US 2088432 A
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July 27, 1937. H0. PE ERSON 2,088,432
FREQUENCY CONVERTER CIRCUIT Filed Feb. 17, 1934 2 Sheets-Sheet 1 d Z/TPUT INVENTOR H.O. PETERSON ATTORNEY July 27, 1937. .H. o. PETERSON 2,088,432
FREQUENCY CONVERTER CIRCUIT Filed Feb. 17, 1954 2 Sheets-Sheet 2- INVENTOR H.O. PETER5ON ATTORN EY Patented July 27, 1 937 UNITED STATES Harold Olaf Peterson, Riverhead, N. Y., assignor to Radio Corporation of America, a corporation of Delaware Application February 17, 1934, Serial No. 711,773
This invention relates to frequency changer or converter circuits.
The expressions frequency changer or frequency converter device as herein used is ap- 5 plied to the tubes and circuits in a heterodyne receiver which are used to generate the local frequency and to mix it with the incoming radio signal to produce a different frequency, such as an intermediate frequency.
In the past, the usual method of heterodyning involved employing a mixer tube in which the radio signal and local frequency were applied to the same grid. The local frequency was generated by a separate tube or within the mixer tube. Such a method generally depends on coupling the oscillator or mixed circuits by either capacitive or inductive means.
A more recent method of frequency conversion depends upon the electron stream as a coupling agent instead of the use of reactive coupling. This last method offers advantages in eliminating undesired intercoupling efiects between signal, oscillator and mixer circuits and in the reduction of local frequency radiation. Furthermore, not only may simpler circuits be utilized by this last method, but there is also obtained freedom from the effects of variationsin oscillator voltage. A simple device depending on the electron stream as a coupling agent is one in which the space current ofthe mixer tube is modulated by a variation in cathode emission, such variation being accomplished by placing a grid and a supplemental anode-grid between the cathode and the control grid and by using these electrodes in conjunction with a cathode to accomplish the modulation of the cathode current. With this latter arrangement, the cathode and the first two grids may be regarded theoretically as a composite cathode which supplies a modulated electron stream. This modulated cathode stream may be further controlled and utilized by means of the addition of other grids and an anode. An arrangement of this last type is known to the art as a pentagrid converter tube, although other types of pentodes and tetrodes have made it possible to combine'quite efficiently the functions of rectifier and oscillator in the same tube to give a heterodyne frequency changing device.
In the frequency converter circuits heretofore 50 used, there has been someinherent difficulty due to inter-electrode coupling between the oscillator circuit and the tuned input circuit, this effect being in the form of a slight variation of oscillator frequency as the input circuit is tuned through resonance. It has also been found diflicult to make the oscillator circuit function at the higher frequencies with some of the'tubes available to the art. According to the present invention, reaction between input circuit tuning and frequency of oscillation is eliminated by operating the oscillator at a sub-multiple (or approximately a sub-multiple) of the input frequency, for example, the oscillator may be operated at approximately one-half of the input signal frequency. In this way, the input frequency and the oscillator frequency are made vastly different and, consequently, any adjustments made in the input circuit will have very little effect on the oscillator frequency because the input circuit is far off tune with respect to the oscillator frequency. It will be apparent from the foregoing that since the oscillator may be operated at approximately half the signal frequency, such oscillator will not be required to function at as high frequencies as if it were operated at the signal frequency. For instance, an oscillator operating between 5 and 10 megacycles will serve to heterodyne a signal anywhere between 10 and 20 megacycles.
The accompanying Figures 1 to 4 illustrate the various embodiments of frequency converter circuits in accordance with the principles underlying the present invention.
In Figure 1 there is shown, by way of example, a heterodyne receiving circuit comprising two pentagrid converters Pl, P2 of the type above de- 6 scribed having their control electrodes connected together and their anodes connected together, the control electrodes being in circuit with a suitable input circuit to which the signal frequency fl is applied. The first two grids l and 2 of each of the pentagrid converters are connected to outside circuit elements which constitute a push-pull oscillator generating a frequency f2. The control grids of the converters of the tubes Pi and P2 and their anodes are shown connected in pushpush, to the latter of which is connectedany suitable output circuit wherein the beat frequency is appears. The input and output tuned circuits 4 and 5 respectively may, if desired, be made multirange circuits by means of either plug-in or switching arrangements. Also, the oscillator and signal frequency circuits may be ganged together in ways already generally used to give unicontrol action, an example of which is shown by the unicontrol means 6 connecting the two variable plates in the oscillatory circuit which generates frequency f2. The midpoint of the two variable condensers H and it, which are connected in series as indicated in this drawing, is grounded in order to suppress harmonics of the oscillator, 1
The output or beat frequency is appearing in parallel tuned circuit 5 will, in the present case, be equal to the signal frequency f1 plus or minus twice the frequency of the oscillator f2 due to the push-push connection of the anodes. If desired, the frequency changing device or converter circuit can be made to have an output frequency which is equal to the signal frequency plus or minus the oscillator frequency by simply connecting the outputs of the two detector tubes in push-pull arrangement. Such a circuit is shown in Figure 2 wherein a reversing switch l6 functions to connect the two plate circuits either in parallel or in push-pull relationship. This figure differs from the circuit of Figure l by the provision of a transformer l2 having two primary windings l and 8 each of which is associated with an anode of one of the converter tubes PI and P2 and a secondary winding 9 in circuitwith the output it, the latter, in turn, being connected to any suitable translating device such as a pair of headphones II. This circuit further differs from the arrangement of Figure l in minor details such as, for example, by the provision of a radio frequency amplifier herein designed RFA in the input circuit and the provision of a single condenser I 3 for the two condensers I! and ill of the oscillator shown in Figure 1. These minor modifications could just as readily be used in the circuit of Figure 1 if so desired. By the circuit of Figure 2, therefore, one oscillator coil and condenser combination can be caused to operate over a very great frequency range insofar as the signal itself is concerned. As an illustration, one may operate the two plate circuits in Figure 2 in parallel to cover a two or three to one range of very high frequencies. In this condition the oscillator is operating always at approximately one half of the signal frequency. To be exact, the frequency of the signal plus or minus two times the frequency of the oscillator is equal to the frequency of the beat note if switch it is so connected that the anode windings I and 8 are in parallel. Then, by throwing switch it so as to connect the primary windings l and 8 in push-pull relation there will obtain the condition that the frequency of the beat note is equal to the frequency of the signal plus or minus the oscillator frequency. Consequently, it will be apparent that if the oscillator is designed to cover a three to one frequency range it can be caused to take care of signals over a frequency range of approximately six to one merely by arranging a switch such as 16 whereby the circuit can be placed into operation in the two different modes hereinabove described.
Figures 3 and 4 are further modifications. In Figure 3 the incoming signal is fed to the control grids of the pentodes PI and P2 through a push-pull circuit. The outputs, however, are shown connected in parallel. In such an arrangement the frequency of the signal plus the frequency of the oscillator is equal to the frequency of the beat note. In Figure 4 there is shown a circuit having a push-pull input and a push-pull output. In this latter arrangement the frequency of the signal plus or minus two times the frequency of the oscillator is equal to the beat note. In other words, the oscillator operates at approximately half the signal frequency, generally speaking.
It will be apparent, of course, that the circuits of Figures 3 and 4 may be combined in one receiver by the provision of a switch as shown in Figure 2 whereby the output circuit may be arranged either in push-pull or in parallel relationship.
1. A heterodyne receiver circuit comprising two pentagrid converters each of which includes a cathode and an anode, a control signal grid, an auxiliary electrode between said control signal electrode and said cathode and a second auxiliary electrode between the first auxiliary electrode and the cathode, a signal input circuit coupled to both grids of said pentagrid converters, an oscillatory circuit tuned to a submultiple of the frequency of oscillations adapted to be passed by said input circuit connected to corresponding auxiliary electrodes of said pentagrid converters and regeneratively coupled to other corresponding auxiliary electrodes of said converters, the anodes of said converters being connected together and coupled to an output circuit, a circuit including a source of potential for applying a positive potential to the first named auxiliary electrodes of said converters which is positive with respect to the cathodes thereof, the cathode, second named auxiliary electrode and first named auxiliary electrode of each converter forming in effect a composite cathode as respects the remaining elements of the converter, said composite cathode being arranged to emit a modulated stream of electrons.
2. A heterodyne receiving circuit as defined in claim 1 characterized in this, that said input circuit is coupled to the control signal grids in push-pull manner and said anodes are connected to each other in push-push manner whereby there is supplied to said utilization circuit a beat note equal to the frequency of the oscillations in said input circuit plus or minus the frequency of said oscillatory circuit.
3. A heterodyne receiving circuit as defined in claim 1 characterized in this, that said input L circuit is connected to the control signal grids in push-pull manner and said anodes are connected to each other in push-pull manner whereby there is supplied to the utilization circuit a beat note equal to the frequency of the oscillations in the signal input circuit plus or minus twice the frequency of the oscillations generated in said oscillatory circuit.
4. A heterodyne receiving circuit as defined in claim 1 characterized in this, that said input circuit is connected to said control signal grids in push-pull and said anodes are also connected to each other in push-pull, but said auxiliary circuit is connected to said auxiliary electrodes in push-pull whereby there is supplied to the utilization circuit a beat note equal to the frequency of the oscillations of said input circuit plus or minus twice the frequency of the oscillations in said oscillatory circuit.
5. A frequency converter for heterodyne receivers and the like comprising a pair of electronic tubes each thereof being provided with at least a cathode, a grid-anode, an auxiliary grid positioned between the grid-anode and the cathode, a signal grid and an anode, an energizing means for the elements of said tubes including means for impressing upon the anodegrid of each of said tubes a positive potential with respect to the cathode, a common input circuit for both said tubes including a connection between the signal grids and the cathodes of the tubes, a common output circuit for the tubes including a connection, between the anodes and the cathodes thereof, means for impressing signal oscillations across the common input ciraccordance with the generating oscillations, a utilizing means coupled to the common output, circuit, said utilizing means including a circuit tuned to a beat frequency resulting from modulating the incoming energy With the' g enerated 5 energy. l HAROLD OLAF PETERSON.