| 摘要 |
640,903. Radio navigation. RADIO CORPORATION OF AMERICA. Aug. 2, 1946, No. 23156. Convention date, Aug. 30, 1945. [Class 40 (vii)] A radio-navigational system comprises a fixed ground radar station providing a P.P.I. display an image of which is transmitted by a television transmitter to craft in the vicinity of the radar station, means being provided for identifying in the reproduced display on each craft the indication representative of that craft. In a system for aircraft, each aircraft carries a responder re-transmitting pulses from the radar transmitter on a frequency different from that of reception. The radar receiver which comprises one receiver tuned to the radar-transmitter frequency and another tuned to the responder re-transmitting frequency may be arranged to receive on either frequency and the corresponding reflected or re-transmitted pulses are applied to a P.P.I. display upon which is superimposed a map of the district about the radar station. The composite display is televised and transmitted omni-directionally upon a third frequency ; alternatively directional transmission may be used, in which case the directive-aerial rotates with the radar aerial and the television receivers employ long-afterglow cathode-ray tubes. Fig. 3 illustrates one form of aircraft apparatus. The television transmission is received by receiver 41 on frequency f3 and the demodulated signals are applied to the grid of cathode-ray tube 48. Exploring pulses from the radar transmitter are received on a frequency f1 by the receiver portion 57 of transponder 42 and re-transmitted on a frequency f2 from the transmitter portion 59. The demodulated pulse output from 57 is applied to the integrator 62 which delivers a pulse 56 when the radar beam is sweeping past the aircraft. The pulse 56 is applied to the cathode-ray tube to increase momentarily the intensity of the image displayed thereon. By noting the position of the rotating radial trace of the P.P.I. display at the instant of increased intensity, the response due to the aircraft carrying the apparatus may be identified. The pulse 56 instead of being applied direct to the tube 48 may trigger a multivibrator to produce a further pulse of predetermined length which is used to increase the intensity of the display. This is of particular application when the aerial scan is rapid so that the pulse 56 does not occupy a whole frame period. In an alternative system means are provided on each aircraft for switching the responder and the television receiver on and off in synchronism. Indications corresponding to other craft will be not be switched on and off in synchronism with the television receiver and thus they will flicker while that due to the receiving aircraft will be switched on and off regularly. An optical filter, Fig. 1a, bearing a darkened sector rotating with the radial trace of the P.P.I. display may be placed in front of the cathode-ray tube at the ground station to reduce the initial high intensity of the radial trace. |
