Radio age (Jan 1927-Jan 1928)

RADIO AGE for January, 1927 made near a 100-foot wire, supported five feet above the ground, at an angle 45 degrees with the line to the transmitting station. This elevated antenna was tuned to the wave length of this experimental broadcasting station, with the result that a slight distortion of the wave front was recorded. Experiments with the coil aerial, an integral unit of a radio direction-finder, directly under a 100-foot 3-wire antenna, 75 feet overhead, failed to produce any distortion, when the antenna was tuned or untuned. This antenna was stretched at an angle of 15 degrees with the line to the transmitting station. However, when the direction-finder was placed near the lead-in wire the incoming radio wave evidenced a marked deviation. "Very little, if any distortion existed with the antenna untuned," observed Francis W. Dunmore of the Bureau of Standards. "This shows," he emphasizes, "The importance of keeping the direction-finder at a considerable distance (100 feet or more) from any such tuned circuit." Explore Three Channels THIS comprehensive investigation into the reaction of radio waves when they collide with objects in their mad race through the ether involved the design of special equipment for this purpose. For instance, the direction-finder consisted of a coil of wire wound on a frame four feet square. This design made provision for the use of three wave lengths — 400, 625 and 1,400 meters. The frame of this aerial was mounted with its plane vertical on a tripod three feet from the ground. The frame was rotated on a vertical axis by the observer, who was located eight feet away and he manipulated two heavy pieces of cord which were attached to the frame. The detector circuit and batteries were placed on a stool three feet high. The scale on the directionfinder read from zero to 180 degrees, and it could be clamped at any position on the tripod. A pointer on the coil frame turned with the latter and served as an index by which to read the position of the direction-finder. Visual observations were made in determining the direction of the transmitting station, a telescope being mounted upon the coil frame for that purpose. The position of the telescope on the frame was determined by observation made in a large open field, where it was presumed that no distortion existed. The directionfinder was turned to such a position that the signals were inaudible. The telescope was then put in place on the shelf in the middle of the frame so that the image of the transmitting station could be seen on the cross hairs. The telescope was then secured firmly in position. The radio receiving set or detector circuit for the reception consisted of one vacuum tube, of the non-oscillating type. A small air-core transformer was employed, the particular advantage of which was the reduction of the change in direction with reversal of coil leads to about two degrees. The observer, engaged in making distortion observations, would listen to the radio signals received by this detector circuit, turning the frame of the coil antenna until a mini The Magazine of the Hour 17 mum signal is heard. The scale reading on the direction-finder is then recorded. The leads to the detector circuit are reversed by means of a switch, and the observation repeated. The mean or average of these two readings is the basis for plotting the charts showing the distorting effect of radio waves when striking different objects. The transmitting station, established especially for these tests, was located on the grounds of the Soldiers' Home, three and one-half miles from the Bureau of Standards. The transmitting antenna was supported between an elevated water tank and the tower of a building. The commanding location of the Soldiers' Home, situated on one of the highest points of the District of Columbia, was a natural advantage favoring these observations. The magnetic compass was discarded as a means of determining the direction of the transmitting station when taking bearings because of its possible effect upon the deviation of the indications on the scale of the direction-finder. The telescope afforded visual means of sighting directly on the transmitting station, located as it was on a commanding hill. Con(Please turn to page U0) Transmitter used in the tests to determine field distortion