Patent GB-654302-A (GB)
Title: Improvements in data transmission apparatus for aircraft navigation
IPC: G01S7/00
Filed: 1948-01-05
Abstract: 654,302. Radio navigation. RADIO CORPORATION OF AMERICA. Jan. 5, 1948, No. 328. Convention date, Jan. 30, 1947. [Class 40 (vii)] An aircraft radio navigation system including ground radar apparatus comprises a plurality of devices each arranged to provide first signals representing the locations of aircraft in a predetermined altitude layer, arrangements to provide second signals-representing a map of the area, and a keying circuit arranged to apply said first signals to transmitter means on the ground in a predetermined sequence, means arranged to transmit the second signals at a different repetition rate and, where more than one map is represented, in a fixed sequence, together with a craft receiver arranged to receive and selectively compose any of said first signals with said second or one of said second signals. The system is a development of that of Specification 650,451, in which the maps and altitude layer displays are radiated back to the craft on a time sharing basis. The ground apparatus consists of pulse radar apparatus co-operating with responders on the craft which send back return signals consisting of double pulses the time separation of which is a function of. craft altitude. The returned signals are applied to a series of altitude selector circuits 11, 13, 15, 17, 19, 21, which provide a single output pulse only in response to two input pulses having a predetermined spacing, the spacing being different for each selector so that there appear on P.P.I. display tubes 25, 27, 29, 31, 33 and 35 indications of craft in the various altitude layers. Television cameras 39, 41, 43, 45, 47 and 49 are mounted opposite these display tubes and have their outputs passed in sequence by gates controlled by multivibrator ring circuit 57, 59, 61, 63, 65 and 67 to mixer 51 and transmitted at 53. Transmitter 53 also radiates a synchronizing pulse provided by generator 69 at the commencement of each sequence and synchronizing signals from generator 55 such as are supplied to the television cameras and multivibrator ring. Two further cameras 71 and 73 are provided for transmitting images of maps 75 and 77 useful to low and high flying aircraft respectively. Synchronization of the cameras is provided from generator 55 which also controls keying circuits 79 and inverter 81 alternately rendering the cameras effective. The sequential camera outputs and synchronization signals are all radiated by transmitter 85. On the mobile craft an altimeter 99 is used to control the response pulse spacing radiated back by transmitter 93 in response to interrogating signals received at 91. This altimeter is also used to control selector switches 103 and 107, the former of which determines which altitude layer P.P.I. is presented on the craft and the latter which map presentation. There is thus automatically presented on the craft a plan position indication of all craft in the altitude layer in which it is flying superposed on the appropriate map. As the maps are scanned at a greater repetition rate than the layer indications they appear brighter and are easily distinguishable from indications of wavecraft on the same presentation.