GB472352A - Improvements in or relating to modulated carrier wave signalling systems - Google Patents

Abstract

472,352. Wireless signalling; valve generating circuits. MARCONI'S WIRELESS TELEGRAPH CO., Ltd. Aug. 13, 1936, No. 22373. Convention date, Aug. 22, 1935. [Class 40 (v)] In a method of signalling, two saw-toothed oscillatory currents, Figs. 1, 7, 9, in synchronism but of opposite phase are generated at a transmitting station, these are converted into two series of positive impulses 15, 17 which are modulated as to phase or frequency and are applied to stop and start a flow of local energy at 19, from which modulated energy is transmitted to a receiver 101, Fig. II, where it is converted into a series of positive impulses 113, which series is applied with a locally generated series 115 of positive impulses to start and stop a flow of local energy at 117, the resulting currents which are the modulating currents being then utilized. A piezo-electrically controlled oscillator 1 generates a carrier frequency current 3 which is applied to a device 5 from which two saw-tooth wave-forms of the same frequency as the carrier but of opposite phase to each other are obtained. The device 5, Fig. IX, consists of a current limiter 187 such as two valve stages, one stage being biassed " on " and the other " off " so that for a sinusoidal input a flat topped output wave is obtained 'and a differentiator such as a serially connected capacity 189 of large value and resistance 191 of small value so that the flat topped wave is converted into a series of short impulses. The output from the differentiator is fed directly to control a saw-tooth oscillation generator 193, 197, 195 and through a phase reversing valve 203 to control a further saw-tooth oscillation generator 205 so that two saw-tooth wave forms of opposite phase are obtained. Each of the currents 7, 9 is mixed with the modulating signal 33 from a microphone 29 in devices 11, 13 by applying them to two parallel connected valves 215, 221, Fig. X, having a common anode resistance 222. The mixed wave is passed through a current limiter 225 and applied to a differentiator circuit 229, 227 which converts the wave into a series of impulses of varying spacing, these impulses being passed through a rectifier 231 to obtain " off " impulses 15 and " on " impulses 17. These impulses are applied to control an electron relay 19 which consists of a multi-vibrator type of oscillation generator 237,239, Fig. XI, having input terminals 241, 243 and 245,247 and output terminals 249, 251 from which a phase modulated flat topped wave is obtained. This wave may be shaped by passing it through a band pass filter and is applied to the transmission line, if necessary after frequency multiplication or amplification. Frequency modulation may be effected by connecting an integrator circuit such as a series connected condenser of low reactance and resistance of high value shunted across the leads between the microphone 29 and amplifier 31. At the receiver, Fig. II, a radio-frequency amplifier 101 tuned to the band of frequencies covered by the transmission passes the incoming wave to a device 109 which is the same as that shown in Fig. X but excluding the " mixing " stage, so as to generate a series of " off " impulses. At the same time an oscillator 103 synchronized with the oscillator 1 of the transmitter generates current 107 which is converted into a series of " on " impulses in a device 111 similar to 109. These impulses control an electron relay 117 similar to that used at 19 in the transmitter and the resulting modulated flat-topped wave is passed through an integrator and wave trap circuit 121 to produce the signal current for use in a loud-speaker. The device 121 comprises a resistance of high value in series with a large condenser connected across the input, the output being taken across the condenser and shunted by a series tuned circuit to eliminate the carrier energy. The Specification as open to inspection under Sect. 91 described a transmitting arrangement in which a carrier wave is phase modulated and then converted into two series of positive impulses. This subject-matter does not appear in the Specification as accepted.