building a VK2JDS 8 element yagi for 2 metre band

  • building a VK2JDS 3 element yagi for 2 metre band
  • building a VK2JDS 10 element yagi for 2 metre band
  • DL6WU Yagi design page

    8 ELEMENT YAGI FOR THE FM SECTION OF 2 METRES (146-148 MHz) by Dave, VK2JDS. (October 2006)
    This antenna uses a folded dipole driven element with a 4:1 coaxial balun to feed it.
    Its very simple to make and has wider bandwidth than a single dipole element.
    Insulating parts and aluminium are scrounged from old tv or fm aerials from your
    local aerial installer, the tip or neighbours.
    All elements besides the driven element are made from 5mm diameter hard drawn
    aluminium wire, or they can be made from scrounged 8mm tubing from old tv
    antennas etc. Even galvanised fencing wire works ok.
    The pictures shown are of a modification to an existing commercial antenna I
    assembled several years ago, with dimensions as listed:
    Boom length is 3760 mm and it is made of 30mm diameter aluminium tubing.
    Element lengths are:
    reflector	955mm
    director 1	850mm
    director 2	840mm
    director 3	840mm
    director 4	835mm
    director 5	830mm
    director 6	820mm
    Spacings between elements:
    reflector to driven	420mm
    driven to director 1	300mm
    director 1 to 2		370mm
    director 2 to 3		520mm
    director 3 to 4		620mm
    director 4 to 5		720mm
    director 5 to 6 	720mm
    Driven element dimensions:
    overall length from tip to tip is 900mm to cover the segment 146 to 148 MHz
    (945mm for 144.4)
    The driven element is constructed from scrounged tv antenna parts comprising a
    2 piece insulator section and 2 bent pieces of aluminium tubing.
    The elements fold back along themselves and are cut to length then drilled
    and bolted into the plastic mounting.
    Note that there is a strap of aluminium joining the ends together that are
    at the boom but not being connected to the feedline.
    Refer to the picture of the unassembled feedpoint. The spacing between the
    folded elements is 50mm.
    Balun at the feedpoint dimensions:
    Because the folded dipole is approximately 300 ohms impedance we need a 4:1
    balanced to unbalanced transformer which is easily made from some rg213/u coaxial
    cable, the same as you are using for the feedline.
    Cut a piece of coax 670mm long then cut the plastic back from each end and peel
    the braid out so the length of the sheilded section is 630mm.
    Find or make some eyelets for the inner copper of the cable to attach to, then
    solder and trim the overall length including the eyelets to be 675mm.
    The centre conductor of your feedline attaches to one terminal on the driven
    element as does the centre conductor of one end of the balun, the other end of
    the balun has its centre conductor attached to the other terminal on the driven
    Join the 3 braids together as neatly as possible and then waterproof it all with
    silicone etc. Note that the braids dont attach to the antenna at all.
    The antenna was mounted on a plastic mast 4 metres long and bolted vertically
    The VSWR was measured using a VHF swr meter and a 2 metre handheld connected by
    about 15 metres of RG213/U cable. Results indicated zero reflected power at
    146.5 MHz, rising either side of this to 1.5:1 at 145.5 and 148 MHz. Some qso's
    via local repeaters indicated it has quite narrow beamwidth and easily outperforms
    any vertical omnidirectional antenna.

    1. drawing of balun

    2. drawing of folded dipole

    3. showing the assembled feed point

    4. showing the element mounted on the boom

    5. showing the fully assembled yagi

    6. showing the 2metre yagi mounted vertically above the horizontal 6metre yagi