Transmission characteristics of a power line used for data communications at high frequencies

The transmission characteristics of an installed power line used for data communication, and of a model of this actual line, were measured over the frequency range of 10 kHz-50 MHz. It was found that impedance characteristics were not greatly influenced by the working loads at high frequencies, but changed drastically at lower frequencies. For frequencies of less than 100 MHz, the transmission loss did not increase significantly with frequency. The effect of the length of the connections and variation in load impedance were both studied. It was found that for frequencies above 100 MHz, attenuation loss in the power line is divided into losses due to attenuation constant of the line and the loss occurring at wire connections located between the various wires in the wall sockets. The latter loss is proportional to the number of connections. When the transmission loss was measured by opening and closing the wire connections, the fluctuation in the loss was found to be smaller at frequencies above 1 MHz than at lower ones. The transmission loss at the higher frequency shows only fairly slight fluctuations to variations in working load on the power line. The intensity of the noise power spectrum shows a decrease of -40 B/decade. This degradation rate in the noise spectrum is greater than the rate of increase in transmission loss. The increasing transmission loss can be sufficiently compensated by amplification at the receiving end, but it is possible to keep the amplified noise below the level of disturbance.<
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