Patent GB-561977-A (GB)
Title: Improvements in or relating to tuning arrangements for thermionic valve circuits
IPC: H03G5/26
Filed: 1942-12-08
Abstract: 561,977. Automatic control systems. STANDARD TELEPHONES & CABLES, Ltd., and GOLD, W. A. Dec. 8, 1942, No. 17428. [Class 38 (iv)] [Also in Group XL] Tuned circuits are automatically brought into resonance with the carrier wave applied to them by supplying the rectified current output of the tuned circuit to an electromagnetic device which varies a reactance.in the tuned circuit until the attainment of resonance produces a maximum. Rough tuning may first be accomplished by a motor-driven variable reactance also subject to automatic control. The tuned circuits of several amplifying stages, and also the aerial circuit, of a radio transmitter may be automatically tuned in turn under the control of a multi-contact switch. As shown in Fig. 1, the carrier is applied to the grid of an amplifier V1 coupled to a second amplifier V2 both valves having tuned anode circuits LC. The valves operate under Class C conditions, and the input voltage applied to the valve V2 is sufficient to produce a rectified grid current through a resistance r. The resulting voltage is amplified at CA and operates a meter M, the movement of which adjusts the capacity C or the inductance L of the tuned circuit LC until the rectified grid current is a maximum whereupon the control ceases. The meter M may alternatively be controlled through amplifiers by the voltage across a resistance and condenser in the cathode lead of the valve V1, Fig. 2 (not shown). In Fig. 3, an aerial circuit is tuned in two stages, a rough tuning being effected by a motor D adjusting the inductance L1 followed by a fine tuning by the meter M3 operating on the inductance L2. A rectifier V7 and resistance r3 are connected between the aerial A and earth. The control voltage across r3 is amplified at CA and when resonance is reached a relay RY operates to open a contact ry2 and stop the motor D; which had been started by closure of a switch SS. This preliminary tuning carries the adjustment slightly beyond the resonance point, and a fine adjustment in the reverse direction is effected by the meter M3 which is brought into circuit by the opening of a contact ry1 by the relay RY. Fig. 6 shows a device for ensuring that the relay operates only on the peak of the control voltage, which is applied at 1, 2 to a pair of oppositely-connected rectifiers V8, V9 with the relay RY2 connected across a resistance R8 between the anode of rectifier V8 and the cathode of rectifier V9. So long as terminal 1 is positive and rising in voltage, condenser C2 is charged through the valve V8. When the peak is passed, valve V9 becomes conductive and the condenser discharges through the relay RY2, which should be self-locking and released when the tuning is complete. The amplifier CA for the control voltage is shown in Fig. 4, the input resistance r1 being connected to the grid of a valve V4, which has a diode V5 and a resistancecondenser combination R2, C1 connected across its anode circuit. The resistance and condenser are in the grid circuit of a further valve V6 which has the tuning-adjusting meter M1 in its anode circuit. So long as the control voltage across rI is rising, the diode V5 is conductive and the voltage on the condenser C1 rises until the meter M1 has produced resonance. If the meter M1 should overshoot slightly, the resulting drop in the control voltage will not affect the voltage on the condenser C1 and the tuning will be arrested. The same system V4, V5, V6 may be used for tuning several stages of a radio transmitter by switching the input and output to the respective resistances r1 ...r3, and meters Ml ... M3. At. each movement of the switch, a contact S is closed to discharge the condenser C1. In one position of the switch, a contact such as SS, Fig. 3, is closed to start the motor D for effecting a rough tuning of all the transmitter stages, which are subsequently accurately tuned in successive positions of the switch.