US1844374A

US1844374A - Electric coupling circuits

Info

Publication number: US1844374A
Application number: US476541A
Authority: US
Inventors: Harold A Wheeler
Original assignee: Hazeltine Corp
Current assignee: BAE Systems Aerospace Inc
Priority date: 1930-08-20
Filing date: 1930-08-20
Publication date: 1932-02-09
Anticipated expiration: 1949-02-09

Description

FBI). 9, 1932. WHEELER 1,844,374

ELECTRIC COUPLING CIRCUITS Filed Aug. 20, 1930 INVENTOR Harold A. Wheeler ATTORNEY5 Patented Feb, 9, 1932 PATENT OFFIC lElIlllFtlULD A. WHEELER, JAUKSUN HEIGHTS, NEW YORK, ASSIGNOR TO HAZEL'I'INE UORPOMTIUN, A UORPOJRA'IION OF DELAWARE ELECTRIC CUUPLINU- CIRCUITS Application tiled. August $0,193). Serial No. 4%,541.

'lhis'invention relates to hi h fre uenc electric coupling circuits tunable over 'a range in frequency and adapted more especially for ll'llfilCOllllCClllhg successive elements of a high frequency thermionic amplifier or lTl manner which is under the control of the designer; the design in general being preferably such as to produce a substantially constant amplification, i. e. uniform sensitivity throughout the tunable frequency range.

With an elementary type of high frequency coupling circuit, of which a two-winding transformer having a tunable secondary is a typical example, the variation in amplificaiil tion with frequency is not under the control ill the designer, but increases with frequency throughout the tunable range, in a manner well understood, so that the resulting sensitivity is widely different at the lower and higher frequencies.

in the elementary type of coupling circuit referred to-above, there exists between the primary and tunable secondary circuits, a degree of coupling which is substantially constant throughout the tunable range, a condition which is partially responsible for the mentioned increase in amplification with frequency. The present invention avoids the resultant disadvantages of the elementary ent invention both as regards the circuit connections utilized and the specific modes of operation involved, are set forth in Patent No. 1,763,380 issued to C. E. Trube, and in his co-pending applications Serial No.

101,906, filed April 14, 1926 and Serial No.

120.045, filed July 2, 1926.

The coupling circuits of the present invention comprise the following essential elements, namely: a tunable secondary circuitincluding a fixed inductive winding and variable capacity bridged between a pair of output terminals, and a primary circuit including in closed series connection in the order named, a portion or all of the secondary winding, a fixed capacity, a fixed inductance, and a primary winding magnetically coupled to the secondary winding and of relatively small magnitude compared to the fixed inductance. The primary winding is so poled as to give coupling from the primary to the secondary circuit in additive relation to the coupling to the portion of the secondary winding which is included in the primary circuit. lnput terminals are connected to the primary circuit between the fixed capacity and inductance and between the primary and secondary windings, respectively, so that there is provided a pair of parallel paths, one path containing the fixed capacity and the portion of said secondary winding included in the primary circuit, while theiother path contains the fixed inductance and the primary winding magnetically. coupled to the secondary. i

An additional capacity may or may not be connected directly between the input terminalS accOrding to whether or not there is i already present suilicient capacity for the purpose explained below. On the other hand, sufficient capacity may exist between these terminals due to the type of input conne'cted thereto. In any event, the resulting capacitynssociated with the inductance of the primary circuit, including the fixed ca pacity of the closed series circuit which is connected in shunt with the primary circuit, as well as any capacity existing between-the input terminals, should be such as to render the primary circuit resonant at a frequency lower but not greatly lower than the lowest frequency within the tunable range.

The objects-attained by such design (1) provide an effective coupling between primary and secondary circuits which automatically falls ofi as the frequency of tunin is increased, ,at a rate proportioned to profuce a desired variation in amplification with frequency, and (2)" control the variationsin input impedance of the coupling circuit throughout the tunable ran e in such manner as to insure the desired per ormance. j

The manner. in which the results of the present invention are attained will be .more

clearly understood upon detailed consideration of thecircuit connections set forth in the drawihgs, of which:

tubes in cascade relation; while Figure 5 shows an interstage connection employing triode tubes wherein the coupling circuit is arranged in conjunction with a suitable capacity to provide neutralizatiqnof the interelectrode tube capacity.

Like elements are similarly designated in the several figures.

:Referring to the drawings, the coupling circuit of-.Fig. 1 comprises a resonant secondary circuit consisting of a fixed inductive winding L and a variable tuning condenser G bridged between output terminals, and a pri mary. circuit associated with the input terminals I including in closed series connection in the ordennamed, the entire winding L, a

fixed capacity C ,ja fixed inductance L and a primary winding L, magnetically coupled.

to the secondary winding L as indicated, and of relatively few turns compared tofthe fixed inductance L The winding L is so poled asto give coupling from the primary to the secondary circuit in additive relation with the couplin to the winding L.

A pair- 0 input terminals I .are connected I between'the fixed capacity C and theinductance L and between the primary winding L and the secondary windingL respectively,

thereby providing the parallel paths between the input terminals one of which contains the fixed capacity C and secondary winding L,

while the other path contains the fixed inductance L and the primary winding L The capacity C shown dotted is intended to represent the entire capacity connected between the lnput terminals during operationofthe circuit, including any capacity 'efiects due to the input impedanceconnected thereto together with the capacity of'a supplementary condenser which may be connectedbetween these terminals. I

i The capacities C and G together with any additional capacity efiects associated with the primary circuit inductance which includes the elements L L and L, should be such as to render the primary circuit resonant at a frequency lower, but not greatly lower, than the lowest frequency in the tunable range as determined by adjustment of condenserC.

Itis not essential to the operation of the circuit that a capacity (L exist between the input terminals I. In the event that the capacity C is zero, however, itis required that the capacity C be of such magnitude as to render the primary circuit resonant at the low frequency above specified.

The reactances of the primary circuit are so proportioned that the path between the input terminals containing the elements 0 and L is ca acitatively reactive throu h-. out the tuna le range, and. hence of ecreasing impedance for increases in the tuned frequency; whereas the path containing elements L and L being of necessity inductively reactive, the impedance thereof increases with the tuning frequency. Thus, the windings L and L produce efiects in the secondary circuit which vary in opposite fashion with the tuning adjustment, the resultant effect being proportioned to produce an efi'ective coupling between primary and secondary circuits which automatically decreases with increasing tuning frequency, in .a manner' which with suflicientaccuracy is expressed by the following equation:

4 ime oar where is the resonant frequency of the primary circuit,'f 'thefrequency of tuning, while m and m are constants expressed by In Equations (2) and (3) the symbols L, C

and C have the significance shown in the drawings; while M is the mutual inductance between windings L and L. It will be observed from Equation (1) that; the efl'ective coupling must necessarily decrease with increase in the tuned frequency.

' The modification of Fig. 2 differs from Fig. 1 in that condenser C is connected to an intermediate point of winding L so that only a portion L; of the secondary winding L is included in the primary circuit.

The operation of the circuit oat Fig. 2 is substantially identical with that of Fig. 1. The coupling constants m and m however, are changed from those given in Equations {2) and (3) to the following expressions:

where ltl is the mutual inductance between windings L and lb, the significance ot the remaining symbols being the same as for Equations (2) and in Fig. 3 the input terminals T of the coupling circuit cit Fig. 2 are connected to an antenna 1 and a ground 2, respectively, while the output terminals are connected to the grid and cathode, respectively, of a thermionic tube "t1. The capacity C: of Figs. 1 and 2 comprises in Fig. 3 the effective antenna-togronnd capacity or the antenna 1 which in conjunction with capacity C renders the primary circuit inductance comprising elements li la and L, resonant at a frequency below the tuning range.

Tn T ig. lwherein the coupling circuit interconnects a pair ot screen-grid tubes, V and in cascade relation, the input terminals it are connected to the anode and cathode respectively of tube T while the output terminals U are connected between grid and cathode respectively of tube V it. battery B tor supplying space current to tube W} is serially interposed in the shunt path containing elements L and Ti, with the negative battery terminal joined to the grounded conductor 3Q The capacity (5 of Fig. 2 comprises in Fig. l. the anode-to-ground capacity ot tube T7 which together with capacity in renders the inductance of the primary cir- I cuit resonant at the mentioned low frequency.

The coupling circuit of l ig. 5 interconnects a pair ct triode tubes in cascade rela tion, each tube having anode, cathode and grid electrodes only. Tn order to neutralize grid-to-anode capacity of tube V a eondenser G,, is connected from the anode thereof to the point between the fixed inductance T1 and the primary winding T1 this point being at opposite polarity to that of the upper terminal o't winding L to which the interelecrode capacity Q is connected. The neutraliaation is accomplished in the manner disclosed in Patent No. l,lfi9,22fi issued to L. A. lt-laaeltine, April l, 1924.

Tn rug. 5 the capacity C comprises the anode-to-ground ot the tube V, plus the capacity ot the associated neutralizing condenser Un which is etlectively in parallel therewith, owing to the small inductance of the winding L While the coupling circuit of Fig. 2 is shown in all of the various modifications-in Figs. 3 to 5, inclusive, it is to be understood that the coupling circuit of Fig. l'might in each instance have been equally well employed, additional figures including such disclosure being deemed unnecessary.

It will be noted that in Figs. 3 to 5 inclu sive the circuit arrangement issuch that the rotor element of the tuning condenser may be grounded directly, constituting a very desirable feature in that it eliminates certain incidental couplings between the several parts of the amplifier.

ll claim:

1. An electric coupling system comprising a tunable secondary circuit including a fixed secondary winding and variable capacity bridged between output terminals, and a primary circuit including in closed series connection in the order recited, at least a portion of said secondary winding, a fixed capacity, a fixed inductance, and a primary Winding magnetically coupled to said secondary and of relatively few turns compared to said fixed inductance, an input terminal connected between said fixed capacity and inductance, and a second input terminal extending between said primary and secondary windings, the inductance included in said closed series circuit together with the associated capacities including any capacity bridged between said input terminals in the operation of said circuit, being resonant at a frequency slightly below the tunable range.

2. An electric coupling system comprising a tunable secondary circuit including a fixed secondary winding and variable capacity bridged between output terminals, and a primary circuit including in closed series connection in the order recited, at least a portion 0t said secondary winding, a fixed capacity, a, fixed inductance and a primary winding of relatively few turns compared to said fixed inductance and magnetically coupled to said secondary winding, an input terminal connected between said fixed ca pacity and said fixed inductance, and a second input terminal connected between said pri mary and secondary windings, and a fixed capacity bridged between said input terminals, said fixed inductance together with the associated capacities being resonant at a frequency slightly below the tunable range "for controlling throughout said frequency range the coupling between said primary and secondary circuits. I

3. An electric coupling system comprising a tunable secondary circuit including a fixed secondary winding and variable capacity bridged between output terminals, and a' primary circuit including in closed series connection in the order recited, at least a portion of said secondary winding, :1 fixed capacity, a fixed inductance, and a primary compared to said fixed inductance, an input.

' terminal connected between said fixed capacity and said fixed inductance, a second input terminal connected betweensaid primary and secondary windings, said fixed inductance together with theassociated capacities including any capacity bridged between said input terminals in the operation of said circuit, being resonant at a frequency slightly below the tunable range, said primary and secondary windings having opposite polarities.

4. In a radio receiving system the combination of ahigh frequency electric coupling circuit comprising a tunable secondary circuit including a fixed secondary winding and variable capacityf bridged between grid and cathode of a thermionic tube; and a primary circuit including in closedseries con-' nection in the order recited, at least a portion of said secondary winding, a fixed capacity, a fixed inductance and a'prilnary winding magnetically coupled to. said secondary winding, an input terminal connected between said fixed capacity and said fixed. in-

, ductance, a second input terminal connected between said primary and-secondary windings the terminals of which thus joined are of opposite polarity, and an antenna circuit connected to said input terminals, the inductance of said primary circuit together with the associated capacities includingthe capacity of said antenna effectively bridged between said input terminals, being resonant at a frequency below the tunable range, for automatically controlling throughout said range the coupling between said primary and secondary circuits.

5. A high frequency thermionic amplifier comprising the combination of an electric coupling circuit having a tunable secondary circuit consisting of a fixed secondary winding and variable capacity bridged between grid and cathode of a first thermionic tube, a primary circuit including in closed series connection in the order recited, at least a portion of said secondary winding,-a fixed capacity, a fixed inductance, and a primary winding magnetically coupled to said secondary a second thermionic tube having an anode connected between said fixed capacity and inductance,-and a cathode connected between said primary and secondary windings the terminals of which thus joined are of opposite polarity, the inductance of said primary circuit together with the associated capacities including the anode-'to-ground capacity of said second tube being resonant ata frequency slightly below the tunable range, for providing automatically throughout vsaid range uniformly high degrees of amplification. I

6. A high frequency'thermionic amplifier comprising the combination of an electric circuit including a fixed secondary winding and variable capacity bridged between grid and cathode of a first-thermionic tube, a pri coupling circuit having a tunable secondary mary circuit including in closed series connection in the order recited, at least aportion of said secondary windlng, a fixe'd capacity, a fixed inductance, and a primary winding windings the terminals of which thus joined are of opposite polarity, and a condenser magnetically coupled to said secondary 7 proportioned, to neutralize the anode-to-grid capacity of said first tube connected from the anode thereof to a point between said primary winding and said fixed inductance, said fixed inductance together with the associated capacities including the anode-to-ground capacity of said second tube and said condens-- ers being resonant at a frequency below the tunable range, for providing automatically throughout said range .uniformly high degrees ofamplification in the operation of said amplifier.

In testimony whereof I affix my signature.

HAROLD A. WHEELER.