Radio age (Jan-Dec 1926)

12 RADIO AGE for October, 1926 The Fourth National Radio Conference marked an attempt to reach a needed degree of stabilization in radio matters, particularly in the general assignment of frequency bands to various services. Radical changes in frequency assignments by previous conferences, not only prevented rapid compliance with the recommendations of the conferences, but also tended to engender a lack of confidence in the ability of the radio industry to regulate itself by mutual agreement. Each general branch of the radio industry should be able to know reasonably in advance what general frequency bands it may expect to use for the conduct of its business, within which it may be expected to reap the benefits of advances in the art and to settle its own problems. This implies neither rigidity nor stagnation. New services, or improved services can be provided for by suppression in whole or in part of older and less effective ones. T»s>j navy owns and operates one of the largest radio systems under single control in the world. Many things have been undertaken for the express purpose of aiding broadcasting. Owing to the extent of the navy's radio system, which was full grown before the advent of broadcasting, and to the necessity for long and costly development of non-interfering equipment, modernization of the navy's apparatus has not been rapid. Much unjustified criticism has been leveled at the navy on this account, regardless of the facts that research and development consume time; that the forces of national defense cannot adopt new and untried equipment without exhaustive tests as to its efficacy and reliability; and that the provision of public funds for simultaneous rehabilitation of all the navy's equipment is not economically justifiable. World-Wide System WHEN broadcasting started the navy was operating about 150 radiotelegraph stations on shore, in a world-wide system, and radiotelegraph stations in about 500 vessels at sea. Many of the vessels used two or more transmitters for simultaneous communication on different circuits, and practically all the shore stations used two or more transmitters to effect simultaneous communication with two or more ships or other stations. Practically all this apparatus was designed to operate only in The Navy's only broadcast transmitter, NAA, located at Arlington, Va. the band of frequencies (wavelengths) later reserved for the exclusive use of broadcasting. The principal dependence was the cheap, simple, rugged and reliable spark apparatus. Unfortunately this type of apparatus causes disturbance over a wide band of frequencies on either side of the one to which it is adjusted. There were a few arc transmitters ashore and afloat. The arc transmitter is rugged and reliable and can be adjusted so as to occupy a much narrower band of frequencies than the spark. Unfortunately, however, the arc emits energy in a series of harmonic frequencies. Objectionable and interfering energy has been measured in arc harmonics as high as the thirtieth. Also, arcs create in their immediate vicinity The Magazine oj the Hour a form of disturbance known as "mush" which is apparently without frequency adjustments, and which effectively blankets reception on all frequencies. The properties of the vacuum tube were known to the navy, but the tube had not yet proved its reliability for naval use. Tubes were not available in quantity, nor was their average life in service sufficient to warrant their adoption. Suitable vacuum tubes were not then made by American manufacturers, and while foreign procurement would have been possible it would have been unpatriotic and militarily unsound. Since the beginning of broadcasting, the navy has replaced spark transmitters for regular service in 27 shore radio stations. Twenty-four shore radio stations, formerly using spark transmitters have been closed permanently, and the final closing of two more is projected for the near future. Plans for the current year include the replacement of 14 more spark transmitters with vacuum tube transmitters for regular service. Exit the Spark Set COMPLETION of this program will leave but 43 spark transmitters in regular service in the entire shore system of the navy. Of these, 4 are in Alaska, and 12 are outside the continental United States, leaving but 27 in regular service on shore in the United States. Of these 27, 21 are low-powered transmitters restricted solely to use on the radio direction finder frequency which is well removed from the broadcasting band. Four arc transmitters on shore have been replaced with vacuum tube transmitters, and 4 other arcs have been fitted with special devices to reduce their disturbing emissions. Experimental high powered tubes are being developed to replace the high powered arcs. The first of these experimental tubes is already in service and the other is expected to begin operation in a few days. In places where it has been impossible to replace interfering {Please turn to page 50)