1,153,192. Radar. SOC. ALSACIENNE DE CONSTRUCTIONS ATOMIQUES DE TELECOMMUNICATIONS ETD'ELECTRONIQUE " ALCATEL." 14 April, 1966 [15 April, 1965], No. 16423/66. Heading H4D. In a method and apparatus for narrow band transmission of radar data over a communication channel (which may be a telephone line or radio circuit) the radar video signals are converted into binary signals by producing a " 1 " digit when the video signal passes through each of discrete amplitude levels, Fig. 1 (not shown), the radar aerial orientation is converted into binary coded signals, and both sets of binary signals are passed to the communication channel. The invention is particularly applied to a meteorological radar sending data to aircraft. The embodiment, Fig. 3, includes a cyclic counter 1 having forty-nine positions corresponding to 1 km. range separations, the counter being triggered when the radar emits a pulse. The counter is connected via gates 3 to a decoding matrix 2 the output lines from which are connected via AND gates 6 to a register 8 comprising forty-nine bi-stable circuits. The AND gates have their second inputs in parallel from the output of the radar echo video/binary signal converter, the register content being fed to a ferrite memory 12 when the register is re-set. The angular position of the aerial is converted in a signal comprising series of thirteen bits of which the first five are invariable and the last eight contain the angular data; this signal connects an oscillator 19 running at a frequency F 1 , for " 0 " bits, or an oscillator 20, running at a frequency F 2 , for " 1 " bits to the telephone line. Detailed operation.-The distance information is transmitted during every 25 cycles of the 50-position counter 14. In order to achieve separation of the information the differentiator 16 controls the sealer 27 through channel 26. The sealer 27 is triggered on every 25th pulse. Line L is directly connected to the bi-stable circuit element 28. Sealer 27 controls the bistable circuit element 28 in order to connect line L to the reading device 25 through the bi-stable circuit element 25. The latter process enables the reading device to display the angular position information. Line L is supplied with the distance information by the bi-stable circuit element 28 which is controlled from position D 14 of the decoding matrix 15. The distance information is supplied to channel L via the bi-stable circuit element 18. The register 8 sequentially stores information (e.g. a " 1 " or " 0 ") related to echoes or non-echoes over 1 kilometre intervals in the range of 0-50 kilometres and 51-100 kilometres. Bi-stable circuit elements 4 and 5 are initiated by a pulse from the transmission means to supply pulses to the counter 1 which sequentially counts through its 50 positions, and to connect respective counter positions to its decoding matrix 2. If an echo is received by the receiving aerial at a predetermined range, the amplitude level filter F passes a signal to the AND gates 6, coincident with a corresponding range signal from the counter 1 and hence the decoding matrix 2. A corresponding AND gate 6 then supplies a pulse to the register 8 which is stored as a " 1." If no echo is received the register 8 will store a " 0." At the end of the first range sequence (0-50 kilometres), a signal from position 49 of the decoding matrix 2 blocks the output from the bi-stable 5 and the counter 1 stops. The contents of the register are then stored in the memory device 12, the contents in the register are erased, and a signal from the differentiator 16 on line 7 again initiates the bi-stables 4 and 5 to start the 51-100 kilometre range measurements. Similarly, information related to echoes received in the 51-100 kilometre range is stored in the register 8 for subsequent storage in the memory 12. The contents of the memory are passed to the bi-stable 18 which is thereby controlled to supply bursts of pulses from oscillators 19 or 20 (related to the presence or absence of an echo) to line L. The frequency of the oscillators 19 and 20 are adapted to suit the telephone line characteristics. Angular information stored by the reading device 23 is fed to the bi-stable 25 and as with the range information, pulse bursts are supplied either from the oscillator 19 or from the oscillator 20, to line L. Bi-stable 28 sequentially arranges the distance and azimuth information for transmission on line L, the sealer 27 operating bistable 28 during each cycle of the decoding matrix 15.