US1607978A - Transmission circuits - Google Patents

Description

' cuits, and particularl Patented Nov. 23, 1926.;5

UNITED STATES PATENT OFFICE.

WILLIAM L. CASPER, OF BROOKLYN, NEW YORK, ASSIGNOR TO WESTERNE-LECTRIC COMPANY, INCORPORATED, OF NEW YORK, N. Y., A CORPORATION OF NEW YORK.

TRANSMISSION CIRCUITS.

Application filed August 4, 1922. Serial No. 579,593.

This invention relates to transmission cirto such circuits in which amplifying devices are employed.

An object of this invention is to prevent an amplifying device from singing due, for example, to a portion of the output energy, finding its way back into the input circuit of the device.

Another object is to reduce the resonance peak in the transmission characteristic curve of an amplifying device, caused by resonance effects between the capacity existing between the terminals of the amplifying device external inductance elements.

This invention is hereinafter described in detail in connection with an amplifier circuit working into a load which has a falling frequency transmission characteristic. As explained in my Patents Nos. 1,530,648 and 1,530,649, issued March 24, 1925, the leakage inductance of an input transformer of an amplifier or a separate series inductance element of suitable value may be made to resonate with capacity effects between the electrodes of the amplifier to give a transmission characteristic rising with frequency.

Such a rising characteristic over the transmission band is. frequently of importance when the amplifier works into a translating device having a transmission characteristic falling -with the frequency. This 11S1I1g characteristic is frequently obtained by resonating the leakage inductance and the capacity effects at a frequency above the desired transmission range, a suitable filter being employed to suppress frequencies around the resonance frequency, so that the shape and character of the peak doesnot enter-into the transmission characteristic of the repeater system. I In'the absence of such a filter, however, the transmission at or near the resonance frequency may be so much greater than that over the essential range thatthe amplifier. sings or howls at the resonance frequency-an effect which is, of course, undesirable. In accordance with this invention, a simple-and effective way of reducing this resonance peak to a value comparable to the re mainder of the transmission curve is by con-. meeting a condenser across two of the electrodes of the amplifier. This, while lowering the frequency of the. resonance peak, has also been found to reduce to a considerable extent the height of the peak and the conand I 1 illustrates an amplifier circuit em bodylng this invention in which the correcting condenser is connected across the grid and cathode electrodes of the amplifien.

Fig. 2 is a modification of Fig. 1 in which the correcting condenser is connectedacross the grid and anode electrodes.

Fig. 3 illustrates, by means of curves, the effect of shunting two of the electrodes of an amplifier by a condenser.

Fig.1 discloses a vacuum tube amplifier- 10 connectedbetween an incoming line 11, 11 and an outgoing line 12, 12 for impressing upon the outgoing line in am lified form signals impressed upon the tube from incoming line 11. The control electrode 13 and the cathode 14 of the amplifier are connected to the incoming line 11 by an input transformer 15, while the anode 16 and cathode 14 are connected to the outgoing line 12 by a suitable output transformer 17. The cathode 14 i's heated by a battery or other source of volta e 18 and batteries 19 and 20 are employed or maintaining respectively'the grid and the anode at suitable potentials with respect to the cathode. e

As has been explained, it is frequently desirable to have a vacuum tube repeater operating with a transmission characteristic rising with frequency; One way this may be accomplished is to resonatev the capacity effecis existing between the electrodes of the tube with 'a small inductance in 'series with a winding of the input transformer. An actual inductance element separate from the input transformer is not necessary since it has been found that leakage reactance in an input transformer may be adjusted to function the same as a series inductance element. For example, in Fig. 1 the dotted inductances 21 and 22 may represent the effective series inductance caused by leakage reactance in transformer 15. These effective inv ductances maybe made to resonate with the ca acity effects between the grid 13 and catho e 14 at a frequency in the upper sneecll. range such as shown by curve23 of Fig. 3

.am lifier expressed in miles wherein the abscissae represent frequency and the ordinates represent the gain of the of standard cab e. I

This rising transmission characteristic is particularly useful when the amplifier works into a translating device, such as a 'loud speaking receiver, the transmission equivalent of which has a characteristic falling with the frequency. The resonance peak of curve 23 however occurs at a frequency which is generally not essential to give quality.

Y transmission an may, for example, occur at resonating frequency, this invention provides a condenser 24 connected in shunt to the grid and cathode of the tube. The presence of this condenser lowers the resonating frequency and, at the same time, has been found to ive the result that the resonance peak is 0% a considerably less magnitude. Curve 25 of Fig. 3 illustrates, for example, the transmission characteristic obtained by employing a condenser 24 of such a value that the resonance peak occurs in the neighborhood of 6000 cycles per. second. This curve shows that the resonance peak is of a considerably less height and also rapidly falls ofi for frequencies above the resonating frequency so as to act substantially as a cutoff filter. Due to the pre ence of condenser 24Eand the resulting lowering of the resonance peak the amplifier l0 can be worked at greater amplification without danger of singing being produced.

It has been found that substantially the same results may be obtained by connecting the correcting condenser between the grid and anode. Fig. 2 illustrates a condenser 27 connected across the grid 28 and anode 29 of a vacuum tube repeater 30. This condenser 27 may be made to resonate with the leakage reactance of the input transformer 31 and the capacity efiects between the elec trodes of tube 30 to give the transmission characteristic illustrated as curve 32 of Fig. 3 whereas the absence of the correcting condenser 37 would give a transmission char.- acteristic similar to curve 2?.

As a specific example of the value co'ndenser 2a of Fig.1 may have, it may be stated that in one case where the effective grid cathode capacity was 100 micromicrm farads and the leakage reactance gave an mary winding, its value will, of course, be

dependent upon theimpedance ratio of the transformer and should be Inulti lied by the im. edance ratio to determine t h in uctance resonating pacity. r

While this invention has been described above in certain specific embodiments, it is to with the shunt caother different forms without departing in any wise from the spirit of the invention as defined in appended claims.

The invention claimed is:v

e effective be understood that the invention may-possess 1. The combination with two transmission lines across one of which an-appreciable capacity efl'ect exists, and means for coupling said lines to providesubstantially constant transmission between said lines for a wide band of frequencies, said capacity efiect tending to cause,the upper frequencies of said band to be,less efiiciently transmitted than the intermediate frequencies thereof, and means tendin to resonate. with said capacity to substantially equalize the transmission at said intermediate frequencies and said upper frequencies while maintaining the transmission efiiciency for said intermediate frequencies substantially unchanged at the value caused b said capacity effect; of a capacity connector across one of said lines and proportioned to lower the frequency at which .said first mentioned capacity and means tend to resonate.

2. The combination with means comprising a transformer and a space'discharge de-- vice, said means having a transmission frequency characteristic showing high transmission eliiciency for electrical variations over a wide frequency band, said means including inductance effectively in series with a w1nding of said transformer, and said dcyicc comprising electrodes and an effective input capacit -tending to causethe upper frequencies 0 said band to be less efficiently transmitted than the intermediate frequencies thereof, said effective input capacity resonating with said inductance at such a frequency that the transmission frequenc characteristic of said means rises with e uency'at and above the upper limit of said and and remains substantially unchanged for said in termediate frequencies at the value caused by said efiective input capacity; of a. capacity connected across certain of said electrodes and of such a value that the transmission frequency characteristic of said means is lowered at the frequency of said first mentioned resonance.

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3. The combination with means comprising a transformer and a space discharge device, said means having a transmission frequency characteristic showing high transmission efliciency for electrical variations over a wide frequency band, said means including inductance effectively in series with a'winding of said transformer, and said device including a cathode and a control electrode between which an appreciable capacity effect exists tending to cause the upper frequencies of said band to be less efficiently transmitted than the intermediate frequencies thereof,

said capacity resonating with said inductance at such a frequency that the transmission frequency characteristic-of said means rises with frequency at and above the upper limit of said band and remains substantially unchanged for said intermediate frequencies of a capacity connected across said cathodeat the value caused by said capacity effect;

and control electrodeand of such a value that the transmission frequency characteristic of said means is lowered at the frequency of said first mentioned resonance and maingainad rising with frequency above said 4. A transmission circuit comprising an incoming line and an outgoing line, an amplifier for repeating from said incoming line to said outgoing line electrical variations extending over a wide frequency band, said amplifier having electrodes between which an appreciablepapacity effect exists,

the transmission eificiency for said intermemediate frequencies remains substantially unchanged at the value caused by said capacity effect, and a capacity connected across two of the electrodes of said am lifier and of such a value that-the transmission efliciency of said amplifier is lowered at the frequency of said first mentioned resonance.

In witness whereof, I hereunto subscribe quencies and said upper frequencies while my name this 2nd day of August, A. D. 1922.

WILLIAM L oAsPER.

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