Coaxial Cable Specifications

What are the key specs of a coaxial cable?

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- everything RF

Jul 22, 2019

The coaxial cable was developed for transmitting RF and Microwave signals from one point to another with minimal signal loss. A typical microwave coaxial cable consists of inner and outer conductors separated by a polymer dielectric. These three layers are then encapsulated by a polymer jacket. The outer jacket protects the cable and the signal within it from any external interference.

Coaxial Cable Specifications:

Velocity of Propagation (Vp): Transmission speed of electrical energy in a specific length of cable compared to the speed of light, expressed as a percentage, is called Velocity of Propagation.

Bend Radius: The radius measured from the inside curvature of a cable, by which you can bend a cable without damaging it or altering the electrical characteristics of the signal going through it is called bend radius.

Attenuation (Insertion Loss): It is the loss of signal power from the input of the cable to the output. Attenuation is measured in dB loss per length of cable (ex. 19 dB/50Ft.). Attenuation increases with increasing frequency.

VSWR (Voltage Standing Wave Ratio): The ratio of maximum effective voltage to minimum effective voltage measured along a transmission line. The lower the VSWR the better. A higher VSWR would mean more reflections at the cable interface.

Dielectric: The dielectric separates the inner conductor from the outer conductor. The type of dielectric used determines the electrical characteristics of the cable i.e. the level of attenuation, propagation velocity and the frequency up to which it can operate.

Transmission Line Impedance or Characteristic Impedance: Characteristic impedance is a relationship between the capacitance per unit length and the inductance per unit length. The inner and outer conductor diameter ratios and the dielectric constant in the cable define the parameters involved in determining characteristic impedance. Coaxial cables are usually available in two impedance values of 50 and 75 Ohms, where 50 Ohms cables are used in data signal applications and 75 Ohms are used in video signal applications.

Shielding: Conductive envelope made of wires or metal foil that covers the dielectric and the center conductor of the cable.