US2091271A - Receiver - Google Patents

Description

Aug. 31, 1937. J.' w, ONKUN 2,091,271

' RECEIVER origiral Filed Jan. 17, 1955 2 sheets-sheet 1 afm/*m ffm/Hm) www@ INVENTOR- JAMES W. CONKUN ATTORNEY Aug. 31, 1937. J. w. coNKLlN 2,091,271

RECEIVER original Filed Jan. 17, 195s 2 sheetssheet 2 INVENTOR- JAMES W, CONKUN ATTORNEY- Patented Aug. 31, 1937 f UNrrEo sTATEs PATENT OFFICE RECEIVER James W. Conklin, Rocky Point, N. Y., assignor to Radio Corporation of America, a corporation of Delaware 4 Claims.

This invention relates to a method of and means for receiving radio signals, and more in particular to a method of and means for receiving radio waves or oscillations which vary in phase and/or frequency in a manner characteristic of signals to be transmitted.

Receivers for phase or frequency modulated radio waves or oscillations have been known heretofore in the radio art. These receivers in general comprise signal absorbing means and/or amplifying means followed by elaborate selective filters and devices requiring accurate aligning and tuning to the signal frequency by means of complicated tuned circuits.

An object of this invention is to provide a new and improved phase or frequency modulated signal demodulatng means.

A more specic object of the present invention is to provide a simplified receiving arrangement by means of which phase or frequency modulated oscillations or waves may be converted into intelligible signals.

Another object of the present invention is to provide a simplified receiver by means of which frequency or phase modulated oscillations or Waves may be received and demodulated and which do not necessitate the use of delicate tuning or frequency balancing, and do not depend upon selective lters and devices requiring accurate aligning of the signal frequency with tuned circuits or filters.

Briefly, the objects enumerated above are attained in accordance with the present invention by the use of a signal absorbing means, signal amplifying means, and means for splitting the received signal into two separate portions, one of which is fed through a suitable control apparatus directly to the detector or demodulator, and the other portion of which is fed through a retardation element or phase shifting device and a suitable control means to the detector and/ or demodulator, where it will be recombined with the other portion.

In accordance with the present invention, the retardation device will have an electrical length equivalent to a fraction of a cycle of the highest audio modulation frequency to be transmitted, with the maximum permissible length being equivalent to half a cycle of the highest audio frequency to be transmitted and the optimum determined as a compromise between distortion and sensitivity. The retardation device, which in' practice may be one of the common types of artificial electrical transmission lines, functions (Cl. Z50-20) to furnish a delayed signal to the detector or demodulator.

In accordance with the present invention, the detector or demodulation device will function to respond to a shift in phase between the direct and retarded signal in such a manner as to produce an audio frequency response which is substantially a reproduction of the audio frequency modulation on the transmitted signal.

It is a further object of this invention to provide suitable control means and/or unilateral coupling means in the direct and/or retarded channel to the detector or demodulator.

Inasmuch as the phase oscillations produced by frequency modulation are inversely proportional in magnitude to the audio modulation frequency and the phase oscillations produced by phase modulation are independent of the modulation frequency but proportional to the amplitude of the modulating current and the output of the detector or demodulator, by virtue of the characteristics of the retardation device, will be substantially proportional to the modulating frequency, the output of the detector or demodulator will be substantially a true and faithful reproduction of the audio frequency modulation of signals having the characteristics of frequency modulation but will be proportional to the audio modulation frequency of signals having the characteristics of phase modulation.

It is therefore a further object of this invention to provide means subsequent to the detector or demodulating device, or comprising a feature thereof, to alter the output of the detector or demodulator insofar as it is dependent on the frequency of modulation, in such a manner as to cause the output to be substantially a true and faithful reproduction of the audio frequency modulation of signals having the characteristics of phase modulation.

In order to obtain a most proper action of the detector or demodulator and to insure that the signal output currents of the detector or demodulator will be substantially a true reproduction of the original signal impulses, it is necessary that the direct and retarded radio frequency signal impulses impressed on the detector or demodulator bear substantially a particular electrical phase and magnitude with respect to each other.

In the general case, the proper phase relation between the retarded and direct signal impulses will be approximately ninety degrees, but this may be `varied to advantage depending on the characteristics of a particular signal. It is therefore a further object of this invention to provide means whereby the electrical phase relation and relative magnitude of the direct and retarded signal impulses to the detector or demodulator, may be controlled.

The novel features of the present invention have been pointed out with particularity in the claims appended hereto.

The nature of the invention, the operation thereof, and the advantages to be gained by the use thereof will be better understood from the following detailed description thereof, and therefrom when read in connection with the drawings in which:

Figure l illustrates diagrammatically the manner in which a shift in phase of the two portions of the signal reaching the demodulator is effected;

Figure 2 shows diagrammatically the electrical phenomena which takes place in applicants novel receiver;

Figures 3 and 4 show diagrammatically the fundamental elements incorporated in applicants novel receiving means; while,

Figure 5 shows the details of a practical device for retarding the phase of a portion of the signal wave.

In explaining the manner in which the signal is divided into two portions and the relative phase of the two portions shifted, reference will be made to Figure 1 of the drawings.

If a carrier wave is frequency or phase modulated in accordance with varying signal potentials, the modulated wave resulting is of constant amplitude but is displaced in phase with respect to the original carrier wave by an amount proportional to the instantaneous magnitude of the signal wave, and in the case of the frequency modulated wave, inversely proportional to the frequency of the modulation wave or signal wave. The resultant wave may be represented by a vector which is of constant frequency but which oscillates back and forth in phase at the modulation frequency and to a degree proportional to the modulation amplitude, and, in the case of the frequency modulated wave, inversely proportional to the modulation frequency.

In the diagram cf Figure 1 RD is a vector representing a high frequency wave which is to be frequency modulated but on which no frequency modulations have been impressed. is a vector representing frequency modulated oscillations which is oscillating between A and B, that is, oscillating with respect to R0. These vectors represent respectively an unmodulated signal and a frequency modulated radio signal absorbed by an absorption member and/or relay but before they have been impressed on the input circuit cf the retardation device included in applicants novel receiver. The signal is then divided, as shown diagrammatically in Figure 1, into two portions and sent over two channels I and 2, the first of which includes a retardation device to be described more in detail hereinafter, and the second of which is a` direct channel between the energy pick-up means and the combining means. R0 at the output end is a vector representing a high frequency wave which is to be frequency modulated but on which no frequency modulations have been impressed. r1 is a vector representing the frequency modulated wave appearing in the output of channel I. r2 is a vector representing the frequency modulated oscillations appearing in the output of channel 2. It will be noted that frequency modulated vector r2 is unchanged in direction and sense with respect to 1, while frequency modulated Vector T1 is displaced in time, that is, in direction and sense by half a wave. In addition to the time phase displacement of r1 with respect to R0 the whole picture will have to be rotated a number of times, depending upon the retardation of the line for the radio frequency used. By selecting a line of a particular electrical length the retardation effect of the line will rotate R0 approximately or an odd multiple thereof. For example, in Figure 1 the retardation device of channel I is an electrical length sufhcient to rotate the vector R0, representing the input oscillations, 90D or an odd multiple thereof so that it is in quadrature phase to the vector Ro representing the output energy in channel 2. When there is no modulation, the relative phase of the outputs of the two channels will remain constant and cause no apparent variation of signal intensity on the detector or demodulation device.

A better picture of what takes place in the two channels, as illustrated in Figure 1, will be had by reference to the vector diagrams of Figure 2. In this description it will be assumed that frequency modulation has been applied to the oscillations or radio wave and that the retardation device in channel I will displace T1 by the retardation angle of the line of channel I for the audio frequency modulations. Adding the two vectors will give a resultant vector, the length of which is dependent upon the resultant phase displacement of the vectors r1 and r2.

Thus, for example, in line I of the vectors diagram of Figure 2, it is assumed that no modulation is applied. Vectors R and i' at the inl put of the two channels are in phase. Likewise, the vectors representing R and r2 at the output of channel 2 will be in phase since no retardation takes place in this channel. However, the retarding effect of the channel I causes vectors R and T1 to be in phase but displaced 90 with respect to the vectors representing the same oscillations at the input of the line. These vectors are in quadrature to the vectors representing the output of channel 2 and they will add to said vectors to give a mean resultant as indicated in the last column in line 2.

In line 2 it is assumed that the high frequency oscillations have been audio frequency modulated. In the input of the two channels r is displaced by an angle with reference to R, as indicated. In the output of channel 2, which has no retarding effect, the vectors R and 1'2 are in the same direction and displaced an amount equal to the displacement between the two vectors at the input. In the output of channel I, however, due to the retardation effect of said channel, the vector 1'1 has been advanced or rotated an amount representative of the retardation angle of the channel I for the audio frequency. The Vector R has also been displaced or rotated 90, or an odd multiple thereof, so that its direction is in quadrature to the direction of R at the output of. channel 2.

The vectors r1 and Tg when added give a resultant as indicated in the last column. In the same manner it can be shown by reference to lines 3, 4, 5, 6, I, and S that the energies combine to produce resultants which, when plotted along a line representative of time or phase angle, result in a curve, as indicated in the last column of Figure 2.

'If the vectors referred to above represent voltages and we apply r' to the input circuit of a detector or demodulator tube, the tube will give CII an audio output Corresponding to the variations in T. The retardation angle will vary in proportion to the modulationfrequency so that the response Will be approximately proportional to a sign function of the modulation frequency, as roughly indicated in the last column of Figure 2.

In the vector diagrams above the angle of displacement between the several vectors has not been given since applicant Idoes not intend to limit his invention toany definite phase displacement. It will be understood, however, that this angle may vary between certain limits, as, for example, between zero and 60. Applicant has, however, found that if the retardation angle of the retardation device of channel I is maintained somewhere near 45, or less, thefrequency distortion taking place will be negligible. The amplitude distortion introduced with normal levels of modulation by this retardation device will be negligible.

In practice a receiver, as indicated in Figure 3, may be used. This receiver comprises an absorption member 4 connected with radio frequency relaying or amplifying means 6, which is in turn connected with the channels I and 2. The channels I and 2 may be connected with amplifying and/or rectifying means as indicated and to an indicator.

In case the radio waves to be received are of short wave length the signal may be heterodyned as indicated in Figure 4. This is accomplished by connecting a first detector and/ or intermediate frequency amplifier 8 between the thermionic relay 6 and the lines I and 2. A source of local oscillations 9 is connected with the detector and/or intermediate frequency amplifier 8. The channels I and 2 may be fed through amplifiers I4 and I5, as indicated, to a second detector I6 connected with an audio amplifier I8. In this arrangement tuning is simplied since the frequency of the intermediate amplifier, or of the heterodyne wave, may be adjusted to the line, that is, to channel I, for proper null point rather than adjusting the line to the frequency.

The nature of the retardation device in channel I will be understood by reference to Figure 5. In this figure it is assumed that the retardation device and the direct line, comprising channels l and 2 of the receiver of Figure 4, are combined. Here the output of the intermediate frequency amplifier is passed through an inductance 20 coupled to balanced inductances 2| and 22, as indicated. The retardation device comprises a series of series inductances I cooperating with parallel capacities C to form a tuned lter circuit. A resistance 23 is connected across the terminals of the tuned filter network, which is channel I of Figure 4, while a resistance 24 is connected across the terminals of the direct channel 2. An electron discharge tube or thermionic relay tube 25 has its input electrodes connected, as indicated, across the terminals of resistance 23, while a similar tube 26 has its input electrodes connected across the terminals of resistance 24. Resistance 28 connects the anodes of the tubes 25 and 26 together and to a source of potential 30. The twoI portions of the frequency or phase modulated oscillations referred to above appear in the output circuits of 25 and 26. These oscillations appearing in the output of 25 are themselves displaced and the frequency or phase modulations thereon caused by the audiofrequency are displaced with reference to the same oscillations and modulations appearing in the output of tube 26. These relatively displaced oscillations flow in the two portions of resistance 28 and the required amount of each thereof is impressed on the control grid electrode 3| and cathode 32 of the second detector 34 by means of taps so that a resultant representative of the displaced phase or frequency modulations impressed o-ri the carrier appear on the anode 33 of tube 34 and in the transformer T connected between the anode 33 and a source of potential 35, as indicated. The demcdulatedi waves appearing in the transformer T may be utilized in any manner.

The retardation circuit etc. of Figure 5 may of course be used in the receiver 3. In this case the device responds to the absorbed signal rather than to an intermediate frequency wave to which the signal has been changed.

Where phase modulation reception is accomplished a frequency distorting circuit may be used to make the audio frequency output inversely proportional to the modulation frequency to compensate for the proportional frequency response of the detector. The non-linear characteristic of the receiver may be corrected in the audio output for either frequency or phase modulation in any of the well known manners. For example, correction circuits of the type shown in Crosbys United States application Serial Number 618,154, led June 20, 1932, may be used.

Having thus described my invention and the operation thereof, what I claim is:

1. A device for translating a carrier wave modulated in phase or frequency at signal frequency to produce observable indications comprising, signal modulated carrier Wave responsive means, signal modulated carrier wave amplifying means of the electron discharge tube type coupled with said responsive means, a circuit connected at its input end with said signal modulated carrier wave amplifying means, said circuit including a channel made up of series inductances and parallel capacities which offer substantial impedance to the signal modulated carrier wave impressed on the input thereof, and a channel comprising conductors only which is of substantially zero impedance to the signal modulated carrier wave impressed on the input thereof, said channels serving to separate said signal modulated carrier into two portions, resistances terminating each of said channels, electron discharge coupling tubes having their input electrodes connected together by way of said resistances, a resistance connected between the output electrodes of said coupling tubes, and rectifying means variably coupled to said last named resistance.

2. A device for translating frequency or phase modulated signals into readable signals comprising, a signal receiver of the heterodyne type including an intermediate frequency amplifier, a circuit connected at its input end with said intermediate frequency amplier for separating said signals of changed frequency into two portions, said circuit including a branch having an electrical length equivalent to a fraction of a cycle but not greater than half of a cycle of the highest signal frequency to be translated and a branch of negligible electrical length as compared to said first branch, electron discharge tubes having input and output electrodes connected in push-pull relation, means connecting said input electrodes with the output ends of said branches, and a signal demodulating circuit connected with the output electrodes of said tubes.

3. In a p-hase or frequency modulated oscillation analyzing circuit, a pair of transmission channels one of which includes series reactances and parallel reactances, said combined reactances having an electrical length equivalent to a fraction of a cycle but not greater than half a cycle of the highest signal frequency to be analyzed and the other of which channels is non-reactive, means for impressing a portion of said phase or frequency modulated oscillations on the input of each of said channels, a pair of electron discharge tubes each having a control grid, a cathode, and an anode, impedances connecting the control grids and cathodes of said tubes in push-pull relation with the outputs of said channels, impedances connecting the anodes and cathodes of said tubes in push-pull relation, and rectifying means coupled with the anodes and cathodes of said tubes.

4. A device for translating a carrier Wave modulated in phase or frequency at signal frequency to produce observable indications comprising, signal modulated carrier Wave responsive means, signal modulated carrier Wave amplifying means of the electron discharge tube type coupled with said responsive means, a circuit connected at its input end with said signal modulated carrier wave amplifying means, said circuit including a channel made up of inductive and capacitive reactances of substantial impedance to the signal modulated carrier Wave impressed on the input thereof, and a non-reactive channel of small impedance to the signal modulated carrier wave impressed on the input thereof, said channels also serving to separate said signal modulated carrier into two portions, a pair of electron discharge tubes having input and output electrodes connected in push-pull relation, a circuit connecting the input electrodes of one of said tubes to the output of one of said channels, a circuit connecting the input electrodes of the other of said tubes to the output of the other of said channels, and rectifying means variably coupled to the output electrodes of said tubes.

JAMES W. CONKLIN.

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