Radio Broadcast (May-Oct 1922)

ii8 RADIO BROADCAST which voice or music can reach the ears of a large audience — by sound waves in the air, byelectric currents on wires, and by radio. Each of these methods has its advantages and its defects, most of which are evident at fn-st glance. Everybody knows, for example, that after the initial investment, a radio receiver costs little to operate, but its results are far from dependable at certain seasons, due to atmospheric conditions. The problem of paying for programmes sent out by radio is still unsolved. As broadcasting ceases to be a novelty, the publicity secured by an entertainer or lecturer through giving a "broadcast" performance will disappear, and these people will properly insist on payment for their services. But by whom? If broadcasting is to become a permanent feature of our life, it is worth while to consider the real obstacles to its development, and examine wire broadcasting as a possible substitute for radio. The fact that the former system is limited to those persons who are "wired up" to it has certain decided advantages to its financial backers, and, paradoxical as it may seem, to its users. For a definite group of subscribers at so much a month is in a position to demand the sort of programmes it wants, and to insist on high-grade "transmission," free from noises and interruptions. The management of such a service is in the position of a theatre which will make money in direct proportion to its success in pleasing its patrons. Such a sound economic foundation is indispensable for any permanent service. It can safely be assumed that the cost of maintaining special wires to connect subscribers with broadcasting stations would be prohibitive— to say nothing of the difficulty of placing the wires in congested districts. This fact has been a stone wall which has blocked all attempts to develop this branch of the art. However, this particular wall has a gate whose key has been discovered within the last five or six \ ears. Perhaps the analogy would be more accurate if we said that a ladder has been found by which we could climb up to a window and climb down again on the other side of the wall. The gate or the window, as you prefer, is the use of existing wire plants, either of the electric light or telephone systems. There is nothing new in this idea; it occurred to many people years ago, yet the window was just out of reach. For instance, it was found that if telephone currents were passed through an electric arc, the original sound would be reproduced audibly, just as the old-fashioned alternating-current arc-lights would "hum" at the pitch of the circuit which supplied them. Some one proposed that a telephone transmitter should be connected to a city's arc-lighting system to broadcast police calls, news of robberies, etc. The difficulty, however, was that the arc-light was not a sufficiently "loud-speaking" receiver to be heard above street traffic, so nothing ever came of the idea. Voice Frequencies "mounted" on Carrier n Voice Frequencies up to 2000 Cycles per Second Carrier Current 5000 Cycles -BROADCASTING STUDIO Power Current 60 Cycles POWER PLANT Carrier and Power Currents can travel together on the Wires -WIRE LINES Carrier and Power Currents Separated at Receiving End Voice Frequencies "dismounted' from Carrier ■LISTENING SET Fig. 2. How use of high and low frequencies allows wires to carry power and broadcasting at the same time