| 摘要 |
1,205,728. Compandor systems. PHILIPS ELECTRONIC & ASSOCIATED INDUSTRIES Ltd. 14 May, 1969 [17 May, 1968], No. 24532/69. Addition to 1,137,457. Heading H4R. In a compander system of the type described in Specification 1,137,457 in which the degree of compression given to a signal is signalled as frequency modulation of a pilot signal, which is also transmitted through the compandor system so that restoration of the pilot signal to the standard level is controlled both by the frequency and the amplitude of the pilot signal, the control signal which varies the degree of compression at the transmitter is applied to the variable gain network via a delay network which has a delay equal to the difference in time taken for the signals to travel from the compressor to the expander, relative the time taken for the control signal to travel from the frequency demodulator controlling the compressor at the transmitter to the frequency demodulator controlling the expandor at the receiver. The transmitter, Fig. 1, is identical to that of the parent Specification referred to above except for the addition of the delay network 53 in the control line of the compression network 9 and the addition of a frequency transposition by modulator 47 in the pilot signal feed, which arrangement increases the accuracy of the frequency modulation by allowing the use of a low-frequency oscillator 31. The receiver, Fig. 2, is the same as that of the parent save for an additional expandor network 54 connected in front of the normal expandor network 21 and controlled directly by the output of the frequency demodulator 39, and a frequency transposition including modulator 50, the inverse of that in the transmitter. |
