Radio Broadcast (May-Oct 1922)

RADIO BROADCAST The principal difficulty in the use of electric and telephone wire lines is not in getting the " voice current " on to the wires but in getting it off. For electric light is usually alternating current, which at any commercial frequency is plainly and unpleasantly audible. And the telephone lines are built for the purpose of individual communication, which cannot be interfered with by "broadcasting." The problem of putting on another stream of "talk" without interference was only solved when a reliable method was found for using a high-frequenc\ electric current as a "carrier." This is where our analogy of the ladder comes in. The carrier in effect "lifts" the pitch of the intruding talk-stream to a point where it is inaudible, so that it does not interfere with the original use of the wires. At the receiving point it is then possible to separate the highpitch (new) current from the low-pitch (original) current, and bring the high-pitch current down to its original (audible) pitch which may be heard in a telephone receiver or loud-speaker. This explains in a rough manner what lies behind recent proposals to use electric light wires for broadcasting. We might have a central broadcasting station at the centre of a great power system, sending out its programmes over high-tension transmission lines to relay stations in each community. Here the "talk-stream" would be transferred to the distributing network reaching every house. Then by connecting a simple receiving set to any lamp-socket or wall-plug, we could "listen in" to news and music sent out hundreds of miles away. Such a service offers attractive possibilities to electric service companies. Suppose such a company operates a system having one or more power plants connected with substations by high-tension lines. A broadcasting studio is built at any convenient central point and connected to the high-tension network through suitable protective devices. This studio might send out three or more programmes simultaneously— news and advertisements, popular and dance music, classical music, etc. Each of these programmes is carried by a different frequency, say 5000 cycles apart. By amplifiers at the substations, the losses in the transmission lines are made good, and the high frequencies transferred to the networks of distributing lines in each town. Where desired, a local programme can be sent out to the customers of a single substation. The apparatus used by the customers can be as simple to adjust as one of 5000 Cycle Amplifier Line from Central Station carrying General Program 5000 Cycle Carrier Power Transformer 10,000 Cycle Generator Local News and ^ I I Shoil Advertisements ' ' 15,000 Cycle Generator Notices of Meetings and K)_ Longer Advertisements By Pass Listening Set, Tunable ^ to any Carrier (•) Loud Speaker Fig. 3. Showing iiow three carriers can be used to give three programmes simultaneously the radio sets now on the market which sells for I65. Loud-speaking receivers can be supplied at varying rentals according to size, allowing their use in public places, such as hotels, restaurants, etc. So much for the technical side of wire broadcasting. Commercially it offers several advantages to its users. The service would be furnished by a central organization fully responsible for the provision and upkeep of apparatus, just as are the telephone companies now. Users would have very little adjusting to do, and skilled assistance would always be available. With no static or fading to worry about, an evening's entertainment could be depended on at any season of the year. All these advantages tend toward making broadcast receiving an exact science, instead of an art. To-day, skill and ingenuity count for a great deal. One reason why Jones builds a set is that his friend Smith has built one, and Jones isn't going to let Smith get ahead of him. Too, there is a powerful appeal to the imagination in tuning up a radio set and picking up stations all over the country. Perhaps it is the spirit of adventure that takes us on these journeys through the ether, rather than the absorbing interest of a lecture on ink or the charm of a church soprano's voice. If a large enough section of the public is interested in results, rather than in technical operation, then wire broadcasting offers a far better field for development than radio.