Spiral antenna. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / VHF antennas
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I propose a more practical type of helical antenna in use, which replaces the whip helical antenna 16 - 18 cm long. The "without antenna" radio station, in addition to its unusual appearance, will be very compact. The antenna was made in the form of a frame of glued strips of plexiglass to the size of the radio station body as a continuation of it in the upper part, as shown in the figure.
The antenna frame is glued to the body of the radio and can be of various sizes depending on the size of your radio. With a frame height of 25 mm, winding with a wire of 0,3 - 0,5 mm should be started at a distance of 5 mm from the body. This place will make it possible to more accurately adjust the antenna by shifting the coils. Winding is carried out until the frame is filled in one layer. After tuning, the coils are covered with BF-2 glue and closed on top with a cap made of glued strips of plastic 1–1,5 mm thick, so that the cap does not differ in size from the body of the radio station. You can attach the cap from above to the body of the radio station with an M2,5-MZ screw in the middle of the antenna.
To tune during transmission, while controlling the level of radiation with the S-meter of another radio station, we smoothly bring our hand to the antenna. If the readings of the S-meter start to decrease, we unwind and bite off 1 turn of the antenna and continue on like this. After some time, bringing the fingers to the antenna, we notice that the S-meter readings first increase and then decrease as the hand approaches the antenna further. This means that we have approached the resonance of the antenna. We perform further adjustment by smoothly pushing the antenna turns along the frame and achieving the maximum readings of the S-meter.
If at the very beginning of the tuning, when the hand approaches the antenna, an increase in the readings of the S-meter is observed, then few turns are wound and it is necessary to rewind with a thinner wire in order to get more turns on the same frame. The same method is suitable for tuning any kind of helical antennas.
Author: A. Kucher; Publication: cxem.net
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