Patent GB-624559-A (GB)
Title: Improvements in or relating to circuit arrangements for providing control voltages
IPC: G01S13/70
Filed: 1945-06-22
Abstract: 624,559. Automatic control systems. WILLIAMS, F. C., and MOODY, N. F. June 22, 1945, No. 16036. [Class 38 (iv)] [Also in Group XL (c)] A circuit arrangement for providing a control voltage, proportional to the degree of coexistence, when a recurrent input signal and a recurrent locally generated signal partially or wholly co-exist comprises a local circuit rendered effective to provide a similar and approximately equal control voltage if the input signal strength falls below the level required to operate the arrangement. A number of uses in radio navigation and radiolocation for such a circuit are mentioned with references to Specifications 582,503 and 584,670, [Group XL]. The embodiment described is an improved walking strobe unit for the radio navigation system described in Specification 624,558, [Group XL (c)], the circuit of Fig. 2 replacing the circuits of valves 10 to 17 shown in Fig. 3 of that Specification. In the present arrangement, two strobe pulses are generated with coincident front edges, one being 1“/Á sec. long and the other 2¢/Á sec.; when the strobe is locked to an echo signal, two currents proportional to the overlap of the echo, and the respective strobes are generated. The current derived from the longer strobe pulse and echo overlap is in opposite phase and half the amplitude of the current derived from the echo overlap with the shorter strobe. A control voltage is generated proportional to the resultant of the two currents and is applied to a capacitor which when the input signal falls below a predetermined minimum value, discharges through a load to provide the substitute control. The normal control signal (or its substitute) are applied to velocity and range valves as referred to in Specification 624,558 and maintain the strobe in co-incidence with the echo signal and normally near the centre of the longer pulse. The positive going trigger pulses (from V5 of Fig. 3 of Specification 624,558) are fed at T3 to V5 which forms part of a delay circuit as described in Specification 582,758, [Group XL], and produces a positive giving waveform A, Fig. 1, the width of which is determined by the voltage to which the V5 is allowed to rise. This waveform is fed to V7 which is normally biassed to cut-off and gives rise to a negative waveform applied to a delay network DN short-circuited at one end and terminated by the characteristic impedance R39 at the other. Each section ab, bc, cd provides a delay of #/Á sec. and thus the output at " a " consists of 2¢/Á sec. positive and negative pulses as shown at B and the output at " - " of 1“/Á sec. pulses with front edges coincident with those of the corresponding longer pulses as at C. These outputs are applied respectively to V13 and V10 and as these valves are both normally cut off, only the positive pulses, which are delayed behind the initial trigger pulse an amount determined by the maximum anode voltage of V5 are effective. These reduce the cathode potential of diodes V12 and V15 from +150 volts to 0 volts for the duration of the associated strobe pulse. Amplified echo signals are applied at T4 and cathode follower V9 passes them to V12 and V15 through capacitors C16 and C22 as positive pulses. If there is no overlap between the echo and strobe pulses the diodes are cut off, if, however, an echo overlaps the short strobe V12 conducts and there is a consequent reduction in the potential of the grid of V1. Similarly, during the overlap of an echo signal with the long strobe, current flows away from C24 and this flow, reversed in phase and halved in amplitude by the circuit of V16, produces an increase in potential at the grid of V1. There is no resultant change in the grid potential of this valve when the echo is in the centre of the long strobe pulse and therefore half overlaps the short strobe pulse; any relative movement of the echo and strobes produces a variation in grid potential causing an alteration in the strobe timing tending to maintain coincidence. With relay MR operated, C1 is connected between the anode and control grid of V1, smoothing the input thereto, the grid being normally maintained at - 5 volts and the current flow through R1 being balanced with that through R93. The anode voltage of V1 corresponds to the " velocity voltage " referred to in Specification 624,558 and is 165 for zero velocity of the strobe. The velocity voltage is integrated by V2, operating in a circuit similar to that of V14 in Fig. 3 of Specification 624,558, to provide the " range voltage." The velocity and range voltages are fed to the pulse width control unit via T1 and T2 as described in the aforementioned Specification and the range voltage is also applied to the cathode of diode V4 to limit the rise in anode voltage of V5 which controls the positioning of the strobe pulses and maintains coincidence. The walking strobe is initially manually adjusted to coincidence by R18 before S2 is thrown to its automatic following position. Relay MR in the anode circuit of V17 is operated during reception of satisfactory echo signals, but releases if these signals fade. With no echo signals V18 holds the junction of R81 and R82 at - 30 volts and current flows through R85 and R83, the anode voltage of V17 is high and insufficient current flows through the relay MR to operate it. When echo signals overlap the longer strobe pulse the anode voltage of V16 rises, V18 no longer conducts, and the current flowing through R83 decreases. If the incoming signal is strong enough, Vi7 passes sufficient current to operate the relay. With the relay operated, mr4 connects - 5 volts to the lower plate of C3 and mr3 connects the upper plate through resistor R8 and the smoothing circuit R7, C2 to the anode of V1. C3 is thus charged to the mean " velocity voltage " plus the - 5 volts applied by mr4. If the incoming signals fade relay MR releases and C3 and resistor R8 are connected between the anode and grid of V1 in place of C1 and maintain the velocity voltage at its mean level before the fade for about 1 minute and it is therefore likely that the strobe will maintain coincidence during a signal fade of less than this period. The circuit constants of the relay operating circuit prevent release of the relay if the fade does not continue more than # sec. In order to prevent the relay de-energizing whilst manually moving the strobe into coincidence, S5 is used and contacts S5, 2 connect T1 to the 165 volt'line to prevent incorrect signals passing to the pulse width control unit.