Patent GB-517068-A (GB)
Title: Improvements in or relating to radio receivers
IPC: H03J5/14
Filed: 1938-07-11
Abstract: 517,068. Wireless receiving sets. MARCONI'S WIRELESS TELEGRAPH CO., Ltd. July 11, 1938, No. 20430. Convention date, July 10, 1937. [Class 40 (v)] [Also in Group XXXVIII] In radio receiving apparatus having a motordriven tuning device, the motor shaft moves axially upon energization of the motor to effect mechanical coupling to the tuning device and to operate contacts which render inoperative automatic tuning correction means whilst the motor is running. The motor may be controlled for tuning to particular stations by pushbuttons arranged both on the set and at a remote point. The contacts controlled by the motor shaft may also serve for muting during tuning. As shown, the tuning-condenser shaft 8 may be set manually by a shaft 9 or may be driven through a coupling pinion 28 through gearing 27 from the shaft of a motor 21. The coupling pinion 28 is mounted on a pivoted member 30 controlled through a pin-and-slot connection by a switch shaft 33 in such a way that when the switch 42 is moved three steps from the position shown into the position for manual tuning the pinion 28 is withdrawn. A pointer 12 moving on a guide 18 and controlled by a cord 16 passing over a sheave 17 on shaft 8 indicates the station selected. When the motor 21 is energized, axial movement of the motor shaft 46 causes a pin 48 to engage with a curved arm 49 on pinion 22 to effect mechanical coupling to shaft 8 and also by means of a collar 55 closes contacts 50. The motor circuit may be closed at contacts 75 by operation of any of a series of push-buttons 67, 68 &c., the contacts being self-locking by means of catches 80, 81 and these catches being interlinked so that operation of one releases any others. The motor circuits include springs 70 engaging rings 71, each ring having a small insulating segment 72a, Fig. 5, so that the circuit is broken at a certain setting appropriate to the push-button operated. The rings 71 are mounted in an assembly 86 coupled to the condenser shaft 8 by a flexible coupling 88, the rings being individually adjustable by inserting a key 94 into a slot 73 to hold a particular ring stationary and adjusting the condenser manually until the desired station is accurate tuned in as shown by a tuning indicator 11. The rear end of the assembly 86 has an arm 89 controlling a switch 91 for reversing the direction of the motor at each end of the condenser range. Fig. 5 shows the circuit arrangements. With the switch 42 in its first position as shown, the motor circuit 116 is completed from ground 130 over one of the rings 71, one of the remote-control pushbuttons 137, link 141, motor windings 115, 116, the direction of current in the latter being dependent on the position of the reversing switch 91, to supply winding 120. Contacts 50 controlled by the motor shaft ground the automatic-frequency-control lead 164 to render the control inoperative whilst the motor is running and also ground the grid of the audiofrequency amplifier 182 to prevent output from the set. In the second position of switch 42, the push-button contacts 75 on the set are connected in place of the remote-control contacts 137 and an indicating lamp 144 is lit. In the third position of switch 42, for manual tuning, the motor is disconnected, the pinion 28 is disengaged, the automatic frequency-control is suppressed at link 149, and lamp 145 is lit.