US2517230A - Multistrand electrical conductor - Google Patents

Description

Aug. 1, 1950 E. B. PAssow MULTISTRAND ELECTRICAL CONDUCTOR Filed Jan. 16, 1947 Fig./

. EDWARD B. PASSOW INVENTOR.

H/s ATTORNEY Patented Aug. 1, 1950 2,517,230 MULTISTRAND ELECTRICAL CONDUCTOR Edward B. Passow, Park Ridge, Zenith Radio Corporation, a

Illinois 111., assignor to corporation of Application January 16, 1947, Serial No. 722,325

2 Claims.

The present invention pertains in general to variable inductance tuning systems for radio receivers, and more particularly to improvements in core tuned coils for such systems.

One of the objects of this invention is to provide a coil that in conjunction with a fixed capacitance, can be core tuned over an extended range of frequencies, and that at the same time is ideall suited to being wound to give a logarithmic or other desired non-linear relationship between the position of the adjustable iron core member within the coil and the resonant frequency of the tuned circuit incorporating the coil.

Another object is to provide such a coil which is particularly adapted to ,high frequency uses.

The features of the present invention which are believed to be novel are set forth with particularity in the appended claims. The present invention itself, both as to its organization and manner of operation, together with further objects and advantages thereof may best be understood by reference to the following description taken in connection with accompanying drawings in which:

Figure 1 illustrates the mechanical construction of a tuning element incorporating the invention, and

Figure 2 is a schematic diagram of a superheterodyne frequency modulation receiver using such tuning elements.

Described briefly, the embodiment of the invention illustrated herein comprises an inductonce coil wound with a fiat, unitary multi-strand tinsel.

The word tinsel, as used herein, is meant to include any thin conductive material composed of a plurality of conductive strands woven in tape form in such manner as to allow the material to be flexed in all directions transverse to its length. It i preferred where the conductive strands are woven together with non-conductive strands that the non-conductive strands be spun glass to facilitate the soldering of the conductive strands where required. It is also preferred that the conductive strands be very thin, flat metal strips one adjacent the next; adjacent strands not being insulated from each other but being in contact at many points along their length.

In Figure 1 there is shown an adjustable iron core in the form of a cylindrical slug i0 preferably molded from powdered iron and a suitable binder which is slideabiy secured within a molded phenolic coil form II which is fixedly mounted on a radio chassis 12 by the engagement of a spring clip H with its shank I4. The core I0 is ad- Justably secured to any suitable tuning means (not shown) by a threaded rod IS. A tinsel tape coil [6 is wound about the right hand portion of the form H. As the tuning means (not shown) is adjusted, corresponding movement is imparted to the rod I5 to move the iron core l0 within the coil IE to change the inductance thereof.

In Figure 2 a dipole antenna [1 is connected in series with a primary inductance I8 of an input transformer 19. A variable secondary inductance 20 is connected in series with bypass condenser 2| between control electrode 22 and cathode 23 of a discharge device 24. A fixed condenser 25 is connected in shunt with the variable inductance 28 to resonate at the frequency of any desired signal, as determined by the position within the inductance 20 of an inductance varying means 26, such as a powdered iron core.

Screen electrode 21 of device 24 is connected through a by pass condenser 28 to the cathode 23, and through a voltage dropping resistance 29 to the positive terminal of a source 30 of space current, the negative terminal of source 30 and cathode 23 being grounded. The anode 3| of device 24 is connected through the primary inductance 32 of transformer 33 to the positive terminal of source 30. Signals appearing across tuned circuit 20, 25 are amplified in device 24 and appear across inductance 32 in greater amplitude. These signals are coupled to secondary winding 34 whose inductance is a function of the position of an inductance varying means 35. A fixed condenser 36 is connected in shunt with the variable inductance 34 to form a resonant circuit. The tuned circuit 34, 36 is made to resonate at the same frequency as the tuned circuit 20, 25 by adjustment of the inductance varying element 35. Signals appearing across secondary 34 are impressed on signal grid 31 of converter tube 38. These signals are heterodyned against the signal generated in the local oscillator circuit including tank circuit 33,

3 grid 40, cathode 4| and screen grid 42. Tank circuit 38 includes a variable inductance 43 shunted by capacitance 44. Oscillations are maintained in this circuit by means of cathode tickler portion 45 of the inductance 43.

The frequency of oscillation is varied by adjusting the position of a core 46 in inductance 48 until it differs from the frequency of the signal impressed on the signal grid 31 by the so-called intermediate frequency. The mechanism by which the oscillator signal and the signal on grid 31 are heterodyned to give on an anode 41 the desired intermediate frequency signal are well known and need not be discussed here.

The intermediate frequency signal appearing on the anode 41 is impressed across a primary coil 48 of an intermediate frequency transformer 48. This primary coil 48 is resonated at the intermediate frequency by means of capacitance 50.

Anode current for converter 38 flows through the primary coil 48 from source 80.

The intermediate frequency signals appearing across the primary coil 48 are magnetically coupled to a secondary winding M which is shunted by a capacitance 52 and tuned to the resonant frequency of the primary circuit 49, 5%. These signals are appropriately amplified and detected in the circuits included in an amplifier detector arrangement 53 and audio modulation voltages on these signals are reproduced by a speaker 54. Included in the amplifier detector arrangement 53 are circuits for deriving automatic volume control voltages which are impressed on grid 22 through a conductor 55, and the secondary coil 20, a filter network 56 being interposed therebetween.

Bias for the oscillator grid 40 is developed across the parallel combination of a resistance 51 and a capacitance 58.

The core members 26, 35 and 46 are each adjustably coupled to a common tuning member 59.

The inductance of the winding 20 is varied by the movement of the core member 26 at the same time that the inductance of the windings 34 and 43 is varied by the movement of similar members 35 and 45, respectively. Each one of these windings 20, 34 and 43 is wound with a progressively varying winding pitch so as to cause the inductance thereof to bear a substantially logarithmic relation to the displacement of its associated core member.

When the core in, in Figure l, is entirely within the coil It the resonant frequency of the circuit which it tunes changes but slightly with movement of the core I0. Also, when the core member is entirely outside the coil IS the resonant frequency changes but slightly with the position thereof. Intermediate these two extremes, the relationship between resonant frequency of the tuned circuit and the position of the member is complex if turns of the coil is are uniformly spaced. However, when the turns of the coil iii are wound with variable pitch, as best shown and described in the copending application of John L. Rennick, Serial Number 560,706, now Patent No. 2,440,390, assigned to the same assignee as this application, a logarithmic relation between th resonant frequency of the tuned circuit and the position of the core member can be obtained over the desired range of frequencies.

This discussion of variable pitch windings is entered into here, only to show that such coil windings are often required and that tinsel tape can best adapt itself to such windings.

The tuning range of a given core and coil depends upon the core and coil geometry and the current distribution over the surface of the coil. With a given core the tuning range increases (a) as the coil length increases up to the length of the core; (b) as the coupling between the core and the coil is increased; and (c) as the current distribution approaches a theoretically uniform current sheath over the surface of the coil.

At high frequencies the inductances involved are small; this means short coils with wide spacing between turns. Both of these conditions tend to decrease the tuning range. Some improve-- ment can be obtained by increasing the length of coil at the expense of winding density, but under these conditions the current distribution over the coil surface is very poor-the current is concentrated in narrow bands widely spaced, whereas it should be uniformly distributed over the entire surface.

The use of multi-stranded tinsel tape is ideal in solving the aforementioned problems. With the large ratio of width to thickness, and with the pitch of the turns maintained at the wide spacing necessary for a large tuning range, a theoretically uniform current sheath results.

All the aforementioned desirable characteristics linked with coil windings of tinsel tape can likewise be obtained by the employment of multifilar windings of insulated copper wire, but in the employment of multifilar windings it is required that the strands be uniformly and closely spaced in a single layer over the surface of the coil form for best results. In attempting to wind two, three or more strands side by side, as is required in a multifilar winding, no trouble is encountered if the windings are maintained at constant pitch. But, in-attempting to wind two or more strands side by side with a variable pitch, it is diihcult to maintain the necessary tension on all the wire strands as the pitch of the turns is decreased or increased, whichever the case may be. Thus, gapping or pulling away of the strands from the coil form results at some parts of the winding.

When tinsel tape windings are employed, not only is it possible to have a tunable coil of large tuning range with a theoretically uniform current sheath but, in addition, tinsel tape is ideally suited to windings of variable pitch. The windings of tinsel tape snugly encompass the coil form when a variable pitch winding is employed and thus, as gapping of the winding is eliminated, the coupling between coil and core is increased.

While particular embodiments of the present invention have been shown and described, it will be obvious to those skilled in the art that changes and modifications may be made without departing from this invention in its broader aspects, and, therefore, the aim in the appended claims is to cover all such changes and modifications as fall within the true spirit and scope of this invention.

I claim:

1. An inductance coil comprising: a plurality of turns of a multi-stranded flat conductive tape which has a thickness small compared with its width and which is flexible in all directions transverse to its length; said tape including a plurality of flat conductive strips positioned in side by side relation in electrical contact along portions of their adiacent edges and a flexible strand inter- 8 woven with said conductive strips to form in conjunction therewith said flat tape.

2. An inductance coil comprising: a plurality oi turns of a multi-stranded flat conductive tape which has a thickness small compared with its 5 width and which is flexible in all directions transverse to its length; said tape including a plurality of flat conductive strips positioned in side by aide relation in electrical contact along portions of their adjacent edges and a flexible strand of spun glass interwoven with said conductive strips to form in conjunction therewith said flat tape.

EDWARD B. PASSOW.

I nmmmcss 0mm The following references are of record in the tile 0! this patent:

UNITED STATES PATENTS Number Name Date 1,131,187 Von Arco Mar. 9, 1915 1,977,291 Sconeld Oct. 16, 1934 2,030,369 Heintz Feb. 11, 1936 10 2,394,391 Martowicz Feb. 5, 1946 2,407,359 White Sept. 10, 1946 FOREIGN PATENIB Number Country Date 92,818 Switzerland Mar. 1, 1922

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