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A somewhat asymmetrical loop. . .

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  • Phil
    Well, today I bought the PVC pipe for the tuned loop antenna. The plans were to make it an X (Actually a + ) with four 3 foot cross-arms, all joined in the
    Message 1 of 4 , Oct 2, 2012
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      Well, today I bought the PVC pipe for the tuned loop antenna. The plans
      were to make it an "X" (Actually a "+") with four 3 foot cross-arms, all
      joined in the middle with a "PVC 4 way cross section". As mounted it
      would be a "Diamond" shape. I needed to use 1 1/2 inch Sched 40 PVC
      pipe to allow a standard TV mast to be run perhaps halfway up the center
      so that could be inserted into the rotator.

      Well, NONE of the hardware stores in this town has the four way cross
      section in a size to accept 1 1/2 inch PVC pipe, just in smaller sizes.
      So, my ONLY alternative was to use two "Tee sections", mounted one above
      the other for the two horizontal cross arms. Of course, right off the
      bat that means that it won't be exactly "square" as one horizontal arm
      is 5 inches higher than the other.

      THEN, when I was putting it together and cut all the sections, the top
      three arms were all cut to the proper 32 inches (allowing for the
      additional space occupied by the Tees and Elbows etc). Then I 'somehow'
      cut the lower section to 36 inches and had it glued in place along with
      the bottom Tee section BEFORE I noticed it (sweat was pouring into my
      eyes and my vision was a bit blurred anyway).

      Well, if it were ONLY the one tee section I needed to replace I'd have
      just cut it out and bought another one. BUT that Tee section was
      "pre-assembled" (read glued) with the pre-amp section and housing all
      assembled. I used a PVC Tee, caps etc to house the pre-amp as I figured
      it would be more weather-tight and sun-proof than a cheap project box
      from Radio Shack.

      It'd cost too much to buy all the fittings just to shorten the bottom
      section some 4 inches (All the PVC pipe, fittings etc cost me nearly $60
      as it was, but I bought more pipe than I needed as it was cheaper to buy
      the "pre-cut" lengths than to have them cut it to length).

      YES, I could have built it in a cheaper manner, just the cross-arms with
      no cross bracing etc, but we get a lot of gusty wind here, and that
      along with high temperatures quickly takes it's toll on unsupported PVC
      structures.

      ASK ME HOW I KNOW THIS :(

      Oh well, the asymmetry (elongated diamond with longer lower section)
      shouldn't have any effect on it's electrical characteristics or
      performance as a loop antenna. If anyone sees it and asks I'll just
      tell them that it was designed that way to "Suck the waves in better" ;-)

      --
      73 de Phil, KO6BB
      http://www.qsl.net/ko6bb/ (Web Page)
      http://www.ipernity.com/home/ko6bb (NDB Audio Archive Blog)

      RADIOS:
      Grundigs: S-350 (2006) & G6 (2011).
      Icom: R-75 with Cascaded 250Hz CW Filters.
      Kenwood: TS130S HF Transceiver (circa 1980).
      Radio Shack: DX-380 digital portable (circa 1990).
      Zenith: Royal-7000 Transoceanic (circa 1969).

      ACCESSORIES: Homebrew LF-MF Pre-Amp, MFJ-949E HF Tuner
      Timewave DSP-599zx and Homebrew 6 Hz Filter.

      ANTENNAS: 88' Long Ladder-line fed dipole at 35 feet AGL.
      Ratzlaff 3 Foot Active Whip at 36 Feet AGL for LF/MW

      Merced, Central California, 37, 18, 37N 120, 30, 6W CM97rh
    • Bob
      Hi Phil Just cut a piece out of the long section and insert a joiner. Bob VK7ZL ... -- LF/HF QRSS Grabber: http://tinyurl.com/26callh NDB & Navtex Logging:
      Message 2 of 4 , Oct 2, 2012
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        Hi Phil

        Just cut a piece out of the long section and insert a joiner.

        Bob  VK7ZL


        On 3/10/2012 07:15, Phil wrote:
          THEN, when I was putting it together and cut all the sections, the top
        three arms were all cut to the proper 32 inches (allowing for the
        additional space occupied by the Tees and Elbows etc). Then I 'somehow'
        cut the lower section to 36 inches and had it glued in place along with
        the bottom Tee section BEFORE I noticed it (sweat was pouring into my
        eyes and my vision was a bit blurred anyway).

        -- 
        LF/HF QRSS Grabber: http://tinyurl.com/26callh
        
        NDB & Navtex Logging: http://tinyurl.com/255zfm2
        
        
        
        
        
        
      • Richard (Rick) Karlquist
        ... Coincidentally, I was just on line today looking for exotic PVC fittings to build antennas with. The 4 way cross you were looking for is available in some
        Message 3 of 4 , Oct 2, 2012
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          On 10/2/2012 2:15 PM, Phil wrote:

          > Well, NONE of the hardware stores in this town has the four way cross
          > section in a size to accept 1 1/2 inch PVC pipe, just in smaller sizes.
          > So, my ONLY alternative was to use two "Tee sections", mounted one above
          > the other for the two horizontal cross arms. Of course, right off the
          > bat that means that it won't be exactly "square" as one horizontal arm
          > is 5 inches higher than the other

          Coincidentally, I was just on line today looking for exotic PVC fittings
          to build antennas with. The 4 way cross you were looking for is
          available in some retail stores, but going on line you can get
          a 5 way side outlet cross, or even a 6 way junction. They sell these
          fittings for construction/furniture as opposed to plumbing. Google
          "5 way side outlet cross" and you should get several vendors, such as
          formufit, flexpvc, pvcfittings direct, and US plastics. Lots of
          interesting parts for making loops. In a 4 way cross, you can get
          up to at least 4 inch fittings on line.

          Rick N6RK
        • Phil
          Thank you, I DON T know why I didn t think of that (too simple I guess ... horizontal arms making it a slightly squashed X . I also got the 1 inch cross
          Message 4 of 4 , Oct 3, 2012
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            Thank you, I DON'T know why I didn't think of that (too simple I guess
            :) Anyway, I did it and it's more symmetrical now with just the offset
            horizontal arms making it a slightly "squashed X".

            I also got the 1 inch cross braces in place now so that it's much more
            rigid. I didn't want it swaying in the wind as I figure that would put
            more stress on the rotator and support mast. Since it'll be above the
            roofline of the mobile home it'll see some pretty vicious wind gusts.

            The frame is completed and now all I need to do on that part of the job
            is to insert and secure the TV pole, then wind the 22 turns of 18awg
            enameled wire and wire it to the varactor tuned pre-amp module.

            I'm not as young as I once was and so rarely work on it more than an
            hour or so at a time (and my work is slower). There was a time the
            entire job would have been completed in a day, maybe two at the most.

            Then the fun job of mounting the rotator to the mast and getting the
            whole assembly up in the air begins. . .

            73 de Phil, KO6BB
            http://www.qsl.net/ko6bb/ (Web Page)
            http://www.ipernity.com/home/ko6bb (NDB Audio Archive Blog)

            RADIOS:
            Grundigs: S-350 (2006) & G6 (2011).
            Icom: R-75 with Cascaded 250Hz CW Filters.
            Kenwood: TS130S HF Transceiver (circa 1980).
            Radio Shack: DX-380 digital portable (circa 1990).
            Zenith: Royal-7000 Transoceanic (circa 1969).

            ACCESSORIES: Homebrew LF-MF Pre-Amp, MFJ-949E HF Tuner
            Timewave DSP-599zx and Homebrew 6 Hz Filter.

            ANTENNAS: 88' Long Ladder-line fed dipole at 35 feet AGL.
            Ratzlaff 3 Foot Active Whip at 36 Feet AGL for LF/MW

            Merced, Central California, 37, 18, 37N 120, 30, 6W CM97rh

            On 10/2/2012 9:45 PM, Bob wrote:
            >
            >
            > Hi Phil
            >
            > Just cut a piece out of the long section and insert a joiner.
            >
            > Bob VK7ZL
            >
            >
            > On 3/10/2012 07:15, Phil wrote:
            >> THEN, when I was putting it together and cut all the sections, the top
            >> three arms were all cut to the proper 32 inches (allowing for the
            >> additional space occupied by the Tees and Elbows etc). Then I 'somehow'
            >> cut the lower section to 36 inches and had it glued in place along with
            >> the bottom Tee section BEFORE I noticed it (sweat was pouring into my
            >> eyes and my vision was a bit blurred anyway).
            >
            > --
            > LF/HF QRSS Grabber:http://tinyurl.com/26callh
            >
            > NDB & Navtex Logging:http://tinyurl.com/255zfm2
            >
            >
            >
            >
            >
            >
            >
            >
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