Patent GB-431702-A (GB)
Title: Radio receivers
IPC: H03J5/06
Filed: 1934-01-15
Abstract: 431,702. Wireless receiving systems. RADIO FREQUENCY LABORATORIES, Inc., 708, Main Street, Boonton, New Jersey, U.S.A. Jan. 15, 1934, No. 1417. Convention date, Sept. 29, 1933. [Class 40 (v)] [See also Group XXXVI] The suppression of noise and undesired signals when tuning from one preselected transmission channel to another is effected by disabling the receiver and automatically restoring normal transmission only when the tuning means is set to positions corresponding to the carrier frequencies of the desired channels. An independent manual control may be provided to permanently cut out the receiver disabling means and allow the tuning means to operate in normal manner. In one embodiment, Fig. 1, the tuning control 11 of a receiver carries a contact 18 which, when the control is set to receive a predetermined transmission, engages one of the contacts 19, to short-circuit the resistance 15 which removes a prohibitive negative bias normally applied to the control grid of the last I.F. amplifying valve 3 of the receiver. The resistance 15 together with a volume control resistance 13 form part of the cathode resistance of valve 3 and carry biassing current from a source + B supplied through resistance 14. An independent switch 16 may be provided to short-circuit the resistance 15 permanently and allow the receiver to be operative at all positions of the tuning control 11. In modifications, the muting means may comprise a high resistance in the cathode circuit of a radio frequency amplifier, Fig. 2, (not shown), or the switching means may operate directly to complete the loud-speaker circuit at the predetermined positions of the tuning control, Fig. 3, (not shown). The control means may comprise a tuning dial 21, Fig. 4, provided with adjustable contact members 30 each corresponding in position to a desired transmission, the pointed resilient tips 30<1> of which are adapted to contact with a fixed contact 33, Figs. 4 and 5, mounted on and insulated from a bracket 34 which is so shaped as yieldingly to locate the moving member exactly in the required tuning position. The contact 33 is connected to the junction of resistances 13, 15, Fig. 1, the remainder of the metal parts being earthed. In a modification, Figs. 7 and 8, the tuning dial 37 carries a single resilient contact 36 and co-operating contacts 38 are provided which may be moved in the slot 43 on the fixed support 39 and clamped in the required positions by screws 40. The co-operating contacts are shaped as shown so as accurately to locate the tuning control in the correct position. In a further modification, Figs. 12, 13 and 14, the translucent tuning dial 50 is fixed and the tuning spindle 44 carries an arm 45 provided with a rigid contact 46, like the contact 33 of Fig. 5, which co-operates with resilient fixed contacts 47, the tips 49 of which are adapted to be brought into close proximity to adjacent contacts when two desired stations are closely spaced. The fixed contacts 47 may be slid to their required position along the arcuate slot in a fixed member 48. The arm 45 also carries a pilot lamp 51 in a housing 52, the upper wall 53 of which is translucent and provided with a slot or mark to cast a shadow on to the dial 50 indicating the setting of the tuning spindle. Slips 55 marked with the call letters of desired stations may be provided and yieldingly held in place on the dial 50 by a resilient clamping strip 56.