Radio-Relay-Systems Development by the Radio Corporation of America

Now that television is ready to provide a new American industry there is need for a nationwide network to distribute the programs. This network may handle many auxiliary services. Radio relays offer a promising means for establishing the network. Twenty years of RCA radio-relay development made it possible, in 1940, to demonstrate a system for automatic relaying of the present standard television. It operated on frequencies near 500 megacycles, used frequency modulation with amplitude limiting in repeaters, and included a repeater retransmitting the waves on the same frequency as they were received. The problems of relay-system design are reviewed and formulas, based on reasonable assumptions, are given for calculating the required repeater gain, the output power, and required antenna heights for various spacings between repeaters and for various frequencies. These indicate that the largest spacings for which adequate antenna height can be provided, and the highest frequencies up to some undetermined limit, result in least over-all repeater gain. Preliminary cost analysis indicates optimum repeater spacings will be 35 to 45 miles. A striking characteristic of radio-relay systems is that they require much less repeater gain than existing coaxial-cable installations when both are adjusted to accommodate the present standard television modulation bands. This difference will be increased if the standards are raised. Experimental data on cross couplings between antenna systems, an important factor in relay systems, and practical expedients for minimizing them are given.