Patent GB-469077-A (GB)
Title: Improvements in or relating to wireless and like receivers
IPC: H03J7/16
Filed: 1936-01-10
Abstract: 469,077. Wireless receiving systems. ROBINSON, J. Jan. 10, 1936, No. 903. [Class 40 (v)] An automatic tuning system for a superheterodyne radio receiver comprises two highly selective circuits S1, S4 Fig. 1, respectively tuned to frequencies slightly above and below the intermediate frequency, and two broadly tuned circuits S2, S3 having substantial response at frequencies 4-5 kc. on each side of the I.F., the outputs of S1 and S2, S3 and S4 being combined and rectified at D1, D2 to vary the tuning of the I.F. amplifier 13 in known manner by the coupling 17, 18 and potential source 16. Thermionic relays Rl, R2 in circuit with the broad circuits S2, S3 are controlled by circuits S1, S4 so that when the outputs from the sharp circuits S1, S4 are high the outputs from S2, S3 are interrupted or reduced and only circuits S1, S4 are operative to control tuning. Fig. 2 shows the response curves of the circuits referred to f1, f4 for S1, S4 and f2, f3 for the broad circuits S2, S3. The circuits S2, R1, S3, R2, may be dispensed with and S1 and S4 may then be piezo-electric crystals with shunt impedances to give asymmetric response on each side of the I.F. The arrangement described serves to prevent operation of the automatic tuning system by an interfering station of frequency, adjacent that desired, by virtue of the high control response obtained at the desired frequency. The provision of A.V.C. either in the receiver proper or as shown at 15 in Fig. 1, is a further safeguard ; also, in a further modification the selective devices S2, S3 may be designed to have zero response at the interfering frequencies, e.g. 9-10 kc. each side that desired, by associating with each a highly selective device tuned to the interfering frequency and combining the two in opposition. In a modification, Fig. 3 (not shown), two broadly tuned circuits such as S2 and S3 are coupled to the I.F. stage as in Fig. 1, and their outputs are combined after rectification to control a reversing relay in the circuit of a motor driving the tuning element of the local oscillator. One highly selective device tuned exactly to the I.F. controls a second relay, which opens the motor supply circuit when the receiver is exactly in tune. In a further modification shown in Fig. 5, a single broadly tuned circuit S3, tuned 4-5 kc. on one side of the I.F., is associated switchably with a condenser 60 which tunes it to a frequency 4-5 kc. on the other side of the I.F. The rectified output of D3 controls the power supply to motor 54 through relay 50. The tuning knob 62, controlling the oscillator and preselector circuits, is frictionally associated with a ring 61 pivotally attached to a change-over switch 58, 59. Rotation of 62 in one direction closes switches 59 and 58 to rotate the motor in one direction ; rotation of 62 in the other direction opens 59 and connects 58 to the contacts for reversing the motor 54. When the exact tune position is obtained the highly selective device S5 opens contact 64 through rectifier D5 and relay 63, thereby de-energizing relay 50 to open the motor circuit at 51. Specifications 407,057 and 465,515 are referred to.