| 摘要 |
1,177,010. Automatic phase control systems. C.I.T. COMPAGNIE INDUSTRIELLE DES TELECOMMUNICATIONS. 4 July, 1967 [26 July, 1966], No. 30759/67. Heading H3A. A variable frequency oscillator 30 is stabilized at a selected harmonic of a stable generator 10 by means of an auxiliary oscillator 58. Initially, the oscillator 30 is controlled by a sweep generator 61 until its frequency is near that of oscillator 58 when an output from mixer 51 passes to a logic circuit L which changes over the switch unit K so that oscillator 30 is controlled by the output of a phase discriminator 40 supplied with inputs from a mixer 20 and direct from harmonic generator 10. If the frequency is to be changed, the crystal 59 of oscillator 58 is removed, and a detector in the logic unit L detects the absence of oscillations and restores the switch unit K to its second position. In practice the switch unit K is a bistable circuit (56, Fig. 2, not shown) controlling the bias across a diode which short-circuits the output of the phase discriminator. When the diode is reverse-biased, the output of the discriminator is fed to a varactor diode in the oscillator 30 and also reduces the power supply to a multivibrator (61) forming the sweep generator so that it does not oscillate. The logic circuit L may comprise an AND gate (54) fed from mixer 51 and also from a monostable (53) triggered by the output of a band-pass filter (52) supplied from the main mixer 20. |
