Patent GB-393344-A (GB)
Title: Improvements in or relating to radio distance determining system and apparatus
IPC: G01S11/02
Filed: 1931-12-24
Abstract: 393,344. Wireless signalling. GAGE, E. G., 41, Garden Place, Brooklyn, New York, U.S.A. Dec. 24, 1931, No. 35686. Convention date, Dec. 26, 1930. [Class 40 (v).] The distance between a wireless transmitter and receiver is determined by comparing the amplitudes at the receiver of two signals of the same frequency but of different attenuations from the transmitter or of one of these signals and the radiation from a local oscillator. In one transmitter, two different forms of aerial system 120, 121, Fig. 2, are energized alternately from the same radio-frequency source 124 through a code wheel 127, the fields produced thereby being initially of different amplitudes but the stronger signal being more rapidly attenuated than the weaker so that at a predetermined distance from the transmitter there exists a zone of equal signal strength beyond which the initially stronger signal becomes the weaker. Alternative transmitting systems are described, one of which utilizes loop aerials of different areas and electrical constants energized alternately with different code letters, Fig. 3 (not shown), while the other comprises an asymmetrically tapped loop aerial the two parts of which are utilized for the two different transmissions, Fig. 4 (not shown). The receiving system, Figs. 1 and la, comprises a highfrequency valve 22, detector 25, low-frequency amplifiers 41,43, 50, 51 and a rectifying valve 60 feeding a current meter 78 which may be followed by a microphone amplifier and further amplifying and rectifying valves feeding a large current meter, Fig. lb (not shown). A loud-speaker 76 or telephone 77 is also shunted across the output. A loop aerial 11 and an open aerial 10, coupled thereto through a reversing switch 13 and coil 12, feed the valve 22 and a heterodyne oscillator 100 coupled to the loop 11 produces a heterodyne frequency of about 700 cycles to which, the output transformer 54 of the valves 50, 51 is tuned by condenser 61. A reaction coil 27 is also coupled to the loop 11. A further local oscillator 105 tuned to the signal frequency may be coupled to the loop 11 to replace the effect of one of the signal transmissions or to a coil 114 which may be connected to the receiver by the switch, 20 which simultaneously disconnects the loop 11. One method of making the comparison between the signal strengths consists in adjusting a shunt 79 across the instrument 78 so that the weaker signal produces a deflection of the needle to an artificial zero position 81 on.a scale 82 and then noting the deflection on the scale corresponding to the stronger signal. The scale may be calibrated in distance units. An alternative method of making the distance determination, for use when one of the signals is too weak to utilize as above, or when only one of the signals is being transmitted, comprises the use of oscillator 105 which is moved over the scale 116 until the needle reaches the position 81 and then switched off. The position of the needle due to the signal from the transmitter is then read off on the scale 82<1> which may be calibrated in distance units. A further alternative is to vary the amplitude of the signal currents in the aerial 10 by means of the calibrated resistance 15 so that the signals in the loop 11 are in turn just balanced out, the switch 13 being in the position in which said signals oppose each other. The difference between two readings of the resistance 15 thus obtained may be translated into a distance.