ANTENTOP- 01- 2008, # 010

Two Elements YAGI for 145 MHz:

Balcony Project

By: Aleksandr, RZ3AIX, kcb121@yandex.ru

Credit Line: www.cqham.ru

Two-Elements YAGI for 145-MHz: Balcony Project

Well, why I did a Two- Elements YAGI? Why not Three, Four or more Elements YAGI? Or, say, so popular 2-5/8 or 3-5/8 Vertical Collinear Antenna?

Okey, at first, just begin from the beginning. From the theory. As the theory says, multi elements antennas (in the case, YAGI) have a large near field zone. The more elements the antenna contains- the more sized near field zone the antenna has. All subjects that are located inside the near field zone are influenced to the parameters of the antenna.

Conclusion: So- the more elements an antenna is contained - the more free space should be around the antenna.

The conclusion was proved by me. For a while I had to use a commercial (from www.tangenta.ru) made Four and Six Elements YAGI. The antennas are perfect antennas only the antennas have enough large free

space around, for example, the antennas are installed on the roof. But I need a balcony antenna. Place at balcony was very limited. I could install only antenna that goes at 1- 1.5- meters outside the balcony. Only the limitation makes me to look for an antenna suitable for such conditions.

Four Elements YAGI works bad at such close to wall (up to 1-meter) installation. There was so called "ladder" effect. The effect means that at one frequency a station is going at 59, step to 25- kHz the station is going at 58, another step 25-kHz- 59. The more elements have YAGI- the more the "ladder" effect presents. Where a Two Elements YAGI is working at 1 meter from a wall there Four Elements YAGI is required 1.5-meter distance from the wall.

Second question is- why not collinear but YAGI. Collinear works badly at my installation on the balcony. Lots reflected and spurious signals from nearest buildings do the reception too noise and unpredictable.

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