GB1289378A - - Google Patents

Abstract

1289378 Digital transmission systems SIEMENS AG 15 Sept 1970 [16 Sept 1969] 43959/70 Heading H4P Received signals are analysed for quality also amplitude and if both conditions are present (absent) for more than a determined time, receiving equipment is switched on (off). Parallel data transmitted by FSK is received at a terminal FL and passed normally through an amplifier VE, bandpass filters F1-F3 and amplifiers V1-V3 to demodulators and low pass filters D1-D3 which detect the transmission of frequencies fl-f4 of each group A-C. An analyser circuit AS analyses the quality of received data and determines the probability of a transmission fault, e.g. the code condition. If one frequency only is detected in each group a signal appears online 8 which is passed through a decoupling stage E to AND gate G together with voltages from amplifiers V1-V3, which if up to a determined level causes with an E input an output to be supplied through a delay ZG, e.g. an RC network to a bi-stable trigger K, e.g. a Schmitt trigger circuit which switches on the receiving equipment. In an improvement the spacing combination of the frequencies f1-f4 at the commencement of transmission may be monitored by arranging the circuit AS to apply a signal direct to gate G if, within the interval determined by the delay element, the spacing combination appears. In a further modification a fault signal on line 9 drives the outputs circuits of demodulators D1-D3 into a specific state so that parasitic voltages produce no output signals on lines 1-4 until commencement of transmission. Before transmission it is advantageous if the output lines carry the spacing combination so that this exists at the commencement of transmission. Telephonic reception may be applied via a hand set contact kl to a receiver FSP and a return " good " or " bad " acknowledge signal may be transmitted from RS through contact k2 in parallel with a low frequency speech transmitter amplifier PV.