Radio broadcast .. (1922-30)

104 RADIO BROADCAST B Circuit diagram of radio direction finder. A is the direction finder coil, B the tuning condenser, C the Mesny compensating condenser used for obtaining sharper indication of direction, D the electron tube detector, E the filament battery, F the plate battery, G the ground connection, H the telephone receiver direction of radio waves and what precautions should be taken in using the radio direction finder in order to be as sure as possible that the direction obtained is the correct one. It was soon learned that the direction of the radio waves was noticeably different when the direction finder was placed near large metal bodies than when the direction finder was located in a large open space. But if this change in direction is once definitely determined for given conditions, it can be used in interpreting and making entirely correct the observations subsequently made in the use of the direction finder in practice. The most complete series of experiments was conducted on land with a portable direction finder and receiving set which could be taken to a large variety of places to determine the direction and amount of various individual cases of radio wave distortion. The direction finder was fitted with a scale for reading the angular position of the frame on which the coil was wound. This frame was also fitted with a telescope for use in securing a direct view of the radio transmitting station and thus determining visually the true direction. The coil wound on this frame was connected with the necessary tuning condenser, detector, amplifier, and telephone receivers for hearing the radio signals sent out from the radio transmitting station. A radio transmitting station was installed in one of the buildings of the Soldiers Home located in the northern part of the District of Columbia. This location was selected because the tower which supported one end of the transmitting antenna was visible from most points in the District of Columbia. The transmitting station was equipped with electron tube apparatus for sending out interrupted continuous waves. It was also arranged to transmit automatically a series of long dashes for use in making the tests of direction. The receiving apparatus was so assembled as to be conveniently moved by motor truck to various points in Washington, D. C. The places selected were in open regions so far as possible with only one rather simple object near by which might cause the radio waves to change their direction in their passage through that vicinity. In taking readings, the direction finder frame was turned until the transmitting station was seen through the telescope. With the frame held in this position the scale was turned until the pointer read zero. The receiving operator then listened to the radio signals which were being transmitted at that time. He turned the direction finder frame until the signals were weaker than for any other position of the frame. The direction finder was then in the line of the wave front and the reading of the pointer on the scale was observed. If there were no objects causing any distortion or change in direction of the radio waves, this radio scale reading was zero, that is, the same as the scale reading found after the visual observation. If any difference was found between these two readings it showed a change in the direction of the radio wave from the true direction to the transmitting station. As the direction finder was moved nearer to or farther from the object being tested, the distortion or change in direction of the waves became greater or less. Near the trolley wire of an electric interurban line the direction finder sometimes showed that