GB1159887A - Sequential Frequency Combiner for Frequency Standard Systems - Google Patents

Abstract

1,159,887. Automatic phase control systems. VARIAN ASSOCIATES. 24 Nov.. 1967 [9 Dec., 1966], No. 53663/67. Heading H3A. A frequency standard apparatus comprises means for selecting one of a plurality of standard frequency generators 1-4 as a master standard and transmitting its output to the output terminal, means for phase-locking the other generators to the master, and means for selecting another master if the first one should fail. As shown one of the generators is connected through a gate 6-9 to a line 5 which is connected to an output terminal 1 via a crystal filter 17 and amplifier 20; a second output channel to terminal 2 guards against failure of the crystal 17. The signal on line 5 is inverted in unit 21 to provide the reference signal for phase detectors 22-25, the outputs of which are fed to a control circuit 31 for controlling the respective generators. The outputs of the phase detectors are monitored by a threshold circuit 32 which detects when a predetermined phase difference (e.g. 12 degrees) is exceeded by any of the generators; in such a case a corresponding lamp 33 is lit, and a signal is fed to programmer 15 to prevent that generator from being selected as master. The amplitude of the signal on line 5 is monitored in circuit 35, and if it is too low the programme unit 15 is activated to select a new master. In the example shown generators 1 and 2 are atomic standards which provide alarm outputs when synchronization is lost; these alarm outputs are fed to programme unit 15 to cause a change if that generator is the master or otherwise to prevent the generator being selected as the master. The programme unit 15 opens the gate 6-9 corresponding to the selected master and also energizes a corresponding indicator lamp 37. The crystal filters 17 and 18 should have a decay time greater than the switching time to ensure continuity of the output when the master standard is changed.