GB660023A - Automatic receiver tuning in multi-channel transmission systems - Google Patents

Abstract

660,023. Automatic frequency control systems. PATELHOLD PATENTVERWERTUNGS & ELEKTRO-HOLDING AKT.-GES. Oct. 18, 1948 [Oct. 17, 1947], No. 27037/48. Class 38 (iv). A radio receiver for multi-channel pulsesignalling systems is provided with automatic tuning control. The incoming pulsed carrier is passed through the usual frequency-changing stage to an I.F. amplifier 1, Fig. 2, which feeds a frequency discriminator giving an output in the form of short positive pulses, Fig. 1, or short negative pulses, according to the sense of the mis-tuning. These are applied through a condenser 23, which suppresses the D.C. component, to an amplifier 3, the output of which is fed to a peak rectifier 12 and condensershunted load resistor 25. A fraction of the output voltage from the valve 3 is fed from a potential divider 14 to the grid of a valve 4 which is thus excited at the same amplitude as the valve 3 but with inverted polarity. The inverted pulses are peak rectified by diode 13 and load 26. Resistors 25, 26 are connected in the grid circuits of valves 3a, 4a respectively, and apply positive voltages equal to the amplitudes a, b, Fig. 1. The larger voltage b opens the valve 3a and allows current to pass to a relay 8 to close a switch 9 for correcting the tuning. The smaller voltage a does not open the valve 4a owing to the provision of a bias resistor 11 in the common cathode lead of the valves 3a, 4a. If the mis-tuning is in the opposite sense, valve 4a opens and relay 7, 10 operates to effect correction. In Fig. 4, the pulses are applied with the same polarity to the double valve R, and the two outputs are applied to two oppositely-poled diodes 19, 20 having their load resistors 25, 26 connected in series so that the voltage across the output terminals 21 represents the difference between the absolute values of a and b and can be used to control an amplifier connected in series with a frequency control device. In a further modification of Fig. 2, the valves 3a, 4a are replaced by hexode valves, the common bias resistor 11 is omitted, and the pulses from one of the anodes of valves 3 or 4 are applied to oppositely-poled rectifiers which apply to the outer grids of both hexode valves a negative voltage equal to the sum of the absolute values of a and b, Fig. 3 (not shown).