US2280187A - Carrier-signal receiver - Google Patents

Description

ApriI2 1 ,-1942 I NR CASE 2,280,187

V CARRIER-SIGNAL RECEIVER Filed July 10, 1940 o- DELAYED- Auolo- DETECTOR AND FREQUENCY v SUPPLY AMPLIFIER I 7 -0 ol REIPPM- L AMPLIFIER 5' g h a f g n hl ll l lg! {PM ulj'u gun I: 7 c i k W F|G.2. LL] l5 ,la 19 -O & o BROAD-BAND DELAYED- AUDIO- 43 DETECTOR AND FREQUENCY AMPLIFIER Avc SUPPLY AMPLIFIER I l -O 9 9 0-4-4) 0- I I o- 44 fia- FI ;.3.

I AMPLIFIER o "'P" BROAD-BAND AMPLIFIER LIMITER ATTORNEY Patented Apr. 21; 1942 2,280,187 CARRIER-SIGNAL RECEIVER Nelson 1. Case, Great Neck, N. Y., assignor to llaaeltine Corporation, a corporation of Delaware Application July 10, 1940, Serial No. 344,648

. Claims.

The present invention relates to an improved carrier-signal receiver and more particularly to a carrier-signal receiver analogous to the homodyne type wherein the apparent selectivity of the receiver is substantially increased by adding to' the desired received modulated-carrier signal locally-produced unmodulated carrier signals of relatively large amplitude and of a frequency equal to that of the received carrier signal.

One of the problems in carrier-signal communicationhas concerned the selectivity of the carrier-signal receiver; that is, the ability of th receiver to select a desired carrier signal to the exclusion of undesired carrier signals which may occupy adjacent channels in the frequency spectrum and may have a strength frequently very much greater than that of the desired signal. The superheterodyne type of carrier-signal receiver, which furnishes one solution to this problem, increases the apparent selectivity of the receiver by locally producing carrier s gnals indi vidually-modulated in accordance with the modulation of the desired and undesired carrier signals, These new carrier signals are-produced by combining the received carrier signals with 10- cally-generated oscillations of a different frequency to produce intermediate-frequency carrier signals which may be subsequently amplified at intermediate frequency and applied to a suitable signal-translating device. However, the superheterodyne type of receiver has certain disadvantages, among which are the problems of image-frequency reception, the failure of the receiver .to pass the desired carrier-signal frequency and its entire complement of modulation side-band components, and the difficulty in accomplishing adequate and proper tracking of the local oscillator with the radio-frequency se lcctor circuits.

To avoid these inherent disadvantages of the superheterodyne type of carrier-signal receiver, the homodyne type of carrier-signal-receiver was proposed as an additional solution of the selectivity problem, This receiver is capable of givmg greater apparent selectivity than other cillations of the desired known arrangements having a like number of tuned circuits. Like the superheterodyne type of receiver, the homodyne receiver employs locallygenerated osci.lations but, unlikethe superhetercdyne rcceiver, the frequency of the locally-generated oscillations is the same as that of the desired carrier signal. The homodyne receiver has the disadvantage, however, that the frequency of the lccally-generated oscillations is critical and,

if it differs only slightly from that of the desired v eral, been relatively sensitive to variations in amplitude of the received signal so that reception is unsatisfactory under certain conditions of operation of the receiver. Furthermore, even though the frequencyof the locally-generated oscillations is maintained exactly equal to that of the desired carrier signal, the homodyne receiver has the additional disadvantage that considerable distortion in the reproduction of the desired signal and considerable reduction in the volume of the reproduced signal occur when the locally-generated oscillations do not have the proper phase relationship with respect to the oscarri-er signal. Arrangements for controlling the phase between the received and locally-generated oscillations have also generally been either quite complicated or responsive to the amplitude of the received signals and for that reason, in general, have not been commercially adopted. Even where the conditions of reception are such that the amplitude of the received carrier signal does not materially change, many of the phasing arrangements of the prior art have not satisfactorily maintained the correct phase relation necessary to produce optimum volume of distortionless reproduction of the received signal.

It is an object of the present invention, therefore, to 'provide a new and improved carriersignal receiver of the homodyne type and one which avoids one or more of the above-mentioned disadvantages of the prior art receivers.

it is a further object of the invention to provide a homodyne type of carrier-signal receiver which derives the umnodulated oscillations necessary for homodyn reception from the received carrier signal itself, whereby the consequent omission of the local oscillator heretofore conventionally employed in such receivers eliminates the many limitations and faults formerly characteristic of this type of receiver which arose from the use of such local oscillator.

It is an additional object of the invention to provide a homodyne type of carrier-signal receiver wherein all received carrier signals of usable signal strength are amplified to a uniform predetermined amplitude level in order that the desired carrier signal may be selective- 1y applied from this group of amplified signals to the signal-translating channel of the receiver,

,signal receiver tunable over a range'of frequencies comprises a main signal-translating channel adapted to have applied thereto received carrier signals the amplitude of a desired one of which may be less than that of adjacent nudesired carrier signals applied to the channel. An untunable broadly-responsive auxiliary signaltranslating channel is coupled to the main chan-, nel and includes limiting means for limiting to a uniform predetermined amplitude level all received carrier signals in the vicinity oi and including the desired carrier signal. There is also provided signal-translating means selectively responsive to the desired carrier signal for deriving the desired carrier signal from the auxiliary channel and applying it to the main signal-translating channel to develop therein a desired carrier signal the amplitude of which is in excess of that of undesired carriersignals.

In accordance with a specific form of the invention, the carrier-signal receiver comprises a main signal-translating channel to which is coupled an auxiliary signal-translating channel including signal-amplifying means having a broad-band frequency-response characteristic for amplifying uniformly all received carrier signals in the vicinity of and including the desired carrier signal and there is coupled to the amplifying means, means for limiting to a uniform predetermined amplitude level the carrier signals translated by the amplifying means. The receiver also includes means for selectively applying to the signal channel the uniformly limited desired carrier signal to develop in the signal channel a desired carrier signal the amplitude of which is in excess of that of undesired carrier signals. The receiver also includes signal-demodulating means coupled to the main signal channel and means for rendering the demodulating means unresponsive to carrier 618- system l3, l4 and tuned by a tuning condenser l2. Connected to the output of radio-frequency amplifier I0 is a broad-band radio-frequency amplifier l6 having an input circuit comprising a radio-frequency transformer l6 and tuning condenser H. The radio-frequency amplifier 15 may include one or more stages of amplification and is designed to amplify uniformly signals within a relatively wide range of carrier frequencies applied to the input circuit l6, l1. Connected in cascade with the output circuit of the radio-frequency amplifier IS, in the order named, is signal-demodulating means, comprising a delayed detector and automatic amplification control or A. V. C. supply I8, an audio-frequency amplifier l9, and a sound reproducer 20. The output of the automatic amplification control supply is applied to the input circuits of one or more of the tubes of the radio-frequency amplifiers l0 and I! in conventional manner. There is coupled to the tunable input circuit ll, l2 of the main signal-translating channel an untunable broadlyresponsive auxiliary signal-translating channel. including signal-amplifying means having an untunable broad-band ;frequency-response characteristic for amplifying uniformlyall received carrier signals in the vicinity of and including the desired carrier signal. The auxiliary channel also includes means coupled to the amplifying means for limiting to a uniform predetermined amplitude level all such received carrier signals. This auxiliary channel comprises an untunable broadly-responsive, radio-frequency nals having an amplitude substantially less than invention, together with other and further objects thereof, reference is had to the followin description taken in connection with the accompanying drawing and its scope will be pointed out in the appended claims.

Referring now to the drawing, Fig. 1 is a circuit diagram, partly schematic, of a complete carrier-signal receiver embodying the invention; Figs. 2a-2d are graphs representing the strengths of the carrier signals at various points in the receiver of Fig. 1 and are used in explaining the operation of the invention; while Figs. 3 and 4 are circuit diagrams, partly schematic, of re ceivers incorporating modified embodiments of the invention.

Referring now more particularly to Fig. 1, there is represented schematically a complete carrier-signal receiver embodying the present invention in a preferred form. In general, they receiver includes a main signal-translating channel having an input circuit tunable over a range of frequencies and adapted to have applied thereto received carrier signals the amplitude of a desired one of which may be less than that of adjacent undesired carrier signals applied to the channel. This channel comprises a tunable radio-frequency amplifier l0 having an input circuit comprising a radio-frequency transformer H which is connected to an antenna-ground The amplitude limiter 22 may be of any conventional type so long as the level of limiting is fixed by the constants of the limiting system and does not depend upon the intensity of carrier signals applied thereto. The limiting system here shown forms no part of the invention butis disclosed and claimed in the copending application of Jasper Okrent, Serial No. 337,653,

' filed May 28, 1940, now'United-States Letters Patent No. 2,271,203 dated January 2'1, 1942' It includes a pentode vacuum tube having anode and cathode elements serially connected between the input transformer 23 and an ouput transformer 25, the tube elements being so energized that limiting occurs on the negative half-cycles of the applied carrier signal by anode current cutoff and on the positive halfcycles by anode current saturation.

There is also included in the carrier-signal receiver signal-translating means selectively responsive to the desired carrier signal or, in other words, tunable to the frequency of the desired carrier signal, for deriving the desired carrier signal from the auxiliary channel and applying it to the main channel to develop therein a desired carrier signal the amplitude of which is in excess of that of the undesired carrier signals. This means comprises a secondary winding 26 provided in the transformer 25 which is connected in a tunable link circuit comprising winding 26, a winding 21 coupled to the input circuit ll, l2, and a tuning condenser 28. The

and, therefore, couples through winding 21 signal in the tuning range of the receiver.

In considering the operation of the carriersignal receiver just described, it will be assumed that the tuning condensers of the receiver are operated in unison to tune the receiver to a desired carrier signal applied to the input circuit ll, i2 from the antenna-ground system i3, H.

The desired carrier signal may have a relatively the amplification of one or both of the units l and I! to maintain the signal input to the detector it within a relatively narrow range for a wide range of received signal intensities.

In this operation,' it may be noted that reinforcement of the desired carrier signal by the small amplitude as represented by the vertical line e of Fig. while adjacent undesired carrier signals may appear in the input circuit ll, l2 with relatively larger amplitude as represented by the vertical lines f-i, inclusive, of Fig. 2a. This group of carrier signals appearing in the input circuit ll, i2 is amplified uniformly by the broad-band untunable amplifier 2| and is limited by the amplitude limiter 22 so that it appears in the output circuit thereof as a group of carrier signals without modulation and with uni-' form predetermined amplitude levels, as indi cated by the vertical. lines e'-i', inclusive, of

Fig. 2b, the repeating ratio of the amplifier 2! being sufiicient to amplify the weakest usefulcarrier signal to this predetermined level.

The carrier signals of uniformly limited amplitude developed in the output of the limiter 22 are applied through transformer to the tuned circuit 26, 21, and 28, which, being tuned by the condenser 28 to resonance with the desired carrier signal 0', is selectively responsive thei eto hto the input circuit ll, 12, the group of cai rier signals e"'-i", inclusive, of Fig. 2c corresponding to the respective received carrier signals e-i, inclusive. The carrier signals e"-i", inclusive, add with corresponding ones of the received carrier signals e-i, inclusive, to produce in the input circuit II, I 2 the reinforced carrier signals e"'-i"', inclusive, of Fig. 2d, the resultant desired carrier signal thus being so reinforced that its amplitude is larger than that of any of the group of undesired carrier signals.

The reinforced group of carrier signals is ap plied to the radio-frequency amplifier HI, ampilfied therein, and applied through the tuneu circuit I6, I! to the radio-frequency amplifier ii, the circuit I8, ll further discriminating in favor of the desired carrier signal. The group of carrier signals is amplified in the broad-band .untunable radio-frequency amplifier IS-and applied to the detector ID. The detector 18 preferably has a delayed response characteristic such that it responds only to carrier signals having an amplitude greater than that of the strongest undesired carrier signal of the group. The detector i8 thus is responsive only to the desired carrier signal, which it demodulates to derive the modulation components. The modulation components are ampified by the audio-frequency amplifier i9 and are resproduced by the sound reproducer 20 in a conventional manner. The

detector l8is preferably a peak detector having the well-known property of discriminating in favor of the strongest carrier signal applied thereto. This characteristic aids in improving the apparent selectivity of the carrier-signal receiver. The automatic amplification control or coupled, this latter carrier'signal of uniformly limited amplitude,

the limiter 22, may cause oscillation in the receiving system in the absence of a strong desired signal, although the amount of energy fed back front the limiter 22 to the input circuit II, I! cannot exceed a predetermined value due to the inherent action of the limiter.

. The modification of the invention represented in Fig. 3 is essentially similar to that of Fig. 1, similar circuit elements being designated by similar reference characters, except that the winding 21 of the tuned link circuit 26, 21, 28 is coupled to the input circuit I6, I! of the radio-frequency amplifier i5 which, it will be seen, is at a point in the main signal-translating channel succeeding the pointtherein to which the input circuit of the auxiliary signal-translating channel is point comprising, of course, the tuned circuit II, II. The radio-frequency amplifier ll thus constitutes an isolating amplifier to prevent direct feedback of energy from the output circuit of the limiter 22 to the input circuit ii, l2. The possibility of self-oscillation of the receiving system is accordingly greatly reduced. In this arrangement, the radio-frequency amplifier it preferably has little amplification for strong desired signals applied to antenna-ground system i3, ll, in order that the amplified desired carrier fed to theinput circuit i6, I1 of radio-frequency amplifier l5 should not be large compared to the desired carrier component fed to this circuit from the limiter 22 by way of the link circuit 26, 21, 28. The operation of this modification is essentially similar to that of Fig. 1 and will, for that reason, not be repeated.

The modification of the invention represented in Fig. 4 is likewise similar to that of Fig. 1, and similar circuit elements are designated by similar reference characters. In this modification, the output of the limiter 22 is tuned to the desired carrier signal by a condenser I! which is mechanically connected for unicontrol with the tuning condensers l2 and IT. The output of the limiter; 22 is applied through the "radio-frequency transformer 25 to the input circuit of a A. V. C. supply of, unit l8 derives from the desired carrier signal an automatic control or A. V. C. bias. This bias is effective to control radio-frequency amplifier II, the cathodecircuit of which includes serially arranged resistors 32 and 33. The resistor 32 provides a normal operating bias for the control electrode of the amplifier ii forlinear amplification while the resistor 33 provides a sensitivity control or delay bias for the detector 18, the purpose of which is to render the detector I8 unresponsive to carrier signals having an amplitude slightly less than that of the desired carrier-signal output of. the limiter 22. The output circuit 25, 30 is tuned to the desired carrier signal and, therefore, selectively applies the desired carrier signal of limited amplitude from the output circuit of the limiter 22 to the radio-frequency amplifier 3i. Since the resistor 33 is included in the output circuit of the amplifier 3|, there is also developed across this resistor, in addition to the delay bias, a group of carrier signals having the relative amplitudes represented generally by the vertical lines e"i", inclusive, of Fig. 20. This group of carrier signals is thus coupled by the resistor 33 into the output circuit of the main signal-translating channel, specifically into the detector l8 where the desired carrier signal from the radio-frequency amplifier is reinforced and the reinforced desired carrier signal is demodulated substantially to the exclusion of the undesired carrier signals. The operation of the Fig. 4 embodiment is otherwise similar to that of the Fig. 1 embodiment. From the above description of the Fig. 4 arrangement, it will be seen that the resistor 33 and amplifier 3| comprise means for rendering the demodulating means or detector l8 unresponsive to carrier signals having an amplitude substantially less than the amplitude of the desired carrier signals developed in the circuit of the detector. Further, it will be evident that the tuned circuit comprising circuit elements 25, 30 and the amplifier 3| comprise signal-translating means sejlectively responsive to the desired carrier signal for deriving the desired carrier signal from the auxiliary signal-translating channel and applying it to the demodulating means or detector Hi to develop therein a desired carrier signal the amplitude of which is in excess of that of the undesired carrier signals.

While there have been described what are at present considered to be the preferred embodiments of this invention, it will be obvious to those skilled in the art that various changes and modifications may be made therein without departing from the invention, and it is, therefore, aimed in the appended claims to cover all such changes and modifications as fall within the true spirit and scope of the invention.

What is claimed is:

1. A carrier-signal receiver tunable over a range of frequencies comprising, a main signaltranslating channel adapted to have applied thereto received carrier signals the amplitude of a desired one of which may be less than that of adjacent undesired carrier signals applied to said channel, an untunable broadly-responsive auxiliary signal-translating channel coupled to said main channel and including limiting means for limiting to a uniform predetermined amplitude level all received carrier signals in the vicinity of and including the desired carrier signal, and signal-translating means selectively responsive to said desired carrier signal for deriving said desired carrier signal from said auxiliary channel and applying it to said main channel to develop therein a desired carrier signal the amplitude of which is in excess of that of said undesired carrier signals.

2. A carrier-signal receiver tunable over a range of frequencies comprising, a main signaltranslating channel adapted to have applied thereto received carrier signals the amplitude of a desired one of which may be less than that of adjacent undesired carrier signals applied to said channel, an untunable broadly-responsive auxiliary signal-translating channel coupled to said main channel at a predetermined point therein and including limiting means for limiting to a uniform predetermined amplitude level all received carrier signals in the vicinity of and including the desired carrier signals, and signaltra'nslating means selectively responsive to said desired carrier signal for deriving said desired carrier signal from said auxiliary channel and applying it to said main channel at a ,point succeeding said predetermined point to develop in said main channel a desired carrier signal the amplitude of which is in excess of that of said undesired carrier signals.

3. A carrier-signal receiver tunable over a range of frequencies comprising, a main signaltranslating channel adapted to have applied thereto desired carrier signals of a predetermined frequency and undesired carrier signals of different frequency, an untunable broadly-responsive auxiliary signal-translating channel coupled to said main channel and including limiting means for limiting to a uniform predetermined amplitude level all received carrier signals in the vicinity of and including the desired carrier signal, and signal-translating means tunable to said predetermined frequency for deriving said desired carrier signal from said auxiliary channel and selectively applying it to said main channel to develop therein a desired carrier signal the amplitude of which is in excess of that of said undesired carrier signals.

4. A carrier-signal receiver tunable over a range of frequencies comprising, a main signaltranslating channel having an input circuit and adapted to have applied thereto desired carrier signals of a predetermined frequency and undesired carrier signals of different frequency, an untunable broadly-responsive auxiliary signal-translating channel coupled to said input circuit and including limiting means for limiting td a uniform predetermined amplitude level all received carrier signals in the vicinity of and including the desired carrier signal, and signaltranslating means tunable to said predetermined frequency for deriving said desired carrier signal from said auxiliary channel'and for selectively applying it to said main channel to develop therein a desired carrier signal the amplitude of which is in excess of that of said undesired carrier signals.

5. A carrier-signal receiver tunable over a range of frequencies comprising, a main signaltranslating channel having an input circuit tunable over said range of frequencies and adapted to have applied thereto received carrier signals the amplitude of a desired one of which may be less than that of adjacent undesired carrier signals applied to said input circuit, an untunable broadly-responsive auxiliary signaltranslating channel coupled to said main channel and including limiting means for limiting to a uniform predetermined amplitude level all received carrier signals in the vicinity of and including the desired carrier signal, and signaltranslating means tunable with said input circuit to be selectively responsive to said desired carrier signal for deriving said desired carrier signal from said auxiliary channel and for selectively applying it to said main channel to develop therein a desired carrier signal the amplitude of which is in excess of that of said undesired carrier signals,

6. A carrier-signal receiver tunable over a range of frequencies comprising, a main signaltranslating channel adapted to have applied 'thereto received carrier signals the amplitude of a desired one of which may be less than that of adjacent undesired carrier signals applied to said channel, an auxiliary signal-translating channel coupled to said main channel and including signalamplifying means having an untunable broad-band frequency-response characteristic for amplifying uniformly all received carrier signals in the yicinity of and including the desired carrier signal and means coupled to said amplifying means for limiting to a uniform predetermined amplitude level the carrier signals amplified by said ampliiying means, and signal-translating means selectively responsive to said desired carrier signal for deriving said desired carrier signal from said auxiliary channel and for applying it to said main channel to develop therein a desired carrier signal the amplitude of which is in excess of that of said undesired carrier signals.

7. A carrier-signal receiver tunable over a range of frequencies comprising, a main signaltranslating channel including a carrier-signal amplifier having an output circuit and having an input circuit adapted to have applied thereto received carrier signals the amplitude of a desired one of which may be less than that of adjacent undesired carrier signals applied to said amplifier, an untunable broadly-responsive auxiliary signal-translating channel coupled to said input circuit and including limiting means for limiting to auniform predetermined amplitude level all received carrier signals in the vicinity of and including the desired carrier signal, and

signal -translating means selectively responsive to said vdesired carrier signal for deriving said desired carrier signal from said auxiliary channel and for applying it to the output circuit of said signal amplifier to develop therein a desired carrier signal the amplitude of which is in excess of that of said undesired carrier signals.

8. A carrier-signal receiver tunable over a range of frequencies comprising, a main signaltranslating channel adapted to have applied thereto received carrier signals the amplitude of a desired one of which may be less than that or adjacent undesired carrier signals applied to said 9. A carrier-signal receiver tunable over a range of frequencies comprising, a main signaltranslating channel adapted to have applied thereto received carrier signals the amplitude of a desired one of which may be less than that of adjacent undesired carrier signals applied to said channel, an untunable broadly-responsive auxiliary signal-translating channel coupled to said main channel and including limiting means for limiting to a uniform predetermined amplitude level all received carrier signals in the vicinity of and including the desired carrier signal, signaldemodulating means coupled to said main channel, and signal-translating means selectively responsive to said desired carrier signal for deriv ing said desired carrier signal from said auxiliary channel and applying it to said demodulating means to develop therein a desired carrier signal the amplitude of which is in excess of that of said undesired carrier signals.

10. A carrier-signal receiver tunable over a range of frequencies comprising, a main signaltranslating channel adapted to have applied thereto received carriersignals the amplitude of a desired one of which may be less than that of adjacent undesired carrier signals applied to said channel, an auxiliary signal-translating channel coupled to said main channel and including limiting means for limiting to a uniform predetermined amplitude level all received carrier signals in the vicinity of and including the desired carrier signal, signal-demodulating means coupled to channel, an untunable broadly-responsive auxiliary signal translating channel coupled to said main channel and includinglimiting means for limiting to a uniform predetermined amplitude 'level all received carrier signals in the vicinity of and including the desired carrier signal, signaldesired carrier signal for deriving said desired carrier signal from said auxiliary channel and applying it to said main channel to develop therein a desired carrier signal the amplitude of which is in excess of that of said undesired carrier signals, signal-demodulatingmeans coupled to said main channel, and means for rendering said demcdulating means unresponsive to carrier signals having an amplitude substantially translatingmeans selectively responsive to said i said main translating channel, a vacuum tube amplifier having a cathode resistor and having an input circuit coupled to said auxiliary channel and selectively responsive to desired carrier'signals for developing across said cathode resistor said desired carrier signal, said amplifying means also developing across said cathode resistor a unidirectional bias, means for applying said, desired carrier signal developed across said cathode resistor to said demodulating means to develop therein a desired carrier signal the amplitude oi which is in excess of that of said undesired carrier signals, andmeans'responsive to said unidirectional potential bias for rendering said demodulating means unresponsive to carrier signals having an amplitude substantially less

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