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Re: [loopantennas] Sourcing 1

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  • Chris Trask
    ... Some time ago, John Popelish came up with the idea of using a string of toroids instead of a solid rod. You might want to join the Yahoo! group that he
    Message 1 of 7 , Dec 30, 2009
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      >
      > Looking for a source for 1" dia ferrite rod (length TBD) to build
      > giant loopstick antenna - CWS Bytemark does not show as a stocking
      > size - any other source?
      >

      Some time ago, John Popelish came up with the idea of using a string of toroids instead of a solid rod. You might want to join the Yahoo! group that he runs:

      http://groups.yahoo.com/group/ferriterodantennaexperimenters/

      He built them by using a piece of insulated material, such as a plastic rod or wood dowel, and then simply stacking the toroids. There were a number of variations, such as epoxying the toroids together or using a piece of heat-shrink tubing to hold them together. This is much cheaper and certainly more readily obtainable than those large rods.

      Using toroids is every bit as good as a solid rod, perhaps better at low frequencies as the gap between the toroids decreases the hysteresis and eddy current losses. In magnetic materials, the bulk of the flux is in a thin layer at the surface, known as "magnetic skin effect", which is the same concept as the skin effect in electrical conductors.

      You can buy large ferrite and powdered iron toroids by the truckload from Amidon.


      Chris

      ,----------------------. High Performance Mixers and
      / What's all this \ Amplifiers for RF Communications
      / extinct stuff, anyhow? /
      \ _______,--------------' Chris Trask / N7ZWY
      _ |/ Principal Engineer
      oo\ Sonoran Radio Research
      (__)\ _ P.O. Box 25240
      \ \ .' `. Tempe, Arizona 85285-5240
      \ \ / \
      \ '" \ IEEE Senior Member #40274515
      . ( ) \
      '-| )__| :. \ Email: christrask@...
      | | | | \ '. http://www.home.earthlink.net/~christrask
      c__; c__; '-..'>.__

      Graphics by Loek Frederiks
    • AlienRelics
      Actually Adam E. runs that group. And I don t understand why we d want to fragment the knowledge, this group covers all kinds of loop antennas and it isn t
      Message 2 of 7 , Dec 31, 2009
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        Actually Adam E. runs that group. And I don't understand why we'd want to fragment the knowledge, this group covers all kinds of loop antennas and it isn't going away.

        Steve Greenfield

        --- In loopantennas@yahoogroups.com, Chris Trask <christrask@...> wrote:
        >
        > >
        > > Looking for a source for 1" dia ferrite rod (length TBD) to build
        > > giant loopstick antenna - CWS Bytemark does not show as a stocking
        > > size - any other source?
        > >
        >
        > Some time ago, John Popelish came up with the idea of using a string of toroids instead of a solid rod. You might want to join the Yahoo! group that he runs:
        >
        > http://groups.yahoo.com/group/ferriterodantennaexperimenters/
        >
        > He built them by using a piece of insulated material, such as a plastic rod or wood dowel, and then simply stacking the toroids. There were a number of variations, such as epoxying the toroids together or using a piece of heat-shrink tubing to hold them together. This is much cheaper and certainly more readily obtainable than those large rods.
        >
        > Using toroids is every bit as good as a solid rod, perhaps better at low frequencies as the gap between the toroids decreases the hysteresis and eddy current losses. In magnetic materials, the bulk of the flux is in a thin layer at the surface, known as "magnetic skin effect", which is the same concept as the skin effect in electrical conductors.
        >
        > You can buy large ferrite and powdered iron toroids by the truckload from Amidon.
        >
        >
        > Chris
        >
        > ,----------------------. High Performance Mixers and
        > / What's all this \ Amplifiers for RF Communications
        > / extinct stuff, anyhow? /
        > \ _______,--------------' Chris Trask / N7ZWY
        > _ |/ Principal Engineer
        > oo\ Sonoran Radio Research
        > (__)\ _ P.O. Box 25240
        > \ \ .' `. Tempe, Arizona 85285-5240
        > \ \ / \
        > \ '" \ IEEE Senior Member #40274515
        > . ( ) \
        > '-| )__| :. \ Email: christrask@...
        > | | | | \ '. http://www.home.earthlink.net/~christrask
        > c__; c__; '-..'>.__
        >
        > Graphics by Loek Frederiks
        >
      • Chris Trask
        ... I m hearing from a number of people lately who have made this antenna. It was the result of a more ambitious project to make a remotely tuned transmitting
        Message 3 of 7 , Jan 1, 2010
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          >
          > I want to build an electronically tunable, receive-only mobile HF
          > antenna mainly for 160/80/40 meter bands, tuned with a varactor
          > diode as part of a feedpoint matching network.
          >
          > After learning of a very interesting paper written by Chris Trask
          > (thanks, Chris!!!) a couple of months ago, I successfully reproduced
          > his varactor matcher for a small receiving loop (now lives in the
          > back yard and is a great 80-40-30M antenna),
          >

          I'm hearing from a number of people lately who have made this antenna. It was the result of a more ambitious project to make a remotely tuned transmitting loop antenna that did away with the Faraday matching loop or the Delta matching, which many people did not care for. The result was similar to the varactor-tuned receiving loop, but with a motor-driven variable capacitor in place of the varactors:

          http://www.home.earthlink.net/~christrask/Paper012.html

          >
          > so I'm inspired now (with parts on order, and anxiously awaiting
          > the long-backordered miniVNA) to make something along these lines
          > (ferrite transformers and a varactor biased with a bias-tee) with a
          > ferrite loopstick antenna that would be attached (maybe horizontally)
          > to the roof rack of my car (yes, the car roof is steel, so this may
          > be a distraction, but I'm looking forward to the learning as much as
          > anything...)

          Ferrite loopsticks are a bit tricky due to the high impedance when parallel tuned as well as the terribly low voltage or current when the number of turns is reduced to accomodate the varactor capacitance. I designed an active ferrite loop with remote varactor tuning that you may be interested in:

          http://www.home.earthlink.net/~christrask/Paper006.html

          This approach uses a small toroidal inductor in parallel with the loopstick, so a large number of turns can be used on the loopstick to get a higher signal voltage when the smaller inductor is parallel tuned with the varactors. Painfully simple, but very effective.

          Chris
        • david feldman
          Here s a question - I looked at stormwise.com as a possible source for large ferrite rod to use in such a project, but they re not cheap, so I m doing some
          Message 4 of 7 , Jan 2, 2010
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            Here's a question -

            I looked at stormwise.com as a possible source for large ferrite rod to use in such a project, but they're not cheap, so I'm doing some research. I suspect (but haven't tried to confirm) that stormwise rods are internally a string of large ferrite beads like those put over coax to build a RF choke (or otherwise control EMC on a round cable), packed into a piece of PVC tubing readily found at local hardware store.

            I found a source for EMC control beads at mouser (I'm sure there are many other varieties and distributors, but I have an order at mouser going out soon so I'm interested if these might be suitable). The catalog page I'm looking at is at the bottom part of the page below.

            http://www.mouser.com/catalog/catalogUSD/640/956.pdf

            These particular beads are made by steward (acquired by Laird Technologies). On Laird's website, the "28" prefix corresponds to a bead suited to tens of MHz frequencies (they have a lower- and higher-frequency material).

            So my question is this - if indeed stormwise large ferrite rods are indeed a bunch of big beads packaged in PVC tubing (and there are no convenient sources for monolithic ferrite rods in the 1" diameter range), then I'd like to experiment with making my own such ferrite rod so I can try variations.

            Any comment or suggestion on taking this approach to build a loopstick's ferrite rod core (or other suggestion to source such beads, etc.?)

            Thanks,

            Dave

            > > so I'm inspired now (with parts on order, and anxiously awaiting
            > > the long-backordered miniVNA) to make something along these lines
            > > (ferrite transformers and a varactor biased with a bias-tee) with a
            > > ferrite loopstick antenna that would be attached (maybe horizontally)
            > > to the roof rack of my car (yes, the car roof is steel, so this may
            > > be a distraction, but I'm looking forward to the learning as much as
            > > anything...)
            >
            > Ferrite loopsticks are a bit tricky due to the high impedance when parallel tuned as well as the terribly low voltage or current when the number of turns is reduced to accomodate the varactor capacitance. I designed an active ferrite loop with remote varactor tuning that you may be interested in:
            >
            > http://www.home.earthlink.net/~christrask/Paper006.html
            >
            > This approach uses a small toroidal inductor in parallel with the loopstick, so a large number of turns can be used on the loopstick to get a higher signal voltage when the smaller inductor is parallel tuned with the varactors. Painfully simple, but very effective.
            >
            > Chris


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          • xtemporize
            ... Chris, a question about the circuit. I am accustomed to seeing the opposite kind of loop to tuned circuit coupling, I mean, a low inductance small turns
            Message 5 of 7 , Jan 2, 2010
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              --- In loopantennas@yahoogroups.com, Chris Trask <christrask@...> wrote:
              > http://www.home.earthlink.net/~christrask/Paper006.html
              >
              > This approach uses a small toroidal inductor in parallel with the loopstick, so a large number of turns can be used on the loopstick to get a higher signal voltage when the smaller inductor is parallel tuned with the varactors. Painfully simple, but very effective.
              > Chris

              Chris, a question about the circuit. I am accustomed to seeing the
              "opposite" kind of loop to tuned circuit coupling, I mean, a low
              inductance small turns winding either in series with the main tuned L
              or tapped onto it. I wonder, how does the self-inductance and shunt
              capacitance effect of the large antenna winding affect the L1 tuned
              circuit. I would expect the shunt capacitance to limit the tuning range
              of L1. Also, you say the turns on the antenna winding can be adjusted
              for other tuning ranges. So what criteria do we apply when doing this,
              for the number of turns = self resonance of the antenna winding? Also,
              if more turns on the antenna winding => higher voltage developed,
              what defines the upper limit of turns here?
              Also, one post mentioned buiiding this for a mobile loop. That
              reminded me of an article I saw in Wireless World (UK) that had such
              an antenna for vehicle MW reception - but it used two loops, at 90
              degrees, and a simple phase shift circuit, to offset the signals by
              (if i recall) something like 30 degrees so that there was never a null
              signal point. That was to eliminate loss of the signal while driving.
              Of course the magnetic antenna benefit of disfavoring electric field
              noise still applied. -Hue Miller
            • John Popelish
              david feldman wrote: (snip) ... They are suited to absorb energy over a wide range of frequency, but make good, high Q rods only at the lower end of that
              Message 6 of 7 , Jan 2, 2010
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                david feldman wrote:
                (snip)
                > I found a source for EMC control beads at mouser (I'm
                > sure there are many other varieties and distributors, but
                > I have an order at mouser going out soon so I'm
                > interested if these might be suitable). The catalog page
                > I'm looking at is at the bottom part of the page below.
                >
                > http://www.mouser.com/catalog/catalogUSD/640/956.pdf
                >
                > These particular beads are made by steward (acquired by
                > Laird Technologies). On Laird's website, the "28" prefix
                > corresponds to a bead suited to tens of MHz frequencies
                > (they have a lower- and higher-frequency material).

                They are suited to absorb energy over a wide range of
                frequency, but make good, high Q rods only at the lower end
                of that range. Type 28 can be pushed (with thin shims
                between beads to work pretty well through the AM band, but
                their permeability is falling and their losses are rising
                fast above 1 MHz.

                > So my question is this - if indeed stormwise large
                > ferrite rods are indeed a bunch of big beads packaged in
                > PVC tubing (and there are no convenient sources for
                > monolithic ferrite rods in the 1" diameter range), then
                > I'd like to experiment with making my own such ferrite
                > rod so I can try variations.

                > Any comment or suggestion on taking this approach to
                > build a loopstick's ferrite rod core (or other suggestion
                > to source such beads, etc.?)

                I have built many test rods with this brand of bead with
                pretty good results. For frequencies below 500kHz, I had
                better results with the LFB (low frequency bead) material
                cores. I like the ones that fit inside 1/2 or 3/4 inch thin
                walled PVC pipe. LFB174095-000 is 17.4mm diameter by
                28.58mm long and cost about $2 each (out of stock at the
                moment at Digikey, unfortunately). Though they do not
                appear on the page you listed, Mouser appears to have some
                in stock.

                Going all the way up to 1 inch diameter beads showed no
                improvement over these smaller ones in my tests (up to 1
                foot long rods). Perhaps at two feet length and below
                100kHz, there might be an advantage of the larger diameter.

                --
                Regards,

                John Popelish
              • Paul V Birke PEng
                for one I thought IPEX tubing was better for RF than plain PVC best Paul VE3PVB ________________________________ From: david feldman To:
                Message 7 of 7 , Jan 2, 2010
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                  for one I thought IPEX tubing was better for RF than plain PVC

                  best Paul VE3PVB




                  ________________________________
                  From: david feldman <wb0gaz@...>
                  To: loopantennas@yahoogroups.com
                  Sent: Sat, January 2, 2010 6:48:33 PM
                  Subject: [loopantennas] RE: Sourcing 1



                  Here's a question -

                  I looked at stormwise.com as a possible source for large ferrite rod to use in such a project, but they're not cheap, so I'm doing some research. I suspect (but haven't tried to confirm) that stormwise rods are internally a string of large ferrite beads like those put over coax to build a RF choke (or otherwise control EMC on a round cable), packed into a piece of PVC tubing readily found at local hardware store.

                  I found a source for EMC control beads at mouser (I'm sure there are many other varieties and distributors, but I have an order at mouser going out soon so I'm interested if these might be suitable). The catalog page I'm looking at is at the bottom part of the page below.

                  http://www.mouser com/catalog/ catalogUSD/ 640/956.pdf

                  These particular beads are made by steward (acquired by Laird Technologies) . On Laird's website, the "28" prefix corresponds to a bead suited to tens of MHz frequencies (they have a lower- and higher-frequency material).

                  So my question is this - if indeed stormwise large ferrite rods are indeed a bunch of big beads packaged in PVC tubing (and there are no convenient sources for monolithic ferrite rods in the 1" diameter range), then I'd like to experiment with making my own such ferrite rod so I can try variations.

                  Any comment or suggestion on taking this approach to build a loopstick's ferrite rod core (or other suggestion to source such beads, etc.?)

                  Thanks,

                  Dave

                  > > so I'm inspired now (with parts on order, and anxiously awaiting
                  > > the long-backordered miniVNA) to make something along these lines
                  > > (ferrite transformers and a varactor biased with a bias-tee) with a
                  > > ferrite loopstick antenna that would be attached (maybe horizontally)
                  > > to the roof rack of my car (yes, the car roof is steel, so this may
                  > > be a distraction, but I'm looking forward to the learning as much as
                  > > anything...)
                  >
                  > Ferrite loopsticks are a bit tricky due to the high impedance when parallel tuned as well as the terribly low voltage or current when the number of turns is reduced to accomodate the varactor capacitance. I designed an active ferrite loop with remote varactor tuning that you may be interested in:
                  >
                  > http://www.home earthlink. net/~christrask/ Paper006. html
                  >
                  > This approach uses a small toroidal inductor in parallel with the loopstick, so a large number of turns can be used on the loopstick to get a higher signal voltage when the smaller inductor is parallel tuned with the varactors. Painfully simple, but very effective.
                  >
                  > Chris


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