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现在国内许多城市的电视节目都用两个频道同时播送,所采用的两个频道大多不是互相靠近而是频率相差较大的。因此要获得良好的接收效果,用户最好使用双频道或宽频道式室外接收天线。这里介绍几种用复合振子做的双频道接收天线,其特点是成本低、效率高,又便于制作。一、复合振子普通的折合振子只能工作在一个频道上。如果要使它工作于另一频道,它的增益就会降低。这是因为工作频率改变后,天线方向图以至最大接收方向都要改变,副瓣也增大了;另一个原因是频率改变之后,天线的输入阻抗也随之改变,不能继续与电视机相匹配,传输效率就下降了。
Now many cities in China’s television programs are broadcast simultaneously with two channels, most of the two channels used are not close to each other but the frequency difference between the larger. Therefore, to get a good reception, the user is best to use dual-channel or wide-channel outdoor receiving antenna. Here are several dual-channel receiver antenna made with composite vibrator, which is characterized by low cost, high efficiency, but also easy to make. First, the composite oscillator ordinary oscillator can only work on a channel. If you want to make it work in another channel, its gain will be reduced. This is because after the change of working frequency, the antenna pattern should be changed up to the maximum receiving direction and the side lobe also increases. Another reason is that after the frequency is changed, the input impedance of the antenna also changes and can not continue to match with the television set , Transmission efficiency is declining.