Radio age (Jan 1927-Jan 1928)

24 RADIO AGE for September, 1927 der this tower. The tower is approximately 10 feet in circumference at its base; gradually narrowing down to a peak at its apex. It extends over the top of the radio room so that there will not be an unbalanced electrical effect in the operation of the radio equipment in conjunction with the triangular loopantenna. Extending from the apex of this tower are four wires, running to four points of the compass, to distan;es of 150 feet. At the termini, the wires are connected to pulleys, which in turn are staked to posts by means of 200-pound weights. These antenna wires, forming a single-turn triangular loop, are run back to the radio room, the wires being supported 8 feet above the ground by three posts set in concrete. These socalled base wires are insulated from the posts by use of large glass insulators. The 200-pound weights at the termini of the base wires serve the purpose of slackening or tightening the antenna. The wires leading from the top of the tower appear, at first glance, to be guy wires but in reality they constitute the antenna system — the somewhat odd arrangement of two Showing ignition shielding installed on Liberty motor as means of suppressing noises in radio reception on aircraft A double-beam radio beacon for aircraft enormous loops crossed at right angles. It is a giant loop antenna when compared with our usual conception of loops; 1,256 feet of wire being utilized in constructing the two single-turn triangular loops. The College Park aircraft radio beacon station was constructed by Haraden Pratt. Francis W. Dunmore, and Carl B. Hempel of the Radio Laboratory of the Bureau of Standards. The radio aids to air navigation are being developed and perfected under the direction of Dr. J. H. Dellinger, Chief of the Radio Laboratory, who is leaving Washington soon for a three months' study of aids to air navigation in European countries. The Aeronautics Branch of the Department of Commerce is vested with the work of establishing radio beacon stations, a step of far-reaching significance. Preliminary to determining the equisignal zone of a directive radio beacon, the Bureau of Standards made ground tests with radio equipment installed on a motor truck. Fortunately, the equisignal line corresponded with the test road, thus facilitating the ease of making observations. At points 13, 21, 34, 38, and 51 miles distant from the transmitting station observations were made on crossroads running perpendicular to the equisignal line. The width of the zone at these points was found to be as follows: at 13 miles 360 feet, at 21 miles 400 feet, at 34 miles 400 feet, at 38 miles 450 feet, at 51 miles 500 feet. In measuring the width of the zone at these points the following method was used : The signals were tuned in and the radio amplifier adjusted until the strength of the signals was of medium intensity. The motor truck was then driven back and forth on a line at right angles to the equisignal line until the middle point was found ; that is, where the intensities of the signals were equal. Then the truck was slowly driven north until the inequality of the signals became noticeable, this point being taken as one limit of the zone. The truck was then driven due south past the middle point of the zone until the inequality of the signals again became noticeable. This point was taken as the other limit of the zone, the distance between the two limits as determined was taken as the width of the zone. The equisignal zone thus determined was found to extend due west, not exceeding 500 feet in width at any point up to 50 miles from the transmitting station. "As the distance from the transmitting station increased," reports the Bureau of Standards, "the sharpness of the zone decreased, which necessitated closer observation to determine the exact width of the zone. It is interesting to note that observations could not be made close to overhead wires of any kind or in the lee of a high hill or wooded section. It was found that wires running parallel to and in the immediate vicinity of the equisignal zone have the effect of blending the two signals, distorting the position of the zone, and in many cases doubling the strength of both signals." In an airplane test using a 200foot trailing wire antenna the results were markedly different, owing to the directional characteristics of the trailing wire. This test showed that signals were stronger when the airplane was flying away from the transmitting station than when flying toward it. This effect resulted in an apparent shifting of the equisignal (Continued on page 48)