Patent GB-685352-A (GB)
Title: Improvements in the transmission of signals by electric waves
IPC: H04B14/04
Filed: 1951-02-23
Abstract: 685,352. Cathode-ray tubes. RADIO CORPORATION OF AMERICA. Feb. 23, 1951 [March 1, 1950], No. 4482/51. Class 39(i) [Also in Group XL(c)] In an electric signal transmitter comprising a plurality of power devices capable of supplying carrier waves to an output circuit, and a control means for selectively determining the number of said power devices which are operative to deliver carrier waves to the output circuit, this number depending on the magnitude of the intelligence signals (see Group XL(c) ) the control means comprises a cathode-ray tube level sorter 24, Fig. 1, provided with a gun 26 of a known type which projects a beam of electrons in the form of a horizontal line 40. The output of the signal source 18 is applied through an amplifier 20, whose output voltage is proportional to the square of the input to provide a voltage proportional to the power level of the signal, to the deflection plate 22 of the tube. The no signal position of the beam is adjusted to the dottedline 28 by means of the potentiometer 30. Three equally wide vertical strips 34, 36, 38, of different height are mounted on the inner face of the tube, so that when each is struck by the beam it produces a given voltage, the bottom of the strips being located at the point where the beam is deflected when the signals are at their their maximum amplitude. The strips 34, 36, 38, are connected to the keying circuits 10, 12, 14 respectively. When the beam 40 is between the dotted line 28 and the top of the strip 34 none of the power amplifiers 4, 6, 8, supply R.F. energy from the carrier source 2 to the aerial, but when the signal is large enough to deflect the beam to strip 34 the power amplifier 4 supplies R.F. energy to the aerial. Similarly power amplifiers 6 and 8 are successively turned on as the beam is deflected downward to impinge on the strips 36 and 38. In an alternative arrangement Fig. 4, the difference between the quantized output signal and the signal that varies in accordance with the intelligence to be transmitted is utilized to modulate a power amplifier whose output is added to the stepped output signal. The R.F. source 120 supplies the power amplifiers 122, 124, and 126, and is controlled by the keying circuits 128, 130 and 132, respectively, the keying circuits being controlled by the voltages developed by the target strips 134 136 and 138, forming part of a cathode-ray tube 141 whose beam 142 is deflected in accordance with the amplitude of the signal from the source 144. The target also comprises the four triangular shaded portions 143 which are connected together and from which the residue signal is derived, the zero signal position of the beam being adjusted to coincide with the apex of the top triangular portion and the maximum signal being sufficient to deflect the beam to the base of the bottom triangular portion. As the beam moves down a triangular target 143 the area of the beam 142 intersected by the target increases, and the voltage on the lead 139 correspondingly increases, this voltage being utilized to modulate the power amplifier 140. The outputs of the amplifiers 122. 124, 126 and 140 are combined in the aerial 176 by means of the bridge networks 149, 156 and 174. The cathoderay tube may be arranged as a quantizer, Fig. 4a (not shown). The three target strips are connected together to form a step-shaped target, which is connected via a single lead to the three keying circuits, and in order to operate a key on each successive level of the quantized wave thus produced the keys are separately biased by means of a potentiometer.