US2925495A - Tuner with primary coil on moving sleeve - Google Patents

Description

Feb. 16, 1960 I F. G. MASON ETAL 2,925,495

TUNER WITH PRIMARY COIL ON MOVING SLEEVE Filed Jan. '6, 195a FIqZ TORS

gm; Francls ason BY Harold T. Lqman TUNER WITH PRIMARY COIL ON MOVING SLEEVE Francis G. Mason, Weston, and Harold T. Lyman, Milford, Conn., assignors to Aladdin Industries, Incorporated, Nashville, Tenn., a corporation of Illinois Application January 6, 1958, Serial No. 707,314 Claims. (Cl. 250-40) This invention relates to tuners, particularly those adapted to cover a wide frequency range at high radio frequencies such as those employed for television broadcasting and the like.

One object of the present invention is to provide a new and improved tuner in which the effective inductance of a coil is varied by moving a conductive sleeve therealong, and in which the sleeve is arranged to carry an additional coil so that the coupling and transformation ratio between said coils will be varied by the movement of the sleeve.

A further object is to provide a tuner of the foregoing character in which the coil carried by the sleeve is adapted to be employed as a primary coil, while the other coil is employed as a secondary coil in a tuned circuit, and in which the coupling and transformation ratio between the coils is progressively increased as the inductance of the secondary coil is decreased by the movement of the sleeve.

Thus, it is an object of the present invention to provide a new and improved tuner in which the coupling and transformation ratio between primary and secondary coils is progressively varied with changing frequency of operation, so that the band width aflorded by the tuner may be maintained substantially constant.

A further object is to provide a new and improved tuner of the foregoing character which is durable, inexpensive and easy to manufacture.

Further objects and advantages of the present invention will appear from the following description, taken from the accompanying drawings, in which:

Fig. l is an elevational view of a tuner to be described as an illustrative embodiment of the present invention.

Fig. 2 is an elevational view of the coil employed in the tuner of Fig, 1.

Fig. 3 is a fragmentary enlarged elevational view of the tuner, showing a slight modification.

Fig. 4 is a fragmentary central longitudinal sectional view of the tuner.

Fig. 5 is a fragmentary greatly enlarged longitudinal sectional view to show details of the tuner.

It will be seen that the drawings illustrate a wide-range tuner which is especially arranged and particularly well adapted for tuning the antenna stage of a television receiver for covering the very high frequency (VHF) television bands, It will be understood, however, that the tuner 10 may be utilized in many other situations, either in the particular form shown or any suitably modified form. In a certain aspect, the tuner 10 may be regarded as an improvement upon the tuner covered in the copending application of Harold T. Lyman, Serial No. 438,043, filed June 21, 1954, now Patent No. 2,832,891 granted April 29, 1958. Thus, the tuner 10 comprises a coil 12 which is tuned by means of a conductive sleeve 14 movable along the coil. In this case, both the coil 12 and the sleeve 14 are substantially cylindrical in form, although other forms might be employed. The sleeve 14 is closely received around the coil 12 but is freely slidable therealong. A suitable di- States Patent 0 would be caused by a sliding conductive connection.

electric or insulating material is preferably provided between the coil 12 and the sleeve 14 so that the coupling therebetween will be substantially capacitive, rather than conductive. This arrangement eliminates the electrical noise which would be caused by conductive coupling. In this case, the dielectric takes the form of an insulating coating or sheath 16 over the coil 12, as shown to best advantage in Fig. 5. However, it will be understood that the dielectric might be provided in some other manner, as by merely providing an air space between the sleeve and the coil, or by providing a thin layer of insulation inside the sleeve. The dielectric coating 16 of the illustrated arrangement may be made of a synthetic epoxy plastic, or any other material having good electrical and mechanical characteristics. The coating 16 should be hard, smooth and wear-resistant, and should aflord low frictional resistance to movement of the sleeve.

In the illustrated construction, the coil 12 is advantageously formed as a thin conductive ribbon carried on an insulating cylindrical support or form 18. It is preferred to form the coil 12 on the support 18 by suitable circuit-printing techniques, which are known to those skilled in the art and need not be described. The support 18 may be of a ceramic or other suitable insulating material.

It will be seen from Fig. 2 that the pitch of the coil 12 increases progressively between its upper and lower ends. Thus, the inductance per unit length of the illustrated coil decreases between its upper and lower ends. While this arrangement is quite advantageous, it is not strictly necessary to the present invention, as will be apparent shortly.

Means are provided for making a circuit connection to at least one end of the coil 12. In this case, a lead 20 is simply soldered or otherwise connected to the lower end of the coil 12. Thus, the circuit connection is of a conductive character, but it will be understood that it might be of some other character, such as capacitive. A circuit connection might also be made to the opposite end of the coil, chiefly for the purpose of utilizing the coil as a direct current path tosupply a direct current potential to the lower end of the coil.

Means are also provided for establishing a circuit connection to the movable tuning sleeve 14. In the arrangement shown to best advantage in Figs. 1 and 5, the circuit connection is of a capacitive character. Thus, a capacitive coupling electrode, in the form of a ring 22, is mounted in closely spaced relation to the sleeve 14. Thus, the ring 22 is closely received around the sleeve. A dielectric or insulating material is preferably provided between the sleeve 14 and the coupling ring 22 so that the coupling will be capacitive rather than conductive. This arrangement again avoids the electrical noise that In the arrangement illustrated in Fig. 5, the dielectric takes the form of'a thin insulating coating 24 on the outside of the sleeve 14, although it will be understood that the insulation might be on the inside of the ring, or might simply be an air gap therebetween.

Generally, the coil 12 and the coupling ring 22 are stationary, while the sleeve 14 is movable. However, this situation might be reversed, the important thing being that the sleeve on one hand, and the ring and the coil on the other hand, are relatively movable. Various means may be provided for effecting such relative movement. In the arrangement illustrated in Fig. 1, the sleeve 14 is adapted to be moved by a flexible rod 26 which is suitably connected to the upper end of the sleeve. The rod 26 is connected between the sleeve 14 and a swingable operating arm 28 or the like. The rod26 may be secured to a disc 30 mounted in the upper end of the sleeve 14, as shown in Fig. I, or may be connected directly to the wall of the sleeve, as shown in the modified arrangement of Fig. 3. In the arrangement of Fig. 1, it is preferred to form the rod 26 of metal, while formingthe disc 39 of insulating material. However, the rod '26 may be made of suitable insulating material, such as nylon or the like. The specific arrangement of Pig. 3 utilizes a metal operating rod 26a which is soldered or otherwise secured to the outside of the sleeve 14, the ring 22 being dispensed with. The circuit connection to the sleeve 14 is then made through the flexible operating rod 26a. It is often convenient to connect the rod 26a to ground, as indicated by a grounded lead 32 in Fig. 3. However, the rod 26a may be insulated and connected to some point in the circuit other than ground.

It Will be understood that the sleeve 14 is capacitively coupled to the portion of the coil 12 within the sleeve. Thus, the effective inductance of the coil is provided by the uncovered portion between the sleeve 14 and the end lead 20. As the sleeve 14 is moved along the coil, the effective inductance is varied over a wide range. When the sleeve 14 is withdrawn to the upper end of the coil 12, the inductance is high. As the sleeve is moved to the lower end of the coil, the effective inductance is progres sively decreased. The inductance may be resonated by the distributed capacitance of the coil and the various stray and circuit capacitances between the terminals of the tuner.

Thus, the tuner provides a two-terminal tuned circuit, with the end lead 20 and the sleeve 14 as the opposite terminals. In the arrangement of Fig. l, a circuit lead 34 is connected to the coupling ring 22 to complete the connection to the sleeve 14.

In'the arrangement illustrated to best advantage in Fig. 4, the inside of the tuning sleeve 14 is stepped to reduce the losses in the tuned circuit. At its outer end, the sleeve 14 has a reduced inner surface-or bore 36 which is closely received around the coil 12. This surface 36 is in close capacitive coupling withthe coil. The remainder of the sleeve 14 is stepped outwardly on the inside to provide an enlarged inner surface or bore 38 which is spaced outwardly some distance from'the coil and thus. is not in close capacitive coupling thereto. capacitive coupling between the sleeve 14 and the coil 12 is largely restricted to the reduced inner surface 36, so that the capacitive current transfer is localized at this point. Thisavoids any need for the current to flow any distance along the unused portion of the coil within the sleeve 14, and has the effect of greatly reducing the losses in the tuned circuit.

The sleeve 14 eliminates or greatly reduces spurious resonances in the coil 12 by largely or completely enveloping the unused portionof the coil, which might otherwise cause spurious resonances of a serious character. By

being closely coupled to the unused portion of the coil a in an inductive sense, the sleeve virtually short-circuits the unused portion of the coil, or at least greatly detunes the unused portion so as to displace any resonances a to a frequency far away fromv the frequency range covered. by the tuner. The sleeveretains its value in suppressing spurious resonances, even when the enlarged portion 38 is spaced outwardly some distance from the unused portion of the coil.

The tuner of the present invention is provided with a primary coil 40 which is. carried by the movable sleeve 14 sothat the turns ratio and the percentage coupling between the coils 40 and 12. may be varied as the sleeve is moved along. the coil. In this case, the primary coil 40 is formed by a few turns of wire wound around an insulating extension 42. secured to the lower end of the sleeve 14.. It will beseen that the extension 42 projects from the lower end of the sleeve 14 toward the lower end of the coil 12'. The extension 42 may be generally cylindrical. inform and may be made of nylon or other suitableinsulating; material.

Accordingly, the

i 4 Other suitableconnections may be made to the In the construction illustrated to best advantage in Fig. 4, the'extension 42 has 'a main or lower bore 44 which fits closely around the coil 12 and is freely slidable therealong. At its upper end, the extension has an enlarged bore 46 which is fitted over a reduced lower end portion 48 on the sleeve 14 and is cemented or otherwise suitably secured thereto. The illustrated extension 42 =has'a lower portion 519, of reduced outside diameter, on which the primary coil 40 is supported.

Within the primary coil 40, it is preferred to provide an electrostatic shield 52 of the Faraday type, to minimize capacitive coupling between the primary coil 40 and the secondary coil 12. With such a shield, the primary coil 40 may be arranged to be substantially balanced with respect to ground, so that an efiicient connection may be made between the coil and an antenna lead-in which is balanced to ground. It will be seen that the electrostatic shield 52 comprises a plurality of spaced longitudinal conductors 54 which are connected together at the upper ends by a split metallic ring 56, the split being parallel to the coil axis as indicated at 57. In the illustrated construction, the conductors 54 and the ring 56 are formed as portions of a thin split metal cylinder, which is formed with longitudinal slots 58, opening from its lower end, to define the conductors 54. Thus, the longitudinal conductors 54 resemble fingers or bars on the lower end of the shield 52. It will be seen that the shield 52 is closely received over the reduced portion of the extension 42, while the primary coil 40 is directly wound over the shield.

The coil 40 may be made of insulated wire so as to be insulated from the shield. Of course, the insulating extension 42 insulates the shield and the coil 40 from the moving sleeve 14.

Circuit connections may be made to the ends of the primary coil 40 by various means, such as the illustrated flexible leads 60 and 62, which may simply constitute the ends of the wire employed in winding the coil. A third flexible lead 64 may be soldered or otherwise connected to the shield 56. This lead 64 is usually connected to ground, as indicated in Fig. 4. The flexible leads 60 and 62 may be connected to an antenna leadin, often through a suitable network. The leads 60, 62 and 64 should be of a highly flexible character, highly resistant to breakage and affording little resistance to the movement of the sleeve 14. Wire for such leads, giving extremely long life, is available commercially. The leads must be of adequate length to avoid any interference with the movement of the sleeve. With the provision of the shield 52, the primary leads 60 and 62 are substantially balanced to ground.

The secondary coil 12 may be connected to various circuits, such as the input circuit of an amplifier of a television tuner, for example. Various other connections are feasible, as to a crystal or other mixture, or the like, for example. With respect to the embodiment of Fig. 1, it has already been noted that the efiective terminals of the secondary coil 12 are the lead 20, connected to one end of the coil, and the lead 34, connected to the coupling ring 22. V Merely by way of example, the lead 34 is shown connected to an inputel'ectrode 66 of an amplifier 68. While amplifier 68 might assume various forms, it is shown as a neutralized'triode tube, which may constitute the first stage of a cascode amplifier. 'In this instance, the input electrode 66 comprises the grid of the triode 68. i i amplifier triode 68. In this case, the triode 68 has a cathode 70 which is connected to ground. The end lead 20 of the coil is connected to ground through a small trimming inductance 72 and a capacitor74, connected in series.

The illustrated triode 68 has a plate or anode 76 from which the. output of the triode is taken by way of an output: lead. 78.. A. small neutralizing capacitor 81}- is connected between the plate 76 and the junction of the inductance 72 and the capacitor 74.

A small variable trimming capacitor '82 may be connected between the grid 66 and ground. Automatic gain control voltage may be supplied to the grid 66 from a suitable source, indicated merely as a terminal 84. In this case, a high value resistor 86 is connected between the grid 66 and the terminal 84. A bypass capacitor 88 may be connected between the terminal 84 and ground.

It will be understood that various other amplifier arrangements may be employed within the scope of the present invention.

It will be understood that the primary coil 40 is inductively coupled to the main or secondary coil 12. As the tuning sleeve 14 is moved downwardly along the coil 12, the inductance of the coil 12 is decreased. This raises the resonant frequency of the tuner. As already noted, the inductance of the coil 12 is resonated by the distributed or stray capacitance of the coil itself and the circuit connected thereto, plus the inductance of the trimmer 82 (Fig. 1) and the input capacitance of the amplifier 68.

In this case, the primary coil 40 is essentially untuned. However, the primary coil is inductively coupled to the active portion of the secondary coil 12, below the sleeve 14 (Fig. 1) so that energy is transferred from the primary coil to the secondary coil 12. As the tuning sleeve 14 is moved downwardly along the coil 12, the coupling between the primary and secondary coils is changed in two respects: (a) the effective primary-to-secondary turns ratio is changed; and (b) the percentage coupling or linkage between the primary and secondary coils is changed.

The change in the percentage coupling is employed to maintain the proper band width in the secondary tuned circuit. The change in'the primary-to-secondary turns ratio is utilized to present the proper matched impedance to the primary circuit. When the primary coil is connected to an antenna, it is desirable to provide a primary impedance to match the characteristic impedance of the antenna. With the type of amplifier shown in Fig. l, the input impedance of the amplifier changes substantially over the very high frequency (VHF) television hand. For example, the input impedance to the triode 68 might be of the order of 3,000 to 5,000 ohms at television channel 2, while dropping to about 300 to 500 ohms at channel 13. Throughout this tuning range, the number of turns in the primary coil 40 remains constant, while the number of active turns in the secondary coil 12 decreases substantially. Thus, the primary-tosecondary turns ratio increases with increasing frequency. This increase tends to maintain the primary impedance at the desired substantially constant value, despite the sharp decrease in the secondary impedance.

With the arrangement of Fig. 1, the percentage coupling between the primary coil 40 and the secondary coil 12 increases substantially with increasing frequency, as the sleeve 14 is moved downwardly toward the high frequency end of the coil 12. This effect is highly desirable in this case, because the decreasing input imped ance of the tube 68 decreases the factor of merit or Q of the secondary circuit. Thus, the increase in the percentage coupling may advantageously be utilized to maintain the desired band width. In some cases, the secondary coil 12 may be connected to a device of more nearly constant input impedance, such as a crystal mixer, in which case the increase in the percentage coupling may be controlled and minimized by spreading the turns of the coil 12 at the high frequency end.

It will be apparent that the mounting of the primary coil on the movable tuning sleeve is a great advantage in the design of a practical television tuner, or the like. This great advantage is obtained in a construction which is highly serviceable, yet is remarkably simple, inexpensive and easy to manufacture. i

Various other modifications, alternative constructions and equivalents may be employed without departing from the true spirit and scope of the present invention, as exemplified in the foregoing description, and defined in the following claims:

We claim:

1. In a tuner, the combination comprising a generally cylindrical inductance coil having first and second ends, a lead connected to said first end of said coil for establishing a circuit connection thereto, a generally cylindrical conductive sleeve slidable along and around the outside of said coil between said first and second ends thereof for varying the effective inductance of said coil between said sleeve and said first end, an insulating coating on the outside of said coil to insulate said sleeve therefrom so that said sleeve will be capacitively coupled to said coil, a conductive electrode adjacent said sleeve, means insulating said electrode from said sleeve to establish capacitive coupling therebetween, a lead connected to said electrode for establishing a circuit connection thereto, a generally cylindrical insulating extension mounted on the end of said sleeve directed toward said first end of said coil, a thin conductive generally cylindrical shield mounted around said extension, said shield having a plurality of longitudinal slots therein opening from theouter end thereof and defining shielding fingers on said shield between said slots, a first flexible lead connected to said shield for establishing a circuit connection thereto, a primary coil wound around said shield and movable with said sleeve, said primary coil being received around said inductance coil and being movable therealong, said shield being disposed between said primary coil and said inductance coil, and second and third flexible leads connected to the ends of said primary coil for establishing circuit connections thereto.

2. In a tuner, the combination comprising an inductance coil having first and second ends, means for establishing a circuit connection to said first end, a sleeve closely received around the outside of said coil and slidable therealong to vary the effective inductance between said sleeve and said first end, dielectric means between said sleeve and said coil to provide for capacitive coupling therebetween, means for establishing a circuit connection to said sleeve, a primary coil carried on said sleeve at the end thereof adjacent said first end of said coil, means mounting said primary coil on said sleeve to provide for inductive coupling between said primary coil and said inductance coil while insulating said primary coil from said sleeve, said primary coil being disposed around the outside of said inductance coil and being movable with said sleeve along said inductance coil,

and means for establishing circuit connections to the op-' pcsite ends of said primary coil, the movement of said sleeve along said inductance coil toward said first end thereof being effective to decrease the inductance of said inductance coil while changing the coupling between said primary coil and said inductance coil.

3. In a tuner, the combination comprising an inductance coil having first and second ends, means for establishing a circuit connection to said first end, a conductive V sleeve closely received around the outside of said coil and movable therealong between said ends for varying the eifective inductance between said sleeve and said first end, dielectric means between said sleeve and said coil to provide for capacitive coupling therebetween, means for establishing a circuit connection to said sleeve, an in sulating extension mounted on the outer end of said sleeve and extending toward said first end of said coil, a conductive electrostatic shield mounted around said extension, said shield comprising a plurality of spaced longitudinal conductors, means for establishing a circuit connection to said shield, a primary coil mounted around said shield and insulated from said shield and said sleeve, and means for establishing circuit connections to the opposite ends of said primary coil, said primary coil being 7 disposed around the outside of said coil and being movablewith said sleeveto' vary the turns ratio between said primary coil and said inductance coil, saidtur'nsi'i'atio being increased as the inductance of said inductance coil is decreased by the movement of said sleeve toward said first end of said inductance coil.

4. In a tuner, the combination comprising an inductance coil, means for establishing a circuit connection to one end of said coil, a sleeve closely received around the outside of said coil and slidable therealong to vary the effective inductance between said sleeve and said one end, means for establishing a circuit connection to said sleeve, a primary coil carried on said sleeve at the end thereof adjacent said one end of said coil, means mounting said primary coil on said sleeve to provide for inductive coupling between said primary coil and said inductance coil, and means for establishing circuit connections to the opposite ends of said primary coil, said' primary coil being disposed around the outside of said inductance coil and being movable with said sleeve along said inductance coil, the movement of said sleeve along said inductance coil toward'said one end thereof being eifective to decrease the inductance of said inductance coil while changing the coupling between said primary coil and said inductance coil.

5. In a tuner, the combination comprising a generally cylindrical inductance coil having first and second ends, a

lead connected to said first end of said coil for establishing a circuit connection thereto, a generally cylindrical conductive sleeve slidable along the outside of said coil between said first and second ends thereof for varying the effective conductances of said coil between said sleeve and said first end, an insulating coating on the outside of said coil to insulate said sleeve therefrom so that said sleeve will be capacitively coupled to said coil, a conductive electrode adjacent said sleeve, means insulating said electrode from said sleeve to establish capacitive coupling therebetween, a lead connected to said electrode for establishing a circuit connection thereto, a generally cylindrical extension mounted on the end of said sleeve directed toward said first end of said coiL a primary coil disposed around said extension and movablewith said sleeve, said primary coil being disposed around the outside of said inductance coil, and flexible leads connected to said primary coil for establishing circuit connections thereto.

References Cited in the file of this patent UNITED STATES PATENTS Mason Mar. 11, 1958

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