UHF antenna. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / Television antennas
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The antenna, a schematic representation of which is shown in the figure, is a "wave channel" of ring elements for receiving signals in the UHF range. It consists of three directors D1, D2, D3, a reflector R and a dual active vibrator V1-V2.
Such an antenna has good back lobe suppression (up to 30 dB), a relative bandwidth of about 10% and a higher gain than a conventional "wave channel" of the same length.
When the cable is connected from below, as shown in the figure, the antenna receives signals with horizontal polarization. The circumference of the antenna elements is determined from the ratios: R=1,08l; V2=1,02l; V1=0,98l; D1=0,95l; D2=0,94l; D3=0,93l, and the distances between them - according to the formulas: lR=0,2l; lV=0,125l; l1=0,06l; l2=0,12l; l3=0,23l, where l is the average wavelength of the received interval (or channel) in the UHF range (it varies from 633 mm for the 21st television channel to 382 mm for the 60th channel).
The carrier horizontal rod of the antenna with a length of about 0,75 l is made of insulating material. For the manufacture of ring elements, copper or aluminum wire with a diameter of 3 ... 4 mm is used. Passive elements (directors and reflector) can also be made from strips 8 ... 10 mm wide. The distance between the centers of the conductors of the connecting line of the vibrators is equal to two wire diameters. The antenna is adjusted by changing the position of the director D1. At the cable connection point, for the purpose of balancing, a ferrite ring with a relative magnetic permeability of 400 ... 600 is put on it.
Ring size is not critical. It is secured with insulating tape.
Author: N. Turkin, St. Petersburg; Publication: N. Bolshakov, rf.atnn.ru
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