Cellular Telephones

Cellular telephones transmit and receive radio frequencies in the range 824.040 - 848.970 MHz. This is described as being 45 MHz below the base frequencies assigned by the FCC, implying that a 45 MHz beat frequency is used in the detection scheme. Communication on a cell telephone involves two frequencies, one for transmission and another slightly different for receiving, an arrangement referred to as "full duplex" transmission. This permits simultaneous input and output signals. In a given city it is typical to have 832 frequencies, representing 395 full duplex voice channels and 42 control channels. Each "cell" of base towers has 56 voice channels, or 1/7 of the total, with the distribution arranged on a hexagonal grid. The channels are 30 kHz apart. Early cell phones transmitted the signal by frequency modulation, but the technology is rapidly moving toward digital sound imaging.

蜂窝电话在824.040 - 848.970 MHz的频率范围内发射和接收无线电波。这被描述为比联邦通信委员会（FCC）分配的基频低45 MHz，这意味着在检测方案中使用了45 MHz的拍频。蜂窝电话通信涉及两个频率，一个用于发射，另一个稍有不同用于接收，这种安排称为“全双工”传输。这使得输入和输出信号可以同时进行。在一个城市中，通常有832个频率，代表395个全双工语音通道和42个控制通道。每个“cell”（基站）有56个语音通道，即总数的1/7，这些通道按六边形网格排列。这些通道之间相隔30 kHz。早期的蜂窝电话通过频率调制传输信号，但技术正在迅速向数字声音成像技术发展。