GB1468191A - Transmitter receiver set for radio communication systems - Google Patents

Abstract

1468191 Automatic level control; radio signalling COMPAGNIE INDUSTRIELLE DES TELECOMMUNICATIONS CITALCATEL 17 June 1974 [15 June 1973] 26697/74 Heading H4R and H4L In a transmitter receiver for a radio communication system an attenuator in the receive channel is adjusted during reception to maintain the output level corresponding to a received signal substantially constant, at the same time a signal is transmitted back which, received at the station originating the originally received signal, lowers the transmission level by an amount bearing a fixed relation to the level by which the originally received signal exceeded a reference level. As described a received signal exceeding a threshold level causes the transmission level of the other station to reduce by half the excess in dB of received signal over the threshold level. The arrangement is said to reduce interference between pairs of stations engaged in separate conversations. Preferred embodiment, Fig. 2. The received signal passes through a variable attenuator 11, amplifier 71, mixer 73. If amplifier 74, detector 75, and audio amplifier 76 for reproduction on receivers 14. Calling signals or the reply signals of a station being called are tapped off after the detector 75 and recognized by decoder 89 which opens gate 79, to allow the carrier level of the received signal to pass to a threshold amplifier 80, and operates a logic circuit 90 to 95 which generates timing signals for the gain setting operation. If the carrier level exceeds the threshold set in amplifier 80 the attenuator 11 is adjusted to restore the signal level substantially to the reference level. At the same time the excess over the threshold is quantized at 83 and causes the generation of a digital code in coder 84 which is fed via gate 61, modulator 64, filter 65, amplifier 66, attenuator 33 and RF amplifier 67 to the duplexer 2 for transmission as a transmission level setting signal. At the other station participating in the call the level setting signal is detected by decoder 97 and sets an A to D converter 98 to produce a reference level to comparator 69, to the other input of which is applied the transmitted signal so that the comparator output adjusts attenuator 33 to reduce the difference between the transmitted level and the reference level substantially to zero. As shown the references 93, 94, 95 are monostable triggers providing timing signals for the various operations which take place at the start of each connection, 60 is gate which admits calling or reply signals to the transmitter channel, and 31 is a microphone for the conversation signals.