US2912618A - Circuit arrangement in radar receivers for controlling the deflection of the cathode-rays in cathode-ray tube indicators - Google Patents

Description

C. LE COMTE Nov. 10, 1959 CIRCUIT ARRANGEMENT IN RADAR RECEIVERS FOR CONTROLLING THE DEFLECTION OF THE CATHODERAYS IN CATHODE-RAY TUBE INDICATORS Filed Dec. 5, 1958 FIGI INVENTOR CORST AAN LE COMTE CIRCUIT ARRANGEMENT 1N RADAR RECEIVERS FOR CONTROLLING THE DEFLECTION OF THE CATHODE-RAYS 1N CATHODE-RAY TUBE 1N- DICATORS Corstiaan le Comte, Hilversum, Netherlands, assignor to North American Philips Company, Inc., New York, N.Y., a corporation of Delaware Application December 5, 1958, Serial No. 778,459

Claims priority, application Netherlands December 19, 1957 1 Claim. (Cl. 315-27) This invention relates to circuit arrangements in radar receivers for controlling the deflection of the cathode-rays in cathode-ray tube indicators.

When magnetic deflection is used, in order to ensure the required linearity and constant loading of the supply source generally the arrangement is such that two ends of a deflector coil are connected to the anodes of two control valves, a tapping on the deflector coil being connected to an anode voltage supply source. By adjustment of the rest currents of the valves the beam can be adjusted to a definite rest position, which may correspond to the centre of the radar image but alternatively may be situated without the display screen. Furthermore provision is made of means for periodically supplying a saw-toothshaped control voltage to the valves in phase opposition in order to cause the light spot to describe a path over the display screen starting from the rest position. Frequently the efiective time during which the saw-tooth voltage is set up, is only a slight fraction of the repetition period so that the beam is in the rest position for the major part of the time.

This arrangement has a limitation in that the dissipation of one or both valves is comparatively large, particularly if the rest position of the beam lies without the display screen, and increases in proportion as the active deflection period is shorter. For deflecting the beam to the screen edge a certain current is required. For maintaining the rest current a low anode voltage would be sufficient. However, during the deflection a comparatively high induction voltage is produced across the deflector coil. Since the effective anode voltage of the valves must remain positive with respect to the cathode during deflection, the voltage of the supply source must be comparatively high, so that a considerable dissipation can occur in the valves.

In a known arrangement of this kind the anodes of the valves are connected to the anodes of two normally cut off auxiliary valves the cathodes of which are connected to a supply source, the voltage of which is lower than that set up at the cathodes of the first-mentioned valves. During the deflection of the cathode-ray the auxiliary valves, which consequently have an anode voltage greatly exceeding that of the other valves, are rendered conductive for controlling the deflection. This method has a limitation in that it is diflicult to ensure the linearity of the deflection as a function of time because, owing to the high voltage drop across the deflector coil, the first valves are cut off. In addition, several supply voltage sources and two auxiliary valves are required.

In the circuit arrangement in accordance with the invention, a tapping on the deflector coil is connected through an inductance coil to the anode voltage supply and to the anode of a normally conducting third valve which is provided with negative feed-back in accordance with the voltage, while during the application of the sawtooth control voltage to the control valves the anodes of which are connected to the ends of the deflector coil, a

voltages return to their rest values.

negative voltage pulse is supplied to a control electrode of the third valve.

In order that the invention may readily be carried out, an embodiment thereof will now be described, by way of example, with reference to the accompanying diagrammatic drawings.

Fig. 1 is a diagrammatic illustration of a circuit embodying the invention.

Figs. 2a, 2b, and 2c are graphs illustrating current and voltage changes in the circuit.

In Fig. l, S denotes a deflector coil of a cathode-ray tube indicator (not shown) in a radar receiver. The ends of the deflector coil are connected to the anodes of two control valves B1 and B2, the cathodes of which are connected to earth and which preferably are pentodes. The middle of the coil S is connected to the anode voltage supply +Vb through an inductance coil L which for the time being must be assumed to be short-circuited. The control grids of the valves B1 and B2 are connected to a sawtooth generator ZG which periodically is rendered 0perative under the control of pulses supplied by way of a terminal K. The pulse repetition frequency is, say, 2500 p.p.s., so that the duration of a repetition period is 400 micro-seconds. If an indication is to be provided over a rangeof, say, 16 nautical miles, the deflection period must be about 200 micro-seconds, the beam being adjusted to a fixed rest position for the rest of the time. If this rest position lies without the display screen of the cathode-ray tube, the valve B1 at a certain turns number of the deflector coil S must be adjusted during the rest period to a rest current of, say, ma. and the valve B2 to a II in the valve B1 decreases and the current 12 through current of 20 ma. During a deflection period the current the valve B2 increases linearly with time, as is shown in Figure 212. Hence a constant induction voltage is set up across the deflector coil S so that the effective anode voltage Val of the valve B1 is increased to a value which is materially higher than the anode alternating voltage Vb, the effective anode voltage Va2 of the valve B2 being decreased by the same amount, as is shown in Figure 2b.

If the induction voltage set up across the two coil halves is, for example, 100 volts, the anode voltage Vb must be volts for a sufficiently high positive anode voltage Va2 to be maintained at the valve B2 during a deflection period. During the rest period the various currents and Under the conditions described the total dissipation of the valves is about 22 /2 watts. If the indicating range of the arrangement must be about 4 nautical miles, as is the case, for example, in harbour radar, the effective deflection time is about 50 micro-seconds. Since the variation of the control currents must now take place in a period four times as short as in the preceding case, the induction voltage across the coil halves is four times as high, i.e. 400 volts. The anode voltage Vb must consequently be 460 volts for an effective anode voltage of 60 volts to be left for the valve B2 during deflection. The total dissipation of the valves is 75 watts.

This dissipation cannot be materially reduced by increasing the number of turns on the deflector coil S. If, for example, the turns number were doubled, the various current strengths must be halved to obtain the same deflection.

However, since the inductance of the deflector coil S increases by a factor 4 during the deflection periods there is set up across the deflection coil an induction voltage twice that produced in the former case. Hence, the anode rest voltage Vb must also be doubled so that the dissipation is substantially the same.

In the circuit arrangement shown in Figure 1 there is connected between a tapping A on the deflector coil S and the anode voltage supply +Vb an inductance coil L.

trol grid being connected through a grid leak resistor R2 to an output of a mono-stable trigger circuit M. The trigger circuit M normally is in a rest position in which there is supplied to the control grid of the valve B3 a voltage such that this valveis conductive.

By starting pulses, which are applied at a terminal K and periodically render a sawtooth generator ZG operative, the trigger circuit M is also brought in the working condition, a highly negative output voltage of, for example, -SO volts being produced, so that the valve B3 wouldrbe cut off. However, the anode of the valve B3 is connected, through a capacitor C and a leak resistor R1,

to the control grid, so that the tube is provided with negative voltage feed-back. The sum of the currents through the valves B1 and B2 during the deflection period is equal to the sum of the rest currents, since the current through the valve. B1 is increased by the same amount by which the current through the valve B2 is decreased. The currents must be about equal to the rest value in spite of the negativervoltage which is supplied to the control grid through the resistor R2. Since the control grid voltage 'of the valve B3 also rnust initially remain constant/the voltage drop which would be produced by the output voltage of the monostable trigger circuit M must be compensated for by a sudden voltage increase at the point A. Hence this voltage increase must be equal to R1/R2 times 2,912,618 i V a T the variation of the output voltage of the trigger circuit M. During the deflection period the current through the valve B3 decreases, so that the voltage of the point A is maintained at a high value. Then the variation of the eflective anode voltages is as shown in Figure 2c. Owing to the voltage increasing eflect of the choke coil L, which compensates the voltage decrease of the effective anode voltage of the valve B2 by the inductance of the deflector coil S, in this circuit arrangement the anode voltage Vb can have a comparatively low value which is sufficient to supply the rest currents through the various valves. The fly-back time of the trigger circuit M is about equal to the effective deflection time. During the subsequent rest period the current through the inductance coil L again is increased to the initial value under the control of the valve B3. r J e What is claimed is: I l r A circuit arrangement in a radar receiver for controlling the deflection of the cathode-ray in a cathode-ray tube indicator, in which the ends of a deflector coil are connected to the anodes of two push-pull connected control valves and a tapping on the deflector coil is connected to an anode voltage supply source, means being provided for periodically supplying in phase opposition a sawtooth control voltage to the valves, characterized in that the said electrode of the third valve during the application of the saw-tooth controlvoltage to the control valves.

No references cited.

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