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电视天线放大器是将室外天线接收到的微弱电视高频信号,经过放大后再送入电视机的一种高频、低噪放大器。一般来说,使用天线放大器后,能改善图象的清晰度和伴音。本文介绍的放大器,制作简单、调试容易、工作稳定,最高增益可达28 dB。一.原理简介原理图见附图。图中B是300Ω/75Ω阻抗变换器。从天线上接收到的电视高频信号经B转换成75Ω后,送入由L_1、L_2、L_3、C_1、C_2、C_3组成的通带滤波器,滤去45 MHz以下信号后进入由BG_1、BG_2组成的直耦式宽带放大器。为使宽带放大级工作稳定,BG_1的射极电阻用得较大,BG_2接成共基极电路。由于共基极电路的接入,虽然使该级牺牲了一些增益,但充分发挥了末级共射电路的增益,提高了整机工作的稳定性。增益28 dB时,不产生自激。放
TV antenna amplifier is an outdoor antenna to receive weak television high-frequency signals, after amplification and then into the TV a high-frequency, low-noise amplifier. In general, the use of antenna amplifiers, can improve the clarity and sound image. This article describes the amplifier, making simple, easy debugging, stable work, the maximum gain up to 28 dB. I. Principle Introduction Schematic diagram shown in the accompanying drawings. In the figure, B is a 300Ω / 75Ω impedance converter. The high-frequency TV signal received from the antenna is converted to 75Ω by B and fed into a passband filter consisting of L_1, L_2, L_3, C_1, C_2, C_3 and filtering out the signal below 45 MHz into BG_1, BG_2 Composed of a direct-coupled broadband amplifier. In order to make the work of broadband amplification stage stable, BG_1’s emitter resistance is used more, BG_2 is connected as a common base circuit. Due to the access of the common base circuit, although this level sacrifices some gain, it gives full play to the gain of the final stage common-emitter circuit and improves the stability of the whole machine. At a gain of 28 dB, no self-excitation occurs. put