US2066940A - Radio receiving system - Google Patents

Description

W. R. KOCH RADIO RECEIVING SYSTEM Jan. 5, 1937.

yOriginal Filed May 27, 1929 Patented Jan. 5, 1937 UNI-TED STATES Pa'bii' @FFME 2,066,940 RADIO RECEIVING SYSTEM Winfield R. Koch, Camden, N. J., assigner to Westinghouse Electric & Manufacturing Company, a corporation of Pennsylvania Original. application May A27, 1929, Serial No.

Divided and 'this application October 6, 1933, Serial No. 692,451

3 Claims. (Cl. Z50-8) Superheterodyne systems, as at present con-1 structed, have many advantages over systems of l5 the straight amplifier-detector type but trouble has heretofore been experienced in preventing them from responding to undesired frequencies whichdiifer from the frequency of the oscillator byan amount equal to one-half of the differ- 20 .ence in frequency between the desired frequency and the said undesired frequencies. Such undesired frequencies are known as image frequencies. It has also been founddifficult to so arrange the various circuits that the rotors l 25 of all of the tuning condensers may always be maintained at ground potential, insofar as radio frequency is concerned.

Superheterodyne receiving systems Vhave also,

by reason of their extreme sharpness of tuning,

30 been somewhat unsatisfactory, insofar as theV quality of music reproduction is concerned.

It is, accordingly, an object of my invention to provide a radio receiving set of the superheterodyne type wherein all of the necessary 35 tuning condensers may be maintained at ground potential, insofar as radiofrequencies are concerned. Y

Another object of my invention is to provide a radio receiving set of the type described where- 40 in the selectivity is improved without sacrifice of tonal quality.

Another object of my invention is to provide a radio receiving set'of the Vtype described wherein a common source of plate potential may `be utilized without causing the generation of undesirable oscillations.

Another object of my invention is to provide ay radioreceiving system that shall be relatively 50 insensitive to extraneous and interfering disturbances Another object of my invention is to provide a radio receiving system wherein the grid-biasing potentials for all of the necessary thermionic 55` tubes may be derived from a common source of platepotential in such manner as toY preclude the generation of undesired oscillations.

Another object of my invention is to provide, in a receiving system of the type described, a plurality of independent means for volumecontrol.

Another object of my invention is to provide a radio receiving system that shall comprise devices for simulating the action of a band-pass nner.

Another object of my invention is to pro-vide a radio receiving system, the tuning of which is unaifected by changes in the energy-receptor or antenna to which it is connected.

A still further and more specic object of my 1 invention is to provide a radio receiving system that shall be equally well applicable to the reception of telephone signals or continuous-wave telegraphic signals.

The novel features that I consider character- 2() istie of my invention are set forth with particularity in the appended claims. inasmuch as the invention itself, however, comprises numerous elements and sub-elements, all combining to permit the attainment of the aforementioned objects and other objects hereinafter, referred to, it will best be understood from the following description of a specific embodiment, when read in connection with the accompanying drawing.

The single figure of the drawing is a diagrammatic view of a complete radio receiving system of the superheterodyne type comprising preferred embodiments of my invention.

A receivingl system illustrated in the drawing comprises a coupling tube I, a first radio frequencyV amplifying tube 2, a second radio-frequency amplifying tube 3, a first detector tube 6l, to which is coupled an oscillation generator 5,

a first high intermediate frequency amplifier tube 6, and a second detector tube l. A plural- 40 ity of oscillation generators 8 and Il] are coupled to the second detector tube l, for purposes which will hereinafter be referred to more in detail, and the second detector tube isfollowed byV a secon-d high intermediate-frequency amplifier tube il, a third detector tube l2, a first audiofrequency ampliiier tube I3, and a power audiofrequency amplifier tube M.

Each of the tubes in the receiving system is of the equipotential-cathode type, comprising an anode 2B, a control grid 2l, a thermionc cathode 22, and a cathode heater 23. The choice of tubes of this particular type, in connection with the circuits later to be described, is an intentional part of my invention.

The radio receiving system is supplied with cathode-heating current, grid-biasing potentials and plate potentials from a rectifier 24 which is arranged according to the description on page 141 of the publication by Van der Bijl, Thermionic Vacuum Tubes, and need no; specific description. The use of a plurality of equi-potential cathode tubes 25 and 26 in the rectifier, however, is a part of my inventive thought, inasmuch as it permits the energizing of all of the cathodes in the radio receiving set proper from the same source that is utilized to energize the said rectifier tubes.

The rectifier is provided with an output resistor 2l across which is developed approximately twice the potential delivered by the secondary winding 28 of the power transformer 30, in the manner explained in the aforesaid Van der Bijl publication.

A plurality of conductors 3|, 32, 33, 34, 35 and 36 extend from points on the output resistor that are maintained at +200, +90, +45, zero, 4.5, and -9 volts, respectively. These conductors will be later referred toV as bus-Wires in describing the manner in which the various grid, plate, and cathode potentials are supplied to the receiving system.

Before attempting to explain the specific manner in which the various objects of my invention are attained, it is considered advisable at this point, to brieiiy describe the manner in which the system operates in the reception of continuous-wave signals. For purposes of explanation, it is assumed that it is desired to receive an incoming signal of the continuous wave type having a carrier frequency of the order of 500 kc.

The carrier frequency, together with other incoming frequencies and disturbances, is impressed across a resistor 40, one end of which is connected to the grid of the coupling tube and the other end of which is connected to the cathode of the tube through a condenser 4I, an inductor 50 and a condenser 5I. The purpose of the circuit 50--5I will be hereinafter described in detail.

The amplified signal then traverses the first and second RF amplifying tubes 2 and 3 the input circuits of which are tuned to the frequency of the incoming signal, and is impressed upon the input circuit of the first detector tube 4. The first RF oscillator 5 is so adjusted if the incoming signal is at a frequency of 500 kc. as to generate oscillations at a materially higher frequency, 1000 kc. signals being a good value to choose in the specic example given. Beat-frequencies of 500 kc. and 1500 kc. will, accordingly, exist in the output circuit of the first detector tube I, and either of these frequencies may be chosen for further amplification. In! order that the selectivity of the system may be improved, I find it preferable to choose the higher frequency, namely, 1500 kc. and the input circuit of the highest intermediate frequency tube `B is accordingly tuned thereto.

The output of the higher intermediate frequency tube 6 is impressed on the input circuit of the second detector tube 'I wherein, by reason of the action of the second high-frequency oscillator 8, it is altered to either a higher or to a lower second intermediate frequency, and is thereafter amplified by the second intermediatefrequency amplifier tube II.

If the incoming signal is of the continuouswave type an audio-frequency oscillator may be utilized to reduce the signals to an audible notey for further amplification.

The second intermediate frequency is demodulated in third detector tube I2, and the resulting audio-frequencies are next impressed upon the first audio-frequency amplifier tube I3, and, thereafter, upon the second audio-frequency or power-amplifier tube I4.

By reason of the successive heterodyning of the incoming signal by the first and second highfrequency oscillators, the desired signal may bey widely separated from interfering signals before amplification in the second intermediate amplifier. This feature is of particular value, under present conditions, since signals from many stations, which would otherwise interfere, and which lie within the range of receiving sets of the usual superheterodyne type, are thus prevented from being heard.

In addition to the general arrangement of the circuits thusfar described, my invention further consists in the specific circuit details of the various stages, which details, in their entirety, mutually contribute toward sensitivity, selectivity and ease of operation. These details will now be taken up in their proper order, and an effort will be made to point out the novel features of each.

It will be noted that an inductor 50 and a variable condenser 5I are included in the cathode circuit of the coupling tube I, a radio-frequency choke-coil 52 being connected in shunt to the\ variable condenser. The inductor and the condenser constitute a tunable circuit that may be adjusted to the frequency of the desired incoming signal, to a slightly higher frequency or to a slightly lower frequency. When the circuit is adjusted to the frequency of the desired signal, the coupling tube will amplify the said signal to the exclusion of signals at adjacent frequencies, irrespective of the fact that the input circuit of the tube is aperiodic.

Although not so illustrated in the drawing, one or more radio-frequency amplifying stages may be interposed between the coupling tube I and the first radio-frequency tube 2, each of the stages preferably comprising an equi-potential cathode tube, the cathode circuits of which may include reactors similar to the reactors 50 and 5I in the cathode circuit of the coupling tube. By tuning one of the said stages to a frequency somewhat lower than the desired frequency and by tuning another of the stages to a frequency higher than the desired frequency, a band-pass filter effect may be secured without resorting to expensive band-pass filters. In fact, the Shape of the response curve of the receiving system may so be adjusted as to have any desired contour.

It is often desirable, in the event that the receiving system is used at a point closely adjacent to a higher-power transmitter, to interpose a wave trap in the input circuit thereof. It is'- much better, however, to incorporate means equivalent to a wave trap directly in the receiving system itself. For that reason, I have included a parallel resonant circuit, constituted by an inductor 60 and a tuning condenser 6I, in the cathode circuit of the first radio-frequency tube 2. When this circuit is tuned to a strong interfering signal, it prevents the first radio-frequency stage from amplifying the said signal and, although the interfering signal may be impressed upon the input circuit of the said radio-frequency stage, it will not be amplified and appear 'lasl in the output circuit thereof. The circuit GII-VBI also has the important function of reducing image-frequency response, when properly tuned.

It often happens, in the operation of sensitive tuned radio-frequency amplifiers, that parasitic oscillations at ultra-high frequencies, or at high frequencies lying within the tuning range, are developed. In order that such oscillations may be minimized, I have included a variable reactor 62 in the cathode circuit of the second radio-frequency amplifying tube. This reactor, when. properly adjusted, tends to stabilize the system and to prevent oscillations at high frequencies.

As previously pointed out, it is highly desirable that the rotors of all the tuning condensers shall be maintained at ground potential, insofar as radio frequency is concerned. It is also desirable that the various oscillation generators and the amplifying tubes shall be supplied with plate potential from the same source. In addition, I have established the fact that an oscillator of the soi-.called Hartley type is, perhaps, the best to use in a superheterodyne receiver. These desirable features cannot be satisfactorily attained if thermionic tubes of the usual filament type are employed, since it is impossible to maintain the filaments thereof at varying potentials with respect to each other, inasmuch as they must all be supplied with power from the same source. By choosing equi-potential cathode tubes, however, I am enabled to maintain any desired potential differences between the grids and cathodes thereof, between the anodes .and grids thereof, between the anodes and cathodes thereof and between the several cathodes.

It will be noted, from an inspection of the drawing, thata coupling coil 63, for the first oscillator 5, yis serially connected between the cathode oi the first detector tube 4 and the buswire 31, which wire is maintained at effective ground potential, insofar as radio frequency is i concerned, by reason of the by-pass condenser 4i, connected between it and the ground. The rotor of a tuning condenser 64, comprised in the input circuit of the first detector tube, and the rotor of la frequencydetermining condenser 65, associated With the oscillation generator, are also connected to the conductor 34 by short leads 65 and El respectively, thus maintaining the rotors effectively at ground potential. It will further be noted that the oscillating; potentials from the oscillation generator tube 5 are applied simultaneously to the grid and the anode of the first detector tube, in phase. The oscillator is, therefore, not quite so effective as in systems of the usual type, but the slight lack of effectiveness is more than compensated for by the advantages accruing from the grounding of the condenser rotors.

Inasmuch as the cathode of the oscillator tube has an inappreciable capacity to ground, no deleterious effects arise from grounding the rotor of the condenser. It should be apparent to those skilled in the art that these results cannot be obtained without complicated circuits, when using detector and oscillator tubes: having filamentary .cathodes supplied from the same power source.

In order that the volume of the signal output from the entire system may be easily con tro-lled, I have included a variable resistor l0 in the cathode circuit of the first high-intermediate-frequency amplifier tube' (i. Since the entire plate current in the said tube must, of necessity, traverse the resistor, the potential,

applied to the plate of the tube obviously varies inversely as the magnitude of the resistor.

It will also be noted that a connection 'H extends from the midpoint ofthe inductor constituting the input circuit of the said tube to the bus-wire 35 which is maintained at 41/2 volts and that, accordingly, any change in potential between the anode and the cathode of the tube, occasioned by a variation of the resistor l0, is accompanied by a change in the potential of the grid with respect to the said cathode. The volurne-control resistor l!) therefore, serves to control the amplification in the first high-intermediate-frequency amplifier both by occasioning variations in the plate potential applied thereto and in the grid potential with respect to the cathode thereof.

The second high-frequency oscillator is coupled to the second detector through an inductor that is-included in the cathode circuit of the said tube. The advantage of this type of coupling hasbeen previously mentioned in connection with the first detector tube.

The audio-frequency oscillator is coupled to the second high-frequency oscillator through an inductor 3l which is included in the cathode circuit of the said second high-frequency oscillator. The oscillations generated by the said second high-frequency oscillator may, accordingly, be modulated at the frequency generated by the audio-frequency oscillator.

A switch 82 is included in the plate circuit of the audio-frequency oscillator for the purpose of deenergizing it in the event that the incoming rsignals are not of the CW type.

It will be seen, from a close inspection of the drawing, that the circuits of the three oscillation generators 5, 8 and i0 differ in details although each of the three circuits is essentially of the Hartley type. The circuits so shown are interchangeable and are given merely to illustrate the manner in which my invention permits the grounding of the rotors of the tuning condensers associated therewith. The circuits of the first radio-frequency oscillator and the audio-frequency koscillator are perhaps the most satisfactory of the three circuits illustrated.

A volume-control network of alternative type is shown in connection with the second intermediate-frequency amplifier stage. The nete work comprises a resistor connected in shunt to the B and +45 volt terminals of the output resistor of the power supply. A connection 9i is made between the cathode of the amplifier tube and a movable contact device 92 associated with the resistor. The potential of the cathode with respect to both the anode andi grid of the tube may, accordingly, be varied by moving the contact device toward either the positive or the negative end of the resistor.

The input circuit of the third detector tube i2 preferably comprises a grid leak l and a grid condenser iti. Plate potential for the third detector tube is supplied from the |200 volt bus-wire over a variable resistor E02.

The grid of the first audio-frequency ampliivo :ist

tsl

fier tube I3 is directly connected to the plate of K the third detector tube, and the potential of the said grid is, accordingly, determined by the IR. drop along the variable resistor. A connection |03 extendsfrom the cathode of the first audiofrequency amplifier tube to the +90 volt buswire, and plate potential for the tube is supplied from the |200 Volt bus-wire. A potential difference of Volts, therefore, would normally exist between the grid of the tube I3 and the cathode thereof but, by properly adjusting the no-signal plate current in the third detector tube I2, the potential drop along the variable resistor, may be so determined that the grid of the said tube assumes a suiiioiently negative potential to bias it almost to the cut-off point.

An incoming signal, however, causes a diminution in the plate current of the third detector tube, The IR drop in the variable resistor is, accordingly, lessened to a value which permits the grid of the rst audio-frequency tube to acquire a sufciently less negative potential to permit satisfactory amplification of the uctuating audio-frequency potentials existing across the variable resistor by reason of the incoming signals.

An ammeter I2 is preferably included in the cathode circuit of the third detector tube I2 as an aid in determining when the signal is properly tuned in, accurate tuning being indicated by minimum current through the ammeter.

A loud speaker I2I, or other signal indicator, is preferably included in the cathode circuit of the second audio-frequency amplier tube I 4, and a resistor I22 is connected in series therewith.

The grid of the amplifier tube I4 is connected to the resistor I 22 at that end to which the loud speaker is also connected. The plate current flowing in the resistor, accordingly, determines the grid potential, and the tube is thus automatically biased to the best operating point.

From a careful consideration of the foregoing description of a superheterodyne receiving system comprising my invention, it will be apparent that, by utilizing tubes of the equi-potential type, I am enabled to provide a receiving system that has many advantages, among which may be mentioned extreme selectivity, sensitivity, simplicity, fidelity of reproduction and lessened danger to the operator from high potentials.

Although I have illustrated my invention as particularly applicable to receiving systems of the superheterodyne type, it is equally useful in other receiving systems of the types well known to those skilled in the art. The description of certain specific circuit details in connection with particular stages of the systems is not to be construed as an admission that the said details are only useful in the said stages. For example, the tuning ammeter |20 might well be included in the cathode circuit of the first detector, or in the cathode circuit of the second detector, with substantially the same results. The several oscillation generators 5, 8 and ID, might all comprise circuit-networks of the same type as the circuit network described in connection with any one of the said generators. In fact, substantially all of the circuit details shown are capable of use in positions other than those specifically illustrated.

My invention, therefore, is not to be restricted except insofar as is necessitated by the prior art or by the spirit of the appended claims.

I claim as my invention:

l. In a system of the radio type, an oscillation generator comprising an electron discharge device and associated frequency determining circuit, a second oscillation generator, a common source of anode voltage for said oscillation generators, and means independent of the frequency determining circuit oi said rst oscillator for coupling said second oscillation generator to said first oscillation generator, said means being interposed between said source of anode voltage and the cathode of said first oscillation generator in modulating relationship therewith.

2. In a system of the radio type, an oscillation generator comprising an electron discharge device of the indirectly heated cathode type and associated frequency determining circuit, and a second oscillation generator, a source of cathode heating current and a source of anode voltage common to said oscillation generators, and means independent of said frequency determining circuit for coupling said rst oscillation generator to said second oscillation generator, said coupling means being interposed between said source of anode voltage and the cathode of said rst oscillation generator.

3. In a radio receiving system, an electric discharge detector tube of the indirectly heated cathode type, an electric discharge oscillation generator of the indirectly heated cathode type, a source of cathode heating current and a source of anode voltage common to said detector tube and said oscillation generator, coupling means to said oscillation generator interposed between the cathode of said detector tube and said source of anode voltage, a second oscillation generator, and a coupling thereto interposed between the cathode of the first-mentioned oscillation generator and said source of anode voltage,

WINFIELD R. KOCH.

Images