Patent GB-451223-A (GB)
Title: Improvements in and relating to wireless and like receivers, and tuning control apparatus for use therewith
IPC: H03J1/18
Filed: 1935-01-30
Abstract: 451,223. Wireless receiving systems. COOPER, A. H., Appledore, Syke Ings, Iver, Buckinghamshire. Jan. 30, 1935, No. 3099. [Class 40 (v)] In a remote-control tuning system for a wireless receiver, final accuracy of tuning is obtained by means of a magnetic brake actuated in dependence on received signal strength and acting on the tuning control shaft, the action of the brake being prevented except when the receiver is tuned to the desired signal. In the arrangement shown in Fig. 1 (Prov.), the shaft 16 of the tuning condenser unit 1 is operated either manually or, as shown, by a reversible A.C. motor 17. Remote control is effected by a bridge arrangement comprising a potentiometer 7 at the remote point and potentiometer 11 at the receiver, the slider of the latter being driven by the tuning spindle 16 ; a relay 9 across one bridge diagonal actuates contacts 23, 24, 25 which control forward or reverse operation of motor 17. Part of the output from the I.F. amplifier 2 is passed to a circuit 26, sharply tuned to the I.F. and rectified at 27. When the receiver is exactly in tune with the desired signal, relay 28 closes the energizing circuit of relay 31 through armature contact 29 ; the armature 32 of relay 31 applies a brake 33 to the disc 34 on tuning shaft 16 and at the same time contact 35 opens, thereby removing a short-circuit on the loudspeaker 6 at the remote point. Remote control of waveband switching is effected by switch 15 which puts resistance 14 in parallel with resistance 7, the latter being in series with relay coil 13 and battery 12 at the receiver. The resulting increase in current operates relay 13 to actuate switch contacts 36. Remote control of volume is obtained by a potentiometer 37 in shunt with the remote loudspeaker 6. The switches 38, 39, 40 effect the changeover from remote to local control, the circuit of battery 12 being thereby interrupted The inclusion of resistance 41 into the brake energizing circuit enables the tuning to be turned through an undesired station against the action of the brake. Fig. 1 (Comp.) shows a method of causing the brake to be automatically released after a predetermined interval thus overcoming the drawback of the above system of moving the tuning member against the brake. Signals from the I.F. amplifier 2 are applied through a sharply tuned circuit 26 to a diode-triode 44 the bias on the triode varying with signal so that its anode current falls sharply when the receiver is exactly tuned. The resultant positive pulse charges up condensers 49 and 55, and the corresponding increase in anode current of triode 56 actuates the brake magnet 28. The charge on 49 leaks away across resistance 52 and the brake is released. If the receiver is now detuned while signals are still received, a negative pulse appears on the anode of triode 44 ; diode 50, 53 prevents condenser 49 from becoming negatively charged. Diode 50, 54 prevents condenser 55 from charging up except by potential across resistance 52 which persists for more than a predetermined period. The time constant of 55 and 58 is such that the brake is not actuated when the receiver is tuned rapidly through a number of stations. The time constant of the brake circuit may be increased by an inductance in series or condenser in shunt with the relay winding 28. A mechanical or piezo-electric resonator may be employed in the circuit 26. Specification 451,346 is referred to.