Patent GB-509509-A (GB)
Title: Improvements in or relating to pre-selective tuning mechanisms for radio receiving systems and the like
IPC: H03J5/08
Filed: 1938-01-22
Abstract: 509,509. Adjusting wireless apparatus. MARCONI'S WIRELESS TELEGRAPH CO., Ltd., and BELL, D. A. Jan. 22, 1938, No. 2186. [Class 37] A preselector tuning mechanism comprises a plurality of abutment members (one for each station), fast with the tuning member, a corresponding number of co-operating stop members individually movable into and out of the paths of the abutment members, and selector members (keys, press-buttons, &c.), one for each station, for moving the corresponding stop members into operative position, any selector member upon operation moving the tuning member to a datum position against the action of a biassing device (spring) and then releasing it to move under its bias until stopped by the selected stop-member engaging the appropriate abutment member. If the pressure required to operate the selector members is excessive, a servo-device may be included to provide part or all of the necessary operating force. Manual tuning and preferably A.F.C. are provided. As shown, the tuning shaft 1 has rigid therewith a drum 2 on the periphery of which abutments 3-4 are formed, preferably along a helical line HP, by screws 5 adjustable in lugs 6. The stop members 9 are pivoted in a row on a rod 11 parallel to shaft 1 and each is biassed by a spring or weight 10 to the position shown. The station selector members or keys 14 are mounted to pivot about a common shaft 31, and each has pivoted thereto a member 15a having an extension 15 which, in the inoperative position of the key, extends over a bar 16 common to all the keys. Depression of any key first causes the corresponding extension 15 to depress the bar 16 which through a rack 17 and pinion 18 turns the tuning shaft 1 to the datum position against the action of a biassing spring 13. When the datum position is reached, the member 15a is rocked clockwise to release the bar 16 by a roller 20 engaging a cam surface 19. Simultaneously, the appropriate stop member 9 is rocked anticlockwise by the member 15a through a strip 22, and the tuning shaft 1 is now rotated by the spring 13 until stopped by the selected stop member 9 engaging the appropriate abutment screw 5, the screw entering a recess in the stop 9 to prevent movement of the latter when the depressed key is released. During depression of the key 14, any previously depressed key is released and the operated key is held partly depressed by the extension 15 engaging under the rack. A spring 21 biassing the member 15a anticlockwise may be omitted if the tension applied by the spring strip 22 is adequate. Two wave-bands are provided for, the waveband switch being actuated through a shaft 25 by a projection 30 or 30a on any key lever 14a depressing a bar 28 or 29 common to all the keys and rigidly connected to shaft 25 through arms 26, 27. Preferably, the receiver is muted during tuning by opening a circuit until an abutment member is engaged by its stop member, and an indicator showing the operator when a tuning operation has been completed may be similarly operated. Manual tuning. Two keys 14 marked " manual " and automatic" are provided having associated elements 15-21 similar to the stations keys, but no corresponding stops. These two keys operate on opposite ends of a rocker arm to oscillate a forked lever 32, Fig. 2, engaging a grooved collar 33. Thus, when the "manual" key is depressed, a gear-wheel 34 is moved axially to the left and the tuning shaft after being returned to the datum position and released advances until the end abutment 4, Fig. 2, engages a stop 38 on the gear-wheel when manual tuning may be effected by a knob 37. Modifications. The stop carrying levers and selector members may be arranged in several banks. Each selector key may have a solenoid associated therewith, or a single solenoid common to all the keys may be used to rotate the tuning shaft to the datum position, the stop members only being set mechanically. Alternatively, particularly for remote control, wave-band setting and the other two operations common to all keys may be effected electrically.