Patent GB-1055169-A (GB)
Title: Improvements in or relating to communication systems
IPC: H04B1/66
Filed: 1963-08-01
Abstract: 1,055,169. Bandwidth compression system. WESTERN ELECTRIC CO. Inc. Aug. 1, 1963 [Aug. 7, 1962], No. 30555/63. Heading H4R. In a communication system selected frequency components of a voice signal are delayed and transmitted in the gaps between the energy bursts of the remaining frequency components of the signal. In the embodiment of Fig. 1A the band 200 to 1700 cps. of the speech signal from transducer 1 is selected by a filter 11 and transmitted to the receiver while the band 1700 to 3200 cps. selected by filter 10 is transposed to the band 200 to 1700 cps. in, e.g. modulator 13A, and then delayed by the interpolator 14 so that it is transmitted during the gaps between the energy bursts in the original speech. At the receiver the original low frequency components, i.e. 200 to 1700 cps. are switched by a relay 19 through a fixed delay 17, having a delay equal to the maximum permissible delay given the high frequency components at the transmitter, while the original high frequency components are fed, via relay 19, to a synchronizing unit 15 where each energy burst is given a delay which, together with the delay provided at the transmitter, produces a total delay equal to the delay given the low frequency components in delay 17. The output of the synchronizer 15 is then transposed back to the original band of 1700 to 3200 cps. and added to the low frequency band in adder 18 and reproduced by receiver 2. The selection of the delay in the interpolator 14, the delay in the synchronizer 15, and the operation of switching relay 19 is controlled by a signal produced by squaring the rectified output of the transducer in the energy burst detector 12. By providing a frequency translator similar to 13A in the low frequency channel instead of, or in addition to, the one in the high frequency channel the output signal may occupy a reduced bandwidth having any desired centre frequency, Fig. 1B (not shown). Interpolator, Fig. 3.-The high frequency components of the speech are delayed until the end of the energy burst from which they originated in the tapped delay line 140. On the occurrence of an energy burst in the speech, energy burst detector 12 produces a signal output, which operates relay 147, which is maintained for the duration of the energy burst. The energy burst is also detected in detector 141-0 and the leading edge of the resulting waveform differentiated in 142-0 is applied over the contacts of relay 147 to reset the counter 144 so that all stages except 144-1 are in the 0 condition, while stage 144-1 is in the 1 condition and gate 145-1 is therefore open. When the signal appears at point P1 however the waveform is detected in 141-1 differentiated in 142-1 and applied over contacts on relay 147 to step the counter on to the next count, thus stage 144-1 is switched to its 0 condition and gate 145-1 closed before the signal, which has been delayed in delay 149-1, reaches the input of gate 145-1. The process is repeated, i.e. the signal arriving at a point Pn causes the gate 145n to be closed and gate 145n + 1 to open before the signal arrives at the input of the gate via the delay 149-n, until the energy burst ceases when relay 147 reverts to the condition shown and no further stepping pulses reach the counter, the gate last opened then remains open and the signal is fed out to the line delayed by, a period equivalent to the length of the energy burst. Should the energy burst exceed a predetermined maximum length, such that the signal appears at PN, and through a still operated relay 147 the differentiated leading edge steps on the counter so that stage 144(N+1) is in its 1 condition, gate 145(N+1) is opened, relay 148 is operated, and the high frequency burst is bypassed to earth. A burst of energy which exceeds the duration of the following gap will be terminated by the arrival, at detector 141-0 and detector 12, of the following energy burst, the leading edge of which, differentiated in 142-0, will reset the counter to the condition in which only gate 145-1 is open, the gate through which the high frequency band was being fed to the line 32 being closed. Receiver synchronizer, Fig. 4.-A delay, equal to the complement of the delay given to the high frequency components of the signal at the transmitter, is obtained in the receiver at tapped delay line 157, the appropriate tap being selected in the following manner. Marker pulses produced at the transmitter and having a positive value for the duration of the energy bursts in the original speech are applied, at the receiver, via a diode D1 and resistor R1 to charge a capacitor C1, the differentiated leading edge of the marker pulse having momentarily shorted capacitor C1 via relay 152 at the commencement of the pulse. The differentiated trailing edge of the pulse momentarily operates relay 153 to transfer a potential from capacitor C1 on to capacitor C3, the value of the potential being proportional to the length of the marker pulse, and hence the duration of the energy burst of the original speech and the delay given the high frequency components at the transmitter. This potential is applied via a polarity inverter 155 to an adder 156 fed also with a constant potential E so that the output of the adder, fed to the quantizers 151-0 to 151-N, is a potential proportional to the difference between the delay given the high frequency energy burst at the transmitter and the fixed delay given the low frequency components at the receiver (in delay 17, Fig. 1A). Each quantizer 151-0 to 151-N (Fig. 4) is responsive to a predetermined range of voltage within the permissible range such that the appropriate one of the gates 150-0 to 150-N is opened to pass the signal into the appropriate tap of the delay line 157 such that the high frequency burst at the output of the line is synchronized with the low frequency burst from the fixed delay.