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常用的收音机只能接收调幅广播,要收听调频广播和电视伴音则须使用调频收音机。调频广播与调幅广播相比,具有抗干扰性强、频带宽和音质好等优点,在收听戏曲、音乐等节目时效果更好。在标准调频段88～108兆赫范围内,上海地区可收听到第5频道电视伴音和96.2兆赫的调频广播节目。遵义电子管厂设计制造的DCW-2型电调谐超外差电视伴音板除了能收听上述两个节目外,还能收听第8频道的电视伴音。 DCW-2型伴音板的电原理图如图1。其中,高频调谐器由共基极高频放大、电调谐电容三点式振荡和混频电路组成,增益为20分贝;中频采用10.7兆赫标准调频中频,由三级阻容耦合中放组成,增益为60分贝;鉴频器采用比例检波器。
Commonly used radios only receive AM broadcasts, FM radios to listen to FM radio and TV sound. Compared with AM radio, FM radio has the advantages of strong anti-interference, good frequency bandwidth and good sound quality, which is better when listening to programs such as opera and music. In the standard FM range 88 ~ 108 MHz, the Shanghai region can hear the fifth channel TV sound and 96.2 MHz FM radio program. DCW-2 electric tuning superheterodyne soundboard, designed and manufactured by Zunyi Electronic Tube Factory, can not only listen to the above two programs, but also listen to the sound of channel 8 TV. DCW-2 type soundboard electrical schematic diagram shown in Figure 1. Among them, the high-frequency tuner consists of a common base high-frequency amplification, electric tuning capacitor three-point oscillation and mixing circuit, gain of 20 dB; IF using 10.7 MHz standard FM intermediate frequency, 60 dB; frequency detector using the ratio detector.