Patent GB-661378-A (GB)
Title: Improvements in or relating to systems for producing phase-modulated oscillations
IPC: H03C3/34
Filed: 1948-04-27
Abstract: 661,378. Cathode-ray tubes. PHILIPS ELECTRICAL, Ltd. April 27, 1948 [April 29, 1947], No. 11535/48. Class 39 (i). [Also in Group XL (c)] Comprises arrangements of cathode-ray tubes and circuits for effecting phase modulation of a carrier wave by combination of two or more separated phases of the carrier modulated in amplitude by separated phases of the signal, as in Specifications 534,757 and 538,775, [Group XXXIX]. The invention consists in density-modulating the electron beam at carrier frequency and deflecting it so that it traverses two or more anodes which are so cut away or screened that the said amplitude-modulated carrier oscillations are constituted by, or can be derived from, the anode currents. Fig. 1 shows a cathode-ray tube 1 with a carrier source 8 connected to the density-modulating grid 5. The accelerating electrodes 3, 4 are arranged to produce a flat electron beam 15, Fig. 2, which is swept across the anodes 11<SP>1</SP>, 11<SP>11</SP> by deflecting electrodes 9 connected to the signal source 10. The anodes 11<SP>1</SP>, 11<SP>11</SP> are cut away to sinusoidal shape as shown in Fig. 2 with a 90 degrees phase displacement so that the currents to the respective anodes vary according to the sine and cosine of the instantaneous modulating voltage. The amplitudemodulated carriers constituting the anode outputs are given a phase separation of 90 degrees by the networks 6, 7 and are then combined at the output terminal with unmodulated carrier from the source 8. The carrier may be generated by back-coupling connections to tube electrodes 3, 5. The carrier phases are indicated in Fig. 3 by the vectors 6, 7, 12, the modulated amplitudes of 6 and 7 varying as shown by the adjacent curves. The combined output at 13 is a phasemodulated carrier. In a three-phase modification illustrated by Fig. 3a, three anodes are used with a phase difference of 120 degrees in their contours and with their anode outputs combined after appropriate phase shifts of the carrier. One or more of the targets 11<SP>1</SP>, 11<SP>11</SP> may operate as screens allowing the beam to pass to anodes situated behind them. The flat beam may be separated into two or more portions directed to the respective anodes 11<SP>1</SP>, 11<SP>11</SP> and each separately modulated by a different phase of the carrier, applied either to density-controlling grids, or to the anodes. The anode outputs may then be combined without further phase-shifts. In a further modification, only a single anode 11<SP>1</SP> is employed, traversed by two separate densitymodulated flat beams 15, 16, Fig. 2, spaced apart a distance giving the required phasing effect as they cross the shaped anode 11<SP>1</SP>. The carrier wave may be applied in series with the modulating source 10 instead of applying it to the grid 5, and the flat beam may be produced by rapid deflection of a pencil by electrodes arranged in a plane perpendicular to that of the electrodes 9 and energized by an auxiliary high-frequency source. Deflecting coils may replace the deflecting electrodes. In the modified arrangement, Fig. 2a, the anode, or a screen placed in front of the anode, is formed with rows of circular apertures, one row being displaced a distance equal to one quarter of the distance between the centres of adjacent apertures, and equal to the radius of each aperture. The beam width Y is equal to the aperture diameter as shown in dotted lines, and the distribution of electron density in the beam is as shown at X.