US1931677A - Variable condenser - Google Patents

Description

Patented Oct. 24, 1933 PATENT OFFICE VARIABLE CONDENSER Georges Emile Marie assignor,

Pontonnier, by mesne assignments,

Paris, France, to Radio Corporation of America, New York, N. I, a corporation of Delaware Application February s, 1928, Serial No.

and in France February 15, 1927 12 Claims. (Cl. 250-40) My -invention relates to electrical tuning systems, and more particularly to condenser arrangements utilized in electrically tuned circuits.

Variable condensers of the type known as straight line frequency condensers intended for electrical circuit tuning, are frequently employed, at present, more particularly in receiving sets for wireless telegraphy and telephony. The profile, or cross section, of the blades of such a variable condenser, or of the cams or other equivalent driving devices of the rotors of the variable condenser, is easily calculated, if the ratio between the maximum and minimum capacities of the tuning circuit containing the said condenser is known.

- When the ratio between the maximum and minimum capacities of the tuning circuit in which the variable condenser having its blades designed according to the desired profile or cross section, is changed, then it is necessary to alter the design of the profile or cross section, it being understood that the maximum and minimum capacities of the tuning circuit may be obtained when the condenser plate sections are fully overlapped and fully withdrawn from each other respectively. In other words, given an electrical tuning circuit in a receiving set comprising an inductance of a fixed value and a variable condenser provided with blades having a predetermined profile especially designed to obtain straight line frequency over a given range of frequencies, it is necessary, in the prior art, to change the said profile or cross section of the blades, if it is desired to employ the said variable condenser for tuning through a different range of frequencies and retain the straight line frequency characteristic.

Now, I have devised a method of, and means for remedying the aforementioned disadvantage, and it is thereby possible, according to my present invention, to vary the ratio of the maximum and minimum capacities of the tuning circuit in which a variable condenser, operating over its full range and with a straight line frequency characteristic, is employed within fairly large frequency range limits, without materially departing from the initial characteristic of the said variable condenser, the means for accomplishing this novel result embodying capacities added to the circuit in addition to the variable tuning condenser, and added in quantities following a predetermined law.

Accordingly, it is one of the main objects of the present invention to provide a tuning circuit in a receiving set for wireless telegraphy or telephony which tuning circuit embodies a tuning element designed to impart a straight line frequency characteristic to the tuning circuit, and additional means associated with the said tuning circuit for varying the ratio of maximum to minimum capacity of the tuning circuit while substantially adhering to the said straight line frequency characteristic thrqughout a plurality of frequency ranges without altering the physical design of the said tuning element.

Another important object of the invention, which is broader than that set forth in the preceding paragraph in not pertaining specifically to a straight line frequency characteristic, is to provide a tuning circuit arrangement for a receiving set, the circuit arrangement comprising a tunable variable condenser, an additional capacity of a predetermined value in series with said variable condenser, and a second additional capacity of a predetermined value in shunt with said variable condenser, said additional capacities being adapted to vary the ratio of maximum to minimum capacity of the tuning circuit arrangement so as to change the frequency range to another desired frequency range, without altering the physical design of the said .variable condensers', while yet preserving a desired characteristic of variation of frequency with change in capacity of the tuning condenser.

Other objects of the invention are to improve generally the simplicity and efliciency of tuning circuits employing straight line frequency con-' densers, and to provide particularly a tuning circuit for a receiving set which is not only reliable in operation but economicalv to assemble.

The novel features which I believe to be characteristic of my invention are set forth in particularity in the appended claims, the invention itself, however, as to both its organization and method of operation will best be understood by reference to the following description taken in connection with the drawing in which I have indicated diagrammatically several circuit organi- 9 zations whereby my invention may be carried into effect.

In the drawing, 1

Fig. 1 diagrammatically represents one circuit arrangement including the invention,

Fig. 2 diagrammatically shows 'a circuit arrangement embodying a modified form of the invention.

Referring now to the accompanying drawing wherein like characters of reference indicate the same parts in the different figures, Fig. 1 shows the invention embodied in a conventional receiving circuit adapted for wireless telegraphy or telephony. This circuit embodies a source of signal energy 1, which may be any well known type of signal energy collecting means utilized in conventional receiving circuits. As is well known to those skilled in the art, such a collecting means, or more broadly source of signal energy, is coupled, as at M, to a resonant or tuning circuit. While I have shown this coupling M as a transformer coupling, it is of course understood that the energy collecting means may be coupled to the tuning circuit in any other well known fashion.

The tuning circuit includes an inductance coil 3 in shunt relation with a variable condenser 1. The output terminals 2, 2 of the tuning circuit are connected to any well known type of translating device, as well as the terminals of the inductance 3, the same being conventionally shown in the drawing, andthe output circuit of the device may be connected to any well known type of utilization means.

The variable condenser 1 is preferably given such a physical design that its variation imparts a straight line frequency characteristic to the tuning circuit in which it is disposed. This is easily accomplished, as explained heretofore, by proper design of the profile, or cross section, of the blades of the condenser, or of the cams or other equivalent driving devices, and is easily calculated by methods well known to those skilled in the art when the ratio between the maximum and minimum capacities of the tuning circuit is known.

It can easily be seen that in the prior art when the physical design of the variable condenser 1 has been determined for a given range of frequencies, the variable condenser can be used for a different range of frequencies, with the same tuning. characteristic and the same value for the inductance coil 3, only by changing the physical design of the variable condenser 1. Thus, when the variable condenser 1 has been designed for one range of frequencies so as to impart a straight line frequency characteristic to the tuning circuit, the same variable condenser 1 can be used for a diiferent range of frequencies and still possess a straight line frequency characteristic, only by redesigning the profile or cross section of the blades of the condenser 1. As has been explained, this involves serious disadvantages in receiving circuit design of the prior art.

According to the present invention it is not necessary to alter the physical design of the variable condenser 1, in order to employ the same condenser for a different range of frequencies, and yet retain the desired tuning characteristic.

This is accomplished by connecting, in series with the variable condenser 1, an additional capacity I which has a value very much greater than the minimum capacity of the tuning circuit, and connecting in parallel with the variable condenser 1, an additional capacity 7 having a value which is much smaller than the maximum capacity of the tuning circuit and the capacity I.

It will be understood that the values of the additional capacity I and 'y depend upon the ranges of frequency for which the tuning circuit is to be used. Thus, while for one given range of frequencies the tuning circuit including the inductance 3 and the variable capacity 1 has a straight line frequency characteristic, for another range of frequencies it being understood that the physical design of the variable condenser 1 is not altered, the additional capacity I and the additional capacity 7 are connected in series and in shunt respectively with the variable condenser 1, and given values (according to a predetermined cluding the same physical design of the variable I condenser 1 for still another range of frequencies. it is only necessary to change the value of the series additional capacity I and the shunt additional capacity 7 according to the aforementioned predetermined law. Of course, while I have shown these additional capacities as fixed capacities it is to be clearly understood that their values are adjusted when changing from one range of frequencies to another range of frequencies, this being accomplished by substituting fixed capacities of different values, or in any other desired manner.

The numerical values to be given to the additional capacity I and the additional capacity '1 are those that shall satisfy substantially the following equation or relation:

In the lastequation, 0 represents the maximum capacity of the tuning circuit including the tuning condenser and incidental capacities prior to the addition of the fixed condensers I and 'y, and c is the minimum capacity of the same circuit prior to the addition of the fixed condensers I and 'y.

Also, the ratio of the frequencies covered by the whole set of condensers, compared to the ratio of the frequencies covered by the initial condenser is equal to:

It has been found, that the best results are obtained when the variable condenser 1 is constructed for a ratio of maximum capacity to minimum capacity which is about 9 or 10 to 1.

In Fig. 2 I have shown a circuit embodying a modified form of the invention. In this circuit, the additional capacity I still is connected in series with the variable condenser l, but the additional capacity 7 is connected directly in shunt with the variable condenser 1; that is, both the variable condenser 1 and the additional capacity 7 are connected to the same terminal of the additional capacity I. Here, again, as explained in connection with Fig. 1, the terminals of the coil 3 are connected to terminals 2, 2'. The values of the additional capacities are changed depending upon the rangeof frequencies to which the tuning circuit including the inductance coil 3' and the variable condenser 1 is to be employed.

While I have indicated and described several systems for carrying my invention into effect, it will be apparent to one skilled in the art that my invention is by no means limited to the particular organizations shown and described, but that many modifications in the circuit arrangements, as well as in the apparatus employed, may be made without departing from the scope of my invention as set forth in the appended claims.

Having now particularly described and ascertained the nature of my said invention and in what manner the same is to be performed, I declare that what I claim is:--

inductance coil, a variable condenser in shunt relation with said coil, the aforegoing circuit which is small compared to C manor? having a maximum capacity C and a minimum capacity 0, said condenser being adapted to tune the coil between frequency limits f1 and In according to a predetermined Q law, a capacity I which is large compared to c in series with said variable condenser, and a capacity 1 in shunt relation with the latter, whereby the variable condenser is adapted to tune the resulting circuit between diiferent frequency limits F: and F4, substantially according to the aforesaid law and without alter.- ing the physical design of the variable condenser, the relation between all the aforementioned capacities being defined by the equation:

( ea er- 2. In combination, in an oscillation circuit, an inductance coil, a variable condenser in shunt relation with said coil, the aforegoing circuit having a predetermined ratio between its maximum capacity C and its minimum capacity 0, and additional means in said circuit, said means comprising a capacity I which is large compared to c in series with the variable condenser, a capacity 7 which is small compared to C in shunt relation with the latter, the equation defining the relations between all of said capacities.

3. In combination, in an oscillation circuit, an inductance coil, a variable condenser in shunt relation with said coil, the aforegoing circuit having a maximum capacity C and a minimum capacity 0, said condenser being adapted to tune the coil between frequency limits I; and f: according to a predetermined law, a capacityl in series with said variable condenser, and a capacity 7 in shunt relation with the latter, whereby the variable condenser is adapted to tune'the resultant circuit between frequency limits I1+Fa and f:+F4, where F: and F4 are predetermined frequency increments, substantially according to the aforesaid law and without altering the physical design of the variable condenser, the relation between all the aforementioned capacities being defined by the equation:

the capacity 7 being small compared to C, the capacity I being great compared to the capacity c.

4. An oscillation circuit comprising an inductance coil, a tuning condenser in shunt relation with said coil, said aforegoing circuit having a maximum capacity C and a'minimum capacity c, means for adjusting the capacity of said condenser to tune the coil according to a predetermined law, and a capacity network in said circuit including a fixed condenser 01' capacity 1 in series with the tuning condenser, which is large compared to the capacity c, a fixed condenser of capacity 7, in shunt relation with the tuning condenser, which is small compared to the capacity C, the said capacities being chosen according to the equation:

C l r)( E) said network enabling the tuning condenser to tune the resultant circuit according to the said law, for all values of I and 'y satisfying their aforementioned relations.

5. An oscillation circuit comprising an inductance coil, a tuning condenser in shunt relation therewith, said aforegoingmcircuit having a maximum capacity C and a minimum capacity 0, a capacity network in said circuit including a fixed condenser of capacity I in series with the tuning condenser and being large compared to capacity c, a fixed condenser of capacity '7, in shunt relation with the tuning condenser and being small compared to capacity C, means for adjusting the capacity of said tuning condenser, said fixed condensers being chosen to satisfy the relation whereby the ratio of the rates of change, at two ant circuit capacity, with respect to displacement of said adjusting means, is the same as the ratio of the rates of change, at the same two values of displacement of said adjusting means, of the square root of the reciprocal of the capacity of the variable condenser, with'respect to displacement of said adjusting means.

6. An oscillation circuit qmprising an inductance coil, a tuning, condenser in shunt relation with said coil, means for adjusting the capacity of said condenser to tune said coil over a range of frequencies having a given ratio of limiting frequencies, said tuning condenser being operable to give a predetermined relation between frequency variation and displacement of said adjusting means, said aforegoing circuit having a maximum capacity C and a minimum capacity 0, and additional means in said circuit whereby said condenser is adapted to tune said circuit over a range of frequencies having a diiferent ratio of limiting frequencies according to a relation between frequency variation and adjusting means displacement which is related in a desired manner to said first relation, said additional means 7. In combination, in an oscillation circuit, an inductance coil, a variable condenser in shunt relation with said coil, the aforegoing circuit having a maximum capacity C and a minimum capacity 0, said condenser being adapted to tune the coil between frequency limits f1 and f2 according to a straightline frequency variation law, a capacity I which is large compared to c in series with said variable condenser,'and a capacity 7 which is small compared to C in shunt relation with the latter, whereby the variable condenser is adapted to tune the resultant circuit between frequency limits f1+F3 and fa+F4, where F3 and F4 are predetermined frequency increments, substantially according to the, aforesaid law and without altering the physical design of the variable condenser, the relation between all the aforementioned capacities being defined by the equa- 8. In combination, in an oscillation circuit, an inductance coil, a variable condenser in shunt relation with said coil, the aforegoing circuit having a maximum capacity C and a minimum caadapted to tune the resultant circuit between frequency limits n+3: and fa+F4, where F: and F4 are predetermined frequency increments, substantially according to the aforesaid law and without altering the physical design 0! the variable condenser, the relation between all the aforementioned capacities being defined by the equation: 1

the capacity 7 being small compared to C, the

capacity I being great compared to the capacity c.

9. In combination, in an oscillation circuit, an inductance coil and a variable tuning condenser, means for increasing the frequency to which the oscillation circuit is tuned when the variable condenser is adjusted to its maximum capacity position, said means comprising a fixed capacity in series with said variable condenser, and a second means for decreasing the frequency to which said oscillation circuit is tuned when the variable condenser is adjusted to its minimum capacity position, said second means comprising a fixed capacity in shunt relation to said variable condenser, said series capacity being large compared to the minimum capacity of the circuit consisting of the variable condenser and the coil, and said shunt capacity being small compared to the maximum capacity of the last named circuit.

10. A capacity network including a variable condenser, a fixed capacity in series therewith, so chosen that the maximum capacity of the network is made less than the maximum capacity of the variable condenser, and a fixed capacity in shunt relation with said variable condenser so chosen that minimum capacity of the network is made greater than the minimum capacity of said variable condenser, said series capacity being large compared to said network minimum capacity, and said shunt capacity being small compared to said network maximum capacity.

11. In combination with an oscillation circuit consisting of a coil and a variable condenser which is adapted to vary the resonant frequency f of the circuit over a range of frequencies, said above oscillation circuit having a maximum capacity C and a minimum capacity c, an auxiliary condenser I in series with the variable condenser having a capacity large compared to c, and a second auxiliary condenser 7 in shunt with the variable condenser having a capacity small compared to C, said auxiliary condensers being chosen to satisfy the relation sultant circuit varies in such a way that df is substantially constant between predetermined limits of variation of the variable condenser.

12. In combination with an oscillation circuit comprising an inductance coil and a variable tuning condenser in shunt relation with said coil and adapted in the absence of other reactances to tune the circuit over a range of frequencies in accordance with a predetermined frequency curve, means in the aforegoing circuit including condensers of suitable capacity value in series and shunt respectively with the tuning condenser for enabling the tuning condenser to tune the resultant circuit in accordance with a different frequency curve bearing a substantially linear relation with the first mentioned curve.

GEORGES EMILE MARIE PONTONNW.

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