Patent GB-684901-A (GB)
Title: Improvements in or relating to synchronising apparatus for electrical oscillations
IPC: H03L7/00
Filed: 1947-07-15
Abstract: 684,901. Phase difference measurements. SPERRY CORPORATION. July 15, 1947 [July 16, 1946], No. 6798/51. Divided out of 684,831. Class 37. [Also in Groups XXXV and XL (c)] A local oscillation is synchronized with a reference oscillation by a frequency or phasecontrol action exercised by deriving exploring pulses from the local oscillation and applying these, together with the reference oscillation, to a circuit which measures the instantaneous amplitude of the reference wave at the instant of occurrence of each exploratory wave and averaging these over a period long compared with that of the reference oscillation. When this averaged value is below a predetermined level the frequency or phase of the local oscillation is controlled in dependence on each discrete value of the measure and when the averaged value exceeds that level the control is exercised in dependence upon the averaged value. Fig. 1 shows an apparatus according to Specification 684,831, in which two such synchronizing circuits are employed for determining the time interval between pulse waves of the same repetition rate from sources 12, 13 of reference and delayed signals, a continuous reading being provided by an indicator 14. A high-frequency oscillator 15 is employed as a standard and is connected to a frequency divider 16 which reduces the generated frequency to approximately that of the reference and delayed signals. The waves of reduced frequency are supplied to a pulse wave generator 18 producing trigger pulse waves which are applied to a coincidence circuit 21, to which is also applied the reference signal from the source 12. The frequency control waves are supplied to a selective averaging circuit 24 through which there are two paths to the frequency control circuit of the oscillator 15. The first path is normally effective and permits the frequency control circuit of the oscillator 15 to respond to individual frequency control waves when the oscillator 15 is not synchronized with the source of reference signals 12. The second path is normally ineffective and is rendered effective in response to an average amplitude of the frequency control waves above some predetermined level in such manner as to disable the normal conductive path. The means for averaging the frequency control waves is inserted when synchronism has been established in order to maintain this condition with a high degree of discrimination against random noise and other interference. The frequency divider 16 is also connected to a phase shifter 27, the shaft 28 of which is coupled to the indicator 14. The phase-shifted waves are applied to a pulse wave generator 29 which is similar to the generator 18. The trigger waves from the generator 29 are fed to a coincidence circuit 31, corresponding to the circuit 21, to which are also applied the delayed signals from the source 13. The output from the circuit 31 is fed to an amplitude averaging circuit 33, the selectively averaged control waves from which are supplied to a servo amplifier 34 which energizes a motor 35 actuating the shaft 28 of the phase shifter 27. The selective averaging circuit 24 is shown in Fig. 2. The frequency control waves from the coincidence circuit 21 are applied over the lead 23 to the grid 102 of a cathode follower valve 103, the cathode load of which comprises resistors 106, 107, 108 in series. This cathode load is coupled through alternative paths 111, 112, to the grid 113 of a direct voltage amplifier valve 114 having an anode load resistor 115. A lead 25, connecting the selective averaging circuit 24 to the frequency control circuit of the oscillator 15, is connected to the sliding contact of a voltage divider 116. One of the alternative paths 111 comprises a resistor 119 and a diode 122, whilst the other path 112 comprises a resistor 124 and a filter circuit 128 formed by a resistor 129 and a further resistor 132 in series with the resistor 129 and having its other side connected to earth through a capacitor 133. The grid 135 of an amplifier valve 136 is connected to the high potential side of the capacitor 133 in order that the voltage drop through the anode load resistor 137 shall vary in accordance with the average amplitude of the voltage impressed on the path 112. The load resistor 137 is connected in series with resistors 138, 139 between positive and negative sources of potential. The variation in the voltage drop through the resistor 137, caused by change in conduction of the valve 136, alters the potential at the junction 140 of the resistors 138, 139. The cathode 141 of a diode 142 is connected to the point 140, the anode 143 being connected to the conductive path 111 at the anode 121 of the diode 122. The filter 128 comprises a relatively large condenser 131 connected to the anode 125 of a diode 126, the cathode 127 of which is connected to the grid 113 of the valve 114. The conductive path 111 normally couples the cathode follower valve 103 to the amplifier 114, the path 112 including the amplitude averaging filter 128 being normally ineffective. The valve 136, diode 142, and other elements provide means which are responsive to an average amplitude of the waves applied over the lead 23 above a predetermined level for disconnecting the conductive path 111 and coupling the valves 103, 114 only through the amplitude averaging path 112. If several successive pulse waves are applied to the lead 23, indicative of repeated coincidence between the reference signal and the exploratory pulse wave, the capacitors 131, 133 charge, the latter more slowly since it is charged through a higher resistance. The valve 136 is thus caused to conduct by the positive potential on its grid, and voltage drop in the load resistor 137 results in a negative potential at the junction 140, permitting the diode 142 to conduct. The potential of the anode 143, and consequently the anode 121 of the diode 122, falls to a negative value such that no possible negative noise pulse at the junction 110 can cause the diode 122 to conduct and alter the voltage applied to the grid 113 of the amplifier 114. The path 111 is thus effectively disconnected and all control of the valve 114 is transferred to the path 112. This has a large time constant, so that the potential on the anode 125 of the diode 126 can only change slowly, averaging many cycles of the incoming signals. Specification 606,269 also is referred to.