US2224115A

US2224115A - Band-filter coupling circuit for television amplifiers

Info

Publication number: US2224115A
Application number: US136412A
Authority: US
Inventors: Schlesinger Kurt
Original assignee: LOEWE RADIO Inc
Current assignee: LOEWE RADIO Inc
Priority date: 1936-04-16
Filing date: 1937-04-12
Publication date: 1940-12-03
Anticipated expiration: 1957-12-03
Also published as: GB499132A

Description

' Dec. 3, 1940- K. SCHLESINGER BAND-FILTER COUPLING CIRCUIT FOR TELEVISION AMPLIFIERS Filed April 12, 1957' /i shorf wave range A long wave range [/7 Men for":

Patented Dec. 3, 1940 UNITED; STATES BAND-FILTER. COUPLING CIRCUIT FUR TELEVISION AMPLIFIERS 'Kurt Schlesinger, Berlin, Germany, assignor, by

mesne assignments, to Loewe Radio, Inc, a corporation of New York Application April 12,

1937, Serial No. 136,412

In Germany April 16, 1936 2 Claims.

The present invention relates to band-filter circuits for coupling amplifier arrangements used for amplifying wide frequency-bands as they are used for television purposes.

In intermediate-frequency amplifiers for television superheterodynes' and transmission amplifiers for television purposes coupling circuits are known which consist of a pair of coils, each single coil being tuned per se to the unmodulated carrier wave and the two coils being so tightly coupled together that the frequency-curve of this circuit is sufliciently wide to cover the television frequency band. It is known that band-filter coils of this nature such, for example, as already described in the application Ser. No. 24,901 of June 4, 1935, Patent No. 2,131,193, issued Sept. 27th, 1938, drop off sharply only in the shortwave range whilst in the long-wave range they strive to reach an extreme value in the quality of transformation, which is not zero. There is required, however, in the present television art a transformation which drops 01? equally towards both sides.

In the accompanying drawing embodiments of 25 band-filter circuits in accordance with the invention are shown.

Fig. 1 shows a band-filter circuit for transmitting a wide frequency band. The curve of the frequency range transmitted by this arrangement has a sharply dropping off at both sides of the frequency band.

Fig. 2 shows the curve of the frequency band transmitted by the circuit shown in Fig. 1.

Fig. 3 shows a further embodiment of the band- 35 filter circuit according to the invention.

In Fig. 1 a first embodiment of a transformation of this character is shown, which avoids the stated disadvantage of the purely inductive systern. The primary coil 1 is not directly con- 40 nected to the anode of the first tube 3, butis coupled by way of a condenser 4. The tube 3 itself acts in direct fashion on an ohmic resistance 5. The condenser 4 and the primary inductance I are so tuned in relation to one another that series resonance occurs on a wave adjustable by condenser 4, which wave has a frequency lying in that end of the side-band frequency spectrum which contains the higher frequencies (short wave end).

On the other hand the secondary inductance 2 with the accompanying inherent and grid capacity 6 is tuned to a wave which has a frequency lying in the long-wave range of the spectrum or even beyond the long-wave end. There then occurs the effect to be seen from Fig. 2.

The curve a represents the resistance amplification occurring 'at the resistance 5. As well known, this decreases after short waves in proportion to the wave-length owing to the accompanying capacities. 1

The curve b represents the potential across the primary coil I. This has a resonance maximum at l, which is adjusted by series resonance between 4 and I. The magnetic field is represented by a curve 0, and fades less quickly than the 10 potential in the long-wave range of the frequency spectrum. The curve d shows the potential across the secondary coil excited by a constant field. Owing to the natural resonance this curve possessesa resonance peak at 8, and towards the lower frequencies it descends in proportion to the frequency.

The final curve e results from the superimposing of the coupling field curve 0 and the fre-. quency curve d of the secondary circuit. This final curve descends in the short-wave range of the frequency spectrum in similar fashion to the field curve 0. In the long-wave range, however, it drops very considerably owing to the effect of the coupling condenser 4 according to the invention. The desired result is a transformation curve which is limited sharply towards both ends.

To avoid plastic effects at the image screen both coils must be damped at least aperiodically by means of resistances 9 and It). The resistance 5 cannot be made larger than it is determined by the shunted inherent capacities.

Practical dimensions are approximately as follows:

Television image 400 lines, 25 images per second Width of side band, twice 1.6 Resistance 5, 2.500 ohms. Condenser 4=0.2-10 -0.6-10 ,lf Resistance 9, 7.500 ohms Resistance H], 5.000 ohms Coil I having resonance effect at approximately 60 metre wavelength Coil 2 having resonance effect at approximately 120 metre wavelength Carrier wave, 70 metres Extreme side waves, 50 metres and 150 metres resistance [5.

The condenser H connected between the primary and the anode of the tube 3 corresponds to condenser 4 in Fig. 1. Further an additional condenser I3 is arranged between the secondary and the grid of the succeeding tube. This condenser is thus dimensioned as to effect in combination with the natural frequency of the secondary a sharp cutting-off of that end of the broad television frequency band which extends towards the low frequency values.

There is common to both of said circuit systems shown in Figs. 1 and 3 a combination of capacitative and inductive coupling, the capacitative couplings producing series resonance in the short-wave range and the inductive couplings resonance in the long-wave range.

I claim: 1

1. In a television amplifier arrangemenumore particularly for intermediate-frequency amplifier systems, the use of a combined inductive and capacitative coupling circuit between two succeeding tubes having atleast a cathode, a grid and a plate, comprising a, transformer, damping resistances connected in parallel to the primary and secondary of said transformer, and a variable condenser, the primary of said transformer being connected to the plate of the preceding tube via said variablecondenser in serial connection, said variablecondenser being so adjusted as to fall in resonance with said primary at the high-frequency end of the frequency band to be transmitted, the secondary being connected between grid and cathode of the associated tube and tuned with the associated inherent capacities to the low-frequency end of the frequency band to be transmitted.

2. In a television amplifier arrangement, more particularly for intermediate-frequency amplifier 1 systems, the use of a combined inductive and capacitative coupling circuit between two succeeding tubes having at least a cathode, a grid and a plate, comprising a transformer, damping resistances connected in parallel to the primary and secondary of said transformer, and a variable condenser, the primary of said transformer being connected tothe plate of the preceding tube via said variable condenser in serial connection, said variable condenser being so adjusted as to fall in resonance with said primary at the high-frequency end of the frequency band to be transmitted, the secondary being connected between grid and cathode of the associated tube and tuned with the associated-inherent capacities to the low-frequency end of the frequency band to be transmitted, a condenser being inserted between said secondary and the grid of said associated tube.

- KURT SCHLESDIGER.