Page 348 - The ROV Manual - A User Guide for Remotely Operated Vehicles 2nd edition

340 CHAPTER 13 Communications
Transporting electrical signals over distances requires some type of conductive medium through which to send these signals. There are four types of transmission media:
1. Wire pair
2. Coaxial cable
3. Fiber-optic cable
4. Radio
Each of these media has its usages, strengths, and weaknesses. As radio frequency (RF) trans-
mission has limited use in the subsea environment, our discussion will be limited to the metallic and optical fiber transmission media.
13.2.4 Metallic transmission media
The classic metallic transmission line has arrangements consisting of two parallel metallic conduc- tors placed either side-by-side or coaxially. Each has its strengths and weaknesses. The actual conducting media can be any of a number of conductive substances (gold and platinum are much better conductors than copper, but the cost in all but a few cases is prohibitive for normal use). However, the most widely used conductive metal is copper. We will define a conductor here as any substance that conducts electricity, while a capacitor is two conductors separated by an insulator.
The conducting line characteristics can be described using what are termed “primary” and “sec- ondary” parameters. Primary parameters (Figure 13.12) further allow us to describe the secondary parameters and are detailed as follows:
1. Series resistance per unit length (R) of the two conductors
2. Inductance per unit length (L)
3. Capacitance per unit length (C)
4. Leakage conductance per unit length (G) which primarily accounts for the dielectric losses
(insulation losses are generally considered to be negligible)
CΔx GΔx
RΔx LΔx
Δx
FIGURE 13.12
Primary parameters.