Merry Christmas & Happy New Year 2009
I'd like to take this time to wish all of you a very Merry Christmas.
This is a season of giving, peace, understanding and goodwill among all. I hope that this Christmas will find you among friends and family with good food, good times, and good memories. And I hope too that Santa lines the bottom of your Christmas tree with all the Amateur Radio goodies that it can hold!
Wish you a very happy new year, many nice DX contacts, a lot of pleasure with our hobby and see You in 2009 again!
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2 element wire yagi for 80m band |
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Wire antennas are easy and cheap to built. Many amateur radio operators are using for low bands simple wire antennas that are hanged too low to the ground. Radiation angle is 90 degrees, antenna is radiating most of energy to the skies. This is the main reason why is their perfomance decreased by many dB.
There are two solutions: move antenna higher than actually is hanged or use an other antenna. The first is hard to made. But try to take a think about the second: the ARRL Antenna Handbook says in the chapter about two element yagi antennas: the most powerful antennas. Adding only one element to the dipole we got an advantage of lowering radiation angle, good feedpoint impedance and directional radiation. We have deigned a 2 element wire yagi for 80m band as an answer for this request...
We found an inspiration in the old magazine from 1986 „Yagi antenna for 3,5 MHz“. This design was simulated in the MMANA antenna software with an excellent results. Main goal was an optimalization for heights from 10 to 20m above ground. Here are answers:
antenna could be optimized for direct feeding with a 50 ohm coax cable
the resonant frequency is not depending on the height between 10 to 20m height (only bit)
the impedance in the feed point is decreasing with the height. For this antenna is an optimal height above the ground 12 – 15m
the bandwith for SWR<2 is around 100kHz
gain 9,1 dBi. F/B ratio is poor, 7 – 12 dB – depends on the antenna height
The F/B ratio is poor due the fact that the distance between both elements is small. It’s a compromise between antenna size, impedance and better F/B ratio.
The 2 element wire yagi was scaled for a SSB segment of 80m band. The dipole radiator is 2x 20,03m and director is 38,07m, distance between elements is 7,74m.
Wire thickness is 2mm. Feeding is through the balun 1:1.
Construction details: to do the 2 element wire yagi we need around 80m of wire, balun 1:1, four insulators and some hanging ropes. I found very useful thin mountain ropes.
Measure and cut the wires for both elements. Add 0,2m to the each side of element for an insulator anchor. In the centre of radiator mount the 1:1 balun. Bound the distance and hanging ropes to the insulators. That’s all. The 2 element wire yagi is needs four hanging points. That could be trees in the garden or meadow. The advantage of close elements is that we could two of them made on the house.
The tunning should be not necessary. In the height 10 to 15m should be SWR<1,3 (or lower). In heigher heights improve the distance of elements otherwise will be the impedance too low.
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