Another antenna with a capacitive load. Scheme, description

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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING
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Another antenna with a capacitive load. Encyclopedia of radio electronics and electrical engineering

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Encyclopedia of radio electronics and electrical engineering / VHF antennas

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For operation in the 28 MHz band and in the CB band (27 MHz), you can use a "balcony" antenna.

The design of the antenna is so simple that it can easily be replicated at home. It is a flexible steel pin of variable diameter - from 3 to 1,7 mm. At the end of the pin there is a capacitive load in the form of an open ring coaxial with the pin (Fig. 1).

Dimensions are given for the amateur band 28...30 MHz. The dependence of SWR on frequency is shown in fig. 2.

Another antenna with a capacitive load

The antenna was installed horizontally on the balcony of the ninth floor. The metal railing of the balcony, connected to the reinforcement of the reinforced concrete wall, served as a counterweight. Power was supplied to the antenna via a 50-ohm cable, the braid of which at the base of the pin was connected to the fence.

Curiously, closing the ring raises the resonant frequency of the antenna by 0,5 MHz. This is explained simply: a closed ring has the same capacitance, but in an open ring, the inductance of the wire also "works". The addition of other metal spokes is undesirable, and light dielectric spokes and inserts can be used to increase mechanical rigidity.

In the manufacture of the antenna, it is permissible to use pins and tubes of a larger, and not necessarily variable, diameter.

Author: V.Polyakov (RA3AAE)

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