Why The Surveillance Video Cable Is 75 Ohm Trunk Cable

Three reasons for using 75 Ohm Trunk Cable for surveillance video lines:

1.75-ohm coaxial cable, the national standard name is radio frequency cable, including solid and foamed cables. Now everyone calls SYV solid cable as video cable and SYWV as radio frequency cable.

2. Commonly used coaxial cables have two types of the characteristic impedance of 50 and 75 ohms. The communication industry generally uses 50 ohms, and the video transmission in the TV industry and the security industry all use 75 ohms characteristic impedance; the characteristic impedance is the distribution parameter of the transmission line, which is easy to understand in the electromagnetic field and microwave theory. The concept of RLC is not easy to understand. But it can be said that from the perspective of electricians and circuits, a coaxial cable is two mutually insulated coaxial conductors, but the structure is different from the two wires, but from the perspective of electromagnetic fields and microwaves, it can be equivalent to countless The organic combination of tiny inductors, capacitors, and resistors, and its transmission characteristics are analyzed, and the results of theory and practice are completely consistent.

3. These are equivalent to countless tiny inductances, capacitances, and resistances, all of which are "distributed parameters", which are their influence and effect on signals from the perspective of electromagnetic fields. They are invisible in form, and cannot be measured by general instruments. But it is an objective existence, a "parameter" that has a real impact on the transmission signal. For high-frequency signals, these distributed parameter circuits of the cable can finally be equivalent to an impedance of 75 ohms. This impedance is a kind of equal The effective characteristic effect is not a tangible resistance, so it is called "characteristic impedance". The diameter of the inner and outer conductors of the coaxial cable and the dielectric constant of the insulating medium is different, which can be expressed as characteristic impedances of different sizes, which can be large or small, but when the transmission line impedance is different, reflected signals will be generated. Set the characteristic impedance to 75 ohms. Estimates are "normalized" result.