US2278251A - Transmission system - Google Patents

Description

March 31, 19412, R. B. DOME TRANSMISSION SYSTEM Filed May 5, 1941 Inventor: Robert, B. Dome,

Hus Attorney.

Patented Mar. 31, 1942 7 TRANSMISSION SYSTEM Robert B. Dome, Bridgeport, Conn.. asslgnor to General Electric Company, a corporation of New York Application May 5, 1941, Serial No. 391,902

' '3 Claims. (c1. 178-44) of an amplifier.

Another object of my invention 's to provide such a circuit which is well adapted for operation between a source and a load having unequal impedances.

Still another object of my invention is to provide such a system in which all of the shunt capacitance of the system may be considered as a single capacity in shunt with the circuit for all of the purposes of computation, or adjustment, of the constants of the various elements of the system.

The novel features which Ibelieve to be characteristic of my invention are set forth with particularity in the appended claims. My invention itself, however, both as to its organization and.

method of operation, together with further objects and advantages thereof, may best be understood by reference to the following description taken in connection with the accompanying drawing in which Fig. 1 represents an embodiment of my invention and Fig. 2 represents a modification thereof.

Referring to Fig. 1 of the drawing I have illustrated my invention therein as employed in the circuits between a pair of electron discharge devices I and 2 where it may be employed to serve for the transmission of currents from one stage I of an amplifier to the second stage 2 thereof with uniform attenuation over a wide band of frequencies. Such an arrangement is especially adapted for use in connection with the amplification of the video currents in television systems, for example, or in other typ of. systems where it is necessary to transmit currents having frequency extending between a definite lower limit F1, which is above zero, and a higher limit F2. In television systems these frequencies F1 and F2 may be as much as four megacycles, or more, apart.

Signals to be amplified may be supplied between the grid and cathode of the amplifier I through a coupling condenser 3 from a source not shown. Operating potential is supplied to the anode of the amplifier I from a source of unidirectional potential 4 through an inductance '5, the source being by-passed by the usual by-pass condenser 6. Signal potentials appearing on the anode of the discharge device I are supplied through a coupling condenser l to the grid of discharge device 2, the latter of which may be connected to the cathode through a high resistance 8 anda source of bias potential 9. The condenser l' may be a large coupling capacitor such that its impedance'is negligible over the band of frequencies to be transmitted. Similarly, the resistance 8 may be very high such thatits shunt conductance may be neglected at, frequencies to be transmitted. r

In accordance with my invention an additional shunt path is provided comprising a resistance Ill, an inductance H and a condenser l2, the inductance ll being adjusted to resonate with the condenser I! at the mean frequency of the band to be transmitted. The shunt capacitance of the circuit'including the interelectrode capacitances of the discharge devices, and the shunt circuit capacitances may, for the purposes of my mvention, be considered as a single capacitance connected in shunt with the circuit as'indicated by the dotted lines l3. The inductance 5 may then be proportioned to resonate with the capacitance I: at the mean frequency of the bandto be transmitted, that is, at the same frequency at which the inductance ll resonates with the condenser II.

With the system thus adjusted the inductance 5 and-condenser l3 resonate at the mean frequency and thus produce high impedance in shunt with the signal channel. Since inductance II and condenser l2 resonate at this same fre quency the series impedance of these two elements is zero, the resistance III is effectively in shunt with the circuit and thus acts as a damping resistance upon the tuned circuit 6, 13.

In Fyler Patent No. 2,190,513 it has been shown that to obtain uniform transmission over a band creases.

the frequency at which elements II and I2 resonate, be considered to correspond to the lower frequency, zero, of the band of frequencies considered in the Fyler patent. That is,

1 21a F1)C' (1) where R is the resistance of the resistor I and C is the shunt capacitance of the system which is that indicated at I3. As the frequency departs from .the mean frequency, the impedance of the circuits 5, l3, of course, reduces, whereas the series impedance of the elements II and I2 in- These two effects tend to compensate each other to produce a uniform impedance over the band of frequencies to be transmitted, the increased series impedance of inductance I I and capacitance I2 reducing the loading on the circuit 5, I3 produced by resistance II).

To produce such uniform impedance over any desired band of frequencies, the reactance in series with the resistance II) should be half of the resistance of the resistor III at the frequency F2,

1. e. at the highest frequency in the band, or

zm'cfi (2) where L1 is the inductance of the inductance II and C1 is the capacitance of condenser I2. This is a value which has been mentioned in Fyler Patent No. 2,190,513 and may mathematically be demonstrated to be proper for the purposes of producing uniform impedance over the band. Similarly, the reactance in series with the resistance II) at the lower frequency F1 should be half of the resistance of the resistor III, or

Then, solving Equations 2 and 3 simultaneously with the capacity C, represented at I3 at the frequency F0 cycles per second. Therefore,

Since in setting up the system the capacitance I 3 is generally known, as are also the frequencies F2 and F1, the values. of the different elements of the system may be calculated from these equations.

Fig. 2 represents a modification of my invention in which the shunt circuit III, II, I2 of Fig. 1 is dispensed with and in place thereof elements ll, I5 and I6 are added. The element I 4 is an inductance resonating with the condenser I5 at the mean frequency of theband to be transmitted, these elements being connected in series with the coil 5. In shunt with the tuned circuit I4, I5 is the damping resistance I6, Inductance 5 is, of course, adjusted as before with respect to the condenser I3.

As thus arranged, it will be seen that at the resonant frequency F0, that is, the mean frequency of the band, the impedance across the combination I4, I5 is that of the resistance I6 since the combination I4, I5 is resonant, and thus has extremely high, or infinite, impedance. This resistance I6 acts as a damping, or loading, resistance on the circuit 5, I3, which is also resonant at this mean frequency F0. At frequencies departing from the mean frequency F0 thenelements 5 and I3 depart from resonance as do also the elements I4 and I5. Thus, the im- 1 mm-m0 (8) where C is the capacitance indicated at I3. Since resistance R of resistor I6 is in series with the inductance L of coil 5, then CR 41i' F R C Substituting in 8 and 9 for R0, R Z J 10 Since I ust resonate with C at the frequency F0, (x/FiFal it becomes 1 R L h ale 214F 43 (11) Then, by deduction l r F5; F )R where C1 is the capacity of condenser I5. Then also, by deduction R( zF1) I -rm where L1 is the inductance of the coil I4. Now, solving Equation 10 for C, we have 1F 2R With the various elements of the system computed in accordance with th'ese equations, the system will have uniform impedance and hence uniform attenuation over the entire band of frequencies extending from the frequency F: to the frequency F1, and the frequency F1 may be any desired frequency above zero. r

, While I have shown particular embodiments of my invention, it will, of course, be understood that I do not wish to be limited'thereto since different modifications may be made and I contemplate by the appended claims to cover any such modifications as fall within the true spirit and scope of my invention.

What I claim as new and desire to secure by Letters Patent of the United States is:

l. The combination, in a transmission circuit for currents having a wide range of frequencies, of inductance and capacity each connected in shunt to said circuit and resonant at a frequency in series with one of said first mentioned elements to reduce said damping as the frequency departs from the frequency of saidresonance.

3. The combination, in a signal channel for transmitting a wide 'band of frequencies, an inductance element and capacity element connected in paths across said circuit and resonating at a frequency within said band, a resistance connected to damp the resonanceof said inductance and capacity at said frequency and a second inductance and capacity resonant at said frequency connected in shunt with said resistance and in series with one of said first mentioned elements to reduce the damping of said resistance on said first inductance and capacity as the transmitted frequency departs from said first mentioned frequency, said resistance, inductance,

and capacity and said inductance and capacity elements being proportioned with respect to each other to produce uniform transmission through said channel for all currents having frequencies within the band to be transmitted.

ROBERT B. DOME.

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