| 摘要 |
1,193,476. Automatic phase control systems. WESTERN ELECTRIC CO. Inc. 4 Oct., 1967 [5 Oct., 1966], No. 45196/67. Heading H3A. In a differential phase modulated data transmission system as described in Specification 1,193,475 the local oscillator at a receiver or relay station is phase locked to a mean frequency by comparing the sum and difference outputs of the demodulator. The intermediate frequency is fed to a hybrid junction (13, Fig. 1, not shown) providing two outputs fed directly and via a one bit delay respectively to two inputs of a further hybrid 14; this produces a sum output fed to detector 18 and a difference output fed to detector 19. These sum and difference outputs are sampled by means of directional couplers 22 and 23 feeding the phase sensor which produces an output voltage non- trolling the frequency of the local oscillator. The sum and difference outputs a and b are 90 degrees out of phase and are shifted to 180- degree phase difference by a delay network and fed to a hybrid junction 70; the output ports of the hybrid feed amplitude detectors 56 and 59 the outputs of which are subtracted in unit 57 to provide an output voltage. With the system so far described (illustrated in Fig. 5, not shown) the sign of the output voltage depends on the information signal; this can be prevented by attentuating one of the signals a or b, which is done in the arrangement shown by the 10 db. couplers 73 and 74, and by providing a second sensor (based on hybrid 71) the output of which is combined with that of the first in unit 72 to give the final output. |
