves away from the antenna the
              total field stays the same as it is a product of these components .... or
              am I wrong?

              Here we are talking about compromised antennae ... eg short ones hi hi ...

              Lets go back to that 4' dia. 7Mhz loop example. We place a capacitor in
              series and adjust (tune) it to resonance. We couple a 1W transmitter to it
              (lets leave how aside). The current in the loop creates both electric and
              magnetic fields which combine (as a product) in proportion to their values
              to form an electromagnetic field that radiates. Now the proportions of
              magnetic and electric may change as the field leaves the loop (antenna) but
              is a value of this electromagnetic field is (X).

              The literal value of (X) will depend on the quality of construction of the
              loop. We all know that to maximize the current in the loop will contribute
              to increased magnetic field and to a lesser extent electric field. If we
              double the current the radiation may become (2X) or (1.5X). We are not
              creating power from nothing ... all we are doing is increasing radiation by
              reducing the amount of power that is consumed (as heat?) by the loop.

              In tuning the loop with a series capacitor we are creating an electric
              field between the plates of the capacitor. This will dramatically increase
              the currents in the loop and ultimately the radiation. However, the
              electric field contained between the plates of the tuning capacitor is
              wasted as it is not a part of the electromagnetic mix that radiates. Am I
              wrong?

              Is there a way to transfer some of that wasted electric field in the tuning
              capacitor to the loop where it can contribute to radiation. If the design
              of a 4' loop for 7Mhz should require half the tuning capacitor value to
              tune it to resonance then the electric field of the antenna should increase
              with a resultant increase in electromagnetic radiation.


              I can't believe that the amount of electric field possible in a loop is
              fixed .... depending on its diameter. A 4' loop is a 4' loop and if you
              want more electric field build a 5' loop. Perhaps a well designed 4' loop
              can create as much electric field as a poorly designed 6' loop. I don't
              remember ever seeing a chart of loop size vs electric field capability hi hi ..

              Jim Dunstan,
              Thunder Bay, ON
            • dldorrance
              Hi Jim, I don t think the ratio of electric and magnetic fields in an antenna has anything to do with how it works or well it works. As far as I can
              Message 6 of 12 , Nov 4, 2005
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                Hi Jim,

                I don't think the ratio of electric and magnetic fields in an
                antenna has anything to do with how it works or well it works. As far
                as I can determine, the only requirement for an antenna is a
                conductor/wire of some sort along which electrons flow back and forth
                in a time varing fashion, creating a magnetic field around the
                conductor/wire. Whether the antenna has balanced electric and
                magnetic fields, or creates mainly a magnetic field as in a loop is
                not relevant.

                The comments about the fields coming into balance with free space
                impedance of 377 ohms is the magic that occurs where a field becomes
                an electromagnetic wave. The fields are finite and will expand out to
                1 wavelength from the antenna. The electromagnetic wave travels
                infinitely and is the process that Maxwell conceived and modeled with
                mathematics. This process occurs at or beyond one wavelenth from the
                antenna. The electromagnetic wave is viewed as a magnetic field which
                collapses as an electric field is formed. The fields are at right
                angles to each other. This process of one field morphing into the
                other continues infinitely.

                Note that this electromagnetic wave is not dependent on the relative
                abundance of electric and magnetic fields near the antenna. It does
                seem to require a time varying magnetic field. I don't believe the
                concept of a pure capacitor antenna holds much water.

                Somewhere on the internet, I think on the Grimes website (Penn State
                University) is a cartoon of the process of an electromagnetic wave
                travelling. I believe it is generated with Maxwell's equations. I
                will try to find the url and post it later.

                Regarding the "effectiveness" of a loop antenna. By effectiveness do
                you mean gain? If so, the gain of a loop is related to the area it
                surrounds.

                Dave WA6YSO


                --- In loopantennas@yahoogroups.com, Jim Dunstan <jimdunstan@r...> wrote:
                >
                > At 08:34 AM 11/4/2005 -0600, you wrote:
                > >As far as I know, you can't do anything to a loop of a given size to
                > >increase the electric field output in its immediate vicinity.
                >
                > You can't increase the electric field of a loop antenna. What your
                saying
                > is that no matter how you construct a loop the electric field will be
                > exactly the same ... eg whether it is #12 wire or 3'" diameter pipe.
                Hmmm.
                >
                >
                > > As you move
                > >away from the loop the field impedance (E/H) will increase from the
                loop
                > >impedance itself to the impedance of free space, which is 377 Ohms.
                >
                > Lets leave impedance aside for the moment and not confuse the issue. I
                > assume E means electric field and H means magnetic field .... if
                not, what
                > do they mean? As far as I know every antenna that radiates by
                definition
                > has an E and H field. These fields by definition do no by themselves
                > radiate beyond the antenna. however when they come into contact
                with each
                > other they create a new field, an electromagnetic field that leaves the
                > antenna (radiates). A magnetic field does not radiate, an electric
                field
                > does not radiate, but an electromagnetic field does.
                >
                > The radiated electromagnetic field is a product of the two
                > fields. Therefore it is legitimate to ponder how each of the 2
                fields is
                > created and controlled as any design feature that can increase
                either of
                > the 2 fields will have a direct effect on the radiated
                electromagnetic field.
                >
                > I don't mean to be contrary but I'm looking for some ideas that might
                > contribute to increasing the electric field of a loop as well as the
                > magnetic field of a loop. The same question could be asked of a
                vertical
                > or dipole antenna .... but since this is a loop group I am limiting
                to loop
                > antennas.
                >
                >
                > >However, I normally work with very small loops whose reactive
                impedance is a
                > >few Ohms. That wouldn't be the case for a four foot loop at 7 MHz.
                The
                > >rule is that in the quasi-static field (very close to the radiating
                element)
                > >the field impedance mirrors the impedance of the radiating
                element, and the
                > >farther away you are the closer the field impedance will be to 377
                Ohms.
                > >For a small loop the field starts out magnetic (lower than 377
                Ohms) and
                > >becomes more electric. For a short whip, the field starts out electric
                > >(higher than 377 Ohms) and becomes more magnetic as you move away.
                >
                >
                > Here I am confused, I am not sure about "quasi-static field" let
                alone it's
                > impedance? Does this mean a field that doesn't radiate? eg not an
                > electromagnetic field? It is very interesting what you say (leaving
                > impedance out of the discussion); that a radiated field
                (electromagnetic)
                > from a small loop starts out as a predominately magnetic and becomes
                > predominately (at least more) electric .... while a short whip
                radiates an
                > electromagnetic field that is primarily electric and becomes more
                magnetic
                > as it moves away from the antenna.
                >
                > I think what you are saying in the examples above is that the ratio of
                > magnetic to electric component in the electromagnetic field radiated
                from
                > the antenna changes as it moves away from the antenna. However the
                ratio
                > may change as the electromagnetic field moves away from the antenna the
                > total field stays the same as it is a product of these components
                .... or
                > am I wrong?
                >
                > Here we are talking about compromised antennae ... eg short ones hi
                hi ...
                >
                > Lets go back to that 4' dia. 7Mhz loop example. We place a
                capacitor in
                > series and adjust (tune) it to resonance. We couple a 1W
                transmitter to it
                > (lets leave how aside). The current in the loop creates both
                electric and
                > magnetic fields which combine (as a product) in proportion to their
                values
                > to form an electromagnetic field that radiates. Now the proportions of
                > magnetic and electric may change as the field leaves the loop
                (antenna) but
                > is a value of this electromagnetic field is (X).
                >
                > The literal value of (X) will depend on the quality of construction
                of the
                > loop. We all know that to maximize the current in the loop will
                contribute
                > to increased magnetic field and to a lesser extent electric field.
                If we
                > double the current the radiation may become (2X) or (1.5X). We are not
                > creating power from nothing ... all we are doing is increasing
                radiation by
                > reducing the amount of power that is consumed (as heat?) by the loop.
                >
                > In tuning the loop with a series capacitor we are creating an electric
                > field between the plates of the capacitor. This will dramatically
                increase
                > the currents in the loop and ultimately the radiation. However, the
                > electric field contained between the plates of the tuning capacitor is
                > wasted as it is not a part of the electromagnetic mix that radiates.
                Am I
                > wrong?
                >
                > Is there a way to transfer some of that wasted electric field in the
                tuning
                > capacitor to the loop where it can contribute to radiation. If the
                design
                > of a 4' loop for 7Mhz should require half the tuning capacitor value to
                > tune it to resonance then the electric field of the antenna should
                increase
                > with a resultant increase in electromagnetic radiation.
                >
                >
                > I can't believe that the amount of electric field possible in a loop is
                > fixed .... depending on its diameter. A 4' loop is a 4' loop and if
                you
                > want more electric field build a 5' loop. Perhaps a well designed
                4' loop
                > can create as much electric field as a poorly designed 6' loop. I
                don't
                > remember ever seeing a chart of loop size vs electric field
                capability hi hi ..
                >
                > Jim Dunstan,
                > Thunder Bay, ON
                >
              • Tom Curtola
                ... Is this the URL? http://www.ee.psu.edu/grimes/antennas/ I wish these eggheads would produce a website for people like me. Call it EH Fields for Dummies.
                Message 7 of 12 , Nov 5, 2005
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                  > Somewhere on the internet, I think on the Grimes website (Penn State
                  > University) is a cartoon of the process of an electromagnetic wave
                  > travelling. I believe it is generated with Maxwell's equations. I
                  > will try to find the url and post it later.

                  Is this the URL?

                  http://www.ee.psu.edu/grimes/antennas/

                  I wish these eggheads would produce a website for people like me. Call it
                  EH Fields for Dummies.
                  My eyes glaze over every time I see the Greek alphabet, squiggly lines and
                  mathematical voodoo.

                  Tom Curtola
                • dldorrance
                  ... Call it ... lines and ... Yes, that s the site. Problem is I have not yet found the graphic which I was describing in my previous post. Tom, I share your
                  Message 8 of 12 , Nov 5, 2005
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                    --- In loopantennas@yahoogroups.com, "Tom Curtola" <tcurtola@r...> wrote:
                    >
                    >
                    > > Somewhere on the internet, I think on the Grimes website (Penn State
                    > > University) is a cartoon of the process of an electromagnetic wave
                    > > travelling. I believe it is generated with Maxwell's equations. I
                    > > will try to find the url and post it later.
                    >
                    > Is this the URL?
                    >
                    > http://www.ee.psu.edu/grimes/antennas/
                    >
                    > I wish these eggheads would produce a website for people like me.
                    Call it
                    > EH Fields for Dummies.
                    > My eyes glaze over every time I see the Greek alphabet, squiggly
                    lines and
                    > mathematical voodoo.
                    >
                    > Tom Curtola
                    >

                    Yes, that's the site. Problem is I have not yet found the graphic
                    which I was describing in my previous post. Tom, I share your
                    "problem" with the math. My level of understanding of this stuff is
                    on a concept level. Never was very good at math!

                    Dave WA6YSO
                  • Jim Dunstan
                    ... Heh !! who are you calling an egghead hi hi .... hello Tom. I get the same dizziness with the formulas ... I was going to say formulae but thought
                    Message 9 of 12 , Nov 5, 2005
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                      At 08:23 AM 11/5/2005 -0500, you wrote:

                      > > Somewhere on the internet, I think on the Grimes website (Penn State
                      > > University) is a cartoon of the process of an electromagnetic wave
                      > > travelling. I believe it is generated with Maxwell's equations. I
                      > > will try to find the url and post it later.
                      >
                      >Is this the URL?
                      >
                      >http://www.ee.psu.edu/grimes/antennas/
                      >
                      >I wish these eggheads would produce a website for people like me. Call it
                      >EH Fields for Dummies.
                      >My eyes glaze over every time I see the Greek alphabet, squiggly lines and
                      >mathematical voodoo.
                      >
                      >Tom Curtola


                      Heh !! who are you calling an egghead hi hi .... hello Tom. I get the
                      same dizziness with the formulas ... I was going to say formulae but
                      thought better of it hi.

                      How are things back in Toronto?

                      I have been looking at this proposition of increasing the capacitive aspect
                      of antennae .... especially the vertical variety. You know I have been
                      doing a few experiments and have been finding some truth in the
                      pudding. However I find it easier to put my mind around the concept with
                      vertical and dipole types. As they say an antenna is an antenna .... so
                      how does it apply to the loop antenna? How does one go about increasing
                      displacement current (in phase) with the electric current etc.

                      Well to make you more dizzy one of my favorite websites discussing these
                      antenna fundamentals (be cautious there are formulas {ae}) is
                      http://hawkins.pair.com/eRadiation.html

                      I get back to Toronto from time to time ... next time I'll give you a call
                      and maybe we can go for a coffee.

                      73


                      Jim Dunstan
                      Thunder Bay, ON
                    • Tom Curtola
                      Hi Jim, Thanks for the link. Very interesting site. He even has a nice pictorial, which for people like me, really appreciate. Things are going well in
                      Message 10 of 12 , Nov 5, 2005
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                        Hi Jim,

                        Thanks for the link. Very interesting site. He even has a nice pictorial,
                        which for people like me, really appreciate.

                        Things are going well in Toronto. Still operating in the ham shack at the
                        Science Centre on Mondays. Recently slapped together a coaxial receiving
                        loop and was quite astounded that they really do work well at attenuating
                        local noise.

                        Also been playing with an MFJ 1026 Noise Canceller / Antenna Phaser.
                        Interesting little box. Does the job quite well at nulling local RFI. Also
                        can use it to 'sort of' steer the verticals and null out local AM BCB
                        stations to hear DX beneath. That quite impressed me.

                        Next month, at our meeting at the Science Centre, one of the club members is
                        going to bring in his transmitting loop he just built. He's really good
                        with construction projects and I can't wait to see it and learn some of his
                        techniques. I'll snap some pictures and post them to this group.

                        73,

                        Tom Curtola
                        VA3TY

                        ----- Original Message -----
                        From: "Jim Dunstan" <jdunstan@...>
                        To: <loopantennas@yahoogroups.com>
                        Sent: Saturday, November 05, 2005 5:44 PM
                        Subject: Re: [loopantennas] Re: Some loop antenna ideas


                        > At 08:23 AM 11/5/2005 -0500, you wrote:
                        >
                        >> > Somewhere on the internet, I think on the Grimes website (Penn State
                        >> > University) is a cartoon of the process of an electromagnetic wave
                        >> > travelling. I believe it is generated with Maxwell's equations. I
                        >> > will try to find the url and post it later.
                        >>
                        >>Is this the URL?
                        >>
                        >>http://www.ee.psu.edu/grimes/antennas/
                        >>
                        >>I wish these eggheads would produce a website for people like me. Call it
                        >>EH Fields for Dummies.
                        >>My eyes glaze over every time I see the Greek alphabet, squiggly lines and
                        >>mathematical voodoo.
                        >>
                        >>Tom Curtola
                        >
                        >
                        > Heh !! who are you calling an egghead hi hi .... hello Tom. I get the
                        > same dizziness with the formulas ... I was going to say formulae but
                        > thought better of it hi.
                        >
                        > How are things back in Toronto?
                        >
                        > I have been looking at this proposition of increasing the capacitive
                        > aspect
                        > of antennae .... especially the vertical variety. You know I have been
                        > doing a few experiments and have been finding some truth in the
                        > pudding. However I find it easier to put my mind around the concept with
                        > vertical and dipole types. As they say an antenna is an antenna .... so
                        > how does it apply to the loop antenna? How does one go about increasing
                        > displacement current (in phase) with the electric current etc.
                        >
                        > Well to make you more dizzy one of my favorite websites discussing these
                        > antenna fundamentals (be cautious there are formulas {ae}) is
                        > http://hawkins.pair.com/eRadiation.html
                        >
                        > I get back to Toronto from time to time ... next time I'll give you a call
                        > and maybe we can go for a coffee.
                        >
                        > 73
                        >
                        >
                        > Jim Dunstan
                        > Thunder Bay, ON
                        >
                        >
                        >
                        >
                        >
                        > If you've got links, post them in the Links section!
                        > http://groups.yahoo.com/group/loopantennas/links
                        >
                        > For uploading images, I prefer the Files section since Photos only allows
                        > everyone (except the uploader and moderators) to see a max of 300x400.
                        > http://groups.yahoo.com/group/loopantennas/files
                        >
                        > Put them in the appropriate folder, or create one.
                        > Yahoo! Groups Links
                        >
                        >
                        >
                        >
                        >
                        >
                        >
                      • Jim Dunstan
                        At 07:15 AM 11/5/2005 +0000, you wrote: Hi Dave I appreciate your thoughtful response; it has driven me back to my reading (I do most ... or a lot of it on
                        Message 11 of 12 , Nov 5, 2005
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                          At 07:15 AM 11/5/2005 +0000, you wrote:


                          Hi Dave

                          I appreciate your thoughtful response; it has driven me back to my reading
                          (I do most ... or a lot of it on the internet). My favorite site is
                          http://hawkins.pair.com/eRadiation.html . The formulae are a little
                          difficult to follow (especially for me) but I find the way he has broken it
                          down, and the way he presents summary conclusions in text format to be very
                          useful. I have read his web site many times and find new things every time
                          I read it.

                          I find that there is a problem in looking at an antenna in terms of its EXH
                          characteristics because there are a number of pretty goofy experiments out
                          there that blur the basic concepts. I have examined a number of them and
                          the only one I found that made sense in the reading and in practice was the
                          one made by GAP antennas. They call it the "SuperC" antenna and are
                          selling it commercially. I have two home QTH's, this one in Thunder Bay
                          where I have lots of room for traditional antennas and the other in
                          downtown Toronto on the 9th floor of an apartment block.

                          In Toronto my antenna farm was the balcony 5"x12" where I started out with
                          a 20M wire dipole bent and held out with plastic fishing rods in creative
                          ways. It worked fine and I made lots of contacts. However because of the
                          space restriction I kept looking for an alternative. I tried a tuned loop
                          as well but found some difficulty with all the close metal objects in the
                          immediate location .... like the iron railing of the balcony. I came
                          across the GAP SuperC experiment and basically I copied the idea.

                          The result was an eye opener for me. The 20M antenna became a vertical 4'
                          high!! with no loading coil and no radials, just a chicken wire base
                          5'x10'. The vertical element was a copper pipe surrounded by a galvanized
                          metal garbage can! You make do with what you have around hi hi. As I
                          said, I basically followed the same design concept of the GAP SuperC antenna.

                          To be clear the antenna was not better than the dipole but it certainly was
                          different. It appeared to be reasonably efficient (compared to the
                          dipole). Where it differed was the size !! 4' tall with no loading
                          coil. My antenna tuner had no difficulty matching it (it appeared to be a
                          rather low impedance). However what was most fascinating was how immune it
                          was to nearby metal objects. I could bring a metal object next to the
                          vertical element and the SWR would change very little if at all!!

                          I mentioned that I experimented with a tuned loop in the same location. It
                          radiated well but was very narrow in bandwidth and if I did the same
                          experiment of bringing a metal object close to it the swr would jump way
                          out of site!!

                          I am back in Thunder Bay now... with lots of room .... and I plan to build
                          a similar vertical antenna (on the roof of the carport ... what will the
                          neighbors think) but for 80M. The Gap SuperC is not a better antenna it a
                          very DIFFERENT antenna. It looks different and it behaves differently, but
                          works about the same as a traditional antenna of the type. Different but
                          not better ... in certain situations the difference might be an advantage
                          over the traditional antenna.

                          While thinking about the new project I started to think about loop
                          antennas. I always liked the loop antenna .... maybe something about a
                          complete circle hi hi. In any event I thought that if changing the design
                          of a vertical antenna can have such dramatic effects on behavior how could
                          the design of a loop be modified to create some of the same differences
                          .... which drove me back to the basics again and venturing on this
                          loopgroup hi hi.






                          >I don't think the ratio of electric and magnetic fields in an
                          >antenna has anything to do with how it works or well it works. As far
                          >as I can determine, the only requirement for an antenna is a
                          >conductor/wire of some sort along which electrons flow back and forth
                          >in a time varing fashion, creating a magnetic field around the
                          >conductor/wire. Whether the antenna has balanced electric and
                          >magnetic fields, or creates mainly a magnetic field as in a loop is
                          >not relevant.

                          I am convinced the difference in behavior between the SuperC vertical
                          antenna and a traditional vertical antenna (as they claim and I experienced
                          in my knock-off version) is due to the change in ratio between the magnetic
                          and electric fields generated in the antennae. The ratio in a traditional
                          antenna is predominately magnetic (easily affected by local metal objects)
                          while the SuperC antenna has a ratio that is predominately electric (little
                          affect from local metal objects).

                          Indeed electric current flows on the conductor as you say .... however
                          there are two kinds of current flowing on the element; there is the
                          current that flows that is generally referred to as electric and there is
                          the additional DISPLACEMENT current that is associated with the creation of
                          the electric field .... eg like charging a capacitor. According to Maxwell
                          and Poynting the actual power converted to radiation is a product of the
                          mixing of these fields and is expressed as the formula ExH=P .... the power
                          radiated expressed as watts per square meter. (I am paraphrasing Jim
                          Hawkins from his web site http://hawkins.pair.com/eRadiation.html ).


                          >The comments about the fields coming into balance with free space
                          >impedance of 377 ohms is the magic that occurs where a field becomes
                          >an electromagnetic wave. The fields are finite and will expand out to
                          >1 wavelength from the antenna. The electromagnetic wave travels
                          >infinitely and is the process that Maxwell conceived and modeled with
                          >mathematics. This process occurs at or beyond one wavelenth from the
                          >antenna. The electromagnetic wave is viewed as a magnetic field which
                          >collapses as an electric field is formed. The fields are at right
                          >angles to each other. This process of one field morphing into the
                          >other continues infinitely.
                          >
                          >Note that this electromagnetic wave is not dependent on the relative
                          >abundance of electric and magnetic fields near the antenna. It does
                          >seem to require a time varying magnetic field. I don't believe the
                          >concept of a pure capacitor antenna holds much water.

                          Well according to Maxwell and Poynting .... and quotes from Jim Hawkins
                          (WA2WHV) ... YOUR STATEMENT IS IN DIRECT CONTRADICTION. They state clearly
                          that the power in the electromagnetic wave is directly related to the value
                          of the magnetic and electric fields that result from the combined electric
                          and displacement currents (by the way the currents must be in phase [called
                          the Poynting vector] for lift off to take place) and as I mentioned above
                          is expressed as P(power)=ExH

                          I don't think we are talking about a 'pure' capacitor antenna. According
                          to the formula above that wouldn't radiate .... it needs a magnetic field
                          as well .... and not just any magnetic field ... but one created in phase
                          with the electric field. There is no such thing as a purely magnetic or
                          purely capacitive antenna.

                          >Somewhere on the internet, I think on the Grimes website (Penn State
                          >University) is a cartoon of the process of an electromagnetic wave
                          >travelling. I believe it is generated with Maxwell's equations. I
                          >will try to find the url and post it later.
                          >
                          >Regarding the "effectiveness" of a loop antenna. By effectiveness do
                          >you mean gain? If so, the gain of a loop is related to the area it
                          >surrounds.

                          I was too loose with my words .... all antennae can be measured in terms of
                          their efficiency .... that is for 1 watt in and 1 watt of radiation would
                          be 100% , a miracle antenna hi. Gain is really a misnomer and relates to
                          antenna patterns and measurements like front to back ratios and increased
                          signals compared to standard antennas etc.

                          The ratio of power in and power out is always less than 1:1.

                          I guess what I should have said is how can we alter the design of a loop so
                          it can display some of the same characteristics (I outlined above for a
                          vertical antenna). Is it possible to increase the displacement current on
                          the loop?

                          By the way Dave ... my friend Tom is listening in ... he's the one calling
                          me an egg head hi hi.



                          Jim Dunstan VE3CI
                        • Jim Dunstan
                          ... Hi Tom, We had a demo of a transmitting loop at our local QRP group meeting. One of the members brought it .... he had a small motor tuning the loop and
                          Message 12 of 12 , Nov 5, 2005
                          • 0 Attachment
                            At 06:30 PM 11/5/2005 -0500, you wrote:
                            >Hi Jim,
                            >
                            >Thanks for the link. Very interesting site. He even has a nice pictorial,
                            >which for people like me, really appreciate.
                            >
                            >Things are going well in Toronto. Still operating in the ham shack at the
                            >Science Centre on Mondays. Recently slapped together a coaxial receiving
                            >loop and was quite astounded that they really do work well at attenuating
                            >local noise.
                            >
                            >Also been playing with an MFJ 1026 Noise Canceller / Antenna Phaser.
                            >Interesting little box. Does the job quite well at nulling local RFI. Also
                            >can use it to 'sort of' steer the verticals and null out local AM BCB
                            >stations to hear DX beneath. That quite impressed me.
                            >
                            >Next month, at our meeting at the Science Centre, one of the club members is
                            >going to bring in his transmitting loop he just built. He's really good
                            >with construction projects and I can't wait to see it and learn some of his
                            >techniques. I'll snap some pictures and post them to this group.
                            >
                            >73,
                            >
                            >Tom Curtola
                            >VA3TY

                            Hi Tom,

                            We had a demo of a transmitting loop at our local QRP group meeting. One
                            of the members brought it .... he had a small motor tuning the loop and was
                            using a small picki up loop to couple it to an elecraft K1
                            transceiver. It was amazing to watch ... as he tuned the loop with the
                            motor the K1's internal antenna tuner would clunk away following it and
                            producing a 1:1 SWR. When I made a transmitting loop I used a manual
                            system to tune the loop and a manual antenna tuner to match the pickup loop
                            to the transceiver.

                            I also used a tuned receiving loop on the balcony and I had thought about
                            using that MFJ 1026 to see what a pair of crossed receiving loops would do
                            if they could be phased .... just like the old direction finders on the
                            ships. Did you actually buy the 1026 or are you borrowing it hi hi..

                            Please send the pictures




                            Jim Dunstan
                            Thunder Bay, ON
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