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本文介绍一种从2—12频道的电视接收天线,它在57MC 至230MC 的带宽中保持定向特性,且最大接收方向保持不变,天线增益比相应频道的半波折合振子高2db 以上。天线的简图如图1所示,它由两个有源振子、三个寄生振子组成。两个有源振子之间,由一个低通滤波器和一个高通滤波器组成的混合器相隔离。在黑白电视频道,它相当于一个二元八木天线,由较长的折合振子和最长的一根寄生振子(反射器)组成,在彩色电视频道,它相当于一个四单元的八木天线,由较短的一根双频振子和两根寄生振子(引向器)以及一根反射器(借用较长那根折合振子当作反射器)组成。这儿,采用双频折合振子作为有源振子能使天线的阻抗——频率特性更好些。
This article describes a television receiver antenna from 2-12 channels, which maintains the directional characteristics of the bandwidth from 57MC to 230MC, and the maximum receiving direction remains unchanged, the antenna gain than the corresponding channel half-wave folded oscillator above 2db. Antenna diagram shown in Figure 1, which consists of two active oscillator, three parasitic oscillator. The two active oscillators are separated by a mixer consisting of a low-pass filter and a high-pass filter. In black-and-white TV channels, it is equivalent to a two-element Yagi antenna consisting of a longer folded dipole and the longest of a parasitic oscillator (reflector). In a color television channel, it is equivalent to a four-element Yagi antenna A shorter dipole and two parasitic elements (director) and a reflector (borrowing the longer one that acts as a reflector). Here, the use of dual-frequency oscillator as the oscillator can make the antenna impedance-frequency characteristics better.