GB748447A - - Google Patents

Abstract

748,447. Carrier transmission. GENERAL ELECTRIC CO. Dec. 23, 1953 [Dec. 27, 1952], No. 35782/53. Class 40 (4). [Also in Groups XL (b) and XL (c)] Impulses are transmitted over a radio link as interruptions in a 3 kc/s. modulation on the carrier and, on reception, distortion of the impulses is-reduced by using a limiting amplifier with selective negative feedback. The 3 kc/s. impulses are derived from 20 c.p.s. impulses at the transmitter and are re-converted to 20 c.p.s. impulses at the receiver. Impulses of 20 c.p.s. in line 1 are repeated on 3 kc/s. by a tone generator 6 which modulates a carrier in the transmitter 3. At the receiver, speech is passed to line 2 over transformer 9 and the 3 kc/s. impulses are fed through an amplifier 10. Valves 11 and 13 form two stages of amplification and are followed by a rectifying diode 47 and an output pentode 55 which controls a relay 54 and a 20 c.p.s. generator 65 connected to the line 2. A feed-back circuit from the anode of 13 to the cathode of 11 includes a valve 12 and a resistance-capacity blocking filter 32 the effect of which is to reduce the gain of valve 11 at frequencies other than 3 kc/s. Resistor 38 and condensers 36, 37 prevent self-oscillation of valve 12 at frequencies below the characteristic frequency of the amplifier. When relay 54 operates to repeat on impulse, contacts 66 open and reduce the gain of valve 13 so that the voltage fed to the diode 47 follows the curve 73, Fig. 2b, instead of curve 70. In Fig. 2b lines 72, 71 represent the control voltages at which relay 54 operates and releases.