I ran across the original 1926 paper by Hidetsugu Yagi and Shintaro Uda and decided to model the shorter of the two antennas described. I used the AO 9.67 Antenna Optimizer.
The 1926 paper did not specify element diameter. A later paper by Uda describes the directors as telescoping brass tubes and provides the curve above. Response peaks for a director length of about 184 cm. Modeled gain peaks at 184 cm for an element diameter of 1.36 cm. I set driven element length, also not specified, to 196.5 cm.
Original 1926 Yagi Free Space 68.135 MHz ; wavelength = 4.4 meters 25 brass wires, centimeters 1 0 0 -98.25 0 0 98.25 1.36 1 -110 0 -110 -110 0 110 1.36 1 0 -220 -110 0 -220 110 1.36 1 0 220 -110 0 220 110 1.36 1 -55 -110 -110 -55 -110 110 1.36 1 -55 110 -110 -55 110 110 1.36 1 150 0 -90 150 0 90 1.36 1 300 0 -90 300 0 90 1.36 1 450 0 -90 450 0 90 1.36 1 600 0 -90 600 0 90 1.36 1 750 0 -90 750 0 90 1.36 1 900 0 -90 900 0 90 1.36 1 1050 0 -90 1050 0 90 1.36 1 1200 0 -90 1200 0 90 1.36 1 1350 0 -90 1350 0 90 1.36 1 1500 0 -90 1500 0 90 1.36 1 1650 0 -90 1650 0 90 1.36 1 1800 0 -90 1800 0 90 1.36 1 1950 0 -90 1950 0 90 1.36 1 2100 0 -90 2100 0 90 1.36 1 2250 0 -90 2250 0 90 1.36 1 2400 0 -90 2400 0 90 1.36 1 2550 0 -90 2550 0 90 1.36 1 2700 0 -90 2700 0 90 1.36 1 2850 0 -90 2850 0 90 1.36 1 source Wire 1, center
88–108 MHz