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2 Element Yagi Beam Antenna
Here's a simple and cheap 2 element yagi built for the 17mtr amateur band, the antenna elements supports are fibaglass fishing poles, the elements are made from 1mm stainless steel mig welding wire slid inside the poles. The driven element is fed with 70 - 100 ohm flat twin feedline via the internal 4:1 balun in the atu.
Over the past few months I have been evaluating the yagi against the moxon rectangle and have to say that the yagi with a parasitic reflector is a very good antenna for its simplicity and ease of construction compared to the moxon rectangle.
I used the following formulas for a starting point and then tuned the parasitic elements with a grid dip meter for resonance at around 17.1mhz for the reflector and 18.8mhz for the director.
Parasitic Reflector , Split Dipole , Direct Feed Array
Driven element design frequency 18.130 Mhz
Reflector design frequency 18.000 - 5 % = 17.1Mhz
Driven Element 468 / 18.130
Reflector 468 / 17.100
Parasitic driver , Split Dipole , Direct Feed Array
Driven Element 474 / Frequency
Parasitic Director 452 / Frequency
Spacing 120 / Frequency
The above formulas are for feet and inch's to convert to metric multiply by 0.3048
element lengths after tuneing.
Driven element 7'740 mtr.
Director element 7'380 mtr
Element spacing 1'700 mtr
Dip around 18.8mhz
To tune the driven and director elements a dip meter was used,a small coupling loop was formed in the wire element and a clear dip at resonance can be seen as the meter is passed in and out of the loop. The frequency is around 18.800mhz + / - good enough for me.
The split dipole radiator dipped at around 18mhz on the meter and when installed on the mast the swr is 1.5.1 across the band with 3 s point from front to back.
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