Modified birdcage antenna. Scheme, description

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Modified Birdcage antenna. Encyclopedia of radio electronics and electrical engineering

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Encyclopedia of radio electronics and electrical engineering / HF antennas

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In the 60s, the G4ZU antenna, also known as the “birdcage,” was popular among shortwave operators. However, over time, due to the relatively small values of the gain and the forward-backward radiation ratio, it was forgotten.

While experimenting with different antennas, UV6AF and UA6APE modified said antenna by positioning it horizontally and changing the feed point. This made it possible to obtain certain advantages over the original version of the G4ZU antenna, namely: the distance between the current antinodes of the active element and the reflector increased; the parameters and tuning of the antenna began to correspond to the parameters and nature of the tuning of the “double square”; the antenna design has become flatter, making it easier to rotate; the required number of insulating spacers has decreased (compared to the “double square”) - only the “boom” should be insulated (it can also be made of metal pipes with dielectric inserts).

Modified Antenna Birdcage

The disadvantage of the antenna should be considered the need to use high-quality insulating material at points B and C to isolate the elements of the vibrator and reflector, since voltage maxima are at these points.

The antenna was tested by the authors for a long time on the 10- and 20-meter bands. In this case, the forward-backward radiation ratio was more than 30 dB, and the gain was about 7...8 dB. Unfortunately, the authors did not measure the antenna's input impedance.

Literature

Radio No. 11 1982

Publication: cxem.net

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