2020 October 10

Contest antenna

40 meters band 3 elements inverted vee

Flip relays schematic

Best regards to Ron, ve3vn for nice article as inspiration source.

Requirements

1

East / West electric flip

2 x 1.8 uH inductors - 10 turns on T68/2 Amidon cores
2x DPDT relays.

2

10-15 dB F/B Ratio

To be considered a "Beam antenna" , 10-15 dB front to back is required, also a low take off angle

3

Cheap materials

3 wood poles 11 meters height and spaced 6 meters apart.

4

1:2.25 Balun

While antenna impedance is about 17-20 ohms, a special balun is needed to raise it up to 50 ohms

Tech info

  • Coaxial is fed via 2.25:1 impedance transformer to center inverted vee (17 – 22 ohms antenna impedance).
  • Relay box switching 1.8 uH inductance for 1’st and 3’rd element, one normal close and second normal open, where inductance is shortened or not with 12 V coils without power , and reversed if coils are energized (East or Weast).
  • Lenghts is 10.5 meters for central inverted vee, 10.15 meters for 1’st and 3’rd element each side. (using insulated wire, it might vary depending by many factors )
  • Coils are made using 16 turns over a T68/2 toroid cores. Make sure inductance is 1.8 uH using inductance meter measurements including relay parasitic insertions
  • Video gallery

    Photo gallery

    Copyright

    The ruthoff balun schematic image does not belong to me ! I have found it on the interenet long time ago but not anymore, so I cannot tell who copyright belongs to ! It works fine in 14 Mhz also. I did it with 2xFT240-43 stacked, 3 magnet wires and a piece of 25 ohms coaxial. Can be replaced with 2x50 ohms coaxial pieces in parallel.

    MMANA GAL antenna definition

    				
    					*
    7.02
    ***Wires***
    6
    0.0, 0.0, 10.72, 0.0, -8.10235, 3.91849, 8.000e-04, -1
    0.0, 0.0, 10.72, 0.0, 8.10235, 3.91849, 8.000e-04, -1
    7.15, 0.0, 10.72, 7.15, -7.895, 4.015, 8.000e-04, -1
    7.15, 0.0, 10.72, 7.15, 7.895, 4.015, 8.000e-04, -1
    -6.0, 0.0, 10.72, -6.0, -7.895, 4.015, 8.000e-04, -1
    -6.0, 0.0, 10.72, -6.0, 7.895, 4.015, 8.000e-04, -1
    ***Source***
    1, 0
    w2b, 0.0, 1.0
    ***Load***
    1, 1
    w5b, 0, 1.8, 0.0, 0.0
    ***Segmentation***
    800, 80, 2.0, 2
    ***G/H/M/R/AzEl/X***
    2, 0.0, 1, 20.0, 120, 60, 0.0
    				
    			

    How To

    Step 1 - Resonator tuning

    Raise the main element with 1:2.25 balun connected.

    Measure the impedance using an antenna analyzer, and tune the lenght until the impedance will be around 90-120 ohms, but the reactance about  Plus 40 ohms also. (inductive reactance)

    Please trim both sides with equal lenghts at the same time. 

    Step 2 - reflector tuning

    With resonator element already in place and tuned, raise reflector element with inductor and relay  mounted.

    Make sure that with relay not energized and the inductor is series with reflector wires, NOT shorted via relay.

    Measure and trim Reflector until impedance drops to 50 ohms with almost same positive reactance of 40 ohms

    Step 3 - Director tuning

    With resonator and reflector element already in place and tuned, raise director element with inductor and relay  mounted.

    Make sure that with relay not energized, the inductor is NOT in series with director wires via relay.

    Measure and trim director wires until measured impedance is 50 ohms and reactance is about Zero.

    Final Tuning

    By energizing both relays in the same time for flipping, please observe if SWR is equal or not on both directions.

    Fine adjust director / reflector until same values are obtained for East and West.  In real world, if SWR is slight different but within 1:1.3 ,  it’s OK.

    Final step is to connect relays to a 12V power supply via a switch, and observe F/B ratio. Depending by distance,  azimuth and elevation angle, you can achieve 12-15 dB F/B ratio.

    2 thoughts on “40 meters est-west flip 3 elements Inverted Vee antenna

    1. I have used 2-element wire beam and works excellent! It is easy to build, low cost… Three element beam with switching is used by EI8GQB. His QRZ site is full of many inspirating things and the evolution of contest site configuration is outstanding.

      1. Hi Petrik
        Yes indeed, wire antennas can be great unless is too close to ground.
        3 el in 40 meters do produce great results but can be difficult in large contests having big F/B ratio. To compensate this, will build and test a PWM switch and tx lock device, but probably in 2021.
        73 es gl
        Gabriel yo8rxp

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