Patent GB-584334-A (GB)
Title: Improvements in and relating to phase and frequency modulation
IPC: H03C3/34
Filed: 1944-09-20
Abstract: 584,334. Phase and pulse modulation. TELEPHONE MANUFACTURING CO., Ltd., and SARAGA, W. Sept. 20, 1944, No. 17965 [Class 40 (v)] A phase modulated carrier is produced by a cathode ray tube having two or more target electrodes connected to an output circuit, the electron stream being deflected in one direction by a sweep voltage with a frequency equal to a submultiple of the desiredcarrier frequency and in another direction, preferably at right angles to the first one, by the modulating signal. The shape and position of the target electrodes is so related to the wave shape of the sweep voltage that the phase of the output current pulses varies as a function of the instantaneous value of the modulating signal in such a way that the phase of the particular harmonic component extracted from the output current by a selective circuit varies as a predetermined function of the modulating signal. A phase range of many complete cycles can be obtained. The target electrodes may be replaced by a fluorescent screen, the output being obtained from a photoelectric cell or cells arranged behind a mask, the shape of the mask the fluorescent screen or the photoelectric layers corresponding .to that of the target electrodes which the arrangement replaces. In one arrangement, Fig. 3, three target electrodes are used as shown, the sweep voltage being of saw-tooth form, the beam being deflected in a vertical direction and suppressed during the flyback period. The modulating voltage is applied to produce horizontal deflection of the beam, and in this embodiment the electrodes overlap in the horizontal direction so that in the second harmonic output which is utilized there is no discontinuity when the beam is traversed from one electrode to the next. The maximum second harmonic output is obtained when the electrodes and the spaces therebetween are of equal width. The shaded portions of Fig. 5 show the shapes of electrodes for use with a sinusoidal sweep voltage and second harmonic output. The formation of the pulses is also shown diagramatically. The beam in this case is suppressed for half of each cycle of the sweep voltage. A method of producing a beam suppression voltage for the desired interval, 90 to 270 degrees of each cycle, is to phase shift the sweep voltage (a), Fig. 9, by 90' degrees to produce wave (b) which is amplified and clipped to produce wave (c). Curve (d) shows the periods of the deflection voltage during which the beam is suppressed and returned to its starting point. Various other electrode arrangements are described including those in which the basic system is repeated once or more in the sweep direction to increase the output current. The output circuit consists of a resonant circuit tuned to the desired harmonic and connected between a collector electrode and the paralleled target electrodes. The invention can be used for the production of frequency modulated carrier by the introduction of a network, the output amplitude of which is inversely proportional to the input frequency, between the signal source and the phase modulator.