Coaxial cable receives its name because all its parts — outer jacket, grounded return conductor, dielectric layer and inner metallic pin — share a common axis. Many installers assume the purpose of the dielectric layer is to insulate the center pin from the braided or foil shielding, but in reality the way coax works is somewhat more complex. The signal that it conveys depends upon an electrostatic charge in the dielectric layer.
同轴电缆可用于携带适度的电力，但其主要应用是作为射频传输线。即使电能沿与RF相对的方向传播，它也可以同时执行这两个函数。一个例子是，当电缆用于在户外卫星电视盘与接收器之间建立连接时，通常坐在建筑物内50英尺。射频信号（带有音频，视频和同步信息）来自盘子到接收器。但是，盘子上的半导体会从室内调制解调器内置的电源中获得其直流偏置。
同轴电缆能够传达比传统电缆（例如扭曲配对电话线或音频扬声器电缆）传达更高的频率。随着信号的频率上升，电容和感应损耗的重要性更大。电容电抗降低和电感电抗在较高的频率下上升。由于传输线中的电感电抗性是一种串联现象，电容电抗性是平行现象，因此两个电路参数共同降低了信号。
同轴电缆成功地解决了一个频率，具体取决于一个Gigahertz附近的类型。高于此极限频率相关的损失变得不可接受，需要波导。
An important parameter of coaxial cable is its characteristic impedance. Commonly used values are 50 and 75 Ω. The characteristic impedance of coaxial cable depends on the effective diameter and material composition of inner and outer conductors and thickness and dielectric constant of the material that separates them. Characteristic impedance cannot be measured by an ohmmeter (a time-domain reflectometer is required) and it is not related to the length of the cable run. For most work, it is not necessary to measure the characteristic impedance because this is set by the manufacturer. At that level strict quality control is necessary, particularly in regard to conductor spacing as determined by dielectric layer thickness.
At RF frequencies, coaxial cable must be precisely matched to source and load impedance except where mismatch is intentionally introduced for the purpose of attenuation. Any mismatch will give rise to out-of-phase waveforms, making for reflected energy back toward the source, data loss and signal corruption.
自从Oliver Heaviside发明了1880年对电缆申请并申请专利的Oliver Heaviside发明以来，Coax一直是该行业的不变。近几十年来，它部分被类别电缆所黯然失色，但仍然是众多应用程序的最佳选择，包括仪器接线，天线线索和音频/视频链接。
The post同轴电缆的基础知识appeared first on测试和测量技巧。
提交以下：测试和测量技巧，，，，电缆 +电缆管理
