Patent GB-1156183-A (GB)
Title: Improvements in Systems for Transmitting Digital Information Signals and for Distance Measurement
IPC: H04Q9/14
Filed: 1966-09-15
Abstract: 1,156,183. Radio position finding; communication system. COMPAGNIE FRANCAISE THOMSON HOUSTON-HOTCHKISS BRANDT. 13 Sept., 1966 [15 Sept., 1965], No. 41345/66. Addition to 1,107,428. Headings H4D and H4L. In a system of airborne information gathering stations M1-MN, Fig. 1, e.g. radio sonde balloons, at generally low altitude such as to be beyond the horizon for ground stations B 1 -B 3 , high altitude balloons R 1 , R 2  are provided as relay stations, visible to both the airborne and the ground stations, to interrogate each station in turn, to gather said information and also range information and to retransmit all said information to one of the ground stations B 2  provided with decoding apparatus CD. Interrogation signals are at a carrier frequency f 1  and the replies are at a carrier frequency f 2 . Signals are transmitted using FSK for modulation and digital coding. A 0 is represented by a stay at one frequency for a digit period, and a 1 is represented by a stay at one frequency for half a digit period followed by a stay for the other half of the digit period at a second frequency. The digit rate is 3125 p/s. Each relay station on order from station B 2  commences a measuring cycle during which all the other stations are interrogated in succession during a respective calling cycle. One calling cycle line 1, Fig. 3, e.g. that for station M1 comprises four consecutive calling sequences, each commencing with a word of six digits bearing the number N of the station being interrogated. The calling cycle is received at the station M1 with a delay as shown at line 2. The corresponding reply from the station is shown at line 3, and the reply as received by the relay station is shown at line 4. Each sequence may contain up to twenty-four words. On receipt of the first address number N, the station compares it with its own, and if the number is verified, the transmitter of the station is readied, point e, to transmit during the next sequence. Thus, on receipt of the next address number N 2  the station retransmits it, and it is received back of the relay station, with an overall delay a equivalent to the range between the station and relay. At the relay station 0 digits are transmitted to the ground after a period d of eight digits, until the corresponding point is received back from the station. If the delay a is not an integral multiple of digits duration, the part of a left over is stored and transmitted to the ground as a proportional number of 0 digits during the third sequence. The transmission during the second sequence is called the rough measurement, and that during the third sequence the fine measurement. In the fourth sequence the station transmits its gathered information, which is retransmitted by the relay station to the ground. The relay station is shown in Fig. 4 and comprises a clock 11 generating pulses at 200 K p/s., a 64:1 divider 12 producing digit pulses of 3125 p/s., a 6:1 divider 13 providing word pulses, a 24:1 divider 14 producing calling sequence pulses and an output from its first stage, indicating when the address number is to be transmitted; a four-stage 4:1 divider 15 indicating which sequence is being transmitted and the end of a calling cycle, and a six stage-up to 32-counter 16 which advances each time divider 15 produces an end of cycle pulse, and has a digitally coded count therein denoting the number of the station being interrogated. At the beginning of the first calling sequence of a cycle the first stage of divider 14 produces a 1 signal for one word (six digits). This causes (via gate 17), the coded number in counter 16 to be converted from parallel to serial bit form by means PS1 for modulation via opened gate 33 and frequency shifter 31 of the output of transmitter 32. At the interrogated station, Fig. 5, the received address number is decoded, and compared in means 211 with that of the station. Verification causes a 1 to 4 counter 212 to pass to the 1 position whereby the station transmitter 320 is readied. At the beginning of the next sequence the address number is again transmitted, counter 15, Fig. 4, is now, however, in position 2, whereby a bi-stable circuit 27 is triggered and a gate 28 opened to let pass the 200 K p/s. clock pulses to a counter which resets to zero every sixty-four counts, giving an output at each reset. The rate of these reset outputs is 3125 p/s., i.e. the digit rate, and they are fed via gates 103 and 35 to produce a corresponding transmission of 0 digits to the ground. The received address number at the interrogated station is retransmitted by means of frequency shifter 31. The retransmitted number is received back of the relay station, is verified in comparator 24 and causes, after a count of eight digits (delay counter 25), circuit 27 to be reset. The count in counter 26 is thus terminated, there having been produced thereby the rough measurement. The count remaining in counter 26 is the fine measurement, and the complement thereof with respect to 64 is fed out for transmission in the next calling sequence by digits being fed into the counter via gate 101 until the count of 64 is reached. The resultant output from gate 103 stopping the transmission of 0 signals via gate 35. During the fourth calling sequence counter 212 is in the 4 position, whereby a gate 322 is opened and the contents of the gathered information store 321 is fed to frequency shifter 31 for transmission via the relay station to the ground.