Introduction |
This page presents a series of 2-Element HF antennas that are easily constructed, "easily matched and easily tuned". By "easily matched and easily tuned" it is meant that, these antennas can be constructed and tuned on the ground. When the antenna is finally placed at height, there will only be a small decrease in F/B ratio. But the decrease is small and not worth trying to tune at height.
Note: The feed impedance for these yagi designs is 18-20 Ω. This means that a matching device will be necessary for the driven element, if you want to use 50/75 Ω coax or 75/300/450 Ω Ladder Line. See the web page on 2 and 3 Element Yagi Matching.
2-Element Parasitic Beam For 6, 10, or 40 Meters |
2-Element Parasitic Beam For 11, 15, or 20 Meters |
Power Gain = 4.8 dB F/B Ration = 12 dB Radiation Resistance = 20 Ohms |
Power Gain = 5.3 dB F/B Ration = 12 dB Radiation Resistance = 18 Ohms |
Driven Element Length 471/FMHz (ft) || 143/FMHz (m) Director Length 435/FMHz (ft) || 133/FMHz (m) Element Spacing 120/FMHz (ft) || 37/FMHz (m) |
Driven Element Length 475/FMHz (ft) || 145/FMHz (m) Director Length 448/FMHz (ft) || 137/FMHz (m) Element Spacing 120/FMHz (ft) || 37/FMHz (m) |
Bandwidth for 1.75:1 SWR 325 KHz at 40 Meters 1600 KHz at 10 Meters 2800 KHz at 6 Meters |
Bandwidth for 1.75:1 SWR 475 KHz at 20 Meters 700 KHz at 15 Meters 875 KHz at 11 Meters |
Diameter of Elements 40 Meters = 2" 10 Meters = 1-1/2" 6 Meters = 1" |
Diameter of Elements 20 Meters = 1-1/2" 15 Meters = 1" 11 Meters = 1" |
The table on the right is similar to the table in Bill Orr's1 book. I updated the table to include current references and metric dimensions. The antennas are separated into two groups and have slightly different gains. This is because the bands on the left (6, 10, and 40 Meters) have a greater operating bandwidth (>3% at the design frequency). For these bands, the gain is lowered so that the antenna covers a larger bandwidth. Whereas, the bands on the right (11, 15, and 20 Meters) are much narrower (<3% at the design frequency) and can realize a higher gain and still cover the whole band with an SWR <= 1.75:1.
It is important to note that Bill Orr uses a parasitic director in front of the driven element, rather than a a parasitic reflector behind a driven element. This configuration provides higher forward gain and a greater F/B ratio than a configuration using a parasitic reflector.
Some time ago, I set up a group of simulations for 2-Element 10 Meter arrays with parasitic reflectors, parasitic directors, and varying element spacing from 0.02 to 0.30 λ, in 0.01 λ increments. From these simulations, I found that a parasitic director provides for a better F/B Ratio and higher Forward Gain, over a 2-Element array with parasitic reflectors and the same spacing. The best Forward Gain and best F/B Ratio does not happen at the same element spacing, but the 0.12 λ spacing does seem to be a good compromise.
The antennas in the table are detailed below. For the most part, the text associated with each antenna is pretty generic. However, if there is anything specific about an antenna, it will be listed in the description