US2459493A - Tuning means comprising variable condenser and adjustable inductor of the mechanicaly deformable type - Google Patents

Description

1949- w. o. BRADFORD ETAL 93 TUNING MEANS COMPRISING VARIABLE CONDENSER AND ADJUSTABLE INDUCTOR OF THE MECHNICALLY DEFORMABLE TYPE Filed Sept. 26, 1945 Patented Jan. 18, 1949 TUNING MEANS COMPRISING VARIABLE CONDENSER AND ADJUSTABLE INDUCTOR F THE MECHANICALLY DEFORMABLE TYPE William 0. Bradford and Emil G. Zapor, Baltimore, Md., assignors to Bendix Aviation Corporation, South Bend, 1nd,, a corporation of Delaware Application September 26, 1945, Serial No. 618,748

4 Claims. 1

This invention relates to tuning means employing adjustable inductors and more particularly to tuning means of this type employed in connection with high frequency receivers. The desired variation in characteristic is secured by alteration of the mechanical dimensions of the inductor structure.

To secure the performance required in present day radio communication apparatus, it is necessary that the various circuits be accurately tuned with respect to the incoming signal frequency and, in superheterodyne receivers, it is further necessary that the resonant frequency of the oscillator circuits maintain a. special relationship to the resonance frequency of the signal responsive circuits, the two frequencies usually differing by an amount equal to the intermediate frequency of the receiver. To this end, it is customary to employ in the oscillator circuit a coil having inductance different from the coils present in the signal frequency circuit. Since the commonly available gang capacitors have identical individual sections, the necessary difference in tuning ratio is made up by a padding capacitor connected to the capacitor section controlling the oscillator circuit.

In the alignment of such receivers, it is desirable to control the minium oscillator frequency as Well as the tuning ratio of the circuit, and for this reason some means is usually provided for varying the inductance of the oscillator coil. At frequencies below two megacycles per second an adjustable iron core is frequently employed, whose position within the coil is adjusted to provide the desired inductance. At higher frequencies up to thirty megacycles per second, it becomes more difiicult to provide iron whose magnetic properties are satisfactory and there are, therefore, employed devices relying on magnetic fields produced by eddy currents to adjust the coil inductors. A typical example is the use of a brass plunger movable along the axis of the coil. Insertion of the plunger in the coil reduces the inductance thereof because of the eddy current reaction on the magnetic field. In this case, it is evident that power losses are reflected into the coil.

When working with signals of the order of 100 megacycles persecond, it becomes quite difficult to prdouce iron having high enough permeability to permit adequate control of the inductance which, at the same time, has low losses, and the use of the eddy current method in itself relies upon the existence of losses for the control of inductance. Circuit impedances, as controlled by stray capacitors at megacycles per second, are unfavorable to the efficient operation of Vacuum tube amplifiers, and reduction in the operating Q of the circuit due to losses introduced by inductance controlling means greatly aggravate these difficulties.

To escape the disadvantages occurring from the use of conducting or high permeability adjustable coil cores, employment of air coils has been made. For the performance of the alignment or tracking operation, the operator mechanically deforms the coil, changing its effective length or turn spacing to control the inductance. The residual elasticity of the coil inductors makes it impossible to adjust directly to the desired value because of its tendency to return to the original shape. To overcome this, the operator is forced to distort the coil beyond the final desired configuration and trust that he has estimated the elasticity correctly enough to result in the required ultimate adjustment. This adjustment by successive approximation is time-consuming and requires a skilled operator.

One of the principal objects of the invention is the provision of a new and novel tuning means utilizin a conveniently adjustable inductor whose losses are not substantially greater than that of the coil structure itself.

Another object of the invention is the provision of a new and novel tuning means including an inductor, the latter being adjustable by action of a control means which employs neither magnetic nor conductive material in the field of the coil.

A further object of the invention is the provision of a new and novel tuning means utilizing an adjustable inductor of the mechanically deformable type which may be directly adjusted to its final desired value.

The above objects and advantages of the invention are substantially accomplished by the use of a tuning arrangement in which one end of a deformable coil is anchored to a fixed surface and conductively connected to the stator of a rotary condenser while the other end is secured to a pivoted arm which may be swung about its pivot by the action of an eccentric adjusting screw, and secured in its final position by a cooperating locking screw, the arm conductively c0nnecting the coil to the condenser rotor.

Other objects and advantages of the invention will in part be disclosed and in part be obvious when the following specification is read in conjunction with the drawings in which:

Figure 1 is a front view of the coil and the adjusting mechanism;

Figure 2 is a side view of a condenser assembly showing the adjusting mechanism,

Referring now to Figures 1 and 2, there is shown an air core coil '10 with a fixed number of turns determined by the intended frequency range of operation. One end I? of coil is electrically connected to the stator section M of the associated gang condenser, and secured mechanically by a phenolic high frequency insulator strip l6, riveted to the metallic end plate l8 of the frame of the gang condenser. The end of the coil is attached, as by soldering, to one end of the arm 22, having its other end pivotally connected to the end plate 58 by the rivet 24. The arm 22 is fabricated of conductive material and serves as a ground link between the end 20 of coil ID, and the end plate 18. The condenser rotor 11 and the end plate 18 are electrically connected by virtue of the fact that the rotor plates are di-. rectly mounted on the condenser control shaft l9 which is journaled in the end plate 18. Hence, the coil H3 is eifectively connected directly across the electrodes of the variable capacitor assembly and may be tuned to resonance with any desired frequency thereby. The arm 22 is provided with an elongated slot 28 extending longitudinally thereof. An eccentric adjusting means 30 is mounted on the end plate 58. It comprises a circular head 3|, provided with a screwdriver slot, and a shaft portion 33 having one end secured to the underside of the head 3i in an eccentric location. The adjusting means is mounted with the head disposed within the slot 26 and the shaft extending through the end plate IS, the free end being riveted. The adjusting means makes a friction fit with the end plate l8 and the arm 22, thus being rotatable by means of a screwdriver or similar tool for the adjustment of the length of the coil it. A locking screw 28 passes through an arcuate slot 32 formed in the arm 22, the arc of the slot being concentric With the rivet 24, and extends into a tapped aperture in the end plate i8.

When it is desired to adjust the inductance of coil I, the locking screw 28 is loosened and the eccentric adjuster 3i! rotated using a screw driver or other suitable tool, thus rocking the arm 22 about the pivot 24. The movement of the free end of arm 22 now extends or compresses the coil 10 to the extent necessary to adjust the inductance to the requisite value. The locking screw 28 may now be tightened to permanently secure the assembly in this position.

The described mechanism provides for easy, quick, accurate and permanent adjustment of the inductance, and the connection of the adjusting mechanism to the ground side of the coil prevents energy losses.

It will be obvious that many changes and modifications may be made in the invention without departing from the spirit thereof as described in the foregoing description and in the appended claims.

What is claimed is:

1. In combination with a variable capacitor having a conductive end plate electrically connected to a rotor insulated from a stator, an inductive winding, electric insulating means me,- chanically securing one end of said inductive winding to said end plate, means electrically connecting said one end of said winding to said stator, and electrically conductive means carried by and electrically engaging said end plate, said conducting means being secured to the remaining end of said inductive winding and movable with respect to said end plate to vary the length of said winding.

2. In combination with a variable capacitor having a conductive end plate electrically connected to a rotor insulated from a stator, an inductive Winding, electric insulating means mechanically securing one end of said inductive winding to said end plate, means electrically connecting said one end of said winding to said stator, an electrically conductive means carried by and electrically engaging said end plate, said conductive means being secured to the remaining end of said inductive winding, means adjustable to move said conductive means with respect to said end plate to vary the length of said winding, and means operable to lock said conductive means with respect to said end plate.

3. In combination with a variable capacitor having a conductive end plate electrically connected to a rotor insulated from a stator, an inductive winding, electric insulating means mechanically securing one end of said inductive winding to said end plate, means electrically connecting said one end of said winding to said stator, a conductive arm pivotally and conductively secured near one end to said end plate and conductively secured near its other end to the remaining end of said winding, said conductive arm being provided with a slot extending substantially radially from said pivot point, and rotatable eccentric adjusting means secured to said end plate and engaging said slot.

4. In combination with a variable capacitor having a conductive end plate electrically connected to a rotor insulated from a stator, an inductive winding, electric insulating means mechanically securing one end of said inductive winding to said end plate, means electrically connecting said one end of said Winding to said stator, a conductive arm pivotally and conductively secured to said end plate, said arm being conductively secured to the remaining end of said winding and being provided with a first slot extending substantially radially from said pivotal point and a second slot disposed substantially perpendicularly of said first slot, rotatable eccentric adjusting means secured to said end plate and engaging said first slot, and a locking member passing through said second slot and thread edly engaging said end plate.

WILLIAM O. BRADFORD. EMIL G. ZAPOR.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 793.77.? Fessenden July 4, 1905 1,533,749 Meirowsky Apr. 14, 1925 1,552,266 Bradley Sept. 1, 1925 1,913,978 Ewen June 13, 1933 2,106,120 Lindberg Jan. 18, 1938 2,367,576 Harvey et al. a Jan. 16, 1945 FOREIGN PATENTS Number Country Date 542,395 Great Britain Jan. 7, 1942

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