GB1039664A - Improvements in or relating to telecommunication systems - Google Patents

Abstract

1,039,664. Line transmission systems. STANDARD TELEPHONES & CABLES Ltd. June 11, 1964, No. 24248/64. Heading H4R In a telecommunication system a speech channel 1 (Fig. 1) is terminated by a recording head 2 co-operating with a delay device 3 such as a rotating magnetic drum, a magnetic disc or magnetic tape loop. Speech recorded on the delay device 3 is read out by a head 4 and fed to a channel 7, after a delay preferably exceeding 100 milliseconds. Channel 1 is also connected to a detector 8 for detecting periods of silence in incoming speech. The detector output is fed as a stepped waveform to a timing and control circuit 9. This has two timing circuits. The first produces an output which lasts for a period equivalent to the delay of device 3 and commences when a speech burst begins. The second produces an output which also lasts for a period equal to the delay but starts when the speech burst ends. When a period of silence occurs in the incoming circuit the second timing circuit is started. If the period of silence is still present at the end of the timing period a switch 6 is operated changing channel 7 from link 5 to a data store 10. Circuit 9 also initiates transmission of data from store 10. When the silence in incoming speech ends, the silence ends on link 5 at a later time equal to the delay. The first timing circuit output switches the outgoing channel 7 back to the link 5 as the delayed period of silence ends and it also stops the transmission of data from store 10. The timing periods may be slightly altered to obviate undue clipping. Supervisory signals to advise the receiver of changeover are controlled by the two timing circuits. The magnetic drum may carry several tracks for use with several channels. The outgoing channel may serve more than one data source, the control circuit being arranged to connect the channel to the data sources one at a time on a priority basis. A 4-wire " Go " and " Return " system may be arranged so that a conversation and two data messages can be handled together.