US2416305A - Radio receiver - Google Patents

Description

Feb.- 25, 1947. D. 0. GRIEG I I 2,416,305

RADIO RECEIVE? I Filed Sept. 18, 1942 2 Sheets-Sheet l i: 1% a i tafi lfl E 5 IE il-li H a INVENTOR DONHLO D. GR/EG patented Feb. 25, 1947 RADIO RECEIVER Donald D. Grieg, Forest Hills, N. Y., assignor to Federal Telephone and Radio Corporation, a corporation of Delaware Application September 18, 1942, Serial No. 458,854

12 Claims. 1

This invention relates to radio reception and demodulation of time modulated pulse energy and more particularly to a method and means for translating time modulated pulse energy into amplitude modulated pulse energy. 5 By passing the envelop energy through a low Pulse modulation systems to which this invenpass filter to remove carrier pulse harmonics, an tion relates generally are disclosed in the U. S. energy output in accordance with the modulation Patents to A. Reeves Nos. 2,266,401 and 2,256,336; is produced which may be applied directly to a U. S. Patent to E. Deloraine and A. Reeves 2,262,- speaker or other intelligence translating device. 838; and in copending application of E. Labin en- :51 Should the modulated pulse energy include titled Pulse modulation system, Serial No. 386,- amplitude modulation as well as time modulation, 282, filed April 1, 1941; and copending applithe amplitude modulation may be detected in cation of E. Deloraine and E. Labin entitledPulse known manner and the pulse energy passed to a transmission system, Serial No. 425,103, filed sawtooth generator and clipping device for trans- December 31, 1941. .5 lation of the time modulated signals to amplitude In accordance with pulse modulation recurring modulated pulses for intelligent reception in acpulses or pairs of pulses, as the case may be, cordance with the method described above. can be used where variations of the spacing be- For a further understanding of the method tween pulses correspond to signal increments. of this invention reference may be had to the Where recurring pairs of pulses are used, time accompanying detailed description of a form of modulation may comprise displacement of the apparatus by which this method may be pracpulses toward and away from each other in pushticed, the detailed description to be read in conpull manner or one of each pair may be fixed nection with the accompanying drawings, in and the other displaced relative thereto in acwhich: cordance with a signal increment. While the Fig. 1 is a graphical illustration in accordance pairs of pulses may be amplitude modulated as with this invention; well as time modulated for simultaneous trans- Fig. 2 is a block diagram of a form of apparatus mission of two different signals, this invention is which may be used .in practicing the method; and concerned only with demodulation of the time Fig. 3 is a schematic illustration of an electrical modulation part thereof. circuit showing details of parts of the apparatus One of the objects of this invention therefore, of Fig. 2. is to provide a method and means for demodu- Assuming that a train of pulses is time modulating time modulated pulse energy received from lated in accordance with a sine wave a (Fig. 1) pulse modulating systems such as those in the the time modulated relation of the pulses for a aforesaid U. S. Patents and copending applicycle of the modulating wave is shown by the cations. pulse positions b. The spacing of the pulses is Another object of the invention is to provide greatly exaggerated for purposes of illustration, a simplified method and means for translating it being understood that the spacing 151 for untime modulated pulse energy into amplitude modmodulated pulses having a transmission frequency ulated pulse energy. 49 of -6 kilocycles, for example, is about 80 micro- Still another object of the invention is to proseconds, while the maximum degree of pulse modvide a method and means for translating time ulation or displacement as indicated by the intermodulated pulse energy into envelopes of amval i2 is equal to from one to 2 microseconds plitude modulation which may be filtered and thereabouts. It will thus be clear that where applied directly to a speaker. the pulses are observed on the usual oscillograph, Briefly, the method of this invention comprises the degree of modulation as compared with the generating a wave having recurring peaks such, spacing between adjacent pulses is so slight as for example, as a sawtooth wave, controlling the not to be readily perceptible. It is this feature amplitudes of the peaks thereof in accordance of pulse time modulation that is so useful for with the length of the time intervals between the 50 the sending of secret messages. pulses of time modulated pulse energy and clip- In the block diagram shown in Fig. 2, time ping off the portion of the wave below a level modulated pulses are first appliedtoa wave gen or threshold such as is determined by the peak erator 4 adapted to produce a wave having reamplitude of a wave formed by a time interval curring inclined portions similar to a sawtooth between pulses corresponding to the maximum shape. For purposes of illustration a pure sawnegative modulation value. Such a level will provide for demodulation. This provides carrier pulses forming an amplitude envelope in accordance with the time modulated pulse energy.

tooth wave is used as indicated by the wave (Fig. 1). Alternate teeth of the wave thus generated are varied in direct amplitude in proportion to the time variation of the intervals between adjacent pulses. This sawtooth wave is then passed through a clipper detector 5 which is biased to clip off the sawtooth wave below a level 38a such as is determined by the amplitude of the sawtooth waves formed in accordance with the spacing between pulses corresponding to. the maximum negative modulation value. This clipped portion of the sawtooth wave provides a series of pulses which form envelope energy such as illustrated by the curve d. This envelop en-i ergy is then passed through a low pass filter 6, for example, of 6 kilocycles for th elimination of carrier pulse harmonics. The output modulated wave from the filter may then be passed to an audio amplifier stage or directly to earphones or a speaker.

Referring more particularly to Figs. 1 and 3, the sawtooth generator is shown to comprise a form of relaxation oscillator having a high vacuum triode tube 28. The tube is biased through a resistance 22 to a desired cut-off level. The time modulated pulses are applied to the grid terminal 23. The plate circuit 24 of the tube 26 is supplied with a positive potential through a resistance 25 which functions when the plate current of the tube 20 is cut ofi to charge a condenser 26. Connected to the condenser is a peak rectifier tube eilwhich servesas the clipper detector. The tube 38 prevents passage therethrough of sawtooth wave energy below a value or thresh old depending upon the value of the negative bias connected through a variable resistor 34 to the plate circuit 32 thereof. When the tube 20 reaches cut-off and becomes non-conductive, the potential drop through the resistor 25 becomes low and a charge builds up in the condenser 26. The charging rate of the condenser 26 gives a normal sloping characteristic of the sawtooth oscillation. When this charging potential exceeds the cut-off level of the. tube 30, current will begin to flow through the tube 30 and resistor 33 and produce a voltage at the out put 35. The cut-off level of tube 30, however, is chosen to occur in accordancewith the spacing between pulses corresponding to the maximum negative modulation value received at the input terminal 23. .Thus should a pair of such pulses l0 and l I be received at the terminal 23, the timing of the sawtooth oscillation is such that the impulse ill will operate the tube 20 causing the condenser 26 to discharge through the tube 20. This condition is illustrated inFig. 1 by the built-' up slope Illa and the vertical discharge line lDb. Immediately after reception of pulse l0 and the resulting discharge of condenser 26 the voltage from B+ begins to recharge the condenser. This charging rate is represented by the slope Ila which is parallel to the slope Illa and terminates the instant pulse H is received as indicated by the discharge line I lb. This amplitude of sawtooth lla is taken as the value at Which the rectifier is biased for passage of energy, and is represented by the line 30a. At the zero end of the line llb, the condenser 26 begins to recharge forming a slope I211. The slope lZa continues until the next succeeding pulse I2 is received whereupon the amplitude of the sawtooth slope I211 is terminated by the discharge line IZb. Since the pulse I2 is slightly time modulated, that is, .d isplaced slightly from the position I 20,,the slope 12a has had time to build up beyond the cut-01f level 35a. Thus, a small amount of energy represented by the peak l2d extending beyond the line etc has passed through the tube 30. The next succeeding pulse it, however, is time modulated in an opposite direction from the direction of modulation of the pulse l2 so that the next sawtooth slope 53% does not reach the amplitude level of the line 3311 by the time the pulse I3 is received. Thus the sawtooth slope [3a is terminated below the line 36a.

It will be seen that time modulation in accordance with the sine wave a, provides alternately high and low pulses in accordance with the degree of modulation. The peaks of the high amplitude sawteeth comprise carrier pulses and together form an envelope d in accordance with the time modulation of the pulses.

While I have shown for purposes of illustration a'modulation in accordance with a sine wave, it will be clear that modulation by voice or other forms of signals maybe transmitted by time modulation and demodulated in accordance with this invention to provide 'a translation to amplitude pulse modulation. This amplitude modulation is provided by the sawtooth peaks which provide a substantial amount of energy for the wave. The envelope wave, however, may be passed through an audio-amplifier or after having been filtered to remove the carrier pulses may be passed directly to a speaker. I

It will be recognized that demodulation in accordance to this invention is applicable to various forms of pulse modulation wherever the modulation is efiected by variation of the spacing or time intervals between pulses. Thus, even for pairs of pulses where one pulse recurs at fixed intervals and the other pulse occurs at varying intervals in accordance with modulation, the variation of spacing between adjacent pulses of a wave train of each pulse pairs can be used to control the build-up of wave peaks as hereinbefore described. Likewise, where the pulse pairs are spaced apart a larger interval than the spacing of the pulses of each pair, the time modulation of the pulses of each pair provide variation in spacing between the pulses of a wave train thereof whereby translation to amplitude modulation may bemade in accordance with this invention.

While I have shown and described but one form of apparatus by which the method of this invention may be practiced, I recognize that other apparatus as well as variations of the form of apparatus herein shown and described may be made without departing from the invention. It will be understood, therefore, that the form of apparatus herein shown and described is to be regarded as illustrative of the invention only and not as restricting the appended claims.

What is claimed is:

1. A method for translating a train of time modulated pulse energy into an amplitude modulated pulse Wave, comprising initiating generation of a period of said wave having voltage increasing according to a given pattern with time in accordance with the occurrence of a pulse of said time modulated pulse energy, terminatingsaid generation and initiating generation of a new period of said wave by the occurrence of'the generation of a period of said wave. in accord,-

ance. with the occurrence of a pulse of said time modulated pulse energy, said period being in the form of a sawtooth, terminating said generation and initiating generation of a new sawtooth period by the occurrence of the next succeeding pulse of said time modulated pulse energy, and threshold clipping said wave at an amplitude corresponding to the amplitude of a sawtooth produced by two succeeding pulses of maximum neg ative modulation.

3. A method for translating a train of time mod? ulated pulse energy into an amplitude modulated pulse wave comprising initiating generation of a period of said wave having voltage increasing according to a given pattern with time in accordance with the occurrence of a pulse of said time modulated pulse energy, terminating said genera tion and initiating generation of a new period of .3

said wave by the occurrence of the next succeeding pulse of said time modulated pulse ener y, threshold clipping said wave at an amplitude col"- responding to the amplitude of a period of said wave produced by two succeeding pulses of maximum negative modulation, thereby providing an amplitude envelope in accordance with time modulation of said pulse energy, and filteringthe envelope energy to remove pulse harmonics.

4. A method for translating a train of time modulated pulse energy into an amplitude modulated wave, wherein succeeding pairs of pulses define signal increments by the relative time displacement of said pulses in accordance with a modulating signal Wave, said time modulated pulses being characterized by the alternate and intermediate pulses being displaced in push-pull manner toward or away from their succeeding pulses according to the instantaneous amplitude of the signal wave with which said pulses are modulated; said method comprising initiating generation of a sawtooth voltage by the occurrence of one of the pulses of said timemodulated pulses, terminating the sawtooth generation and initiating generation of a new sawtooth by the occurrence of the next succeeding pulse of said time modulated pulses, and threshold clipping said sawtooth voltage at an amplitude level determined by the amplitude of a sawtooth produced by two succeeding pulses of maximum negative modulation, thereby obtaining a succession of sawtooth pulses defining envelopes corresponding to the modulating signal wave.

5. A method for translating a train of time modulated pulses into an amplitude modulated signal wave, said time modulated pulses being characterized by the alternate and intermediate pulses being displaced toward or away from their succeeding pulse according to the instantaneous amplitude of the signal wave with which said pulses are modulated; comprising initiating generation of a sawtooth voltage by the occurrence of one of the pulses of said time modulated pulses, terminating the sawtooth generation and initiating generation of a new sawtooth by the occurrence of the neXt succeeding pulse of said time modulated pulses, threshold clipping said sawtooth voltage at an amplitude level determined by the amplitude of a sawtooth produced by two succeeding pulses of maximum negative modulation, thereby defining amplitude envelopes in accordance with time modulation of said pulse en- 6 v S. ergy, and. filtering; the envelope energy to re, move pulse harmonics.

6. A demodulator for translating a. trainof time modulated pulse energy into amplitude modulated. pulse energy wherein the said time modulated pulses are characterized by at least one set of alternate pulses being displaced toward or away from the intermediate pulses according to the instantaneous amplitude of the signal wave with which said pulses are modulated; comprising generator means to generate a voltage wave increasing according to a given pattern with time, means controlling operation of said generator means in accordance with the pulses of said time modulated pulse energy, whereby generation of a period of said voltage wave is terminated and a. new period is initiated by each pulse, the amplitude of theperiods being thereby controlled in accordance with the time intervals occurring between succeeding pulses of the time modulated pulse energy, and means to clip off the portion of said voltage wave below a level determined by the amplitude of two succeeding pulses whose modulation is of maximum negative value thereby providing amplitude envelope energy in accordance with the time modulation of said train of pulse energy.

7. The demodulator defined in claim 6 wherein .the voltage wave generating means comprises a relaxation oscillator.

8. The demodulator defined in claim 6 wherein the Wave clipping means comprises a peak'rectifier.

9. The demodulator defined in claim 6 wherein the voltage wave generating means comprises a relaxation oscillator and the clipping means comprises a peak rectifier.

10. A demodulator for translating time modulated pulse energy into amplitude modulated energy wherein pairs of pulses define signal increments by relative time displacement of the pulses in accordance with a modulating signal wave, said time modulated pulses being characterized by the alternate and intermediate pulses being displaced in push-pull manner toward or away from their succeeding pulses according to the instantaneous amplitude of the signal wave, comprising meansto generate an energy wave of generally sawtooth form, means to control the amplitude of the sawteeth in accordance with the time intervals occurring between pulses of the time modulated pulse energy, the varying of the time interval between pulses resulting in alternately high and low sawteeth, means to clip ofi the portion of said wave below an amplitude determined by a sawtooth formed in accordance with the spacing between unmodulated pulses, thereby providing envelope energy of sawteeth energy exceeding the clipping amplitude, and means to filter the envelope energy to remove pulse harmonics therefrom.

11. A modulator for translating time modulated pulse energy into amplitude modulated pulse energy, comprising a relaxation oscillator to generate a sawtooth wave, means to control the operation of the relaxation oscillator in accordance with the lapse of time between adjacent pulses of the time modulated pulse energy so that the amplitudes of the sawteeth of said wave correspond with the time intervals between adjacent pulses, and a peak rectifier connected to the output of said oscillator arranged to only pass sawtooth energy above an amplitude level determined by the amplitude of two pulses of maximum negative modulation whereby amplitude'envelope energy is produced in accordance with the v j modulation of said time modulated pulse energy. -.12. A method for translating a train of time. i modulated, pulses into aniamplitude modulated wave, wherein the said time modulated pulses 5 are characterized by at least one set of alternate pulsesbeing displaced toward or away from the I intermediate pulses according to. the'instanta- 1 neous amplitude of the signal wave with which said pulses are modulated, comprising initiating 5 generation of a sawtooth voltage by the occur- 1 rence of one of the pulses of said time modulated pulses; terminating the sawtooth generation and initiating generation of a new sawtooth by the I occurrence of the next succeeding pulse of said 3 time modulated pulses, and threshold clipping said sawtooth voltage-at an amplitude level determined by the, amplitude of a sawtooth voltage produced by two succeeding. pulses of maxi mum negative modulation.

DONALD D. GRIEG.

REFERENCES CITED 2 The following references are of record in the file of this patent:

UNITED STATES PATENTS 10' Number Name Date 1,655,543 Heising Jan, 10, 1928 2,227,596 Luck Jan. 7, 1941 2,266,401 Reeves Dec. 16, 1941 2,061,734 Kell Nov. 24, 1936 2,218,642 Hathaway Oct. 22, 1940 FOREIGN PATENTS Number Country Date 348,656 Italy Feb. 8, 1937

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