US2173495A

US2173495A - Television receiver

Info

Publication number: US2173495A
Application number: US2631A
Authority: US
Inventors: Schlesinger Kurt
Original assignee: Loewe Opta GmbH
Current assignee: Loewe Opta GmbH
Priority date: 1934-01-25
Filing date: 1935-01-21
Publication date: 1939-09-19
Anticipated expiration: 1956-09-19

Description

p 19, 1939- K. SCHLESINGER 2,173,495

TELEVISION RECEIVER Filed Jan. 21, 1935 mwm l.

Patented Sept. 19, 1939 UNITED STATES TELEVISION RECEIVER Kurt Schlesinger. Berlin, Germany, assignor t Radioaktiengesellschaft D. S. Loewe, Berlin- Steglitz, Germany Application January 21, 1935, Serial No. 2,631 In Germany January 25, 1934 3 Claims.

The subject matter of the invention is a heterodyne receiver for wireless television over an ultra-short wave, with simultaneous wireless transmission of the synchronism over the same 5: wave. The apparatus is intended in its developmentfor images having a relatively large number of lines (180-240) The invention relates primarily to the embodiment of the intermediate frequency amplifier.

l0 The applicants have examined different kinds of intermediate frequency amplification as regards their suitability for television purposes. The present invention is directed to an intermediate frequeney .amplifier with resistancecapacity coupling means for use in television receiving sets. The applicants have found that the use of a carrier wave amounting in its frequency to more than approximately four times the maximurn image current frequency does not result in advantages of any kind, but merely in increased diificulties associated with the amplific'ation. Therefore, upon the transmission of say, l80-line images with a maximum image current frequency of 540 k. 0. carrier waves are em- 2'5 ployed, the frequency of which is situated between 10 periods and approximately 2-10 periods. Practical experience with the heterodyne principle has shown that a low ratio of this nature between carrier frequency and image our- 30 rent frequency is fully suificient for proper reproduction of the image and synchronism. It is merely with consideration to the method of synchronizing with short impulses that the use of carrier waves longer, than those stated is not advisable.

In the case of resistance amplification forming the subject matter of the present invention a characteristic difiiculty resides not so much in obtaining sufficient amplification per stage, but 40 more particularly in making the amplification uniform throughout the range of the amplifier. The applicants have discovered that in the operation with resistance amplifiers, if the fre- 45 quency curve of such amplifiers has its maximum exactly in the employed range of the carrier frequency, the following advantages are obtained:

In the first place the intermediate frequency band is in a manner of speaking amplified more 50 than interferences and more particularly incom ing long-wave interferences which are semi-selectively separated.

Furthermore, reaction may be used by means of galvanic back-coupling and thus increases the 55 degree of amplification.

leak resistance 5, operating on 200 metres, which 10 is the wave concerned in the present case, amplification would be reduced at higher frequencies with a simple resistance amplifier. The maximum of amplification would be obtained with .a wave approximately 10 times as long, if 15 the capacity 4 amounts to approximately 0.5-10 to 1104/LF and the resistance 5 to approximately 10,000 ohms. As shown by an earlier theoretical treatise of the applicants (note: Dr. Kurt Schleisinger Resistance amplifier as oscillatory circuit in the Jahrbuch fiir drah*- 1056 p c, the resistance amplifier does not operate exactly in phase outside of the amplification optimum. This is a matter of minor importance in ordinary image operation, 1

but prevents the use of a reaction, as this connection in the case of galvanic coupling is effective only with respect to the immediate vicinity of the peak of the resonance curve, and not at higher operating frequencies. According to the invention, therefore, the coupling is so modified that the best degree of amplification falls within the operating frequency range. As an example of various possibilities in this connection there is shown in the drawing the use of an additional grid condenser 6 and a special resistance l in conjunction with an inductance 8. With the dimensioning 2:4000 ohms, 1:5000, 5:5000 ohms, 6 and 4 each 1-10 F, the best amplification is already situated in the vicinity of 200 metres, whilst beyond that, by means of a resonance choke 8, which is caused to resonate in conjunction with inherent capacities at 200 metres, and the resonance effect of which is increased by reducing the resistance 7.

With a coupling of this nature it is possible by a tapping atin the most simple casean ohmic resistance 9, which is in approximately the same ratio to the Working resistance IQ of the second tube 3 as the square of the amplification per 5 stage, to produce a component potential of the same phase as the potential prevailing in the amplification input, and in this manner to obtain an effective aperiodic back-coupling which is adjustable by a tapping at the resistance 9.

For this purpose there is employed in accordance with the invention a small condenser l I the conductivity of which requires to be good in relation to the grid leak of the first tube (approximately 0.25'10 4[LF). The method may also be mod fied by providing in the back-coupling elements of impedance varying With frequency. This may be accomplished, for example, by an inductance I2, which is in series with 9 or adjusted alone in place of 9, and the natural wave of which falls within the range concerned. The same result is obtained by a damped tuned circuit, and also by many other means knot 21 per se. It is essential in each case that amplifier and back-coupling operate without phase change in the stated carrier frequency range. The effect or" a back-coupling of this nature may be considerable, particularly if all tubes operate in the range of maximum steepness of their characteristic.

I claim:

1. In a superheterodyne television receiving set an intermediate frequency amplifier consisting of a plurality of amplifier stages, resistance-capacity coupling means between the single valves of said amplifier each one containing at least a cathode, a grid and a plate, said coupling means consisting of an anode resistance in the anode circuit of the first of two succeeding valves, a grid leak resistance in the grid circuit of the second of said two succeeding valves, a series condenser between said succeeding Valves and a series resonance network interposed between said series condenser and the anode of the first of said succeeding valves, said series resonance network including a condenser and a resonance choke, which is damped by a resistance, connected in series with said latter condenser between the anode of said first valve and ground and so dimensioned that a resonance efiect is produced within the frequency range best amplified by said resistance-capacity coupling means of said whole amplifier.

2. In a superheterodyne television receiving set an intermediate frequency amplifier consisting of a plurality of amplifier stages, resistance-capacity coupling means between the single valves of said amplifier each one containing at least a cathode, a grid and a plate, said coupling means consisting of an anode resistance in the anode circuit of the first of two succeeding valves, a grid leak resistance in the grid circuit of the second of said two succeeding valves, a series condenser between said succeeding valves and a series resonance network interposed between said series condenser and the anode of the first of said succeeding valves, and means for effecting a potential feed-back from an anode oscillating in phase with the input potential connected to the input of the first of said intermediate amplifier stages, said anode circuit being the anode circuit of an evenly numbered stage, i. e. the second, fourth stage etc., said series resonance network including a condenser and a resonance choke, which is damped by a resistance, connected in series with said latter condenser between the anode of said first valve and ground and so dimensioned that a resonance effect is produced within the frequency range best amplified by said resistancecapacity coupling means of said whole amplifier, said feed-back coupling means consisting of an ohmic resistance.

3. In a superheterodyne television receiving set an intermediate frequency amplifier consisting of a plurality of amplifier stages, resistancecapacity coupling means between the single valves of said amplifier each one containing at least a cathode, a grid and a plate, said coupling means consisting of an anode resistance in the anode circuit of the first of two succeeding valves, a grid leak resistance in the grid circuit of the second of said two succeeding valves, a series condenser between said succeeding valves and a series resonance network interposed betweensaid series condenser and the anode of the, first of said succeeding valves, and means for efiecting a potential feed-back from an anode oscillating in phase with the input potential connected to the input of the first of said intermediate amplifier stages, said anode circuit being the anode circuit of an evenly numbered stage, i. e. thesecnd, fourth stage etc., said series resonance network including a condenser and a resonance choke, which is damped by a resistance, connected in series with said latter condenser between the anode of said first valve and ground and so dimensioned that a resonance effect is produced within the frequency range best amplified by said resistance-capacity coupling means of said whole amplifier, said feed-back means consisting of frequency-dependent impedances.

KURT SCI-ILESINGER.