US2021756A - Coupling arrangement - Google Patents

Description

B. D H TELLEGE N COUPLING ARRANGEMENT Filed Jan. 25, 1935 Nov. 19, 1935.

INVENTOR 55311448005 DOM/M6715 HUfifKTUS 7211560! BY ATTORNEY Patented Nov. 19, 1935 UNITED I STATES PATENT OFFICE hoven, Netherlands, assignor to Radio Corporation of America, a corporation of Delaware Application January 25,1933, Serial No. 653,436 In Germany July 9, 1932 8 Claims.

This invention relates to a capacitive coupling arrangement preferably utilized for connecting a tuned circuit to an aperiodic one. The latter circuit may be constituted, for example, by an aerial or by the untuned input or output circuit of a thermionic valve which may be a radio frequency amplifier. In such a system the tunable circuits as well as the capacitive coupling element are of a predetermined value. The aperiodic circuit on the contrary may be of widely different values. If the aperiodic circuit is formed, for example, by the input or output circuit of a thermionic valve, the capacity present in this aperiodic circuit may be subject to a rather large variation when one of the thermionic valves is replaced by another by reason of the varying valves. The capacities of the different aerials to be employed may also be widely different.

Since the coupling is dependent both on the value of the coupling capacity and on the impedance of the circuits coupled, the coupling is consequently strongly variable unless a very I loose coupling of the circuits is utilized. In

consequence thereof, the transmission of energy is however much more reduced than is required in view of the desired selectivity.

These drawbacks are-removed by the circuitarrangements of my invention.

According to the invention, for connecting a tuned circuit to an aperiodic circuit whose capacity is variable between determined limits, use is made of a capacitative coupling element. The connecting points for the aperiodic circuit are connected by a capacity whose value is located between the limit values determined for the capacity of the aperiodic circuit.

The invention will be explained more fully with reference to the drawing which represents, by

way of example, three embodiments thereof.

Figures 1 and 2 represent arrangements according to the invention in which an aerial is coupled to a tuned circuit; while in Figure 3 an arbitrary aperiodic circuit is coupled to a tuned circuit connected in its turn to an aperiodic circuit.

In Figure 1, l denotes an aerial coupled via a coupling condenser 4 to a tuned circuit 2, 3, comprising an inductance or coil 2 which may be tuned to a desired incoming radio signal frequency by the variable condenser 3. The movable contact M connecting one side of condenser 4 may be adjusted along coil 2. In order to render the coupling substantially independent of the aerial employed a condenser 5 is connected interelectrode capacities of different.

be, for example, of the order of 200 to 400 micro 5 microfarads. The value of this condenser may, for example, be centimeters.

This circuit-arrangement allows not only of making the coupling between the antenna circuit and circuit 2, 3 independent of the aerial, but 10 also of increasing the sensitiveness, more particularly in the case of large aerials. By sensitiveness is meant hereinafter the ratio of the current intensity in the tuned circuit 2, .3 to the voltage or tension occurring in the aerial. 15

This greater sensitiveness is obtained by employing a larger coupling condenser 4. The value of this condenser is in general determined by the fact that with an arbitrary aerial the coupling may differ from the average value not more 20 than a determined percentage. The consequence thereof is, that the greater the difference in capacity between the aerials which may be employed, the smaller must be the capacity of the coupling element 4. Owing to the presence of 25 the condenser 5 the difference in capacity in the aperiodic circuits employing aerials of different capacities is decreased so that a larger coupling condenser may be employed than is otherwise possible with the result that the sensitiveness 30 increases again.

Figure 2 shows another example of an aerial coupling, in which the aperiodic aerial I is coupled to a tuned circuit 2, 3 by means of a capacitative coupling which increases with the fre- 35 quency and of a capacitative coupling which decreases at increasing frequency. For this purpose are provided condensers 4 and 6. The total coupling is in this case substantially independent of the frequency to which circuit 2, 3 is tuned 40 by condenser 3. In order to render this coupling in addition substantially independent of the aerial employed, a condenser 5 has been provided which is connected in series with the condenser 6 and in parallel with the aerial capacity. The 45 series-connected condensers 5 and 6 consequent- 1y correspond in this case to the capacity 5 in Figure 1.

The circuit-arrangement shown permits of obtaining favorable results if the capacity of the 50 condenser 4 is about 6 cms., that of the condenser 5 about 230 cms. and that of the condenser 6 about 5200 cms.

Figure 3 represents a coupling element adapted to be employed between two aperiodic circuits 55 denoted symbolically by the reference letters A and B. These aperiodic circuits are not shown specifically but may be of any known type and may be connected between the points 9, l0 and H, l2 respectively. The aperiodic circuit connected between the points 9, I0 is coupled to the tuned circuit including coil 2 and condenser 3 through condensers 4 and 6 which are so dimensioned that the coupling is independent of the frequency to which circuit 2, 3 is tuned by condenser 3. The circuit 2, 3 is coupled in a similar manner via condensers 6 and 1 to the circuit connected between the points ll, l2, the condenser B being in this case common to all circuits.

In order to render the total coupling also independent of the capacities of the aperiodic circuits, condensers 5 and 8 are provided in the same manner as in Figure 2. The series connected condensers 5 and 6 are consequently connected in parallel with the one aperiodic circuit whereas in parallel with the other are connected the series-connected condensers 8 and 6. The circuit constants of this figure may have the same values as above given for the corresponding elements of Figure 2, that is condensers 8 and 5 may be of 230 cms. capacity, I and 4 may be of 6 cms. and 6 of 5200 cms. capacity.

The invention is not limited to the embodiments above described by way of example, but may be applied in general to capacitive couplings between aperiodic and tuned circuits.

I claim:

1. In combination an aperiodic circuit having capacity, a circuit tunable over a range of frequencies, said circuit comprising a fixed condenser connected in series with a variable con-- denser, and a condenser connected to one terminal of said aperiodic circuit and to the common terminal of said variable and fixed condensers said last named condenser having a capacity value substantially equal to that of said aperiodic circuit.

2. The combination of the preceding claim in which the fixed condenser of said tunable circuit has a capacity value greater than 10 times that of the coupling condenser connecting the aperiodic and tunable circuits.

3. A coupling arrangement for coupling a circuit to a second circuit tunable over a range of frequencies and comprising a coil, a fixed condenser connected in series with a variable condenser across the terminals of said coil, a coupling condenser of small capacity value having one side connected to a terminal of said first named circuit and its other side to one terminal of said coil and a condenser connected in shunt to said first named circuit, said last named condenser having a capacity value substantially greater than that of said coupling condenser.

4. In a coupling device, the combination of an aperiodic circuit, a tunable circuit comprising the series connection of a coil, a fixed condenser and a variable condenser, adjustment of said variable condenser operating to tune said circuit over a range of frequencies, and a condenser having one terminal connected to said aperiodic circuit and a second terminal connected to one end of said coil, the capacity of said last named condenser being so related to that of said fixed condenser that the energy transfer from said aperiodic circuit to said tunable circuit remains substantially constant as said variable condenser is adjusted.

5. In a coupling arrangement, the combination of an aperiodic circuit, a tunable circuit comprising the series connection of a coil, a variable condenser and a fixed condenser, adjustment of said variable condenser operating to tune said circuit over a range of signal frequencies, a circuit connected across the terminals of said variable condenser and consisting of only two condensers connected in series, and a connection between the common terminal of said last named condensers and said aperiodic circuit.

6. The combination defined in the preceding claim in which the capacity value of the fixed condenser of the tunable circuit is substantially greater than the sum of the capacities of the two condensers connected to the aperiodic circuit.

7. A circuit arrangement for transferring a broad range of radio frequency currents from a pair of input terminals to a pair of output terminals comprising the combination of a tunable circuit consisting of the series connection of a coil, a fixed condenser and a variable tuning condenser, a lead conductively connecting one of said input terminals and one of said output terminals and the low potential end of said coil, two condensers connected in series between the other of said input and output terminals and a lead conductively connecting the common terminal of said last named condensers and the high potential end of said coil.

8. The combination of the preceding claim in which the capacity value of the fixed condenser of the tunable circuit is substantially greater than the capacity value of either of the said last named condensers.

BERNARDUS DOMINICUS HUBERTUS TELLEGEN.

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