Term & Definition Air Core Cables that are not gel filled. Air-Gap Dielectric A coaxial design in which a monofilament of plastic holds the center conductor in place in a hollow plastic tube allowing the remainder of the dielectric to be air. Typical velocities of up to 84% can be achieved in this design. Attenuation The decrease in magnitude of a signal as it travels through any transmitting medium, such as a cable or circuitry. Attenuation is usually expressed logarithmically as the ratio of the original and decreased signal amplitudes. It is usually expressed in decibels (dB). Bel A unit that represents the logarithm of the ratio of two levels. One bel equals the base 10 logarithm of the ratio of two power levels. It is also equal to the base 10 logarithm of square of the ratio of two voltage or current levels, provided the impedances are the same at the two levels. See dB. Beldfoil Belden trademark for highly effective electrostatic shield of reinforced metallic foil. Bend Radius Radius of curvature that a flat, round, fiber optic or metallic cable can bend without any adverse effects. Braid A group of textile or metallic filaments interwoven to form a tubular flexible structure which may be applied over one or more wires, or flattened to form a strap. Braid Angle The angle between a strand of wire in a braid shield and the longitudinal axis (i.e.axis along the length of the center) of the cable it is wound around. Characteristic Impedance In a transmission cable of infinite length, the ratio of the applied voltage to the resultant current at the point the voltage is applied. Or the impedance which makes a transmission cable seem infinitely long, when connected across the cable's output terminals. Coaxial Cable A cylindrical transmission line comprised of a conductor centered inside a metallic tube or shield, separated by a dielectric material, and usually covered by an insulating jacket. Used by cable TV companies to distribute signals to homes and businesses. Also used by telephone companies in some applications and by cellular telephone, radio, and television installations. Core The light conducting central portion of an optical fiber with a refractive index higher than that of the cladding. The center of a cable construction. Most often applies to a coaxial cable, where the core is the center conductor and the dielectric material applied to it. HFC Hybrid Fiber/Coaxial. Insertion Loss A measure of the attenuation of a cable and/or component(s) by determining the output of a system before and after the device is inserted into the system. Jacket Pertaining to wire and cable, the outer protective covering that may also provide additional insulation. Loaded Line A transmission line that has lumped elements (inductance or capacitance) added at uniformly spaced intervals. Loading is used to provide a given set of characteristics to a transmission line. Loading A transmission line that has lumped elements (inductance or capacitance) added at uniformly spaced intervals. Loading is used to provide a given set of characteristics to a transmission line. Periodicity The uniformly spaced cable impedance variations that result in addition of the reflections of a signal. The distance between them is the half wavelength most affected. Multiples of that frequency are also affected. Even very slight variations, which appear over and over in a construction or installation, can have major effects on signal integrity because of periodicity. Precision Video Video coaxial cables having very tight electrical tolerances in impedance, velocity of propagation, attenuation and structural return loss. Used in high quality applications such as live broadcast in network studios and pre- or post-production facilities. Propagation Delay Time required for a signal to pass from the input to the output of a device. Reflection The change in direction (or return) of waves striking a surface. For example, electromagnetic energy reflections can occur at an impedance mismatch in a transmission line, causing standing waves. Reflection Loss The part of a signal which is lost due to reflection of power at a line discontinuity. RG/U, A/U, B/U RG is the abbreviation for radio guide, a military designation for a coaxial cable, and U stands for universal a regular PVC jacket. The 'A' means the cable shall have a Black Non Contaminating jacket. The 'B' requires a stranded center conductor with a Black Non Con. jacket. Semi-Solid Dielectric A coaxial design in which a monofilament of plastic holds the center conductor in place in a hollow plastic tube allowing the remainder of the dielectric to be air. Typical velocities of up to 84% can be achieved in this design. Single-ended Unbalanced, such as grounding one side of a circuit or transmission line. Standing Wave The stationary pattern of waves produced by two waves of the same frequency traveling in opposite directions on the same transmission line. The existence of voltage and current maxima and minima along a transmission line is a result of reflected energy from an impedance mismatch. Standing Wave Ratio (SWR) A ratio of the maximum amplitude to the minimum amplitude of a standing wave stated in current or voltage amplitudes. See also Standing Wave. Structural Return Loss Magnitude of the internal cable reflections, measured in decibels, relative to the actual cable impedance, not the system impedance. Measure of signal reflections caused by the structure of the cable without the additional reflections from any impedance mismatch between the cable and the measuring equipment. Measure of internal cable reflections using a reference impedance in the measuring equipment that is adjusted to the nominal or average impedance of the cable. See also Return Loss Sweep Test Testing a characteristic of a cable or device across a range of frequencies. In cable, it usually implies return loss or structural return loss (see also). Transfer Impedance For a specified cable length, transfer impedance relates to a current on one surface of a shield to the voltage drop generated by this current on the opposite surface of the shield. Transfer impedance is used to determine shield effectiveness against both ingress and egress of interfering signals. Cable shields are normally designed to reduce the transfer of interference - hence, shields with lower transfer impedance are more effective than shields with higher transfer impedance. Transmission Line An arrangement of two or more conductors, a coaxial cable, or a waveguide used to transfer signal energy from one location to another. Transmission Line Cable Two or more conductors placed within a dielectric material in such a way as to control the electrical characteristics. Triaxial Cable A cable construction having a conductor, and two isolated braid shields, all insulated from each other. A coaxial cable with a second braid applied over an inner jacket and an outer jacket applied over the outer braid. Commonly used in television camera systems. Velocity of Propagation (VP) The transmission speed of electrical energy in a length of cable compared to speed of light in free space. Usually expressed as a percentage. Voltage Standing Wave Ratio Ratio of maximum voltage of the standing wave to the minimum voltage of the standing wave. See also Standing Wave Ratio. VSWR Voltage Standing Wave Ratio