US2075979A - Amplifying or rectifying device - Google Patents

Description

April 6, 1937.

Filed Feb. 4, 1935 INVENTORS POP/(0 .19. OY/fSTERHU/S JACOB I44 Z007IV ATTORNEY Patented Apr. 6, 1937 UNITED STATES PATENT DFFUJE AMPLIFYING OR RECTIFYING DEVICE Delaware Application February 4, 1935, Serial No. 4,800 In Germany March 15, 1934 4 Claims.

This invention relates to a circuit arrangement for amplifying and/or rectifying electrical high frequency oscillations in which damping reduction by back coupling is used.

If in a receiving arrangement with a back coupling acting on the antenna circuit, the damping reduction caused by said backcoupling has such a value that high frequency oscillations are produced, the latter will be emitted by the antenna and will consequently give rise to disturbing interferences in other neighboring receivers.

It has been sought to avoid this draw-back by introducing the damping reduction not in the antenna circuit, but in another tuned circuit of the receiver by using a back coupling, this circuit being coupled with the antenna circuit through one or more amplifying tubes. This solution gives satisfactory results if either the amplifying tube(s) interposed between the circuit whose damping is reduced and the antenna circuit is (are) furnished with a screen grid, so that the reaction across the anode control grid capacity of the tube may substantially be neglected, or the anode control grid capacity is neutralized in another known manner.

The same result may be achieved by the ar rangement according to our invention without, however, the interposition of an additional tube being necessary.

According to the invention the electrical high frequency oscillations to be amplified or rectified are supplied to one of the grids (control grid) of a thermionic discharge tube having at least three grids, an impedance being inserted in the circuit connected to another grid separated by a screened grid from the control grid, which impedance is coupled with an impedance inserted in the anode circuit or with an impedance interposed in the circuit of another grid which is also separated from the control grid by a screened grid, in such a manner that damping reduction by back coupling occurs in the last mentioned circuit or in the anode circuit.

For a better understanding of the invention reference is made to the accompanying drawing in which:

Figure 1 is a schematic circuit diagram of a regenerative detector embodying the invention, and

Figure 2 is a circuit diagram of a similar detector in which capacitive feedback is utilized.

The electron discharge tube I shown in Figure 1 comprises a directly or indirectly heated cathode 2, four grids 3, 4, 5 and 6 and an anode 1. The 5 control grid 3 of this tube is connected on the one hand through a condenser 8 to an antenna 9 and on the other hand through a resistance It] to the end of a grid bias resistance l l remote from the cathode, which resistance is bridged by a condenser l2. The direct voltage drop occurring across the resistance l I supplies in a known manner the negative bias for the control grid. Both of the grids 4 and 5 succeeding the control grid have a constant positive potential with respect to the cathode and at least one of these grids is designed as a screen grid so that a reaction of the grid 6 and of the anode 1 on the control grid 3 is avoided. The grid 6 is connected-through a resistance I3 to the cathode 2, so that the direct current potential of this electrode corresponds to that of the cathode. Furthermore the circuit connected to the grid 6 comprises an oscillatory circuit M which is connected in series with a condenser l5 and is tuned to the frequency of the oscillations to be received. Finally the anode circuit of the tube is constituted by a reaction coil l6 inductively coupled with the coil 30 of tuned circuit I4. This coil is connected in series with the primary winding 3| of a low frequency transformer I! which is short circuited for high frequency currents by a condenser l8, the secondary of I! being connected to a pair of output terminals 32.

The operation of this arrangement is as follows:

The high or radio frequency oscillations re ceived by the antenna control the grid 3 and consequently a high frequency alternating current will flow in the circuit connected to the anode I. This current sets up a high frequency alternating voltage at the grid 6 owing to the coupling of the coil It with the tuned circuit M, which voltage is rectified in the same manner as with grid rectification and causes a low frequency voltage drop across the resistance IS in accordance with the modulation of the received high frequency oscillations. This low frequency voltage set up at the grid 6 controls the anode current traversing the primary winding of the low frequency transformer, so that the low frequency oscillations may be reproduced, for instance, in a loudspeaker or telephone connected through the secondary winding, if desired with the interposition of a low frequency amplifier.

If the coupling between the coil l6 and coil 3B of the circuit I 4 is made so close that the damping of the circuit connected to the grid 6 becomes zero or negative, then high frequency oscillations are produced.

However, owing to the presence of the grids 4 and 5, at least one of which is a screen grid as has been set out before, said oscillations do not cause any voltage variations in the control grid 3 circuit thus avoiding antenna radiation and incidental disturbances of neighboring receivers due to interference. V

Figure 2 shows another circuit arrangement which substantially corresponds to that represented in Figure l and in which corresponding parts are denoted by similar numerals, but in Figure 2 a capacitative back coupling is used between the third and fourth grids (5 and 6) which back coupling may. be controlled by the variable condenser [9. The radio frequency choke coil 33 is connected between grid 5 and the positive potential source.

It will be appreciated that although in the circuit arrangements above referred to tubes having four grids are shown, the invention is not limited thereto but also includes the use of tubes having three, five or six grids, provided the control grid be separated from the other ones by at least one screened grids Furthermore it is obvious that the invention also applies to arrangements designed only for high frequency amplification of the applied signal voltage.

What we claim is:

1. In a device of the classdescribed, the combination' of a thermionic tube having a cathode, a signal control grid, a screen grid, a third grid and a plate arranged in the order named, a circuitv connecting said cathode and signal control grid including a resistor and means for biasing said control grid negative with reference to said cathode, means for impressing a modulated radio frequency signal voltage on said signal control grid, means for applying a steady positive voltage to said screen grid, a circuit connecting said third grid and cathode including a portion resonant to the incoming signal frequency, and a circuit connected to said plate including a feedback connectio-n to said last named circuit and means for applying a positive potential to said plate.

2. The combination defined in the preceding claim in which a resistor is directly connected between said third grid and cathode.

3. In a device of the class described, the combination of a vacuum tube having acathode, a signal control grid, a screen grid, a third grid, a fourth grid and a plate arranged in the order named, a circuit connecting said cathode and signal control grid including a resistor, means for impressing a modulated radio frequency signal voltage on said signal control grid, means for applying a steady positive voltage to said screen grid, a circuit connecting said third grid and cathode including a coil and condenser connected in parallel and resonant to the incoming signal frequency, a capacity connected between said third and fourth grids and an audio frequency output circuit connected tosaid plate.

4. In a device of the class described, the comv bination of a thermionic tube having a cathode, a signal control grid, a screen grid, a first cold electrode and a second cold electrode arranged in the order named, a circuit connecting said cathode and signal control grid including a resistor and means for biasing said control grid negative with reference to said cathode, means for impressing signal voltage variations of a desired frequency on said signal control grid, a parallel resonant circuit tunable to the desired signal frequency having one end connected to said first cold electrode and its other end to the lower end of said resistor, means for causing oscillatory currents to flow in said parallel resonant circuit, means for impressing a substantially constant positive potential on said screen grid and an audio frequency output circuit connected to said second cold electrode.

' POPKO REINDER DYKSTERHUIS.

JACOB VAN SLOOTEN.

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