US2201794A

US2201794A - Rectifier for television signals

Info

Publication number: US2201794A
Application number: US130718A
Authority: US
Inventors: Schlesinger Kurt
Original assignee: LOEWE RADIO Inc
Current assignee: LOEWE RADIO Inc
Priority date: 1936-03-20
Filing date: 1937-03-13
Publication date: 1940-05-21
Anticipated expiration: 1957-05-21
Also published as: FR819404A; DE730998C; GB490676A; NL49860C; FR819408A; GB492337A

Description

21, 1940- K, SCHLEVSINGER 2,201,794

RECTIFIER FOR TELEVISION SIGNALS Filld latch 13. 1937 In men for:

Patented May 21,. 1940 om'rn PAT NT OFFICE RECTIFIER FOR TELEVISION SIGNALS Kurt Schlesinger, Berlin, Germany, assignor, by mesne assignments, to Loewe Radio, Inc., a corporation of New York Application March 13, 1937, Serial No. 130,718 In Germany March 19, 1936 2 Claims.

lZhe present invention relates to television circuit arrangements and more particularly to television rectifying circuit with an after-connected amplifier-stage and most effective suppression of the carrier-frequency oscillations.

The object of a rectifier in respect of the modulated ultra-short wave or the modulated intermediate-frequency Wave of a television superhet is as follows: Inertialess operation in demodu- -'-lating up to maximum frequency of the image,

the image-point traversing period; further, at least linear response to increasing amplitudes of the carrier wave, and preferably more than linear response, 1. e., increasing slope of the char- .acteristic curve in the case of increasing amplition have all these features necessary for good operation and more particularly the present invention is directed to complete elimination of the carrier-frequency-oscillations in the circuits after-connected to the rectifying stage.

In the accompanying drawing embodiments of the circuits according to the present invention are shown.

Fig. 1 shows a television receiving circuit according to the present invention and Fig. 2 represents a diagram of the circuit shown in Fig. 1 showing the relations between the potential at the grid of the Braun tube and the frequencies to be transmitted.

As well known, the increasing slope of the characteristic with increasing amplitudes is performed by use of anode bend rectification, primarily with short-circuiting of the anode circuit. A three-pole tube I, with the aid of a tapping 3, is so adjusted to a battery 2 having a comparatively low potential of approximately 30 volts that the anode current is just caused to cease. The modulated carrier wave is supplied by means of the transformer 4. In the anode circuit there is provided a resistance 5, which is made so small in its ohmic value that in spite of the inherent capacities it is effective also at the highest image-frequencies. An after-connected amplifying tube 6 is coupled with the anode of tube I in direct fashion. The grid 1 is preferably passed out separately through the glass wall. The cathode of the amplifier 6 is earthed, and the tube itself is a pentode with large amplification factor.

In both anode circuits, that of the detector I and that of the after-amplifier 6 with its anode resistance 8, there arise both rectified modulated oscillations as well as considerable traces of the carrier-oscillations. The anode circuit of the end amplifier is not connected through to the Braun tube 9 directly, but the carrier wave is previously eliminated by a capacitative compensation. For this purpose a differential condenser l0/H is connected with one pole to the anode circuit 8 and with the other pole to the grid 1 of the am- 16 plifier 6. The rotor l2 may then be so adjusted that the carrier wave disappears entirely. A condition for this is that there is not caused by reason of the useful circuit I3/ I4 any inadmissible load on the condenser portion l0/ l2. Merely go the image currents flow through the circuit l3/ l4. According to the invention, the circuit is produced as series connection of a choke l3 and a damping resistance M. It is then possible to find a choke operating in series resonance with u the inherent capacities l5 at the maximum image frequency. As regards all frequencies which are still higher, i. e., more particularly beyond the side band of the carrier wave, the choke then represents a very high resistance, and accordingly the compensation by the differential condenser is very good for the carrier wave.

Fig. 2 shows a diagram showing the relationship (experimentally obtained) between the oscillation potential e at the control grid 9 of the image reproducing device of the circuit of Figure 1 over a wave-length band between 50 metres and approximately 300 metres. The carrier wave-length was 100 m., side band about 50 to 150 m., the number of lines per frame was 400 and the maximum video frequency in was 1.6 10 which corresponds to about 200 m. Choke I3 had a winding surface of 100x mm., and was arranged to resonate at frequency in.

The oscillation potential e at the grid 9 of the 5 of a resonance hump in the neighbourhood of 5 the frequency is. The shape of the resonance hump at frequency ,fB can be varied by varying the value of resistance l4. Curve a was obtained with the damping resistance M at zero,

curve b was obtained with resistance M at 2,000

| 200 lines 20 The neutralisation capacity 10/ l! remains constant, independently of the number of lines, so long as the branch l3/8 in the case of maximum image frequency is adjusted to series resonance and at the same time possesses a sufficiently high impedance.

The synchronisation is branched off at the line which is traversed by the most powerful modulation frequencies, as it is there that the amplitude filtering is possible in the most simple 0.5fashion. It is preferably performed by a twopole tube is having a free cathode, which operates by way of an adjustable bias H on the synchronisation transformers is. It is preferable and possible to fit this two-pole path into the -I three-pole tube l, as merely a very small emission of approximately 2 milliamperes is required in respect of the two-pole tube.

I claim:

1. In combination an electronic amplifier including at least an anode, a control grid and a cathode, having an input and output circuit, a filter circuit and means for balancing out carrier frequency oscillations, said filter circuit and said means being arranged in said output circuit, said 5 means for balancing out consisting of a diilerential condenser having one rotor and two stators, one stator being connected to said input circuit which rectified carrier oscillations with modulation signals are applied to, the other stator being connected to the anode of said amplifier, said rotor being connected to the output terminal of said amplifier, said filter circuit being arranged between said stator connected to said anode and said rotor and having a low impedance to the modulation signals and a high impedance to the carrier oscillations.

2. In combination an electronic amplifier including at least an anode, a control grid and a cathode, having an input and output circuit, a filter circuit and means for balancing out carrier frequency oscillations, said filter circuit and said means being arranged in said output circuit, said means for balancing out consisting of a difierential condenser having one rotor and two stators, one stator being connected to said input circuit which rectified carrier oscillations with modulation signals are applied to, the other stator being connected to the anode of said amplifier, said rotor being connected to the output terminal of said amplifier, said filter circuit being arranged between said stator connected to said anode and said rotor and consisting of a self-inductance and a damping resistance in selies-connection, said self-inductance resonating 3 at the highest modulation-frequency to an extent which is adjustable by varying the value of the damping resistance.

KURT SCI-ILESINGER.