GB1302517A - - Google Patents

Abstract

1302517 Detector circuits TELEVERKETS CENTRALFORVALTNING 30 Jan 1970 [30 Jan 1969] 4697/70 Headings H3Q and H3T In a detector for detecting the envelope of a modulated carrier current A a modulated carrier current is passed through at least two parallel branches 1, 2, the phase of the current is shifted in one of the branches 1 but not the other, the positive and negative half periods of the current in the branches are added respectively in a combined adding and rectifying device D3 D4, D1 D2 and a first amplifying device F2 alternately amplifies the sum of the positive and negative half periods. The first amplifying device F2 is activated from gate circuits Tr1, Tr2 which are actuated by a second adding device H, F1 which adds the currents in the branches whereby an output signal Ut is obtained from the first amplifying device F2 which corresponds to the envelope of the modulated carrier current. As shown the input signal A feeds via paths 1 and 2 the amplifier F1 which produces square waves at its output K which makes the transistors Tr1 Tr2 alternately conduct. When the output pulse from F1 is negative Tr1 is turned off and Tr2 is turned on and positive half periods are passed via diodes D3, D4 to the positive in phase input of the amplifier F2 which produces positive signals at the output Ut. Similarly when the output pulse from F1 is positive Tr2 is turned off and Tr1 is turned on and negative half periods are passed via diodes D1, D2 to the negative phase reversing input of the amplifier F2 which produces a positive signal at its output Ut. Capacitors C1, C2, C3 and resistors R1, R2, R3 may be added to act as filters so as to further improve the output fidelity. The output Ut may be connected to an instrument to compare the output signal with an upper and lower limit and if the voltage of the received signal is not within these limits a fault is registered. The detector circuits may be used for detecting the envelope of a frequency shift or frequency or phase shift modulated signal passed along a transmission line, such as a telephone line.