Relatively speaking, it is relatively simple to choose the impedance of the coaxial cable. In the use of the cable TV network, the impedance of the coaxial cable is almost 75 ohms, while the coaxial cables for other purposes are all 50 ohms.
In a high-speed circuit, in order to effectively transmit the signal energy from the source end to the load end, the characteristic impedance of the transmission line must be matched with the source end impedance and load impedance of the signal. , otherwise the signal will be reflected, resulting in a series of problems such as distortion of the signal waveform.