US1908934A - Electric coupling system - Google Patents

Description

May 16, 1933. Q TRUBE 1,908,934

ELECTRIC COUPLING SYSTEM Original Filed May 14, 1930 j z: L I I'm i A BY ABM 77M 2 ATTORNEYS Patented May 16, 1933 UNITED STATES PATENT OFFICE CARL E. TRUIBE, DECEASED, LATE OF OSSINING, NEW YORK, BY SARAH M. TRUBE,

ADMINISTRATRIX, 0F OSSINING, NEW YORK, ASSTGNOR T0 HAZELTINE CORPORA- TION, .A. CORPORA'IION' OF DELAWARE i ELECTRIC COUPLING SYSTHE Original application filed. May 14, 1930, Serial No.

Serial No. 522,344.

This invention relates to electric coupling systems especially adapted for use with radio-frequency vacuum or thermionic tube amplifiers, and more particularly tocircuit arrangements which operate most effectively over a relatively wide range in frequency. The coupling systems are so arranged as to give a voltage ratio that varies automatically with the frequency. The variation in voltage ratio is accomplished in a primary circuit which includes a fixed self-inductance effectively in parallel with one or more fixed capacities external to the main resonant circuit and which may be electrically'ls'olated from the main resonant circuit. The 'primary circuit is resonant at a frequency lower (but preferably not greatly lower) than the lowest frequency within the range of the coupling system. Coupling systems answering this description are described generally in application for U. S. Letters Patent, Serial No. 292,739, patented June 10, 1930, No. 1,763,380, and in a division thereof, Serial No. 452,464, filed May 14, 1930, patented March 31, 1931', No. 1,798,962. The present application is in turn a division of the mentioned application Serial No. 452,464.

The voltage ratio in an inter-tube coupling system affects the degree of amplification, the stability and the selectivity. At each frequency there is a particular who of output voltage to input voltage that Wlll give the best compromise design. This ratio varies rapidly with the frequency, being relatively high at high frequencies. This invention provides means for securing substantially the most desirable ratio at all frequencies without having any adjustable element except the tuning adjustment.

Referring to the drawing, Fig. 1 lllustrates a vacuum tube and an electric coupling system embodying a simple form of this invention.

Fig. 2 illustrates a modification of Fig. 1 having an additional fixed capacity.

Fig. 3 illustrates a modification of Fig. 2 in which a two-coil transformer replaces an auto-transformer.

Fig. 4 illustrates a modification of Fig. 3

452,464, now Patent No. 1,798,962, dated March 31, Divided and this application filed March 13, 1931.

by which direct voltage is removed from the fixed capacity.

The coupling system of Fig. 1 is tuned by a variable condenserC connected across the primary coil L and the secondary coil L in series. Ordinarily L should have much .fewer turns than L so that ithere is a high step-up voltage ratio between them. The path through the primary coil L from the plate of the vacuum tube to the filament includes also the fixed capacity G which is external to the main resonant circuit C L L In parallel with this path" is a second path including the self-inductance L the value of which is so chosen that its circuit (completed through C and L is resonant at a frequency lower, but not greatly lower,

than the lowest frequency within the range of condenser G I The circuit of L being completed through 5 and L is thereby coupled to themain resonant circuit C L L so that part of the current of C and L will flow through C; and L this part of the current being limited mostly by the reactance of L Since the reactance of L varies directly with the frequency while that of C varies inversely with the frequency, the voltage across C will rapidly fall off relative to the voltage across L as the frequency rises. For a given output voltage E the voltage across L is very nearly independent of frequency, due to the electromagnetic coupling between L and Hence the voltage E between the plate or anode and the filament or cathode, being the sum of the voltages of O and L will fall off relative to E as the frequency rises, but less rapidly than the voltage across 0 alone. This is the condition'which is desired and which results in the maintenanceof a high degree of stability over the frequency range, together with high sensitivity and selectivity.

The operation of the circuit of Fig. 2 is essentially the same as that -of Fig. 1, but

here the circuit of L is completed through range of C lowest frequency within the The voltage ratio E /E is obtained from a double step-up, first between G and the combination of O and C and then between L and L and, with the resonant condition just given, this voltage ratio will automatically vary with the frequency in the same manner as in Fig. 1.

Fig; 3 difi'ers from Fig. 2 only in that the primary coil L is not included in the main resonant circuit. Coil L should here have the same number of turns as in Fig. 2; while the secondary coil L should have the same number of turns as L and L combined, in Fig. 2. The remaining relations are the same as in Fig. 2. V

In Fig. 3 the direct voltage of the plate battery B exists across condensers C and C which is disadvantageous in that these condensers may break down. This difficulty is obviated in Fig. 4 by connecting the lower terminals of condenser G and coil L to the lower, than the lower terminal of coil L instead of to the common lead at the bottom of the diagram. This connection does not alfect the alternating-current relations of Fig. 4, which are identical with those of Fig. 3.

'What is claimed is 1. In a high-frequency system, a thermi onic tube having anode, cathode and control electrodes, an electric coupling system comprising a resonant circuit tunable throughout a range in frequency, and a second circuit including fixed inductance and capacity proportioned to produce resonance at a frequency below said tunable range, said fixed capacity being external to said resonant circuit, andsaid fixed inductance being electromagnetically uncoupled fromsaid tunable circuit, a coupling impedance having a fixed voltage ratio relative to said tunable circuit,

and a path through said coupling system between said anode and-cathode including in series said coupling impedance and at least a. portion of said fixed capacity, said coupling impedance being much smaller than a that of said portion of said fixed capacity throughout said rangein frequency, the elements of said coupling system being so proportioned that the ratio of resonant voltage developed across said tunable circuit to an input voltage impressed between said cathode and control electrodes remains substantially constant as the tuning is variedthroughout said frequency range.

2. In a high-frequency. system, a thermionic tube having anode, cathode and control electrodes, an electric coupling system comprising a resonant secondary circuit tunable throughout a range in frequency, and a primary circuitincluding fixed inductance and capacity proportioned to produce resonance below said tunable range, said fixed capacity being external to said secondary circuit and including the auode-to-cathode capacity of said tube, said fixed inductance being un coupled electromagnetically from said secondary circuit, a coupling impedance having a fixed voltage ratio relative to said secondary circuit, and a path through said coupling system between saidanode and cathode including in series said coupling impedance and a portion of said fixed capacity, said coupling impedance being much smaller than that of said portion of said fixed capacity throughout said range in frequency, the elements of said coupling system being so pro-- portioned that the ratio of resonant voltage developed across said secondary circuit to an input voltage impressed between said cathode and control electrodes remains substantially constant as the tuning is adjusted throughout said'frequency range.

3. In a high-frequency system, a thermionic tube having anode, cathode and control electrodes, an electric coupling system which comprises a main resonant circuit including as elements a secondary coil and a condenser at least one of which is adjustable to vary the tuning throughout a range in frequency, a second circuit including fixed self-inductance effectively in parallel with fixed capacity external tosaid main resonant, circuit, said self-inductance and fixed capacity last mentioned being proportioned to produce resonance in said second circuit at a frequency lower than the lowest frequency within said tunable range, a primary coil electromagnetically coupled to said secondary coil and a path through said coupling system between said anode andcathode including in series said primary coil and at least a portion of said fixed capacity, said primary coil having much smaller reactance than said portion of said fixed'capacity throughout said range in frequency, the elements of said coupling system being so proportioned that the ratio of resonant voltage developed across said secondary coil to an input voltage impressed between said cathode and control electrodes remains substantially constant as the tuning is adjusted throughout said frequency range.

4. A high-frequency coupling system having input terminals and comprising a resonant circuit tunable'througho'ut a range in frequency by adjustment of a single variable element, and a second circuit including fixed inductance and capacity proportioned to produce resonance at a frequency below' said tunable range, said fixed capacity. being external to said resonant circuit, and said fixed inductance being electromagnetically uncoupled from said tunable circuit, a coupling portion of said fixed capacity throughout said range in frequency, the aforementioned proportioning of elements in said coupling system being such that there is developed in said tunable circuit a resonant voltage whose ratio to the voltage impressed between said input terminals automatically rises with frequency as the tuning is Varied throughout said frequency range by adjustment of said single variable element.

5. In a high-frequencysystem,athermionic tube having anode, cathode and control electrodes, an electric coupling system comprising a resonant circuit tunable throughout a range in frequency by adjustment of a single variable element, and a second circuit including fixed inductance and capacity proportioned to produce resonance at a frequency below saidtunable range, said fixed capacity being external to said resonant circuit, and said fixed inductance being electromagnetically uncoupled from said tunable circuit, a coupling impedance having a fixed voltage ratio relative to said tunable circuit, and a path through said coupling system between said anode and cathode including in series said coupling impedance and at least a portion of said fixed capacity, said coupling impedance having a much smaller reactance than said portion of said fixed capacity throughout said range in frequency, the elements of said coupling system being so proportioned that the ratio of resonant Voltage developed across said tunable circuit to an input voltage impressed between said cathode and control electrodes remains substantially constant as the tuning is varied throughout said frequency range by adjustment of said single variable element.

6. In a high-frequency system, a thermionic tube having anode, cathode and control electrodes, an electric coupling system which comprises a main resonant circuit including as elements a secondary coil and a single variable condenser for adjusting the tuning throughout a range in frequency, a second circuit including fixed self-inductance effectively in parallel with fixed capacity external to said main resonant circuit, said fixed self-inductance and fixed capacity being proportioned to produce resonance in said second circuitat a frequency lower than the lowest frequency within said tunable range, a coupling impedance having a fixed voltage ratio relative to said main resonant circuit, and a path through said coupling system between said anode and cathode includ ing in series said'couplin impedance and at least a portion of said xed capacity, said coupling impedance having a much smaller reactance than said portion of said fixed capacity throughout said range in frequency, the aforementioned proportioning of, elements in said coupling system being such that there is developed in said main resonant cir- SARAHv M. TRUBE, Administratriw 0f the Estate of Carl E.

Tru be, Deceased.

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