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Cheap FM Yagi

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  • #61
    MW,
    Its the "grade" of the aluminum, that determines, how strong it is. Channel Master used to use, "aircraft grade aluminum". They were Very strong. Cooper is fairly soft. it may work okay for a vertical ant., don't know about horizontal !

    Gary H.

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    • #62
      I did not know that CM used to use that grade of aluminum. But the large booms on antennas seem to be pretty strong.

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      • #63
        I stopped by Home Depot today to check out antenna parts. The Type M copper tubing was much stronger than I remembered. In fact, I thought someone had mistakenly put thicker Type L pipes in the bin, but all were marked Type M. The ten-foot length flexed a little, but nothing that troubled me. A 4-5 foot FM Yagi element should be plenty stiff.

        I also checked out PVC conduit clamps for mounting the elements above the boom. This mounting method does not require drilling large holes in the boom, which makes it stronger and simplifies construction. The clamps are rigid, U-shaped, PVC pieces with mounting holes at the end of the U. Use two sheet metal screws to hold a copper element. Drill a small hole at the base of the clamp and secure it to the boom with another screw. Five clamps cost $2.13.

        I located the thinner aluminum angle that Home Depot stocks. It is an eight-foot length of 1/2" x 1/2" x 1/20" material. It flexed some, but not badly. I'd use it as element material except that you can order it with 1/16" thickness, which will be even stronger. (For some reason the thicker stuff is cheaper.) You can mount aluminum angle elements to conduit clamps using sheet metal screws or screws and nuts.

        If anyone is interested in a ten-foot Yagi for TV channels 7-13, I designed one using Home Depot parts. Total cost is about $36 for the elements, boom, and clamps.

        http://ham-radio.com/k6sti/tv.htm

        Brian
        Last edited by k6sti; 09-16-2015, 06:02 PM.

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        • #64
          Has anyone, been, one of these, yet ?

          GH

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          • #65
            I meant to say, has anyone "built" one of these antennas, yet ? If so, had well does it work ?

            Gary H.

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            • #66
              After discovering how a critically positioned T-match can improve performance, I redid the Yagi made from parts available at Home Depot. I had to add a second reflector to fully benefit from the T-match, but the secondary boom is short. F/R now is greater than 30 dB across the band and forward gain is higher. I like this design a lot better than the original:

              http://ham-radio.com/k6sti/depot.htm

              http://ham-radio.com/k6sti/curves.htm

              Brian

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