Patent GB-631732-A (GB)
Title: Improvements in or relating to push button control of signal-seeking receivers
IPC: A63F9/06
Filed: 1946-08-21
Abstract: 631,732. Automatic tuning control. COLONIAL RADIO CORPORATION. Aug. 21, 1946, No. 24900. Convention date, Oct. 5, 1944. [Class 40 (v)] An automatically tunable receiver of the type which is progressively tuned over a band by means of an electric motor until a signal is tuned in, is adapted to allow pre-selection of a particular station. For this purpose an oscillator having a frequency adjacent to the desired signal is coupled to the receiver which is so de-sensitized that the tuning passes unwanted signals and tunes to the oscillations. The oscillator is then automatically switched off and the tuning is advanced by the motor to the adjacent signal. The Figure shows a, superheterodyne receiver having a converter 3, an oscillator 5, an I.F. amplifier 6 and a detector stage 7. Tuning is effected by means of a motor 26 which revolves in one direction only and the operation of the receiver is controlled by pushbuttons 17, 11, 12, 13; button 17 initiates normal signal searching while buttons 11, 12, 13 cause the receiver to tune to particular stations. If search button 17 is depressed, contact 21 momentarily opens breaking the circuit to earth (via read 42) of thyratron 28. Relay 29 in the anode circuit therefore releases and its backcontact 29b causes the loud-speaker 8 to be short-circuited while its forward contact 29f releases relay 30. Back-contact 30b1, which is now made, completes the circuit for the motor which causes the receiver to tune over the band until a signal is tuned in, when the output from the cascade arrangement of limiter 9 and carrier filter 10 applied to the grid of the thyratron is sufficient to cause the thyratron to fire and thus to operate relay 29. The forward contact 29f of the relay operates relay 30 to disconnect the motor at contact 30b1, and the back contact 29b removes the short-circuit from the loud-speaker. If button 17 is again pressed the receiver tuning again advances to the next signal. If a station selecting button is depressed, say button 11, contact 21 momentarily breaks to start the motor as before but an additional button contact 22a, which momentarily operates, initiates oscillation of valve 15 by short-circuiting its cathode resistance 37, and a further contact 11a tunes the oscillator by means of condenser 11b to a frequency 6 to 10 kc/s. nearer to the beginning of the tuning range than the desired signal. The bias which is developed at grid 15g when valve 15 oscillates is applied to the A.G.C. line through resistor 25 to decrease the sensitivity of the receiver such that normal signals will not stop the motor. The more powerful local oscillation fed to the receiver via coupling coil 14a and condenser 40 will, however, cause the motor to stop, when the consequent operation of relay 30 disconnects the oscillator H.T. supply at contact 30b2 and also causes a pulse to be applied from H.T. through contact 30f2 and condenser 34 to extinguish the thyratron. The resulting release of relay 29 restarts the motor which then advances the tuning of the receiver to the adjacent signal. Although relay 30, which also operates, reconnects the H.T. to the oscillator, oscillation will not recommence without the starting impulse from button contact 22a. Similarly, the reapplication of H.T. to the cathode of the thyratron will not extinguish it because condenser 34 will not be sufficiently discharged. In " normal " operation (initiated by button 17) the extinguishing of the thyratron by the operation of relay. 30 is prevented by surgeabsorbing condenser 19 which, however, is disconnected at contact 20 when the station selecting buttons are operated. The pushbuttons and tuning oscillator may be located remotely from the receiver.