US2419547A

US2419547A - Wave translator

Info

Publication number: US2419547A
Application number: US485104A
Authority: US
Inventors: Donald D Grieg
Original assignee: Standard Telephone and Cables PLC
Current assignee: STC PLC; Federal Telephone and Radio Corp
Priority date: 1943-04-30
Filing date: 1943-04-30
Publication date: 1947-04-29
Anticipated expiration: 1964-04-29
Also published as: GB582100A; ES182129A1; FR952696A

Description

April 29, 1947. D. D. GRIEG WAVE TRANSLATOR Filed April so, 1945 RE L/- GATE aff-5,?

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O/VLD D. G77/5G BY AITR/YLY Patented -lpr. 29V, 1947 UNITED STATES PATENT OFFICE.

WAVE 'rRANsLAroR Donald D. Grieg, Forest Hills, N. Y., assignor to Federal Telephone and Radio Corporation, Newark, N. J., a corporation of Delaware Application April 30, 1943, Serial No. 485,104

(Cl. Z50-27) 14 claims. 1

This invention relates to radio receivers.

In my copending application Serial No. 459,959, led September 28, 1942, I disclose a demodulator for time modulated pulses. By time modulated pulses I have reference to that form of pulse modulation 'where the pulses are time displaced from given recurrence timing according to the instantaneous amplitude of an intelligence signal wave. This time displacement may take any one of several forms, one of which is known as push-pull time modulation by which the successive pulses are displaced toward and away from each other in push-pull manner. Regardless of the manner of time displacement, the demodulator of my aforesaid application translates the displacement of the time modulated pulses into pulses, the amplitudes of Which correspond to the time displacements of the time modulated pulses.

One of the objects of my invention is to provide a radio receiver adapted to detect and translate amplitude modulated signals into equivalent time modulated signals for demodulation in a T. M. (time modulation) demodulator such, for example, as disclosed in my aforesaid copending application.

Another object of my invention is to provide a method and means for translating an amplitude modulated carrier wave into an equivalent train of time modulated impulses; and further, wherein -the translation operation is such as to substantially eliminate or at least greatly reduce noise Vand other interfering voltage fluctuations occurring on the received carrier.

According to my invention, an amplitude modulated carrier wave is detected in the usual manner" and is then translated into an equivalent train of time modulated impulses by rst limit clipping the modulated carrier between two limits selected where the sides of the undulations of the carrier wave Vary in slope in substantiallylinear proportion to the amplitude variations of the corresponding undulations. This produces a trapezoidal Wave the side edges of each cycle of which slope in proportion substantially to the amplitude of the corresponding undulations of the carrier. This trapezoidal wave is then differentiated to produce alternate positive and negative rectangular pulses one each for each cycle of the trapezoidal wave. The width of each of these rectangular pulses corresponds to the slope of the corresponding edge of the trapezoidal wave and therefore corresponds also with the amplitude of the corresponding undulation of the carrier wave. The amplitude'of the rectangular pulses are also 2 varied according to variations in the slope of the corresponding edges of the trapezoidal wave from which they are produced. It is sometimes preferable to limit the rectangular pulses to the same amplitude. This may be done by passing the train of rectangular pulses through a limiting device such as a gate clipper. By thereafter diierentiating the rectangular pulses, a pair of positive and. negative impulses is produced for each rectangular pulse, one of the impulses of each pair corresponding to the leading edge and the other corresponding to the trailing edge of one of the rectangular pulses. It follows, therefore, that these impulses are time displaced in accordance with the width of the corresponding rectangular pulses and this displacement corresponds with variation in amplitude of the corresponding un-- dulation of the carrier Wave.

The train of rectangular pulses produced from the trapezoidal wave may be directly difierentiated Without being limited to the same amplitude. By differentiating these rectangular pulses, which not only vary in width but also in amplitude, pairs of rnarrow Width impulses will be produced, the impulses of each pair being displaced according to the width of the rectangular pulse from which they are produced. These impulses will also vary in amplitude in accordance with the amplitude of ythe rectangular pulse from which lthey are formed. Before applying this train of impulses to a T. M. demodulator, it will be desirable first to limit clip the impulses to the same amplitude. This may be accomplished by either gate clipping the positive or negative pulses or by including both between the clipping limits Whichever may be desired.

One of the advantages obtained by this conversion process is that the limit clipping opera-V tion of slicing a small portion from the carrier Wave near the axis thereof, eliminates substantially all noise and other interfering voltage liuctuations present on the carrier Wave without advers'elyv affecting the modulating intelligence. Thus, bytranslation, an improvement in the signal-to-'noise ratio is obtained over the usual amplitude demodulation methods.

For a further understanding of the invention, reference may be had to the following detailed description to be read in connection with the ac-l companying drawings, in which:

Fig. 1 is a block diagram of a radio receiver according to my invention;

Fig. 2 is a graphical representation of an am-V plitude modulated carrier wave; and

Fig. 3 is a graphical illustration of a part ofthe Y carrier greatly enlarged together with additional curves illustratin-g the translation operations in accordance with my invention.

Referring to Fig. 1, a radio receiver is shown provided with a radio frequency stage I connected to a receiving antenna I2. The radio frequency stage is connected to an intermediate frequency stage or stages I3. The wave translating feature of the receiver includes a rst gate clipper I4, a rst differentiator I5, a second gate clipper I6 and a second differentiator II. The output of the second diierentiator, which comprises a train of time modulated impulses corresponding in time displacement to variations in amplitude of the input amplitude modulated wave, is applied to a T. M. demodulator I8 for demodulation of the time modulated impulses. While the demodulator I8 may be of various constructions it preferably is of the character disclosed in my aforesaid opending application Serial No. 459,959. This demodulation, for example, preferably is of the character involving the generating o r synchronizing of an energy wave having recurring inclined portions, the period of which is comparable to the time spacing of the impulses. The wave and the impulses are combined, the impulses being superimposed on the wave at points along the inclined prtions thereof according to the time displacement of the impulses, This produces output pulse energy which varies in amplitude according to the time'modulation of the input impulses.

The gate clippers I4 and I6 are preferably of the character arranged to limit clip between two predetermined limits. A gate clipper of this character is disclosed in a copending'application of E. Labin and myself Serial No. 437,530, filed April 3, 1942. The gate clipper therein disclosed includes a diode-doubleflimiter tube. having two limiting levels whereby a Wave applied thereto is limitedfto the breadth determined by those limiting. levels, This double limiting operation producesl a trapezoidal wave form when an amplitude modulated carrier wave such as the wave ''goff Fig. 2 is applied to the gate clipper I4. Should the gate clipper have a narrow band-.pass characteristic, the intermediate frequency at the stage, I3 is` preferably beat down to a low. intermediate frequency before it is applied to the clipper. i4. This low intermediate frequency insures well-defined corners for the trapezoidal wave. Sheuld a, gate clipper be chosen having wide bandpass characteristics, the low intermediate freduencvzy stage or the beating down of high intern'iediate frequency may then be omitted-.

Referring Particularly tc Fis.. 3 in which. the curves thereof are appliedvto the same timey base, Qur-vc s Shows se, enlarged portion Qi the.. ampli- Uls modulated Wave 20. clipped between.

limits

24 and 25,. While I have shown these limiting levels'tolbe equally'spaced on opposite sides of t1?? @Eis Qf the carrier Wave, it will lcs under-A Stod thatthey may be selected to one side o r the. oth r of the axis if desired. The importance of thi selection is that the sides of the undulations. between the limiting levelsshould be such thatthe slopes thereof vary in substantially linear pro-Y portion tothe amplitude variation of the corresponding undulations. It is preferable, therefore,-that the limit clipping operation be made near the axis of the carrier.

It will also be noted that in limit clippingv the carrier wave 2U at the axis thereof that ay lar-ge portion of the undulations ZI, 22, 23 etc. forming the envelopes of the waveare eliminated. TheV portion of the Wai/.s Obtained byY this. operation comprises a trapezoidal wave 3U the sides of which are the only portions of the outer surfaces of the undulations of the wave that are retained, Accordingly, the time interval covered by the sides of the trapezoidal wave comprises a very small percentage ofthe period of the carrier. For eX- ample, this reduction may amount to as great as to 1 or greater depending, of course, on the breadth of the

limits

24, 25. This elimination of such a large percentage of the undulations eliminates to a very large extent such noise and other interfering voltage fluctuations as indicated by the broken lines 2l and 28, The feature of reducing noise and other interfering voltage fluctuations in amplitude modulated carrier waves is the subject matter of my copending application Serial No. 483,36, led April 16, 1943, wherein a very large percentage of interference is eliminated by an operation translating the amplitude modulated wave into a train of pulses which is correspondingly modulated in amplitude.

The sides of the cycles SI, 32, 33 etc. of the trapezoidal wave 3l) vary in slope from cycle to cycle in proportion to the amplitude variations of thecorresponding undulations 2I, 22, 23 etc. If the gate opening of the clipper I4 is small compared to the mean amplitude of the carrier, the change in slope of the side edges of the cycles will be a linear function of the initial modulation of the carrier.

The first differentiator e5 operates to translate the trapezoidal wave 30 into rectangular pulses Sla, Bib; 32a, 32h; etc. as shown by curve b. These rectangular pulses not only correspond in width to the slope of the corresponding side edges of the cycles of the trapezoidal waves but also vary proportionately in amplitude to the steepness of the sloping side edges. The rectangular pulses of curve b shown in solid line represent the output of the second gate clipper I6- after the pulses from the differentiator I5 have been limit clipped between the levels 34 and 3'5. The portions of the rectangular pulses clipped away by this operation are indicated in broken lines. This produces a train of pulses in which the pulses are of the same amplitude.

The rectangular pulses of curve b are differentiated by the second differentiator IIl to produce pairs of positive and negative impulses shown by curve c. The impulses of each pair, such as impulses 31s.@ and 311m, are displaced according to the width of the corresponding rectangular pulss- These. pulses Of. Curve C may be applied directly to the demodulator I8V for demodulation in: accordance with the disclosure in myA aforesaid- Ccpsr-lding application Serial No. 459,959 Br reference to this c cpcndine. application. it will bc ssenv that the positive pulses Slap... Sibp, 3.2md etc. will be used for purposes of demodulation. If; it is desired to use the negative pulses 3Ian, 311m etc.,Y a further clipping operation Will be necessary. Such a clipping operation is indicated by the lmtlevels 4.4 and 4.5. Such a Clipping operation will produce a train of pulses. according to curve d.

The displacementof the pulses of. curve d, de -vv pends upon thev width of the rectangular pulses ofr curve b which inturn depend for their width. upon the steepness, of the sides of the cycles. ofj the trapezoidal Wave Sil. It will thus be observed that the timev displacement of the impulsesr of curves c and d. correspond withV the variations inl amplitude. of the corresponding undulations` off thecarrerwave 20.

In regard totheclipping operation ofthesec.

- the

limits

34 and 35. In other words, the limits may be to one side of the axis of the curve so as to obtain at that point in the system unidirectional rectangular pulses. Dierentiation of such unidirectional pulses will produce the corresponding impulses of curve c.

It'will vbe further recognized that the second gate clipper I6 and the .second differentiator l1 of Fig. 1 may be interchanged so that the rectangularpulses of curve b as indicated in broken lines are rst diiferentiated before a clipping operation isA performed. Such interchanging of the two stages 'I6 and I l will produce impulses for curve c which vary in amplitude proportionately with the amplitude of the pulses (brokenl lines) ofV curve b. By limit clipping such a train of impulses by

limits

44 and 45, for example, a train of unidirectional impulses will be produced similarly as indicated by curve d containing time modulation according to the amplitude modulation of the carrier wave.

While I have shown and described the principles of my invention in connection with specic apparatus, it is to be understood that the illustrations thereof are given by way of example only and not as limiting the scope of the invention as set forth in the objects and the appended claims.

I claim:

1. A method of translating an amplitude mod.- ulated carrier wave into an equivalent train of time modulated impulses comprising translating the undulations of the amplitude modulated carrier Wave into a trapezoidal wave the slope of the side edges of which correspond in substantially linear proportion to the amplitude of the corresponding undulations, translating the trapezoidal wave into rectangular pulses which vary in width according to the slope of the correspond- .ing side edges of the trapezoidal wave, and translating said rectangular pulses each into at least one narrow width impulse corresponding in displacement to an edge of a rectangular pulse.

2. The method defined in claim 1 wherein the first-mentioned translating operation includes limit clipping the carrier wave between two limits where the sides of the undulations of the carrier wave vary in slope in substantially linear proportion to the amplitude variation of the corresponding undulations.

3. The method defined in claim 1 wherein the first-mentioned translating operation includes clipping the wave at two limits selected near the axis of the wave.

4. The method dened in claim 1 wherein the first-mentioned translating operation includes clipping the wave at two limits selected at oppoi site sides of the axis of the wave.

5. The method dened in claim 1 wherein the second-mentioned translating means includes differentiating the trapezoidal wave thereby producing a rectangular pulse for each of the leading and trailing edges of each cycle of the trapezoidal Wave.

6. The method defined in claim 1 wherein the second-mentioned translating means includes differentiating the trapezoidal wave thereby producing a rectangular pulse for each of the leading and trailing edges of each cycle of the trapezoidal wave and limit clipping the rectangular pulses to reduce the rectangular pulses to substantially the same amplitude.

7. 'I'he method defined in claim 1 wherein the third-mentioned translating eperauninciudes differentiating the rectangular pulses thereby producing a pair of positiveand negative impulses from each of said rectangular pulses, one impulse of each pair corresponding to the leading edge and the other to thetrailing edge of a rectangular pulse.

8. A method of translating an amplitude modulated carrier wave into an equivalent train of time modulated impulses comprising translating the undulations of the amplitude modulated carrier into a trapezoidal wave the slope of the side edges of which correspond in substantially linear proportion to the amplitude of the corresponding undulations, diierentiating the trapezoidal wave to produce a rectangular pulse for each of the leading and trailing edges of each cycle of the trapezoidal wave, differentiating the rectangular pulses to produce a pair of positive and negative impulses from each of said rectangular pulses, one of the impulses of each pair corresponding to the leading edge and the other to the trailing edge of a rectangular pulse, and limit clipping the impulses to produce a train of unidirectional impulses the time displacement of which corresponds with the amplitude variations of the undulations of said carrier wave.

9. A system for translating an amplitude modulated carrier wave into an equivalent train of time modulated impulses comprising means to translate the undulations of said carrier wave into a trapezoidal wave the slope of the side edges of which correspond in substantially linear proportions to the amplitude of the corresponding undulations, means to translate the trapezoidal wave into rectangular pulses which vary in width according to the slope of the corresponding edge of the trapezoidal wave, and means to translate each of said rectangular pulses into at least one narrow width impulse corresponding in displacement with one of the edges of a rectangular pulse, the time displacement of such impulses thereby corresponding substantially to the amplitude of the corresponding undulation of said carrier wave.

10. The system defined in claim 9 wherein the rst-mentioned means includes a gate clipper arranged to limit clip the wave between two selected limits. l

1l. The system defined in claim 9 wherein the second-mentioned translating means includes means for differentiating the trapezoidal wave to produce a rectangular pulse foreach of the leading and trailing edges of each cycle of the trapezoidal wave and means to limit clip the rectangular pulses to reduce them to substantially the same amplitude.

12. A system for translating an amplitude modulated carrier wave into an equivalent train of time modulated impulses comprising means to limit clip said carrier wave between two limits where the sides of the undulations of the carrier wave Vary in slope in substantially linear proportion to the amplitude variations of the corresponding undulations, means to diierentiate said trapezoidal wave to produce a rectangular pulse for each of the leading and trailing edges of each cycle of said trapezoidal wave, means to limit clip said pulses, means to differentiate said pulses to produce a pair of positive and negative impulses from each of said rectangular pulses, one of the impulses of each pair corresponding to the leading edge and the other to the trailing edge of a rectangular pulse, the time displacement between the impulses of each pair corresponding 7 substantially to the amplitude of corresponding undulations of said carrier wave.

13. A radio receiver having means to detect amplitude modulated carrier waves, means to translate said carrier waves into equivalent trains of time modulated impulses, and means fordemodulating the time modulated impulses.

14. The receiver defined in claim 13 wherein the translation means include means to limit clip said carrier wave between two limits where the sides of the undulations of the carrier wave vary in slope in substantially linear proportion to the amplitude variations of the corresponding undu lations, means to differentiate the output wave of said limit clipping means to produce rectangular pulses the widths of which correspond substantially to the amplitude of corresponding undulations of said wave, means to limit clip the rectangular pulses to limit them to substantially the same amplitude, and means to differentiate the rectangular pulses to produce for each of said rectangular pulses at least one narrow width impulse corresponding in displacement to an edge of the rectangular pulse, the displacement of such impulses thereby corresponding substantially to the amplitude of the corresponding undulations of said carrier wave.

DONALD D. GRIEG.

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

UNITED STATES PATENTS Number Name Date '2,308,725 Hadeld Jan. 19, 1943 2,308,639 Beatty et al Jan. 19, 1943