US2039634A - Heterodyne receiver radiation suppressor - Google Patents

Description

May 5, 1936 M. e. CLAY 2&39534 HETERODYNE RECEIVER RADIATION SUPPRESSOR Filed Dec. 22, 1932 L 2* M M 0575005 [2 REP/900066? Patented May 5, 1936 UNITED; STATES HETERODYNE RECEIVER RADIATION SUPPRESSOR Murray G. Clay,.New York, N. Y., assignor to Radio Corporation of Delaware America, a corporation of Application December 22, 1932, Serial No. 648,389

2 Claims.

My present invention relates to radiation suppressors for heterodyne receivers, and more particularly to improved arrangements for preventing the radiation of radio frequency energy at local oscillator frequency from a superheterodyne receiver.

It is Well known that radio receivers of the superheterodyne type radiate radio frequency energy from the local oscillator circuit with sufiicient power to heterodyne with radio frequency signals being received by other receivers in the vicinity of the radiating receiver. The result of such heterodyne action due to radiation from a superheterodyne receiver is particularly undesirable since it causes annoying squeals and whistles in the radio receivers which pick up the radiated energy. Various expedients have been proposed to minimize this source of interference.

For example, shielding, obviously an uneconomical device, has been resorted to; blocking arrangements have been utilized with varying results.

Now, I have found that by introducing into the radiating circuit an amount oflocal oscillator energy equal in magnitude and opposite in phase to that reaching the radiating circuit by other paths, the offending radiation can be com-- pletely eliminated, or very materially reduced. Accordingly, it may be stated that it is one of the prime objects of the present invention to eliminate radiation from a radio receiver, or an oscillating electrical system in general, which radiation occurs through the antenna, ground, power line, reproducer, cable, or any other component of the apparatus capable of radiating when energized, the radiation elimination being accomplished by positively'injecting into the radiating component energy from the source of radiation which is equal in magnitude but opposite in phase to the energy of said source which is being radiated.

Another important object of the present invention is to provide an arrangement for eliminating serious interference with signal reception by radio receivers in the neighborhood of a' radiating superheterodyne receiver; to eliminate interference withother electrical or radio equipment such as'field strength. measuring devices and the like; and to avoid detection of the presence of receiving devices, or other equipmentgcapable of radiation, where, secrecy must be maintained, as for example in the vicinity of a, war area. I

Still another object of the presentinvention maybe said to I be the, provision of a means, for.

the suppression of alternating electrical energy in components of apparatus, where desirable, by the use of a suitable form of coupling device feeding energy equal in magnitude and in phase opposition to that to be suppressed from the source of the alternating electrical energy into the apparatus component where the suppression is desired; and to additionally provide means for applying this suppression means to any forms of an electrical device without materially affecting its normally operating functions. I

And still other objectsof this invention are to improve generally the simplicity and efiiciency of superheterodyne receivers, and to particularly provide a superheterodyne receiver which is not only durable and reliable in operation, but economical to manufacture and assemble, and freefrom a tendency to radiate radio frequency energy at local oscillator frequency to neighboring receivers.

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 organizations whereby my invention may be carried into effect.

In thev drawing,

Fig. 1 shows schematically a superheterodyne receiver embodying the present invention,

Fig. 2 shows a modified form of the invention,

Fig. 3 shows a combined'first detector-oscillator circuit embodying another modification of the present invention,

'Fig. 4 shows diagrammatically the application of still another modification of the invention to a radiating energizing power line.

Referring now to the accompanying drawing wherein like reference characters in the different figures designate a corresponding circuit element, there is shown in Fig. 1 a superheterodyne receiver of a well known and conventional type. This receiver comprises the usual signal collecting means, such as a grounded antenna circuit A, the circuit being coupled, as at M, to the tunable input circuit of the first detector tube 1. For the purpose of illustration it is to be understood that the superheterodyne receiver is to be tunable through the broadcast signal range, and that the input circuit of the screen grid tube I therefore includes a variable tuning condenser 2 having a plurality'of grounded rotor plates. The anode of the tube I is connected to a source of positive potential +3, and while the source is not shown it is to be understood that this source may be the usual output of the conventional filtered rectified alternating current. Of course, the energizing power source may also be a direct current source or battery source.

it being pointed out that both tubes I and 5 are of the indirectly heated cathode type, the coil 6 being connected between the control grid and plate of tube 5, and functioning as the oscillator inductance coil. It is notrbelieved necessary to explain in detail theconstruction and operation ofthe local oscillator circuit since it is a conventional one, the plate circuit being regeneratively coupled to the input circuit of tube 5 through the coupling condenser I, the grounded cathode of tube 5 being connected to an intermediate point of the coil 6, and the variable oscillator tuning condenser 8 being connected in shunt. across the coilfi. The energizing source for the anode of tube I .may be used to provide the positive potential for the anode of tube 5 and the proper positive potential for the screen grid of tube I.. The coil Gris magnetically coupled to the coil 9, the latter being connected in series between the cathode of tube I and the bias resistor III having one of its terminals grounded. The bias resistor I0 is shunted by an. appropriate radio frequency by-pass condenser II, and the symbol Ct designates the tube, and other stray, capacities, coupling the oscillator energy to the antenna transformer M, these capacities being shown by the dotted lines between the grid and cathOde of tubel.

The, tuning condensers 2 and B arearranged for mechanical uni-control, as shown by dotted lines I2, and those skilled in the art will understand that the local oscillation circuitis tunable through a range of frequencies which differ from the rangejof'broa'dcast signals bythe operating intermediate frequency. The intermediate frequency is maintained constant throughout the tuning. range of the signal circuit and local oscillation circuit condensers by means which are Well known, and not necessary to be shown.

The intermediate. frequency amplifier is followed by the. usual second detector, audio frequency amplifier and reproducer. Of course, the first detector may be preceded by one or more tunable radio frequency stages if desired, and the intermediate frequency amplifier and audio frequency. amplifier stages may each include one or morestages of amplification. Considering the circuit arrangement of Fig. 1, from a general viewpoint, it will be noted that there is provided a counter-coupling path between the coil 9 in the cathode circuit of tube I and the high potential side of the primary of the transformer M. This path includes a condenser C, which is termed'the counter-coupling capacity.

It will be observed that the grounded antenna circuit A comprises a device capable of radiation when energized. 'Thisradiating device is coupled through the capacity Ct to the source of oscillation, which source includes the coil 9 and the oscillating system coupled to it. The tendency of this source of oscillation to energize the radi-' ating device is overcome by providing the countercoupling path, or'medium, which includes the condenser C.

In other words, there is shown in Fig. 1 an arrangement for counter-coupling an oscillating source to a radiating component to counteract the effect of other couplings which may not be practically or economically eliminated. The counter-coupling capacity C functions to suppress the radiation caused by the tube, and stray, capacities feeding local oscillation energy from the first detector cathode to'the antenna transformer M. This is a practical and economical 'method of suppressing radiation of radio frequency, energy of local oscillator frequency in a superheterodyne receiver which employs a local oscillator coupled magnetically to the cathode circuitof the first detector tube.

The counter-coupling energy, that isthe radio frequency energy fed to the grounded antenna circuitAthrough the condenser C, is of. a magni tude and phase'such that'it substantiallyeliminates the radio frequency energy fed to the circuit A which would otherwise. be radiated to neighboring receivers and cause squeals, and Whistles dueto heterodyning with the broadcast signals received by these neighboring receivers. It is understood, of course, that the radio free quency energy fed back to prevent radiation will constantly be of 1 the necessary magnitude and phase, to perform this function, regardless of the adjustments of the tuning condensers 2. and 8. That is, the phase and magnitude values of the energy fed through the path including condenser C will be correct for radiation Suppression throughout the broadcast tuning range of the condensers 2 .and 8.

In Fig. 2 there is shown a modified form of the counter-coupling arrangement shown in Fig.1. In this modified: form of the invention the local oscillator circuit isnot magnetically coupled to the cathode circuit of the first detector, as in Fig. 1, but instead is coupled to the grid circuit of tubel by a coupling condenser 20. This form of capacitative coupling. between the localoscillator circuit and the grid circuit of the first detector renders it possiblefor local oscillator energy to be fed into the antenna transformer M through the coupling condenser 20. The countercoupling path, then,.is provided by the counter magnetic coupling M: between the coil 6 and the primary of the antenna transformer M. 01' course,athe energy fed to theprimary M1 in the grounded antenna circuit Afrom the 0011.6 isof the correct magnitudeand phase to substantially eliminate the local oscillator energy. fed into the antenna circuit through the coupling condenser 20.. r The presentinvention may .be. employed in a superheterodyne receiver ofthe type using a combined first detector-local oscillator circuit employing a single tube I, in place of the-separate tubes. I and 5.. Such an arrangement is shown in Fig. 3. This combined detector-oscillator circuit primarily differs from the arrangementshown in Figs. 1 and 2 inthat a single screen grid tube I is employed, the resonant local oscillator circuit including thecoil 6" and the variable tuning condenser 8", the coil 6' being magnetically coupled to the coil 9 which is-connected in' the grounded. cathode-circuit of the tube, as in the case of Fig. 1. The resonant local oscillation circuit has one side thereof connected to the anode of tube I through a condenser I, while the opposite side of the circuit is grounded.

The variable condensers 2 and 8 are arranged for mechanical uni-control as in the case of Fig. 1. Fig. 3, then, shows the counter-coupling condenser C, as in Fig. 1, suppressing radiation caused by the tube, and stray, capacities (shown in dotted lines between the grid and cathode of tube I) feeding local oscillator energy from the cathode to the antenna transformer M. It is believed that the operation of this modification will be clearly understood in view of the detailed explanation given in connection with Fig. 1.

Fig. 4 shows a modification of the invention applied to the suppression of serious power line radiation by counter-coupling a suitable amount of local oscillator energy to the power line. By utilizing a counter-coupled voltage drop across a small resistance R, the advantages of both line by-passing and line radiation suppression can be economically realized. The condensers C4 and C5 are the usual and well known non-inductive power line by-pass condensers while the resistor R is a non-inductive resistance of low value having one terminal connected to the midpoint of the condensers C4 and C5 and its other terminal grounded. The symbol S designates the usual on-off switch, and the counter-coupling path is shown connected by an adjustable tap 2| to the local oscillator coil 6, the counter-coupling condenser C having one side connected to the tap 2|, and its opposite side connected to the ungrounded side of resistor R. In the modification of Fig. 4 it will be understood that the local oscillator circuit is coupled to the power line through stray capacitative paths which tend to enhance the radiating properties of the power line.

By providing the path including condenser C between the power line and the local oscillator coil 6, it is possible to feed to the offending power line energy which is equal in magnitude to the radiated energy and 180 degrees out of phase therewith. This phase relationship is, of course, true in the case of the modification of Figs. 1, 2 and 3.

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 may be made without departing from the scope of my invention as set forth in the appended claims.

What I claim is:

1. In a superheterodyne receiver of the type including a local oscillator circuit adapted to produce local oscillation energy of a frequency sufficiently high to produce a super-audible intermediate frequency with incoming signal energy, means for substantially counteracting the effect of a coupling between the local oscillator circuit and a circuit of the receiver adapted to radiate energy of said local oscillation frequency to radio receivers in the immediate vicinity, which means includes a reactive counter-coupling path coupled between said local oscillator circuit and said other circuit, said path comprising suflicient resistance for transmitting to said other circuit energy of a frequency magnitude and phase sufficient to balance out said local oscillator frequency energy fed to said other circuit, said other circuit including the energizing power line of the receiver.

2. In a heterodyne receiver of the type including a local oscillator circuit adapted to produce local oscillation energy of a frequency sufficiently high to produce an intermediate frequency with incoming signal energy, the receiver including a power line for energizing the receiver circuits, means for substantially counteracting the elfect of a coupling between the local oscillator circuit and the power line, said coupling being adapted to permit the power line to radiate energy of local oscillation frequency to radio receivers in the immediate vicinity, said counteracting means including a reactance connected between a point on said local oscillator and a point on said power line, and said reactance being adapted to transmit to the power line energy of a frequency, magnitude and phase sufficient to balance out the effect of said local oscillator frequency energy fed to the power line, and said power line including an impedance connected between ground and said counteracting reactance.

MURRAY G. CLAY.

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