US2038955A - Radio receiving circuit - Google Patents

Description

H. H PARKER RADIO RECEIVING CIRCUIT April 28, 1936.

Filed May 29, 1926 muwmoi Patented Apr. 28, 1936 UNITED STATES PATENT OFFICE RADIO RECEIVING, CIRCUIT Application May 29, 1926, Serial No. 112,516

4Claims. (Cl. 179-171) My invention relates to radio receiving circuits, the object of this invention being to provide means whereby the relay action of electron tubes, connected in cascade, is repeated and amplified more perfectly as to wave form by their associated amplifying devices than by other methods usually employed.

It is well known that iron core transformers introduce considerable distortion into otherwise satisfactory radio reception and when resistance coupling, or other forms of direct or conductive inter-tube coupling, is used to gain better quality of reception it is necessary to separate the steady potential applied to the plate of one tube from the grid of the following tube in order that the grid can be maintained by other means at the proper biasing voltage, so that the tube will operate on the linear portion of its characteristic curve and the output more perfectly reflect the wave-form of the input.

This is usually accomplished by inserting a stopping condenser in the grid lead and connecting the grid, by means of a high resistance usually known as, a leak, to the filament. This may be connected to the filament either directly or through a battery, or other means, and is for the purpose of maintaining the desired stabilizing voltage.

Now when this is done undesirable losses and. other disturbing factors are introduced.

As an example, one of the faults in the above described combination of a stopping condenser and grid leak in the input circuit of an amplifying tube is that the stopping condenser is a r reactance against the signal which is a loss.

Also the value of this reactance is variable being dependent upon the frequency of the currents passed and therefore passes a current of higher frequency with less reactance than a current of lower period which promotes distortion of the signal. Again when a grid resistance is in shunt with the input circuit it consumes energy from the signal currents and it is also probable that at times the negative charge accumulating on the grid is dissipated too fast or too slow, depending upon various factors, and because .of this would throw the repeating action of the tube'from the linear portion of its characteristic curve to a point where the tube itself would create distortion of the signal.

In order, therefore, to avoid the above mentioned faults in a radio receiver and further to amplifyreceived signals with greater freedom from distortion, I have developed a system of amplification-applicable to audio frequency, radio frequency or radio beat frequency, all of which may be used separately or in combination and also in combination with detector tubes and associated apparatus.

The attached drawing and detailed description of this method of radio reception are intended to clearly illustrate the operation and fundamentals involved, and other elements which might be desirable to use in this circuit but not essential to clearly show the scope of the invention are not shown.

Referring to the drawing:

Fig. 1 is a diagrammatic view of a receiving system embodying my invention.

Fig. 2 is a diagrammatic view of a modified form of receiving system but still embodying my invention.

Fig. 3 is a still further modification of the receiving system. 1

In most cases of radio receiving systems a certain condition exists, namely, that when the inter-tube coupling device between any two successive tubes in a radio receiver is direct, or conductive, and is so connected as to offer little or no resistance to continuous current between the plate of one tube and the grid of the following tube, the steady voltage normally applied to the plate of one tube would also be impressed upon the grid of the following tube, thereby rendering said tube inoperative.

In order to use a coupling device of the particular type to be described, with little or no continuous current resistance between the plate of one tube and the grid of the following tube, and to have the A. C. component of the plate. current impressed in as direct a manner as possible on the grid of the following tube, the potential difference between the filaments of two successive tubes is at a fixed value and the required relative voltages of the output circuit of the first tube and the input circuit of the following tube are simultaneously obtained by the common return of this inter-tube coupling being connected to the correct relative location on the source of supply (on the resistance between the two filaments as disclosed on the drawing).

Referring to Fig. 1, there is shown a typical receiving system in which is provided electron tubes l, 2, 3, 4 and 5, and each tube is provided with the usual filament, grid and plate electrodes. In tube l the filament is designated by the numeral 6, the grid by the numeral 1 and the plate by the numeral 8. In tube 2 the filament is designated by the numeral IS, the grid by the numeral l0 and the plate by the numeral ll.

The usual aerial 2| with the primary induction coil 22 is grounded at 23, which is the usual construction employed in radio receiving sets using the outside aerial. While the drawing has disclosed the principle of employing the usual antennae, it is to be understood that the invention will function as successfully wherein a loop is employed or where the induction coil 24 is used as a loop. A second induction coil 24 associated with the primary induction coil 22 is connected into the grid circuit of the first tube. The usual variable capacity condenser 25 is introduced across the ends of the induction coil 24 for the purpose of tuning.

The filaments of the respective tubes, and referring particularly to the filament 6, the description of which will apply to the respective filaments of the other tubes, is connected directly to a secondary coil 26 of a transformer which has a primary 3| connected directly to the source of supply. Similar secondaries 21, 28, 29 and 30 supply the filaments of the respective tubes with the proper voltage to sufiiciently heat them Each filament is provided with a resistance 32 across the terminals thereof, and is further provided with a central tap which is attached to the resistance element I2 at a point 33 thereon. A similar result may be obtained by tapping off from the electrical center of the secondary windings 26, 21, 28, 29 and 30. The secondary windings are insulated from one another as shown in Fig. 1, and are capable of a difference of potential (D. C.) being maintained between them. The primary winding of the transformer is shown as being a continuous winding but this is not necessary and may be composed of separate primaries similar to the secondaries already described.

As a means for supplying the required plate or D. C. volt-age to the respective tubes preferably rectified and filtered A. C. current is supplied to each end of a resistance element I2 or to a number of units connected in series. This resistance element I2 is in communication with the plate of each electron tube, the particular function of which will be hereinafter explained.

As has been heretofore pointed out it has been practically impossible to connect the plate of one tube directly with the grid of a successive tube without the introduction of proper condensers and grid leaks into the circuit between the electrodes of successive tubes. Naturally, if the plate of one tube was connected directly to the grid of a successive tube and the plate potential supplied to that connection, the voltage would be impressed not only on the plate of the first tube but also on the grid of the following tube. This would paralyze the action of the following tube so that it would fail to operate. By the introduction of these particular condensers and resistances a loss of amplification is created as well as non-uniformity of amplification due to the variable action of these elements and thereby hinders perfect amplification.

It is my intention, as disclosed in the drawing, to connect the plate of one tube with the grid of the following tube and to eliminate the condensers and resistances ordinarily employed as heretofore explained. By employing a common return comprising an inductance coil I6 having one end connected into the circuit between the plate and the grid of successive tubes I and 2, and the opposite end connected to the resistor I2 at the correct location thereon the proper plate voltage is obtained. The positioning of this end of the inductance coil I6 upon the resistance element I2 simultaneously controls the proper voltage supplied to the grid circuit of the second tube.

The difference of potential between the plate 8 and the filament 6, D. C. component or steady value, is determined by the drop in voltage on resistor I2 between the points 33 and 36 minus the drop through the inductance coil 26 and part of the balancing resistance 32. The steady value and superimposed A. C. value of voltage on the grid I0 is therefore the same as that of the plate 8 and would normally paralyze the action of tube 2 and in order that the steady voltage rela tions between the input elements of tube 2 be such as will bring this tube into essential operating condition, the voltage of the center of the filament I9 is raised in a positive direction in relation to the filament 6, by an amount approximately equal to the algebraic sum of the difference of potential between the plate 8 and the filament 6 and the voltage difference desired between grid Iii and filament I 9. This is controlled by the location of the tap 35 on the resistance element I2 with respect to the location of the tap 3-3 on the resistance element I2. By this arrangement therefore the voltage existing between points 33 and 35, neglecting minor considerations, is also the sum or difference of the voltages between the filament 6 and the plate 8 of the tube 1 I and the filament 9 and the grid II] of the tube 2 depending upon whether a positive, negative or zero grid is wanted. Therefore the plate and grid voltage is fixed simultaneously by the location of the common return tap 36 on the resistance element l2 and this location may be on either side of the tap 35 or it may be connected to it.

The operation and voltage adjustments as affecting the output and input circuits of the tubes I and 2, above mentioned, is essentially the same for the other tubes as shown and the electrical constant and type of inter-tube coupling employed will determine whether the tubes function as detector, radio frequency amplifier, audio frequency amplifier or radio amplifier of a beat frequency.

It should be noted that the location of the tap 3'! on the resistance element I2 is shown on the far side of the filament of the tube 3. the purpose of supplying a positive grid potential which is desirous in operating the detector tube as this tube operates primarily as a rectifier.

In Fig. 2 a similar arrangement is shown in which the principle is not altered and the operation is essentially the same and differs from Fig. 1 by the simultaneous use of resistor 40 as current supply and voltage distributing unit to a multitube radio amplifier and multi-tube audio amplifier making the resistance element 40 common to both. This particular construction effects economy of power as it means the D. C. voltage across the resistance element 40 is less than if this were not done.

When this form of resistance is used energy is transferred from the output of the first amplifying group to the input of the next by inductive or capacitive means, or in any manner, which preserves the voltage relations in the output circuit of the tube in the most positive position on resistance element 40 and the input voltage relations in input circuit of the tube to which energy is transferred in the most negative position on resistance element 40.

In Fig. 2 tube 4| is considered as the detector This is for i tube and tap 42 is so located on the resistance element 40 to give the correct grid bias to the grid 43, and tap 44 is so located on the resistance element 40 to furnish plate 45 with the correct voltage for detection. 46, 41 and 48 represent respectively the primary windings, the iron core, and the secondary windings of the ordinary audio transformer and 49 and 50 represent the output terminals from the first group of tubes and 49' and 50' represent the input terminals to the second group. It is to be understood, however, that these two groups should be connected together through the means of the terminals just described.

In Fig. 3 the principle of operation remains the same and when a D. C. current in excess of that required to sufiiciently heat the filaments and of sufficiently high steady potential is applied to the terminals of the resistance element 50, this arrangement functions practically the same as the.

system described in Fig. 1.

With the arrangement disclosed in Fig. 3, the filaments of the respective tubes might be considered as being connected in series or a modification of a series system, but I do not claim this arrangement as a part of my invention. In connection with this series arrangement I do claim, however, as being new and novel and. vital to this invention, the means of separating and maintaining the various filaments at the required steady difference of potential between the filaments of successive tubes, as for example, between the terminals 5| and 52 in Fig. 3 or as between the terminals 33 and 35 in Fig. 1.

In Fig. 3 the filament supply is taken from the resistance element 50 by virtue of the fact that the current shunted around the filaments is inversely proportional to the respective resistances of the various filaments and the parts of the resistance element 50 included between their terminals, such as shown by filament 55, and resistance included between points 52 and 54, in which case the total resistance across the resistance element 50 is less with all filaments connected than with them not connected, which change in resistance is immaterial as long as the required relations exist with the filament terminals fixed.

Having thus described my invention, what I claim is:

1. In a tuned radio frequency circuit, a pair of electron tubes having cathode, grid and plate electrodes, means for directly connecting the plate of one tube with the grid of the succeeding tube, separate alternating current circuit means for heating said cathodes, a source of direct current for supplying the grid and plate potentials, cathode leads associated with said source of direct current, a coupling device connected to said plate and grid connecting means and associated with said source of direct current, and a variable tuning element in shunt with said coupling device.

2. An amplifying device comprising the combination of first and second amplifying tubes, each tube having cathode, anode and control electrodes, means for directly connecting the anode of said first tube with the control electrode of said second tube, a source of direct current, a potentiometer connected thereto for supplying operating and biasing potentials for said tubes, means including a coupling element connected between said first means and said potentiometer to supply the desired output and input biasing potentials, leads to the remaining electrodes of said tubes from points of said potentiometer positioned relative to each other and to said potential supply means to furnish the desired operating and biasing potentials between the cathode and anode of said first tube and the cathode and control electrode of said second tube, respectively; a power transformer having a single primary winding and a plurality of independent, insulated secondary windings, and leads connecting said secondary windings to the respective cathode terminals.

3. An amplifying device comprising a potentiometer having its terminals connected to the opposite leads of a direct current supply source,

a plurality of vacuum tubes each having an anode, a grid and a cathode, a direct current connection between the anode of one tube and the grid of the succeeding tube, connections between the tubes and the potentiometer at such points that the voltage on said last named grid, due to anode current, is compensated; other vacuum tubes each having an anode, cathode and grid, a direct current connection between the anode of one tube and the grid of the succeeding tube and connections between the tubes and the potentiometer at such points that the voltage on said last named grid due to anode current is compensated, said last named potentiometer connections being made to points on said potentiometer having substantially the same voltages as those to which said first mentioned potentiometer connections are made.

4. The combination defined in the preceding claim in which the first named plurality of tubes serves to amplify modulated radio frequency currents and in which detecting means is interposed between this group and said second group whereby the tubes of the second group serve to amplify currents of the modulation frequency.

HOWARD H. PARKER.

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