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用过收音机的人都知道,收音机最容易磨损的是调谐用的双联可变电容器和机械式电位器。电位器改用电子电位器后,用数字控制信号来控制信号的分压比,不会有磨损,音量调节也不会产生噪音。收音机的本机振荡频率改用变容二极管调谐后,直流控制电压可以选台。输入回路一般做成88~108MHz的宽带滤波器,也有输入回路也用变容二极管同步调谐的。可是电压大小和频率的关系是非线性的,难以一一对应。频率刻度也不很精准,调谐电压必需特别稳定。自从有了数字频率合成技术后,本机振荡是某一个基准频率的N倍,稳定性特别高,不会跑台。收音机的选台可以通过输入一个确定的数字实现,也可以N+1…..逐步搜索。将频率N减去一个中间频率就是所接收的电台频率,显示特别直观。KC203就是这种“数字调频”收音机。要特别说明的是广播信号的通过对载波信号模拟调制实现的,现代的“数字广播”则是另外一个概念。
Everybody who has used the radio knows that the most easily worn radio is a tunable double variable capacitor and a mechanical potentiometer. Potentiometer switch to the electronic potentiometer, the digital control signal to control the voltage divider ratio, there will be no wear, the volume adjustment will not produce noise. After the local oscillation frequency of the radio is switched to varactor tuning, the DC control voltage can be selected. The input circuit generally made of broadband filters 88 ~ 108MHz, but also the input circuit is also used varactor synchronous tuning. However, the relationship between voltage and frequency is nonlinear, it is difficult to correspond one by one. Frequency scale is not very accurate, the tuning voltage must be particularly stable. Since the digital frequency synthesis technology, the local oscillation is N times a certain reference frequency, the stability is particularly high, will not run the stage. The radio’s station selection can be done by entering a certain number, or by N + 1 .... The frequency N minus an intermediate frequency is the received radio frequency, the display is particularly intuitive. KC203 is this kind of “digital FM” radio. To be particularly noted is the realization of the broadcast signal through the analog modulation of the carrier signal, the modern “digital broadcasting” is another concept.