Radio Broadcast (Nov 1926-Apr 1927)

352 RADIO BROADCAST FEBRUARY, 1927 France, the station at Nauen, Germany, and others. But in spite of the opinion against him, Senatore Marconi was able to convince the British Government and the Dominions that the beam system of short-wave telegraphy was entirely practical. The early predictions of Marconi have been justified, and the Government has officially accepted the first link in the chain between England and Canada after a rigid seven days' test. To get some definite conception of what the inauguration of the new beam system will mean, consider the great long-wave stations which have recently been completed, and which may eventually have to give way to the new competitor. Commercial long-distance radio communication has been accomplished previously by stations employing frequencies from 37.48 up to 9.99 kilocycles (8000 to 30,000 meters), and using several hundreds of kilowatts in power at the transmitting station. One of the latest and largest of these long-wave stations in the United States is located at Rocky Point, Long Island, and is operated by the Radio Corporation of America. Twelve antennas are used to communicate with various points in the world. Each antenna is supported on twelve 440-foot steel towers, and the length of each antenna is in the neighborhood of three miles. From 200 to 400 kilowatts of power are used, and transmission is carried on at two frequencies, 17.15 and 1 8.22 kilocycles (17,500 and 16,465 meters). The British Post Office wireless station at Rugby (England) has an antenna 800 feet high supported on 12 masts, and uses about 500 kilowatts of power. The frequency used in transmission is 21.3 kilocycles (14,080 meters). Buenos Aires, in the Argentine, has an antenna about 680 feet high supported on ten towers, and uses about 800 kilowatts of power. The station normally works on a frequency of from 18.7 to 24.9 kilocycles (16,000 to 12,000 meters). Many other similar stations are operating in Germany, France, Italy, andother countries. Contrast the above stations with the modern short-wave beam station having five masts 277 feet in height and using a power of only 20 kilowatts, and a transmitting frequency of 11,500 kilocycles (26.09 meters). Senatore Marconi said that the average speed obtained by the long-wave stations was 20 words a minute for a daily average of 18 hours. The beam stations, during the official tests, averaged at least 100 words a minute for 18 hours a day. The average 20-word speed of the longwave stations referred to above, is consider ably less than maximum speed, which is said to be 100 words a minute. The maximum workable speed for ordinary telegraphic work on the new "Permalloy" cables is said to be about 500 words a minute. During the tests of the new beam station, a speed of 250 words a minute was maintained for several hours at a time without difficulty. ADVANTAGES OF THE BEAM SYSTEM THERE are several distinct advantages in using the short-wave beam system over the long-wave system for point to point communication over long distances: 1. The cost of equipment is less. 2 It is more economical to operate maintain. 3. The speed is greater. and AT THE BCDMIN BEAM STATION The antenna system for the transmission of directional signals to Canada is here shown. There are five masts, providing four spans of horizontal supporting wires from which the vertical antenna and reflector wires are dropped. Canada, looking at this picture, is "way over" to the right, hence the reflector wires are at the left. The antenna coupling boxes, one for each pair of antenna wires, are shown in the picture, as also is a part of the copper-tubing feeder system Concentrating the radio waves in a beam instead of allowing them to wander to every point on the earth makes it possible to use only 20 kilowatts of power instead of 200 kw. or more (as in long-wave telegraphy). In spite of using less power at the transmitting station, more power is received at the receiving station, and that is the goal that all radio engineers strive for. Economical operation and maintenance costs are in direct proportion to the amount of power used and the size of the antenna, both of which are less in beam transmission than for long-wave stations giving the same kind of service. Another advantage is that the speed in signalling is increased, due to the utilization of short waves. The larger antenna takes an appreciable time to charge and discharge while the smaller antenna takes much less time. Short waves alone, however, would not accomplish the desired result as far as speed is concerned. It is by the use of reflectors at both sending and receiving ends that the signal is stepped up about a hundred times over that which would be possible with ordinary non-directional sending and receiving. The wave is projected out in a narrow beam and is caught at the receiving station by a similar reflector, and concentrated on the receiving antenna. It may be calculated, that, to obtain a signal strength of a hundred times that of another signal, the power required would be ten thousand times as large. Considering the ordinary method of signalling without reflectors, the power applied would have to be 20,000 kilowatts instead of the 20 kilowatts actually used in the beam system! Atmospherics, which have always limited high speed radio sending, do not exist as a serious factor in the new system. Fading is reported to be considerably less in the directional system than in the nondirectional system. True, there is still some fading, but because of the increased signal strength, the margin of reliability is increased. During the test week there were only two bad periods where fading was enough to hamper the service. These were during the appearance of very large sun spots, and during an intense display of the aurora borealis in Canada. No interference was experienced on the long waves, but the cables and land lines were seriously affected. It was also noticed that, by changing the wavelength slightly, a path could be found which was practically free from interference. In the first beam experiments carried out in Italy and in England, the reflectors consisted of a number of vertical wires parallel to the antenna and spaced around it on a parabolic curve of which the transmitting or receiving antenna constituted the focal line, but in the more modern stations an arrangement devised and patented by Mr. C. S. Franklin has been more advantageously employed. In this arrangement, the antenna and the reflector wires are disposed so as to constitute grids parallel to each other, the antenna wires being energized simultaneously from the transmitter at a number of feeding-points, through a special feeding