Patent GB-572006-A (GB)
Title: Apparatus for producing a control voltage for the tuning of radio transmitting and receiving apparatus
IPC: H03J7/02
Filed: 1943-05-11
Abstract: 572,006. Wireless transmitting and receiving circuits. PATELHOLD PATENTVERWERTUNGS- & ELEKTRO HOLDING AKT.-GES. May 11, 1943, No. 7503. Convention date, May 19, 1942. [Class 40 (v)] [Also in Group XXXV] A device for providing a control voltage for the tuning of radio transmitting and receiving apparatus with at least two variably-tuned oscillatory circuits is characterized by the feature that the detuning of at least two oscillatory circuits relative to the applied alternating frequency is varied periodically, and the alternating component of the rectified output of these circuits has its polarity reversed in the same rhythm as the detuning thereof, so that control voltages are produced, the signs of which correspond to the sense of the mean detuning, and the periodical detuning of one of the circuits is arranged not to be of the same phase as the periodical detuning of the other circuit which is in series with it. Fig. 3 shows the invention applied to a transmitter for frequency and amplitude modulation, employing a single generator G1 which can be frequeneymodulated at FM. The output e1 is amplified at A1 and passed through a tuned coupling circuit S2. The output e2 can be amplitudemodulated at AM and passed through a tuned coupling circuit S3 to further stages. Control voltages described according to the invention are employed to maintain the frequency of the generator G1 in tune with a standard tuned circuit S1 and simultaneously to maintain the coupling circuits S2, S3, in tune with the stabilized generator frequency. Part of the output from G1 is passed to the tuned circuit S1, the resonant frequency of which is varied periodically by a circuit Wl energized by a voltage V from a sub-audible or supersonic frequency oscillator N. The periodic amplitude variations in the output from S1 are detected in D1 to give an alternating voltage in which, after filtering and amplification at P1, V1 is intermodulated at M1 with the periodic detuning voltage V. The output p1 after smoothing at B1 provides a direct voltage q1, the size of which depends on the sense of the average detuning of the oscillator G1 relative to the circuit S1. This voltage is employed to restore the oscillator frequency to its correct value. The stabilized generator frequency is applied to coupling circuit S2 which is periodically detuned by the same voltage V to produce by a similar process a control voltage q2 dependent on the average detuning of the circuit S2. This voltage is applied to the circuit S2 to reduce the detuning. The same process is applied to correct any detuning of circuit S3. Since, however, circuits S2 and S3 are in series, it is necessary that the periodic detunings are not in phase and are preferably 90 degrees out of phase. This is ensured by a phase-shifter Q or by using different frequencies for the periodic detuning voltages. In a modification, Fig. 4 (not shown), the periodic detuning is effected by motor-driven condensers and the modulators such as M1 are replaced by commutators driven by the same motor. The invention may be applied to automatic tuning in superheterodyne receivers.