For the propagation and interception of radio waves, a transmitter and receiver are employed. A radio wave acts as a carrier of information-bearing signals; the information may be encoded directly on the wave by periodically interrupting its transmission (as in dot-and-dash telegraphy) or impressed on it by a process called modulation. The actual information in a modulated signal is contained in its sidebands, or frequencies added to the carrier wave, rather than in the carrier wave itself. The two most common types of modulation used in radio are amplitude modulation (AM) and frequency modulation (FM). Frequency modulation minimizes noise and provides greater fidelity than amplitude modulation, which is the older method of broadcasting. Both AM and FM are analog transmission systems, that is, they process sounds into continuously varying patterns of electrical signals which resemble sound waves. Digital radio uses a transmission system in which the signals propagate as discrete voltage pulses, that is, as patterns of numbers; before transmission, an analog audio signal is converted into a digital signal, which may be transmitted in the AM or FM frequency range. A digital radio broadcast offers compact-disc-quality reception and reproduction on the FM band and FM-quality reception and reproduction on the AM band.
说到无线电波的传送和接收，就要用到传送器和接收器。无线电波是信息负载信号的载体，信息可用其传播中的间歇停顿直接编译在电波中(如一点一划的电报)，或用一种调制的方式加载于电波中。在调制后信号的所有信息包含在其边带中，或加载在负有电波的频率中。而不是其电波载体自身。无线电所用最常见的两种调制方式是调幅(AM)和调频(PM)。调频最大程度的减小噪音，并且比调幅的保真度高，调幅是一种较老的传播方法。调幅和调频都是模拟传播系统，也就是说，它们把声音处理成连续不断的与声波相似的电子信号变化模式。数字无线电使用一种传播不连贯电压脉冲信号的传送系统，换句话说，作为数字模式，发射之前，把模拟声音的信号转化成数字信号，可在调幅和调频的波段中传播。数字无线电广播能在调频波段产生并接收CD质量的声音，也能在调幅波段产生并接收调频声波质量的声音。

In its most common form, radio is used for the transmission of sounds (voice and music) and pictures (television). The sounds and images are converted into electrical signals by a microphone (sounds) or video camera (images), amplified, and used to modulate a carrier wave that has been generated by an oscillator circuit in a transmitter. The modulated carrier is also amplified, then applied to an antenna that converts the electrical signals to electromagnetic waves for radiation into space. Such waves radiate at the speed of light and are transmitted not only by line of sight but also by deflection from the ionosphere.
无线电最常见的形式是用作声音(音响和声响)和图像(电视)的传播。声音合图像由话筒(声音)或摄像机(图像)转换为电子信号，经过放大后，用来调制发射器中一个振荡器产生的负载电波。调制后的负载电波也经过放大，然后加载到天线中，天线把电子信号转化成电磁信号，发射到空中。这种电磁波以光速传播，其传播方式不仅通过无线电直线传播，还可通过电离层的反射传播。

Receiving antennas intercept part of this radiation, change it back to the form of electrical signals, and feed it to a receiver.
接收天线的装置接收部分电磁波，将其转换回电子信号，并供给一个接收器。

There are certain differences between AM and FM receivers. In an AM transmission the carrier wave is constant in frequency and varies in amplitude (strength) according to the sounds present at the microphone; in FM the carrier is constant in amplitude and varies in frequency. Because the noise that affects radio signals is partly, but not completely, manifested in amplitude variations, wideband FM receivers are inherently less sensitive to noise. In an FM receiver, the limiter and discriminator stages are circuits that respond solely to changes in frequency. The other stages of the FM receiver are similar to those of the AM receiver but require more care in design and assembly to make full use of FM's advantages. FM is also used in television sound systems. In both radio and television receivers, once the basic signals have been separated from the carrier wave they are fed to a loudspeaker or a display device (usually a cathode-ray tube), where they are converted into sound and visual images, respectively.
调幅和调频接收器有所不同。在调幅的传播中，其负载电波频率是恒定的，但波幅(力度)随着麦克风声音变化而变化；在调频的传播中，其负载电波波幅是恒定的，而频率随着麦克风声音的变化而变化。因为影响到无线电信号的噪音只是部分的，而不是整体出现于波幅变化中，调频宽频的接收器自身对噪音不够敏感。在调频接收器中，限幅器和鉴别器这两个设备仅对频率的变化做出反应。调频接收器的其他部分与调幅接收器相似，但其设计和组装需要更加小心，以充分发挥调频的优势。调频也用于电视声音系统。在无线电和电视两个接收器中，一旦基本信号与载体电波分离，即被供于扩音器或显示设备(通常是阴极摄像管)，在那里它分别被转换成声音和可视图像。