Typical published DC resistance specs for 1,000 ft.
For most of the coaxial cable types used by the cable industry, the metallic conductor loss is a more significant contributor to attenuation than the dielectric, although the latter does play a role.ĭon’t confuse resistive losses in the metallic conductors with the cable’s direct current (DC) loop resistance, a parameter usually specified in ohms (Ω) per 1,000 feet, and important for network powering purposes. So, what’s left? Resistive losses in the cable’s center conductor and shield, and the effect of the dielectric. Modern manufacturing techniques help keep cable impedance uniform, resulting in a negligible impact on attenuation. Likewise, if the impedance match of the devices to which the cable is connected is within spec, then attenuation related to mismatches will be small. As long as the shielding has not been degraded by the environment, improper installation, rodent damage, etc., then radiation (signal leakage) out of the cable because of imperfect shielding will have a negligible effect on attenuation. Practically speaking, coaxial cable used by the cable industry has very good shielding effectiveness. Signal reflection due to mismatches between the cable and terminations or along the cable due to nonuniform impedance”.Signal absorption in the dielectric of the cable.Resistive losses in the cable conductors.Radiation out of the cable due to imperfect shielding.Here’s the answer to the first question: From the book Modern Cable Television Technology, 2nd Ed., “Signal loss (attenuation) through coaxial cable can occur through any of four principal means: Two questions come to mind: First, why does coaxial cable have attenuation, and second, why does the attenuation vary so much with frequency? Figure 1 illustrates a plot of attenuation-versus-frequency for the latter, from 5 MHz to 3 GHz.
Table 1 highlights some examples of attenuation-versus-frequency values for commonly available Series 6 drop and half-inch hardline coaxial cables.
Unlike the more or less flat loss through a passive device over its design bandwidth, the attenuation through coaxial cable is much greater at higher frequencies than it is at lower frequencies. In particular, as radio frequency (RF) signals pass through coaxial cable, connectors, attenuators (pads), equalizers, and passive components such as splitters and directional couplers, those RF signals experience attenuation. What we call attenuation or loss is a decrease in the power of a signal or signals, usually measured in decibels.