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350Re: [loopantennas] Information on Loop Antennas Wanted

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  • Scott Erwin
    Jan 7, 2005
      I only used one "T" copper pipefitting, which
      connected the two, 10-foot long sections of 3/4 inch
      copper pipe. I used a conduit bender to form the loop
      and used 22-degree (+ or -) angles for a total of 16
      bends. This is closer to a circle and hence the
      efficiency is increased slightly. The reason for this
      is the 22 or 23-degree angles are much easier to
      obtain than a 45-degree bend on the copper pipe and
      there are no fittings to buy and solder and less
      chance for a bad solder job. The only joint is for the
      "T" which does two jobs. One is to connect the two
      lengths of pipe and two is making available a place
      for the motor power wires run inside the pipe to have
      a nice place to exit the pipe. Having been an
      electrician it was easy for me to bend the pipe. If
      you can find a local ham with a pipe bender to help
      you out if you do it this way it will save you a lot
      of time and money as you wont need to buy a bender and
      you wont need to buy some cheap 3/4 inch EMT conduit
      to practice on. I made my capacitor by hand. All you
      need is a set of aviation snips to cut the copper
      sheet metal, a drill press, and some construction
      paper to use as patterns for the stator and rotor
      plates. You can practice on some cheap aluminum sheet
      from a building supply store for roofing use. Once you
      get used to cutting the sheet aluminum you can move to
      the copper sheet. It's fun to work with and soon you
      will be making your own project boxes from copper!
      Polished and coated with clear paint your projects
      will impress anyone, ham or not! While I was
      recovering from some surgery I wrote and article on
      how I made my capacitor. The link is
      http://www.eham.net/articles/9527
      Also follow the link to the ON4CEQ site at
      http://www.qsl.net/mnqrp/Loop/Mag_Loops.htm
      for some great information on construction on Magloop
      antennas.
      If your only going to use the Magloop on a single band
      your capacitor can be a section of RG-8 coax cut to a
      length that will provide a 1:1 SWR match at your
      frequency of choice.
      The Magloop will couple to any metal objects close it.
      If you can elevate it above any surrounding metal
      objects it will help out a lot. You can also improve
      it by placing a ground under it. This can be in the
      form of radial wires or sheet aluminum. It only needs
      to cover the same area of the loop. If you have a
      6-foot loop then 6-foot radial wires will work fine as
      would something like a 4 by 8 foot sheet of aluminum.
      You can allow the ground screen to be connected at
      center of the loop at the feed point, which is a
      neutral point, or just allow it to float at RF under
      it. This keeps the loop from coupling to the earth
      below it. I use the aluminum roof of my Magloop for
      this. As for performance the 20-foot Magloop beats a
      40-meter mobile vertical antenna hands down.

      --- Jim Dunstan <jimdunstan@...> wrote:

      > At 05:33 PM 1/6/05 -0800, you wrote:
      > >I currently run a Magloop for 20 and 40 meters
      > using a
      > >single turn element made of 20 feet of 3/4 inch
      > copper
      > >plumbing pipe. I use a homebrew copper butterfly
      > >capacitor rated at 12,000 volts and is 10-pF to
      > 100-pF
      > >capacitance. The efficiency on 20 meters is 91.2
      > >percent compared to a 20 meter dipole at 1/2
      > >wavelength above ground and on 40 meters it's
      > >efficiency is 45.7 percent also compared to a 40
      > meter
      > >dipole at 1/2 wavelength above ground using KI6GD
      > >Magnetic loop antenna calculator V 1.6 software.
      > This
      > >is calculated with a Magloop operated 6 inches
      > above
      > >an aluminum ground screen to prevent earth loss.
      >
      > Hi:
      >
      > I found the description of your Magloop very
      > interesting. I operate from 2
      > very different QTH's; one is more or less
      > traditional with a tower and
      > rotatable dipole up about 50' (Thunder Bay) while
      > the other is less so
      > being in a 9th flr apartment (Toronto). I have 2
      > balconies to work from
      > and settled on a bent wire dipole (20M) held out
      > over the balcony
      > railing. I feed it with open wire line and have
      > great success with it on
      > both 20 es 15 M.
      >
      > However I miss 40M operation. I have a simple
      > Magloop software program and
      > ran your dimensions and find approximately the same
      > results you did; 20F of
      > 3/4" copper producing about 45% efficiency. The
      > diameter would be about
      > 6', about the maximum size I could accommodate on my
      > second balcony. I
      > have experimented with loaded dipoles (12' end to
      > end)... eg like a couple
      > of hamstick mobile type antennas. I have not been
      > able to accurately
      > measure efficiency of this antenna but I am certain
      > it is less than 45%. A
      > 6' dia. loop might be easier to deal with.
      >
      > I would use the loop for 40M only ... Have you tried
      > orienting the loop
      > horizontally? I have been considering this since
      > the area in which I would
      > mount the loop is surrounded on 3 sides by a 3'
      > metal guard railing. I
      > assume you feed your loop with a small coax loop. I
      > would have to keep the
      > power down since I have not found anything like your
      > 12,000 V capacitor. I
      > use a kenwood TS-50s in the apartment shack which
      > runs 3 power levels 10,
      > 50, 100. I would certainly like to use the 50W
      > setting but would need a
      > capacitor with at least 6000 V rating.
      >
      > I also assume you cut the pipe into 8 equal length
      > (approx. 2 1/2') pieces
      > and used 45 deg elbows. It sounds like it might be
      > a fun project out on
      > the balcony hi hi ..
      >
      > Another possible antenna might be one of those
      > strange high capacitance low
      > inductance models. As with the magloop it is also a
      > mechanical
      > construction job .... instead of plumbing one needs
      > to have some sheet
      > metal fabrication skills hi hi. This antenna
      > apparently also boasts high
      > efficiency for small size. However, it has the
      > added advantage of near
      > immunity to close metal objects. Sounds a little
      > space age hi hi ..
      >
      > Hmmm what one won't do to get on 40M! vive 40
      >
      >
      >
      >
      > Jim Dunstan, VE3CI
      > Thunder Bay, ON


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