Radio Broadcast (May 1928-Apr 1929)

JUNE, 1928 HOW CHAIN BROADCASTING IS ACCOMPLISHED 67 MILES FROM NEW YORK ALONG THE CIRCUIT WHAT HAPPENS TO ENERGY IN WIRE CIRCUITS How the voice-frequency currents are attenuated as they travel over long lengths of wire. Note the effect of amplification at the repeater points sands of radio listeners are dependent upon them. Each transmission supervisor, therefore, conducts every morning a thorough test and adjustment of all the circuits under his charge. Transmitting a tone of 1000 cycles over the program circuits, he receives reports by telegraph and directs adjustments at the nearest repeater station, then at the next repeater station, etc., until, in this way, the entire group of circuits under his charge is "lined up." Then a low frequency, about 100 cycles per second, is transmitted and any necessary auxiliary adjustments are made to see that this low pitch is transmitted with the same efficiency as the 1000 cycles. Then a high frequency of about 5000 cycles is transmitted to check the characteristics at this end of the frequency range, and if necessary, appropriate adjustments are made. Finally, music from a phonograph is sent over the circuits to give a working check on their condition. The transmission supervisor is also responsible for the operation of the program circuits during use. As soon as a report of transmission difficulty reaches him, he must take immediate steps to correct it. Whether the trouble is noise on the circuit or low volume, he must proceed immediately with the proper steps. Sometimes the volume delivered by a circuit will diminish or the circuit will become noisy so as to suggest approaching failure. In this case he endeavors to obtain an alternative circuit and substitute it; sometimes this may be done before the radio listeners realize that any trouble has occurred. At other times a circuit may, without warning, fail completely, and at such times the tiansmission supervisor's general knowledge of the situation is put to the test. He may sometimes succeed in obtaining an alternative circuit with only three or four minutes interruption to the program. Sometimes alternative circuits follow different routes and far exceed in length the facilities they replace, such as during the Democratic Convention in 1924 when a connection 1400 miles long was substituted in place of one only 200 miles long. The transmission supervisors even keep informed of the weather conditions over a large part of the country so that, in case of threatening storms, they may obtain emergency routes and hold them in readiness. The heading shows the program circuit control point at Chicago. Repeaters, equalizers, oscillators, transmission measuring devices, and other apparatus, may be seen mounted at the left and in the rear. One cone is connected to the Red Network program, another the Blue Network. another to the Purple Network (the Columbia Chain), and the fourth is a spare. In this way, constant check is kept on the quality of the program transmission. At the right are telegraph operators who transmit messages between the transmission supervisor and the different repeater stations under his direction. NETWORKS REGULARLY OPERATING THERE are now four networks in daily operation, namely, the Red, Blue and Purple networks in the East, and the Pacific Coast network in the West. The eastern networks are supplied with studio programs from New York City and the Pacific Coast network from San Francisco. The total length of program circuits permanently connected into these four networks, or connected on a regular recurring basis, was, on April 1, more than 15,000 miles. To maintain and operate this great amount of program facilities required more than 25,000 miles of telegraph circuit. The daily audiences listening to the programs from these chains are estimated in the millions of persons. Perhaps the reader has wondered how the designation of networks by colors originated. This occurred several years ago when the only network then operating received programs from weaf in New York. The telephone engineers drew in red pencil, on a map, the circuits regularly connected and drew in blue the extensions which were occasionally added. In this way the regularly operating chain became known as the "Red network." Later, when a network was organized with wjz in New York as the key station, the name " Blue network" was, of course, given to this. At the important program control points the designation of the networks by colors is a considerable aid to the transmission supervisor in the necessary switching operations. HISTORICAL SPECIAL HOOK-UPS /^~\N DEFENSE Day, September 12, 1924, two^-^ way conversation between General Pershing in Washington and the Commanding Generals of the various Corps Areas in New York, Chicago, San Francisco and other points was transmitted to a number of radio stations and heard by many thousands of listeners. This occasion remains an unbroken record for the broadcasting of two-way conversation. The largest number of radio stations ever connected was during the Radio Industries Banquet held in New York on September 21, 1927, when a total of 85 radio stations broadcast the proceedings. All four of the regular networks were used and 13 additional points were added. Doubtless many readers will recall the first Dodge Brothers broadcast of January 4, 1928, when well-known persons in Los Angeles, New Orleans, New York, Chicago and Detroit were heard. The circuits used in this broadcast are shown in heavy lines in the drawing on this page, totaling over 20,000 miles of circuit, or over 40,000 miles of wire. Other program circuits operating on this date but not transmitting the Dodge program bring the total program mileage to about 24,000 miles of circuit or about 48,000 miles of telephone wire. In addition to this telephone mileage, about 40,000 miles of telegraph circuit was employed for lining-up and operating the program circuits. As the pick-up point was changed from one city to another, the circuits had to be switched at corresponding!)' widely separated switching-points. To perform these operations in the necessary order within the allotted five seconds required thorough training and a high degree of intelligence. All the pick-up circuits not in use for a few minutes were kept under continuous test to guard against the development of line troubles during these intervals.