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3 Elements Fullsize Yagi Antenna for 40m Band

Here is presented 2 models of 3 elements fullsize yagi antenna for 40m band. The first model is optimized for the boomlength of 16 meters while keep maintain good VSWR < 1:1.5, gain, and F/B ratio. The second model is optimized for lowest VSWR while keep maintain the boom length below 17 meters otherwise. All models are simulated for the installation height of about 24 meters using 4nec-2 software package.

Dimensions

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Parameters Model 1 Model 2 Model 2.rev
Boomlength 16 m 17 m 17 m
Ref - Driven 7.36 m 9.76 m 9.76 m
Driven - Director 8.64 m 7.24 m 7.24 m
Ref (fullsize) 22.63 m 21.23 m 21.46 m connected to boom
Driven (fullsize) 20.96 m (adjust) 20.87 m (adjust) 20.77 m (adjust)
Director (fullsize) 19.41 m 18.86 m 18.57 m connected to boom
tip diameter 6 mm (1/4 inch) 6 mm (1/4 inch) 1/2 inch
center diameter 5 cm (2 inch) 5 cm (2 inch) 1-3/4 inch
boom diameter 5 cm (2 inch) 5 cm (2 inch) 3 inch

About The Telescopic Element sizing

Each of the element is constructed and simulated as a telescopic alumunium tubing. Telescopic taper sizing is consideres as 2 inch dia. alu. tubing at the center and 1/4 inch dia. alu. tubing at the tip (1-3/4 inch at the center and 1/2 inch at the tip for the 2-rev model) Taper schedule from the center to the tip can be adjusted to the alu. tubing dia. which can be purchased locally. The models are correct only for the taper sizing mentioned above. If you, for example, want to swap the taper sizing with another size, the model still can be constructed and be adjusted to your working freq but will not deliver the performances predicted in my models.

Tuning procedure:

  • Mount the antenna at the real installation height.
  • USE A GOOD 1:1 BALUN or CHOKE BALUN at the feed point.
  • Do the tuning procedure using Antenna Analyzer or SWR Analyzer using 50 Ohm Coax as short & practical as possible. Here, you want to eliminates tuning error caused by the long coax. Therefore, use a short coax.
  • Tune the antenna for the lowest VSWR at the center freq of the 40m band, or at any 40m band freq you want. Adjust both end simultaneously.

Typical VSWR:

(derived from simulation)

Parameters Model 1 Model 2
@7.0 MHz 1:1.4 1:1.4
@7.1 MHz 1:1.3 1:1.15
@7.2 MHz 1:1.6 1:1.38
VSWR Bandwidth 1:1.5 190 kHz 250 kHz

*model 2-rev basically is the same as the model 2

Typical Gain and F/B

  • Model 1: 13.0 dBi of forward gain & about 14 dB of F/B
  • Model 2: 13.2 dBi of forward gain & about 15 dB of F/B

Simulation Results (Model 1)

Simulation Results (Model 2)

Real Life Built Result (Model 2)

Propagation Map Simulation (VOACAP Online, Oct 2019 at 20 UTC, 80 W of transmit power)

(both models are virtually the same)

Contributing

  1. Fork it https://github.com/handiko/3E-40M-YAGI/fork
  2. Create new branch (git checkout -b myfeature)
  3. Do some editing / create new feature
  4. Commit your works (git commit -m "Adding some myfeature blah blah..")
  5. Push to the branch (git push -u origin myfeature)
  6. Create a new Pull Request