2009 New ideas and plans
The 4-element full sized OWA Yagi is a large undertaking for me. It requires a substantial investment and is very heavy, reaching 220kg (485 lbs). It will require Rotating Tower and to keep it up and turning, but it will deliver excellent performance over the whole 40-meter band. This basic design has been recalculated by PA1A with different tappering, EU metric and my standards about mechanical enginering.
This OWA design uses reflector-driver-1st-director spacing that applies generally to OWAYagis. The reflector is 0.15 wavelength behind the driver.
The secondary driver is 0.05 wavelength ahead of the fed driver. The overall boom length is abit over 3/8 wavelength. However, the Yagi lacks the 2nd and 3rd directors that lendfurther control to the operating characteristics. Nonetheless, the array shows sig-nificant gain and SWR improvements over the 3-element Yagi.
At 7.15 Mhz (theoretical)
Free space Gain = 8.00 dBi
Front 2 Back Ratio = 23.,99 dB
Feedpoint Z R +/- jX Ohms = 50.2 - j 0.2
50-Ohm SWR = 1.01
Click the images to read the calculated specs.
Gained about 1 dB of gain relative to the 3-element antenna. The average gain is just above 8.0 dBi. Lost 0.75 dB of front-to-back ratio at the band edges. The absence of the controlling directors of a larger OWA design takes a bit of a toll, but performance is still quite good for a 40-metertubular Yagi.
I did some precalculations within Excel.
Element Material Strength of 40.000 (6061-T6)
Calculated Section Parameters are:
Section Weight (POUNDS)
Section Wind Area (SQUARE INCHES)
Total Area (CUBIC INCHES)
Area Moment Section
Modulus Survival Wind Speed, Vmax
Area With Ice
Total Area With Ice
Area Moment With Ice
Section Modulus Survival Speed With Ice
Click the images to read the calculated specs.
TENSILE AND STRENGHT CALCULATIONS