This application relates generally to data transmission, and more particularly to data transmission over power lines.
The use of power lines to transmit data is known. Initially, power line communication systems were limited to relatively low data rates, typically less than 500 kbs. These low data rates are generally useful for applications such as remote control of various switches connected to the power line system. More recently, developments have been made in the area of broadband power line communication systems, also known as power line telecommunications (PLT) systems or broadband power line (BPL) systems. These systems are capable of transmitting data at significantly higher data rates than previous systems. For example, BPL systems can transmit data at rates of 4–20 Mbps.
While existing power line systems are capable of transmitting data at the rates described above, they were not initially designed for data transmission. Instead, they were designed to carry large currents at high voltages so that significant amounts of energy could be distributed at one primary low frequency (e.g., 60 Hertz).
Power line communication systems generally use one or more carrier frequencies in order to spread the data transmission over a wider range of frequencies. The low data rate power line communication systems discussed above generally utilized frequencies in the range of 9 kHz to 525 kHz. In this frequency range the risk of emissions is low as the attenuation of the cable is low and the wavelengths used in the signaling are long with respect to the typical cable lengths in the system. However, the high data rates of BPL systems cannot be achieved using carrier frequencies below 525 kHz. Instead, BPL systems typically use carrier frequencies in the range of 1–30 MHz. At these higher frequencies, it is preferable to employ capacitive coupling rather than inductive coupling in order to implement a broadband communication system using power line cables.
Providing an electrical coupling to medium voltage (MV) and low voltage (LV) power lines as part of a broadband communication system is a dangerous task. Also the coupling must be made secure to withstand hostile weather conditions and to provide reliable communication services. Previous attempts to install such a coupling as part of a capacitive coupling circuit have relied on highly trained and skilled installation personnel. New customer interconnections as well as periodic interconnections with auxiliary electronics such as repeaters, routers, etc. must be done at various points along energized power lines without incurring risk of injury or disruption of both power transmission and broadband communications. There is an important need to develop a technique for providing such interconnections at a safe distance spaced from the energized power lines.