US2123221A - Radio circuit for channel reception - Google Patents

Description

July 12, 1938.

R. H. WQRRALL RADIO CIRCUIT FOR CHANNEL RECEPTION Filed May 11, 1936 T0 LE STAGES 2 ND. BET. fi/VD AUDIO INVENTOR Robert" H. WorraZZ ATTORNEY Patented July 12, 1938 UNITED STATES orrirs 29 Claims.

(Granted under the act of March 3, 1883, as

amended April 30, 1928; 370 0. G. 757) My invention relates broadly to radio receiving circuits and, more particularly, to those suitable for channel type reception.

One object of my invention is to provide a means for amplification and for continuous reception at substantially constant audio frequency of transmitted electrical oscillations whose frequency may vary over a predetermined range.

Another object of my invention is to provide a means for secret communication whereby transmitted electrical oscillations, varied purposely over a predetermined frequency range, at any desired time intervals, may be received continuously, without appreciable change in the frequency of the audio signal.

Other and further objects of my invention will be apparent from the following specification, by reference to the accompanying drawing, in which two circuits embodying the principles of my invention, are diagrammatically illustrated.

The circuits herein described were developed with a view toward enabling an operator, receiving transmitted radio signals of a relatively constant frequency, to continue undiminished reception unhampered by drifting of the transmitted frequency from its assigned value. To accomplish this, in the present invention, I use two similar, parallel input circuits, each containing an input thermionic tube with necessary connections, an oscillator, so arranged that its output will beat with the output of said tube, a detector stage that operates on the beat frequencies thus produced, and a filter unit. The outputs of the filter units are combined in a mixing circuit, from which the resultant energy is led through intermediate frequency amplifiers, a second detector, and audio frequency stages of a conventional superheterodyne receiving circuit. In the preferred embodiment of my invention, the oscillators in the said two input circuits are so tuned that the difference between their output frequencies is always equal to the frequency for which the intermediate stages of the superheterodyne receiving circuit are tuned. Then, by the means a and methods described herein, the received audio signal will remain substantially unchanged in frequency while the frequency of the transmitted signal may drift over a range equal to the said frequency for which the intermediate superheterodyne stages are tuned; and the said audio signal will remain likewise substantially unchanged in volume, so long as the amplitude of the transmitted oscillations remains effectively constant.

Referring to the circuit illustrated in the accompanying drawing, 1 is an antenna or other suitable collector of radiant energy. From this collector, two independent branches take off, one of which leads through coupling coil 2 to ground, and the other, through coupling coil 3, likewise to ground. Inductive coupling coils are shown in the drawing for the purpose of illustration, but any convenient type of coupling means may be used.

One branch circuit continues from coupling means 2 which serves to feed the input of thermionic tube ll, which may be of any type suitable for use in a tuned or untuned input circuit. The output circuit of tube t includes one of the primary windings of a two primary oscillation transformer 6, the other primary of which is included in the output circuit of an independent self-oscillating circuit 8. The output from the secondary of the transformer t feeds the input of thermionic detector tube Hl, which may be of any type suitable for use as a detector. The output from detector tube ii] is led through a wave filter l2, and thence to one primary of a mixing transformer it, which is of a conventional type, having two primaries and one secondary.

Returning to coupling means 3, a second branch circuit, similar to the one just described, is associated therewith and proceeds by identical steps through input tube 5, similar to 4; oscillation transformer l, similar to t, where the output from oscillator 9, similar to 8, ties in; detector tube H, similar to ill; wave filter i3, similar to IE; and the other primary of mixing transformer i l, wherein it joins the branch circuit associated with coupling means 2.

As to the combined circuit beyond the secondary of mixing transformer Hi, this transformer has a tuning condenser it connected across it. In the preferred embodiment of my invention, the output of transformer it and condenser l5 may be fed directly to the input of thermionic tube l6. Referring to the drawing, the circuit here described is illustrated when the portion embraced between the two broken lines is omitted. The tube it, which may be of any convenient type suitable for the purpose, is used as a mixing tube, and its output proceeds to feed the intermediate frequency, second detector, and audio fequency stages of a conventional superheterodyne receiver, as indicated in the drawing.

In a modification of my invention, which is illustrated in the drawing by including in the circuit the portion embraced between the broken lines, the output from the secondary of mixing transformer It, having tuning condenser 15 connected across it as before, is fed to the input of thermionic tube H, which may have characteristics similar to those of tubes 1 and 5. The output of this tube then joins the output of another independent, self-oscillating circuit 118 as these two outputs are each led through one primary winding of the double primary oscillation transformer I 9, which is of a conventional type, similar to 6 and l. The output from. the secondary of this transformer, having tuning condenser 29,

similar to l5, connected across it, is then fed to the input of tube 16, whose output proceeds on to the superheterodyne circuit in exactly the same manner as previously described for the preferred embodiment.

Plate power is supplied to the entire circuit by connecting the positive terminal of a source of potential to the junction points of the double primaries in the transformers 6, l, M, and i9, when the portion of the circuit associated therewith is used. These points are indicated in the drawing by +B. The negative terminal of the plate power source is grounded. The circuit is grounded at the ends of coupling means 2 and 3, and, through blocking condensers, at the plates of the tubes in oscillators 8, 9, and 18. These points are indicated in the drawing by the conventional symbol. Filament power and biasing potential may be supplied by usual means.

In using the principles of this invention in practice, the tubes of the oscillator 8 and the detector l0 may be combined by using a pentagrid convertor, with associated circuits. This also applies to the tubes of oscillator 9 and detector H, and those of oscillator i8 and mixer It. Any of the oscillators described or shown may be crystal or electro-mechanically controlled.

To explain the operation of the circuit, let us assume that the intermediate frequency stages of the superheterodyne circuit be turned for 400 kcs., and that the frequency being received is 10,005 kcs. Under these conditions, the oscillator 8 is set to produce a frequency of 10,200 kcs., and oscillator 9 to an output frequency of 9,800 kcs. The difference between these latter two frequencies, when using the preferred embodiment of my invention, must always be equal to the intermediate channel frequency, and it is convenient to have this difference approximately equally spaced on either side of the incoming frequency. Following a signal through the circuit, and looking first at the circuits associated with tubes 4 and E0, the incoming frequency of 10,005 kcs. passes through the input tube 4, and beats, in the oscillation transformer 6 with the frequency of 10,200 kcs. from the oscillator 8. This produces in the plate circuit of detector tube [0, the sum and difference frequencies of 20,205 and kcs., plus the oscillator frequency of 10,200 kcs. These frequencies are all passed to the filter 12, where all are eliminated except 195 kcs., which is passed on to the mixing transformer l4. Looking now at the circuits associated with tubes 5 and H, by the same process described above, the sum and difference frequencies 19,805 and 205 kcs., plus the oscillator frequency of 9,800 kcs. from oscillator 9, are all present in the plate circuit of detector tube ll. These frequencies are all passed to the filter l3, where all are eliminated except 205 kcs., which is passed on to the mixing transformer M. We now have in the primary of the mixing transformer the two frequencies of 195 and 205 kcs. These two, beating together, produce sum and difference frequencies of 400 to 10 kcs. In the preferred form of the circuit, these two frequencies are passed on directly to the mixer tube l6. From the mixer tube, both pass on the I. F. stages, where the 400 kcs. is amplified and passed to the second detector and audio stages in the customary manner, while the 10 kcs. is eliminated.

From the above analysis, it will be apparent that the transmitter frequency may drift anywhere between the limits of 9,800 and 10,200 kcs.; yet the output of the mixer tube IE will still supply energy at a constant 400 kcs. to the I. F. stages, and the received audio signal will remain substantially constant at its original frequency value. This wide a permissible variation is extreme, even at 10,000 kcs. By using an intermediate frequency, of say 25 kcs., the allowable drift in the transmitted frequency may be narrowed down to plus or minus 12.5 kcs.

If it is desired still further to control the intermediate channel, the modification of my invention, employing the circuits associated with the input tube ll, may be used. Looking back to the output of the mixing transformer M, in the example we have taken, frequencies of 400 and 10 kcs. are impressed upon tube IT, and are present in its output. Another frequency from independent oscillator i8 is brought in to beat with these two frequencies in oscillation transformer l9. By properly controlling the value of the frequency from the oscillator l8, beat frequencies of any desired value may be produced, thus permitting the use of any convenient intermediate frequency channel for the intermediate frequency stages of the superheterodyne circuit.

It will now be apparent from the foregoing discussion that as long as any component of the incoming signal of the frequency chosen for the tuned intermediate frequency superheterodyne stages, is impressed upon the input of the mixer tube i6, whether directly from the output of mixing transformer M or from the output of oscillation transformer 99, the circuit will function as previously described, regardless of the simultaneous impression upon the input of said mixer tube E0 of elements of other frequencies desirable to increase the width of the frequency band over which the apparatus will operate, or to perform the designed function by means of a number of stages bracketing limited frequency bands, the received oscillations may be divided into multiple components in the same manner as described in connection with coupling means 2 and 3, and these components may each be operated upon through circuits similar to those from 2 and 3 to M, then joined with other components in one or a series of mixing devices, while the general principles of operation hereinbefore disclosed will remain the same.

Should it be desirable at any time to shift to other receiving channels, the tuning condensers of oscillators 8 and 9 may be set to new values, and the rest of the circuit will function automatically over the newly chosen band.

The invention disclosed herein may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor.

I claim:

1. A method of amplifying a received radio frequency current of unstable frequency which comprises dividing it into two substantially equal parts, beating one of said parts with a first substantially constant frequency to produce a first beat frequency corresponding to the difference in frequency between the received current and said first substantially constant frequency, simultaneously beating the other of said parts with a second substantially constant frequency, differing from the said first substantially constant frequency by a predeterminedamount, to produce a second beat frequency corresponding to the difference in frequency between the received. current and said second substantially constant frequency, combining these said first and second beat frequencies to produce a signal current having a frequency corresponding to the difference between the said first and second substantially constant frequencies and equal to the sum of the said first and second beat frequencies, then amplifying and detaching this last said signal current.

2; A method of deriving a signal current of substantially constant frequency from a received radio frequency current of unstable frequency which comprises dividing the received current into two substantially equal parts, beating one of said parts with a first substantially constant frequency to produce a first beat frequency corresponding to the difference in frequency between the received current and said first substantially constant frequency, simultaneously beating the other of said parts with a second substantially constant frequency, differing from the said first substantially constant frequency bya predetermined amount, to produce a second beat frequency corresponding to the difference in frequency between the received current and said second substantially constant frequency, then combining these said first and second beat frequencies to produce a signal current having a frequency corresponding to the difference between the said first and second substantially constant frequencies and equal to the sum of the said first and second beat frequencies.

3. A method of amplifying a received radio frequency'current of unstable frequency which comprises dividing it into two substantially equal parts, beating one of said parts with a first substantially constant frequency to produce a first beat frequency corresponding to the difference in frequency between the received current and said first substantially constant frequency, simultaneously beating the other of said parts with a second substantially constant frequency, differing from the said first substantially constant frequency by a predetermined amount, to produce a second beat frequency corresponding to the difference in frequency between the received current and said second substantially constant frequency, combining these said first and second beat frequencies to produce a signal current having a frequency corresponding to the difference between the said firstand second substantially constant frequencies and equal to the sumof the said first and second beat frequencies, beating this said signal current with a third substantially constant frequency which may be adjusted to produce another signal current of any desired frequency, then amplifying and detecting this last said signal current.

4. A method of deriving a signal current of any desired substantiallyconstant frequency from a received radio frequency current of unstable frequency which comprises dividing it into two substantially equal parts, beating one of said parts with a first substantially constant frequency to producea first beat frequency corresponding to the difference in frequency between the received current and said first substantially constant frequency, simultaneously beating the other of said parts with a second substantially constant frequency, differing from the said first substantially constant frequency by a predetermined amount, to produce asecond beat frequency corresponding to the difference in frequency between the received current and saidsecond substantially constant frequency, combining these said first and second beat frequencies to produce a signal current having a frequency corresponding to the difference between the said first and second substantially constant frequencies and equal to the sum of the said first and second beat frequencies, then beating this said signal current with a third substantially constant frequency which may be adjusted to produce a final signal current of any desired frequency.

5. A method of amplifying any received radio frequency currents within a predetermined frequency band which comprises dividing all of such received currents into two substantially equal parts, beating all of the frequencies in one of said parts with a first substantially constant frequency to produce a first group-of beat frequencies, selecting from these the beat frequencies corresponding to the differences in frequency between the received currents and said first substantially constant frequency, simultaneously beating all of the frequencies in the other of said parts with a second substantially constant frequency, differing from the said first substantially constant frequency'by the width of the said predetermined frequency band, to produce a second group of beat frequencies, selecting from these the beat frequencies corresponding to the differences in frequency between the received currents and said second substantially constant frequency, combining all of the previously selected beat frequencies to produce a third group of beat frequencies,selecting from said third group of beat frequencies all those having a frequency similar to the difference between the said first and second substantially constant frequencies and likewise to the width of the said predetermined frequency band, combining these last selected similar frequencies to produce a signal current, then amplifying and detecting this last said signal current. I

6. A method of deriving a signal current of substantially constant frequency from any received radio frequency currents within a predetermined frequency band which comprises dividing all of such receiving currents into two substantially equal parts, beating all of the frequencies in one of said parts with a first substantially constant frequency to produce a first group of beat frequencies, selecting from these the beat frequencies corresponding to the differences in frequency between the received currents and said first substantially constant frequency, simultaneously beating all of the frequencies in the other of said parts with a second substantially constant frequency, differing from the said first substantially constant frequency by the width of 'the said'p-redetermined frequency band, to produce a second group of beat frequencies, selecting from these the beat frequencies corresponding to the differences in frequency between the received currents and said second substantially constant frequency, combining all of the previously selectedbeatfrequencies to produce a third group of beat frequencies selecting from said third group of beat frequencies all those having a frequency similar to the difference between the said first and second substantially constant frequencies and likewise to the width of the said predetermined frequency band, then combining these last selected similar frequencies to produce a resultant signal current.

'7. A method of amplifying any received radio frequency currents within a predetermined frequency band'which comprises dividing all of such received currents into two substantially equal parts, beating all of the frequencies in one of said parts with a first substantially constant frequency to produce a first group of beat frequencies, selecting from these the beat frequencies corresponding to the differences in frequency between the received currents and said first substantially constant frequency, simultaneously beating all of the frequencies in the other of said parts with a second substantially constant frequency, differing from the said first substantially constant frequency by the width of the said predetermined frequency band, to produce a second group of beat frequencies, selecting from these the beat frequencies corresponding to the differences in frequency between the received currents and said second substantially constant frequency, combining all of the previously selected beat frequencies to produce a third group of beat frequencies, selecting from said third group of beat frequencies all those having a frequency similar to the difference between the said first and second substantially constant frequencies and likewise to the Width of the said predetermined frequency band, combining these last selected similar frequencies to produce a signal current, beating this said signal current with a third substantially constant frequency which may be'adjusted to produce another signal current of any desired frequency, then amplifying and detecting this last said signal current.

8. A method of deriving a signal current of any desired substantially constant frequency from any received radio frequency currents within a predetermined frequency band which comprises dividing all of such received currents into two substantially equal parts, beating all of the frequencies in one of said parts with a first substantially constant frequency to produce a first group of beat frequencies, selecting from these the beat frequencies corresponding to the differences in frequency between the received currents and said first substantially constant frequency, simultaneously beating all of the frequencies in the other of said parts with a second substantially constant frequency, differing from the said first substantially constant frequency by the width of the said predetermined frequency band, to produce a second group of beat frequencies, selecting from these the beat frequencies corresponding to the differences in frequency between the received currents and said second substantially constant frequency, combining all of the previously selected beat frequencies to produce a third group of beat frequencies, selecting from said third group of beat frequencies all those having a frequency similar to the difference between the said first and second substantially constant frequencies and likewise to the width of the said predetermined frequency band, combining these last selected similar frequencies to produce a signal current, then beating this said signal current with a third substantially constant frequency which may be adjusted to produce a resultant signal current of any desired frequency.

9. A method of amplifying any received radio frequency currents within a predetermined frequency band which comprises dividing all of such received currents into two substantially equal parts, beating all of the frequencies in one of said parts with a first substantially constant frequency to produce a first group of beat frequencies, selecting from these the beat frequencies corresponding to the differences in frequency between the received currents and said first substantially constant frequency, simultaneously beating all of the frequencies in the other of said parts with a second substantially constant frequency, differing from the said first substantially constantfrequency by the width of the said predetermined frequency band, to produce a second group of beat frequencies, selecting from these the beat frequencies corresponding to the differences in frequency between the received currents and said second substantially constant frequency, combining all of the previously selected beat frequencies to produce a third group of beat frequencies, beating said third group of beat frequencies with a third substantially constant frequency which may be adjusted to produce a signal current of any desired frequency, then amplifying and detecting this last said signal current.

10. A method of deriving a signal current of any desired substantially constant frequency from any received radio frequency currents within a predetermined frequency band which ,comprises dividing all of such received currents into two substantially equal parts, beating all of the frequencies in one of said parts with a first substantially constant frequency to produce a first group of beat frequencies, selecting from these the beat frequencies corresponding to the differences in frequency between the received currents and said first substantially constant frequency, simultaneously beating all of the frequencies in the other of said parts with a second substantially constant frequency, differing from the said first substantially constant frequency by the width of the said predetermined frequency band, to produce a second group of beat frequencies, selecting from these the beat frequencies corresponding to the differences in frequency between the received currents and said second substantially constant frequency, combining all of the previously selected beat frequencies to produce a third group of beat frequencies, then beating said third group of beat frequencies with a third substantially constant frequency which may be adjusted to produce a resultant signal current of any desired frequency.

11. A method of amplifying any received modulated carrier signal currents within a predetermined frequency band which comprises dividing all of such received currents into two substantially equal parts, beating all of the frequencies in one of said parts with a first substantially constant frequency to produce a first group of beat frequencies, selecting from these the beat frequencies corresponding to the differences in frequency between the received currents and said first substantially constant frequency, simultaneously beating all of the frequencies in the other of said parts with a second substantially constant frequency, differing from the said first substantially constant frequency by the width of the said predetermined frequency band, to produce a second group of beat frequencies, selecting from these the beat frequencies corresponding to the differences in frequency between the received currents and said second substantially constant frequency, combining all of the previously selected beat frequencies to produce a third group of beat frequencies, selecting from said third group of beat frequencies all those having a frequency similar to the difference between the said first and second substantially constantfrequencies and likewise to the width of the said predetermined frequency band, combining these last selected similar frequencies to produce a modulated signal current, then amplifying and detecting this last said modulated signal current.

12. A method of deriving a signal modulated current of substantially constant fundamental frequency but of variable amplitude from any received modulated carrier signal currents within a predetermined frequency band which comprises dividing all of such received currents into two substantially equal parts, beating all of the frequencies in one of said parts with a first substantially constant frequency to produce a first group of beat frequencies, selecting from these the beat frequencies corresponding to the differences in frequency between the received currents and said first substantially constant frequency, simultaneously beating all of the frequencies in theother of said parts with a second substantially constant frequency, differing from thesaid first substantially constant frequency by the width of the said predetermined frequency band, to produce asecond group of beat frequencies, selecting from these the beat frequencies corresponding to the differences in frequency between the received currents and said second substantially constant frequency, combining all of the previously selected beat frequencies to produce a third group of beat frequencies, selecting from said third group of beat frequencies all those having a frequency similar to the difference between the said first and second substantially constant frequencies and likewise to the width of the said predetermined frequency band, then combining these last selected similar frequencies to produce a resultant signal modulated current.

13. A method of amplifying any received modulated carrier signal currents within a predetermined frequency band which comprises dividing all of such received currents into two substantially equal parts, beating all of the frequencies in one of said parts with a first substantially constant frequency to produce a first group of beat frequencies, selecting from these the beat frequencies corresponding to the differences in frequency between'the received currents and said first substantially constant frequency, simultaneously beating all of the frequencies in the other of said parts with a second substantially constant frequency, differing from the said first substantially constant frequency by the width of the said predetermined frequency band, to produce a second group of beat frequencies, selecting from these the beat frequencies corresponding to the differences in frequency between the received currents and said second substantially constant frequency, combining all of the previously selected beat frequencies to produce a third group of beat frequencies, beating this said third group of beat frequencies with a third substantially constant frequency which may be adjusted to produce a modulated signal current of any desired fundamental frequency, then amplifying and detecting this last said modulated signal current.

14. A method of deriving a signal modulated current of any desired substantially constant fundamental frequency but of variable amplitude from any received modulated carrier signal currents within a predetermined frequency band which comprises dividing all of such received currents into two substantially equal parts, beatingall of the frequencies in one of said parts with a'first substantially constant frequency to produce a first group of beat frequencies, selecting from these the beat frequencies corresponding to the differences in frequency between the received currents and said first substantially constant frequency, simultaneously beating all of the frequencies in the other of said parts with a second substantially constant frequency, differing from the said first substantially constant frequency by the width of the said predetermined frequency band, to produce a second group of beat frequencies, selecting from these the beat frequencies corresponding to the differences in frequency between the received currents and said second substantially constant frequency, combining all of the previously selected beat frequencies to produce a third group of beat frequencies, then beating this said third group of beat frequencies with a third substantially constant frequency which may be adjusted to produce a signal modulated current of any desired substantially constant frequency.

15. A method of amplifying any radio frequency currents within a predetermined frequency band which comprises separately beating each of two or more similar components of received currents with a different substantially constant frequency, the largest difference between which said substantially constant frequencies de termines the Width of said predetermined frequency band, selecting and combining the beat frequencies thus produced to supply a signal current whose frequency corresponds to the difference between two of said substantially constant frequencies, then amplifying and detecting said signal current.

16. A method of deriving .a signal current of substantially constant frequency from any radio quency band which comprises separately beating.

each of two or more similar components of received currents with a different substantially constant frequency, the largest difference between which said substantially constant frequencies determines the width of said predetermined frequency band, selecting and combining the beat frequencies thus produced to supply a signal current whose frequency corresponds to the difference between two of said substantially constant frequencies, beating this said signal current with a substantially constant frequency which may be adjusted to produce another signal current of 1 any desired frequency, then amplifying and detecting this last said signal current.

18. A method of deriving a signal current of any desired substantially constant frequency from any radio frequency currents within a predetermined frequency band which comprises separately beating each of two or more similar components of received currents with a different substantially constant frequency, the largest difference between which said substantially constant frequencies determines the width of said predetermined frequency band, selecting .and combining the beat frequencies thus produced to supply a signal current whose frequency corresponds to the difference between two of said substantially constant frequencies, then beating this said signal current with a substantially constant frequency which may be adjusted to produce another signal current of any desired frequency.

19. A method of amplifying any modulated carrier signal currents within a predetermined frequency band which comprises separately beating each of two or more similar components of received currents with a different substantially constant frequency, the largest difference between which said substantially constant frequen cies determines the width of said predetermined frequency band, selecting and combining the beat frequencies thus produced to supply a modulated signal current whose frequency corresponds to the difference between two of said substantially constant frequencies, then amplifying and detecting said modulated signal current.

20. A method of deriving a signal modulated current of substantially constant fundamental frequency but of variable amplitude from any modulated carrier signal currents within a predetermined frequency band which comprises separately beating each of two or more similar components of received currents with a different substantially constant frequency, the largest difference between which said substantially constant frequencies determines the width of said predetermined frequency band, selecting and combining the beat frequencies thus produced to supply a signal modulated current whose frequency corresponds to the difference between two of said substantially constant frequencies.

21. A method of amplifying any modulated carrier signal currents within a predetermined frequency band which comprises separately beating each of two or more similar components 'of received currents with a different substantially constant frequency, the largest difference between which said substantially constant frequencies determines the width of said predetermined frequency band, selecting and combining the beat frequencies thus produced to supply a modulated signal current whose frequency corresponds to the difference between two of said substantially constant frequencies, beating this said modulated signal current with a substantially constant frequency which may be adjusted to produce another modulated signal current of any desired fundamental frequency, then amplifying and detecting this last said modulated signal current.

22. A method of deriving a signal modulated current of any desired substantially constant fundamental frequency but of variable amplitude from any modulated carrier signal currents within a predetermined frequency band which comprises separately beating each of two or more similar components of received currents with a different substantially constant frequency, the largest difference between which said substantially constant frequencies determines the Width of said predetermined frequency band, selecting and combining the beat frequencies thus produced to supply a signal current whose frequency corresponds to the difference between two of said substantially constant frequencies, then amplifying and detecting said signal current, then beating this said signal modulated current with a substantially constant frequency which may be adjusted to produce a signal modulated current of any desired substantially constant frequency.

23. A method of secret communication by radio which comprises purposely varying'th'e principal or carrier frequency of transmitted electrical oscillations, within certain predetermined limits, receiving said oscillations in a collector of radiated energy, dividing said oscillations into components, separately beating each of said components with a different substantially constant frequency, the largest difference between which said substantially constant frequencies determines the limits within which the said transmitted oscillations may be varied, selecting and combining the beat frequencies thus produced to supply a signal current whose frequency corresponds to the difference between two of the said substantially constant frequencies, further operating upon this said signal current by additional beating with other substantially constant frequencies, detection, and amplification to produce a final signal current whose principal, or carrier, frequency will remain substantially constant, independent of the frequency variation of the said transmitted oscillations within the predetermined limits, and converting this said final signal current in a signal responsive device, whereby continuous reception, which would otherwise be interrupted, may be accomplished on transmitted oscillations of varying frequency.

24. A method of secret communication by radio which comprises purposely varying the principal or carrier frequency of transmitted electrical oscillations, within certain predetermined limits, receiving said oscillations in a collector of radiated energy, dividing said oscillations into components, separately beating each of said components with a different substantially constant frequency, the largest difference between which said substantially constant frequencies determines the limits within which the said transmitted oscillations may be varied, selecting and combining the beat frequencies thus produced to supply a signal current whose frequency corresponds to the difference between two of the said substantially constant frequencies, further operating upon this said signal current by detection and amplification to produce a final signal current whose principal, or carrier, frequency will remain substantially constant, independent of the frequency variation of the said transmitted oscillations within the predetermined limits, and converting this said final signal current in a signal responsive device, whereby continuous reception, which would otherwise be interrupted, may be accomplished on transmitted oscillations of varying frequency.

25. In a radio signal receiving station; means for intercepting incoming radio frequency waves; means for producing from such a wave a plurality of substantially identical components; a plurality of substantially identical circuits, each actuated by a different one of said components and each including, means for coupling electrically to said component producing means, a thermionic input tube connected in circuit with said coupling means so that the grid circuit of said tube will be controlled by said actuating component, heterodyning means adjustable to produce an individual substantially constant frequency, means for producing interaction between said heterodyning means and the radio frequency currents caused to flow in the output circuit of said input tube as a result of said actuating component acting upon said grid circuit, detecting means operating upon the beat frequency currents produced by said interaction, and filtering means operating upon the detected currents in the outputof said detecting means to pass only currents within a selected frequency band; means for combining the selected frequency currents from all of said substantially identical circuits to produce signal currents having a substantially constant frequency equal to the difference between said individual frequencies of two of said heterodyning means; an output circuit, actuable by said signal currents, and including signal responsive means; and means for coupling said output circuit to said combining means.

26. In a radio signal receiving station; means for intercepting incoming radio frequency waves; means for producing from such a wave a plurality of substantially identical components; a plurality of substantially identical circuits, each actuated by a different one of said components and each including, means for coupling electrically to said component producing means, a thermionic input tube connected in circuit with said coup-ling means so that the grid circuit of said tube will be controlled by said actuating component, heterodyning means adjustable to produce an individual substantially constant frequency, means for producing interaction between said heterodyning means and the radio frequency currents caused to flow in the output circuit of said input tube as a result of said actuating component acting upon said grid circuit, detecting means operating upon the beat frequency currents produced by said interaction, and filtering means operating upon, the detected currents in the output of said detecting means to pass only currents within a selected frequency band; means for combining the selected frequency currents from all of said substantially identical circuits to produce signal currents having a substantially constant frequency equal to the difference between said individual frequencies of two of said heterodyning means; an intermediate circuit comprising an input thermionic tube and additional heterodyning means; means for coupling said intermediate circuit to said combining means; an output circuit, actuable by said signal currents, and including signal responsive means; and means for coupling said output circuit to the output of said intermediate circuit.

27. In a radio signal receiving station; means for intercepting incoming radio frequency waves; means for producing from such a wave two substantially identical components; two substantially identical circuits, each actuated by a different one of said components and each including, means for coupling electrically to said component producing means, a thermionic input tube connected in circuit with said coupling means so that the grid circuit of said tube will be controlled by said actuating component, heterodyning means ad-' justable to produce an individual substantially constant frequency, means for producing interaction between said heterodyning means and the radio frequency currents caused to flow in the output circuit of said input tube as a result of said actuating component acting upon said grid circuit, detecting means operating upon the beat frequency currents produced by said interaction, and filtering means operating upon the detected currents in the output of said detecting means to pass only currents within a selected frequency band; means for combining the selected frequency currents from both of said substantially identical circuits to produce signal currents having a substantially constant frequency equal to the difference between the individual frequencies of said heterodyning means; an output circuit, actuable by said signal currents, and including signal responsive means; and means for coupling said output circuit to said combining means.

28. In a radio signal receiving station; means for intercepting incoming radio frequency waves; means for producing from such a wave two substantially identical components; two substantially identical circuits, each actuated by a different one of said components and each including, means for coupling electrically to said component producing means, a thermionic input tube connected in circuit with said coupling means so that the grid circuit of said tube will be controlled by said actuating component, heterodyning means adjustable to produce an individual substantially constant frequency, means for producing interaction between said heterodyning means and the radio frequency currents caused to fiow in the output circuit of said input tube as a result of said actuating component acting upon said grid circuit, detecting means operating upon the beat frequency currents produced by said interaction, and filtering means operating upon the detected currents in the output of said detecting means to pass only currents within a selected frequency band; means for combining the selected frequency currents from both of said substantially identical circuits to produce signal currents having a substantially constant frequency equal to the difference between the individual frequencies of said heterodyning means; an intermediate circuit comprising an input thermionic tube and additional heterodyning means; means for coupling said intermediate circuit to said combining means; an output circuit, actuable by said signal currents, and including signal responsive means; and means for coupling said output circuit to the output of said intermediate circuit.

29. In a radio signal receiving station; means for intercepting incoming radio frequency waves; means for producing from such a wave a plurality of substantially identical components; a plurality of substantially identical circuits, each actuated by a different one of said components and each including, means for coupling electrically to said component producing means, a thermionic input tube connected in circuit with said coupling means so that the grid circuit of said tube will be controlled by said actuating component, heterodyning means adjustable to produce an individual substantially constant frequency, means for producing interaction between said heterodyning means and the radio frequency currents caused to flow in the output circuit of said input tube as a result of said actuating component acting upon said grid circuit, detecting and filtering means operating upon the beat frequency currents produced by said interaction to produce detected currents within a selected fraquency band; means for combining the detected currents from said substantially identical circuits to produce signal currents having a substantially constant frequency equal to the difference between the frequencies of two of said heterodyning means; an output circuit, actuable by said signal currents, including intermediate amplifying stages and signal responsive means; and means for coupling said output circuit to said combining means.

ROBERT H. WORRALL.

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