US2001622A - Method of and means for reducing electrical disturbances - Google Patents

Description

May 14, 1935. MccAA 2,001,622

METHOD OF AND MEANS FOR REDUCING ELECTRICAL DISTURBANCES -Fi'led OCC. 2'7, 1950 Jae dad c; /*7% Z wwwy @dww' Patented May 14, 1935 UNITED STATES METHOD OF AND MEANS FOR REDUCING ELECTRICAL DISTURBANCES David G. McCaa, Lancaster, Pa.

Application October 27,

3 Claims.

The present invention relates to improvements in means for reducing and limiting interfering pulsations in electrical circuits through which electrical energy is being transmitted in useful form and especially to'apparatus and method adapted to reduce the influence of atmospheric or any other electrical disturbances in signal receiving devices, originating externally of the device and is a specific application of the invention disclosed and claimed generically in my co-pending application, Serial No. 320,849, filed Nov. 21, 1928, United States Letters Patent No. 1,959,275, issued May 15, 1934, which, in turn, is a division of my application, Serial No. 74,087,

- filed Dec. 8, 1925, United States Letters Patent No. 1,814,051, issued July 14, 1931. The present invention is in the nature of a specific embodiment or modification of the generic invention disclosed inmy co-pending applications, Serial No. 492,052 filed Oct. '29, 1930, United States Letters Patent No.1,969,657, issued Aug. 7, 1934, and Serial No. 492,054 filed Oct. 29, 1930.

As is well known, when electrical disturbances are-in-evidence during radio reception, they take the form of audible noises which often completely submerge all other reproduced sounds. The origin of such disturbances cannot be readily controlled northeir arrival at the antenna prevented. yHence the place where their effects,

1 may be decreased is confined to the vicinity of the receiving system itself. To reduce or substantially eliminate the effects of the oscillations, by which such disturbancesare produced, requires that such oscillations be so far as pos- 55. sible nullified and one method of accomplishing this purpose is'to reduce'the ratio of the energy due to disturbing oscillations to the energy due to the desired or signal oscillations. It is, therefore, the object of the present invention to pro- 40" vide a method and apparatus so designed that the effects of electrical disturbances can be controlled and largely reduced without substantially affecting the quality of reception of desired signals, thus permitting the reception of signals with great deal more clarity and substantially as great intensity as when no disturbances'are present.

' Another object is to provide an improved method and device for differentiating in electrical circuits between impulses of electrical energy of different amplitudes,the higher amplitude' waves being damped as, for example, at-

; the desired signal wave.

1930, Serial No. 491,582

Another object of the invention is to provide a method and apparatus by which the effects of electrical disturbances may be substantially reduced to a point where they are no longer troublesome and which can be operated in connection with an ordinary receiving system in either radio or telephone line communication. The apparatus in this respect, including appliances, may be disposed either between the receiving system and the input thereto or connected into the circuit of the receiving system between the output of the system and the sound reproducing device, or in any other convenient position on the re ceiving system.

Other objects and advantages of the invention will appear more fully hereinafter from the following detailed description taken together with the accompanying drawing, in which: The single figure is a schematic wiring diagram illustrating an arrangement for carrying out my invention.

Referring to the drawing, there is shown an antenna circuit l which includes the usual pri-- mary or input coil 2, the other end of which may be connected to earth or ground in the customary manner. Inductively associated with input coil 2 are secondary coils 3 and 4. While the invention is shownapplied to the radio frequency portion of a radio receiver, it will be apparent that it is capable of use in the audio frequency portion as well. In such case, of course, coils 2, 3 and 4 might be wound on a common iron core. Coils 3 and 4 are respectively the input coils for the thermionic devices 5 and 6 which, in the present instance, may be ordinary three-electrode vacuum tubes having the usualgr'id, cathode and anode. The lower ends of coils 3 and 4 are connected together and to a common lead running. to the negative side of a biasing battery 1, the positive terminal of which is connected to the cathodes of tubes 5 and B. The upper end of coil 3 may be connected to a variable resistor IS, the purpose of which will be apparent hereinafter, the other terminalof the resistorbeing connected to the grid of tube 5. The upper end of winding 4 is connected to the positive terminal of an additional biasing battery 8, the negative terminal of which is connected to the grid of tube 6. The anode of tube 5 may be connected toone terminal of a circuit comprising a variable resista ance IT or a resistance and a variable condenser I8, the purpose of which'will be explainedlater,

the other terminal of this circuit being connected to the upper end of a primary winding of transj ing is connected to the anode of tube 6. A common lead runs from the cathodes of tubes 5 and 6 to the negative terminal of the anode potential supply source Ii, the positive terminal of which may be connected through a resistance i5 to the midpoint of the primary winding of transformer l9. Secondary winding i2 is inductively associated with the two halves 9 and ID of the primary winding and itsterminals are connected to output terminals i3 and i4. Coils 9, I and I2 might, of course, be wound on a common iron core if the device were used in the audio frequency portion of a receiving system.

The source of uni-directional potential may be given such a value as will cause a zero value of plate current in the output circuits of the tubes when no incoming waves are being received. That is, the grids of the two tubes are biased by means of the common bias or C battery I to cause the tubes to operate about the zero plate current point on their curves. Tube 6 is further negatively biased by means of uni-directional potential source 8 to block oscillations of smaller amplitude than that of the peak potentialof the desired or signal oscillations. lniother words, source 8 is given a potential value which is equal to the peak potential values of the low amplitude signal oscillations.

Let us assume that the antenna is excited by an incoming wave which comprises both low amplitude or signal waves and high amplitude or disturbing oscillations. On each half cycle of the. incoming oscillations, a potential is set up across winding 2 which alternatelychanges in polarity every half cycle. A corresponding. potential or voltage is established by induction across the extremities of windings 3 and 4. Assume that the potential is such as to cause the upper ex tremities of winding 3 .to be negatively poled, the lower extremity of winding 4 being positively poled. The potential across winding 3 is then of the same polarity as source 1 with respect to the grid of tube 5, and the tube is blocked. Similarly, the potential across winding 4. acts to make the grid of tube 6 still more negative with respect toits cathode and tube 6 is'likewise blocked. On this half cycle of the incoming oscillations, it is apparent that regardless of the amplitude of the incoming waves,'both tubes are-non-conductive and no oscillations appear in the output of the device. Currents which are passed capacitively through the vacuum tubes and 5 balance each other in the output circuit IL A neutralizing system may be added to balance each tube independently if the circuits are not equivalent.

Assume now that .the polarity of. the incoming oscillations is such as to cause the upper extremity 'of winding 3 to be positivelypoled, the lower extremity of winding 4 being negatively poled. The potential across winding 3 now acts in opposition to the biasing source 1 and tube 5 becomes conductive, the plate current of the tube varying in amplitude in proportionto the applied potential. 'Ihepotential across winding 4 acts in opposition to both biasing sources I and 8 and tends to cause tubeB to become conductive. If the incoming oscillation is of .low amplitude, such as a signal oscillation, tube 5 will act as an amplifier thereof, but tube 6 will still. be blocked due to the additional biasing of battery 8. As long as the potential across winding 4 is of lower amplitude than the peak potential of the desired oscillations, tube 6 remains non-conductive and no, plate current flows in its output :18 cm. incomin: .oseillatiomii's, homer,

of greater amplitude than the peak potential of the desired oscillations, the voltage across winding 4 overcomes the biasing effect of both sources I and 8. Tube 6, then becomes conductive whenever oscillations of greater amplitude than the desired signal or low amplitude oscillations are received.

It will be apparent, therefore, that on alternate half cycles of incoming oscillations, a plate current flows in the output circuit of tube 5 through winding 9, as illustrated by the arrow in the drawing regardless of the amplitude of the oscil- Iations. On the other hand, tube 6 becomes conductive on the same alternate half cycles of the incoming oscillations only if the amplitude of such oscillations are of greater magnitude than the desired signal oscillation, and plate current then flows in the output circuit of the tube through winding ID, as indicated by the arrow. Low amplitude or signal oscillations, therefore, pass through and are amplified by tube. 5, appearing in the secondary wind-ing l2. Tube 6 does not conduct or amplify such low amplitude oscillations and no current flows in winding Ill.

However, when oscillations of greater amplitudev than the desired signal oscillations are received, both tubes conduct them and current flows in windings 9 and ID in the directions indicated by the arrows, thereby neutralizing each other in their eifects upon the secondary winding 12;, The circuit of tube 5, therefore, constitutes a nondiscriminating device so far as the amplitudes of the incoming oscillations are concerned, while the circuit of tube 6 discriminates'against the low amplitude signal-oscillations.

For purposes of illustration, the waves of high and low intensity have been considered separately. In actual practice, the waves will in most cases be combined to form a complex waveof form and amplitude corresponding to the original waves. In this complex wave, it willbeseen that when the wave oflowamplitude and the impulse wave of high amplitude are both for instance near their maximum positive .values, the amplitude of the complex wave will be high and will take the form of'a lower frequency wavef modulated by a higher frequencywave, i of course, apparent that if the maximum, wave potential were limited to a fixed value, the modulation on the low frequency wave would be attenuated to a verylow value. However, in this system as the balance does not ocur until the amplitude is very high, the portionsof moderate intensity of the high amplitude impulse wave being attenuated. more andmore proportionately as the amplitude increases, it will be seen that, the higher frequency wave within the predetermined limits will be transferred to the output terminals, although'to a diminishing extent. If this gradual change of attenuation were not in-.- herent in the system, there would be times when the signal desired would be balanced out with and because of the higher wave impulse. However, by allowing a reduced transfer of the high intensity impulse wave, the low intensity wave is never completely. balanced out. It is apparent that there will be a certain distortion of amplitude of the signal because of this action. However; with this device, the low amplitude signal will be successfully received with only minor distortion, whereas without the device, the high amplitude impulse wave might predominate to such. an extent that reception of the low amplitude signal would be practically impossible.

I have found that by pro vidh itvlriable recoming waves.

sistor [6 in the grid cathode circuit of tube 5 and/or a circuit including a variable resistor I! with the possible addition of a variable condenser I 8 in the anode-cathode circuit of the tube, I am able to control the currents flowing through Winding 9 in an efiicient manner to completely neutralize the currents in winding It. It will be understood, of course, that any suitable arrangement for controlling the opposing currents so as to increase their neutralizing efiect may be used. I also provide a resistor it in the common lead of the output circuits of the tubes, the action of which is probably to straighten out the input voltage-output current characteristic curves of the two tubes. This resistor may, of course, have any suitable value which will accomplish its purpose under given conditions.

While, as stated before, the device constituting my present invention may be used as a disturbance reducer either at radio or audio frequencies, it will be apparent that the device operates to conduct only one-half of each cycle of the in- The device, therefor, inherently acts as a detector and is particularly adapted to be used as such. The device may, however, be used as an amplifier or in any manner for which it is suitable. By providing a second device similar to the device shown but associated therewith in a manner to conduct the other half cycle of each wave, a full-wave amplifying device is obtained. This could be done by having the input coil of the second device connected so as to be poled oppositely to coil 2, or by connecting the terminals of the coils corresponding to 3 and 4 reversedly to the tubes corresponding to 5 and 6. As an alternative, a tube corresponding in function to tube 5 may be connected between coils 4 and i9, and another tube correspondingto tube 6 may be connected to coils 3 and 9 to provide full-wave action, as well as push pull amplification. This is a simplification of the previously-mentioned power tube circuit.

The action of this device has been described with the assumption that tube 5 operates at zero plate current in the absence of incoming oscillations. I have found, however, that a desirable amount of discrimination occurs when a moderate amount of plate current flows in tube 5, in the absence of signal, and tube 5 may conveniently be operated so as to have an initial plate current of a small amount under these conditions. As used in the claims,therefore, the term output current cutoff means either the point of zero plate current or the point at which the plate current no longer decreaseswith increasing negative grid bias.

While I have disclosed a single embodiment of my invention for the purposes of illustration, it

is obvious that modifications and changes therethe waves passing through said paths, whereby waves of greater amplitude than said predetermined amplitude substantially cancel each other.

2. In a device for discriminating between electrical waves of different amplitudes, two electrical paths operative with respect to the source of said waves, a'thermionic device in each of said paths, means biasing one of said devices to output current out-off, means biasing the other ofsaid devices beyond output current cut-off an amount comparable to the peak value of waves of predetermined amplitude, and means for opposing to each other the waves passing through said paths, whereby waves of greater amplitude than said predetermined amplitude substantially cancel each other.

3. In a device for discriminating between electrical waves of different amplitudes, two electrical paths operative with respect to the source of said waves, a thermionic device in each of said paths, means biasing one of said devices to output current cut-off, means biasing the other of said devices beyond output current out-ofi an amount comparable to the peak value of waves of predetermined amplitude, means for opposing to each other the waves passing through said paths, and means for controlling the phase relation of the waves in said paths, whereby waves of greater amplitude than said predetermined amplitude substantially cancel each other.

I DAVID G. McCAA.

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