US2421136A

US2421136A - Gain control system for pulse modulation receivers

Info

Publication number: US2421136A
Application number: US597035A
Authority: US
Inventors: Harold A Wheeler
Original assignee: Hazeltine Research Inc
Current assignee: Hazeltine Research Inc
Priority date: 1945-06-01
Filing date: 1945-06-01
Publication date: 1947-05-27
Anticipated expiration: 1964-05-27
Also published as: BE612627A; NL134321B

Description

May 27, 1947. H. A. WHEELER GAIN CONTROL. SYSTEM FOR PULVSE MODULATION RECEIVERS Filed June l, 1945 2 Sheets-Sheet l INVEN TOR. HAROLD A. WHEELER May 27, 1947. H. A. WHEELER 2,421,136

GAIN CONTROL SYSTEM FOR PULSE MODULATION RECEIVERS Filed June 1, 1945 2 Sheets-Sheet 2 IIQEE. v v IIEE.

SHOA

+L |l il Il SllOA INVENTOR. HAROLD A. WHEELER ATTORNEY Patented May 2.7,- 194.1

GAN CONTRL SYgTEM FOR PULSE MODULATION RECEIVERS Harold A. Wheeler, Great Neck, N. Y., assigner,

mesne assignments, to Hazeltlne Research,

Inc., Chicago, Ill., a corporation of Illinois Application June 1, 1945, Serial No. 597,035

1 .8 Claims.

tion-finding system in which the desired information is conveyed by means of a pulse-modulated signal, coded in accordance with a prescribed coding schedule. For example, the coded signal may include a. pair of pulse components, individually having a rectangular wave form and iixed duration but a time separation that is variable in a code sequence. In the preferred systems, the coded signal is received, shaped and passed on to a decoder unit which automatically derives the desired information by deciphering the coded signal. I

Systems of the type mentioned above operate satisfactorily in electrically quiet installations that are substantially-free of interfering signals.

Where there is a strong likelihood of encountering noise or interfering signals of appreciablemagnitude, however, the decoder is liable to produce erroneous information. Assume for the purposes of illustration that a noise or interfering pulse component is present having an amplitude half that of the pulse components of the received coded signal referred to. Further, assume the interfering pulse to occur intermediate the coded pulse components of the received signal. Under the assumed conditions, the decoder may be unable to distinguish between the desired code components and the spurious or interfering signal component appearing in the output circuits of the preceding stages. When such is the case, the spurious signal is accepted as a, component of the received coded signal and the deciphered information derived from the decoder is obviously faulty and misleading.

Quick acting automatic-volume-control arrangements are known in the art which may respond to the leading component of a received signal and reduce ,the receiver gain to such an `extent that an interfering signal of the type to the leading component of the received signal and. establishes a control potential for reducing the receiver gain as required to eliminate the interfering signal mentioned above. The long discharge time constant of the condenser enables the control voltage to hold over and maintain reducedgain in the receiver for the duration of the received signal. After the duration of the received signal, the control voltage is gradually decreased, as the condenser discharges, and normal receiver gain and sensitivity are gradually restored. Such arrangements are operative but the slow process of re-establishing the receiver gain after the termination of a received signal may be undesirable for recurring sets of pulses.

It is an object of the present invention, therefore; to provide a wave-signal translating arrangement for translating modulated signals and which substantially avoids 'the aforementioned limitations of priorarrangements.

It is another object of the present invention to provide an improved arrangement for' translating a modulated signal having a predetermined maximum duration and including a control system for effecting a desired variation in an operating characteristic of the arrangement but only during an operating interval approximately correunder consideration is not translated therethrough and does not appear in the receiver output circuit. Such control arrangements usually comprise a detector and an associated condenser having a fast charging time constant but a slow discharging time constant. Where this arrangement is used, the condenser is charged in response sponding to the duration of the modulated signal.

It is a specific object of the invention to pro- 4 vide an improved arrangement for translating a modulated signal having a predetermined maximum duration4 and including a gain-control system for substantially reducing the gain level of the arrangement but only for the duration of the Q modulated signal.

In accordance with the invention, a wave-signal translating arrangement for translating a modulated signal which may have a predetermined maximum duration comprises a signal-translating channel. The channel has a predetermined operating characteristic which h as a normal value inthe absence of the modulated signal. The arrangement includes means responsive to the modulated signal for deriving a control potential starting early in the. duration of the modulated signal and tending to hold over foi` an interval substantially greater than the aforesaid maximum duration. There are provided means for utilizing the control potential to adjust the operating characteristic of the channel to a value different from its normal value. Additionally, the arrangement has means for effectively interrupting the control potential and for restoring the operating characteristic of the channel to its normal value after a predetermined time into the aforepanying drawings, and its scope will be :pointedn out in the appended claims.

In the drawings, Fig. 1 is a schematic representation of a wave-signal translating arrangement in accordance with the invention; Fig. 2

lated signals which have a predetermined minimum peak value and which may have a predetermined maximum duration. 'I'he nature of the pulse-modulated signal is to be considered more..

particularly in connection with the operation of the illustrated arrangement. This arrangement comprises an antenna-ground system I0, Il for intercepting the pulse-modulated direction-dnding signals and for applying such signals to a signal-translating channel provided by a, pulsemodulated signal receiver l2, a wave-signal limiter I3 and an oscilloscope I4 connected in cascade in the recited order. The receiver unit I2 may constitute any conventional well-known arrangement forV receiving and demodulating pulse-modulated signals. As is well understood in the art, receivers bothof the superheterodyne and superregenerative types may be utilized for this purpose. In the instant case, unit I2 will y be deemed to be of the superregenerative type and Vand. amplitude-limiting actions. This may be accomplished by operating thestage to translate only 'an intermediate amplitude range of an applied pulse eliminating its maximum and minicomprises graphs utilized in explaining the operreflects the value of the receiver gain. A iirst or noise gain-control system I5 is associated with the channel and constitutes means responsive to the quiescent signal translated therethrough for stabilizing the gain characteristic of thev channel at a desired normal value. Unit I5 may include a frequency-selective amplifying circuit and a wave-signal rectifier for rectifying a. selected' portion of the quiescent signal output to derive in the output circuit vof unit I5 a control potential having an amplitude determined by that' of the quiescent signal. A time constant l circuit, comprising the parallel combination of a mum levels by way of anode current saturation i and anode current cutoff phenomenon, respectively. The oscilloscope I4 may be of the familiar condenser I6 and a resistor l1, is included in the output circuit of unit |5.' The values of elements LI8 and I'l'are selected to provide along time con-v stant so that the control potential obtained from unit l5 is not appreciably disturbed by received signal pulses of short duration occurring infrequently and translated in the signal-translating channel. The connection I8 extending from time constant circuit |6, through receiver I2 applies the gain-control potential from unit I5 to a control circuit or bias arrangement of the receiver to eect the desired gain-stabilization phenomenon. A suitable circuit arrangement for receiver I2 and its associated noise gain-control system I5 is fully disclosed in eopending application Serial No. 521,932, filed February 11, 1944, in the name of Harold A. Wheeler and assigned to the same assignee as the present invention.

The signal-translating arrangement has means exclusive of channel `|2|4 and responsive to a received pulse-modulated signal for deriving a second control potential starting early in the duration of the received signal and tending to hold over for an interval substantially greater than the maximum duration of the received signal. This means is designated 2|) and is said to be exclusive of the principal translating channel because wave-signal translation from the antenna I0, to the decoder is accomplished independently of this unit. Unit 20 includes means, a pulse rectifier and amplier 2|, which respond to the leading portion of the pulse-modulated signal for deriving a signal pulse of a given polarity. The pulse rectifier of unit 2| is preferably a peakrectier so that the signal pulse obtained therefrom has a magnitude determined by the peak value of the pulse-modulated signal applied to its input circuit from receiver I2 by way of connection 32. Also, the rectifier of unit 2| preferably has an amplitude-delay bias so as to be cathode-ray type used to monitor the wave-signal translating arrangement under consideration. The pulse-modulated signals obtained in the output circuit of limiter I3 may be applied to an automatic decoding unit (not shown), as indicated by arrow I 9.

In view of the high amplicationobtainablewith receiver I2, a quiescent signal of appreciable magnitude is translated in channel |2|4, inclusive, during operating` intervals in -which modulated signals are not intercepted by antenna 'Y system l0, Il. This quiescent signal is initiated by and represents inherent disturbances within the receiver as, for example, thermal agitation noise, shot eiect and the like. Also, this signal amplitude selective. The value of bias is selected so that the rectiiier'is unresponsive to signals having an intensity less than the minimum peak value of pulse-modulated signals to be received.

' The output circuit of the amplifying portion of unit 2| is coupled through a pair of amplifying or repeating vacuum tubes 22 and 23 of the tetrode type to an energy-storage device 24 which is to be'charged in one sense by the signal pulse from unit 2| to develop a control potential. The input circuit of tube 22 is connected'to unit 2| through a condenser 26 and a grid resistor 21. In similar manner, a condenser 28 and grid resistor 29 couple the output circuit of tube 22 to the input circuit of tube 23. Operating potentials are applied to these tubes from the sources indicated +B, -l-Sc and -Ea A resistor 25 is shunted across the energy-storage device or condenser 24, having such value that the discharge path of condenser 24 has a .Very slow time constant much greater than the maximum duration of the received pulse-- modulated signals. A connection 30 extending vThis means comprises a short-circuited timedelay network 3i having a conventional construction and including series-connected inductors and,

intervening shunt-connected condensers. The

input terminals of network 3l are coupled across a load impedance 35 included in the output circuit of amplifier 22. The impedance 35 is selected to terminate the networkin its characteristic impedance.

While a transmittingunit is customarily associated with a receiving unit of ,the type represented in Fig. 1 to complete the radio-locating and direction-finding system, the present invention may be clearly understood from a consideration of only the receiver portion. For this reason the remainder of the direction-finding system has been omitted from the drawings. The operation of the Fig. 1 arrangement is represented in part by the curves of Fig. 2.

Curve A designates the signaloutput obtained from receiver I2 of the signal-translating channel I2-I4, inclusive. The low-amplitude signal portions designated Sq denote the stabilized quiescent signal output of the receiver, stabilized by control unit I5 in the manner fully disclosed in the above-identified copending application. The pulse components P1, P2 and P3 constitute a received direction-flndingsignal of the pulse-modulated type which has a duration T1 `but which may have a maximum duration To. The leading pulse component P1 is a pilot pulse and the succeeding components P2 and P3 have a time spacing which is coded in accordance with a prescribed coding schedule. Each component has a peak amplitude value exceeding a minimum peak amplitude level represented by broken horizontal line B. The pulse component P4 represents an interfering pulse component, such yas an echo,

-of the applied pulse exceeds the amplitudefdeiay is applied to time-delay network 3I, the remainder being applied directly to the input circuit of tube 23 vas a pulse signal of positive polarity.

This pulse signal vis represented at P5 in curve C.

The pulse signal Ps is further amplified in tube 23. reversed in polarity. and applied to condenser 24, charging the condenser in one sense to develop the control potential of curve D. The control potential is negative and attains its maximum value, indicated e1, after the short time interval tti-t1. The interval tu-ti is short compared with the duration 'to-t2 of the pilot-pulse component P1 and, thus, the pulse gain-control system is seen to be fast acting. It develops the desired control potential of curve D early in the duration of the pulse-modulated signal `of curve A.

The developed control potential is utilized as a bias or gain-control potential, being supplied to the control input circuit of receiver I2 to reduce the gain thereof and the gain of channel I2-I4, inclusive, from the normal value established by the noise gain-control system I5. Preferably, the gain of the signal-translating channel is reduced to decrease the amplitude of the pulse-modulated signal of `curve A in the manner illustrated by curve E. Specifically, the gain is quickly reduced so that only the leading portion of the pilot-pulse component P1 exceeds the amplitude-delay bias of the rectier ,of unit 2l. This reduction in gain determines the wave form of signal pulse P5 of curve C which is consequently of shorter duration than the pilot-pulse compo'nent P1. In view of the slow discharge time lconstant of condenser 24 and resistor 25, the

' modulated signal of curve A is translated to the which is received along with the pulse-modulated 3 signal in the interval between its components P1 and P2. The undesired signal P4 has an appreciable amplitude in comparison with that of the code components. Therefore if the signal of curve A were supplied directly to the decoder, the

. interfering pulse component P4 would cause an sequently', the noise gain-control system I5 prevents the quiescent signal Sq of channel I2-I4, inclusive, from initiating the additional control afforded by unit 20.

At the time to, the pilot-pulse component P1 of the received pulse-modulated signal arrives at the input terminals of unit 2i included in the input circuits of limiter I3 and unit 2l with the wave form of curve E.

The limiter I3 is adjusted, in conventional clipping levels designated by the horizontal broken lines F and G. The clipping process removes the irregular noise components rthat are superimposed on the pulse components P1, Pz and -Pa of the received`coded signal. This process also eliminates signal components of amplitudes rless than clipping level G and deletes the residual portion of thev undesired noise pulse component P4, obtaining the output signal of curve H. This signal, in turn, is supplied to the oscilloscope I4 where the performance of channel I2I4, inclusive, may be determined by reprolducing the waveform of curve H on the screen of a cathode-ray tube in welleknown fashion. The output signal of the limiter is also supplied to the automatic decoder (not shown) wherein the coded information conveyed by means of the time separation of pulse components P2 and Ps is deciphered.

At the time t5, a reflection of signal P5 of curve C appears at the input terminals of time-delay network 3i. The reflected pulse, Ps of curve C, has a time separation to-ts from pulse P5 which corresponds with the total or round-trip delay of the network. This delay is proportional to the geometric mean of the total series inductance and total shunt capacitance of network 3| and pulse gain-control system 20. As the amplitude is preselected to cause the interval tn -ts to be only slightly greater than -the maximum dura.- tion To of the coded signals'to be received in the operation of the system. The reected pulse .A

Pe is of negative. polarity, receiving apolarity reversal atthe short-circuited termination! oi' the network 3|. The delayed 'and :reversed polarity signal pulse Pe is translated through tube 23 to condenser 24. This pulse charges the condenser charges condenser 24 to interrupt or terminate the control potentialof curve D. With the con-fv trol potential of curveD' terminated, the noise gain-control system I v'resumes ,control and restores the gain of channel l2l4, inclusive, to its normal or stabilized value.

By way of review, the arrangement -of Fig. 1

. will be seen to include two gain-control systems.

The first, noise gain-control system l5, establishes a desired normal or stabilized gain in channel i2-l4, inclusive. The second, pulse gain-control system 20, is ineiective in the absence of a, received signal. Upon receipt of a signal, however, unit 20 responds rapidly to develop a control potential for materially reducing the channel gain early in the duration of the received signal.

The amplitude-delay bias feature of unit 20.

renders this unit responsive to only the leading portion of the received signal. TheV discharge time constant of condenser 24 and resistor 25 -is preferably several times the total delay of netl work 3i so that the condition of reduced gain tends to endure for an operating interval much greater than the maximum duration of the received signals.v The delay of network 3l is selected so that this reduced gain condition is terminated and normal gain restored to the chan-y nel after an interval only slightly longer than the maximum duration of the received signals. Consequently, While the channel has a reduced gain for about the duration of the received pulsemodulated signal in order to minimize the eects of spurious pulse components of the type shown at P4, the normal high gain is re-established just after the received pulse has been translated. In-this manner, the arrangement is returned 4to a condition of high sensitivity promptly to be certain to translate the next succeeding pulsemodulated signal even though it be of reduced intensity.

A modification of the invention is included in the representation of Fig. 3 showing a signaltranslating arrangement embodying a receiver of the superheterodyne type. The arrangement has an antenna-ground system 40, 4| for supplytively, of Fig. 1. A control potential obtained in unit 45 is applied over a conductor 41 to units 42, 43 and 44 to stabilize the gain` of the rst channel at a desired normal value. A control potential obtained from unit` 46 is applied over a conductor 43 to intermediate-frequency ampli` iler 44 to shift the gain level of the flrst channel g.- l from its normal Avalue to a diil'erent'value fo operating intervals during which received signals are being translated.

The other, or second,` channelvis coupled to oscillator-modulator 43 through a time-delay network 50. This channel has an intermediate- A frequency ramplier 5l of one or more stages, a

in an opposite sense tothe charging effect of the direct pulse Ps or, expressed differently, dis` lo wave-signal detector and amplifier 52, a limiter 53 and an oscilloscope 54. The output signal of limiter 53 may also be supplied'to an automatic de'coder, as indicated by arrow 55. Input terminals of intermediate-frequency'amplifier 5i receive connections from conductors 41 and 43,- extending the control of systems 45'and 46 to the gain characteristic of the second channel.

The operation of the Fig. 3 arrangement will be understood from the foregoing description and.

` quiescent signal of the receiver to stabilize the gain, or other controlled operating characteristic,

of the iirst and second channels of the Fig. 3 arrangement at a desired ncrmalvalue. This control is superseded by the eiect of unit 46 in the presence of a received signal, such as that of curve A';

The signal of curve A diifers principally fromthat of 'curve A in that it represents one-half of the envelope of the signal output of oscillatormodulator 43 and that it contains no pilot-pulse component'. Such a component is not required to achieve the desired control in a system of the type of Fig. 3. The pulse components P2 and Ps are similar to components P2 and P3 of Fig. 2, having a time separation in accordance with a prescribed coding schedule. At'the time to', pulse component P2' is applied to unit 46 which derives the control potential of curve D' in the manner recited above. y l

The control potential of curve D' obtains its maximum value e1 at the time ti'. This control potential as applied to intermediate-frequency amplifiers 44 and 5l reduces the gain level in both the rst and second signal-translating channels to suppress interfering signals of the type represented by pulse component P4'. The

time-delaynetwork 50 through which the output signal of oscillator-modulator 43 is applied to the second channel is selected to have a time delay tof-ts. The delay interval tif-ts is selected to be slightly longer than the time tlf-t1' required for the gain level of the second channel to be reduced under the control of unit 46. As a consequence, the output signal of detector and amplifier 52 has the wave form of curve E'. It is clipped in unit 53 and supplied to both oscilloscope 54 and the automatic decoder (not shown) with the wave form of curve H.

Inasmuch as the received coded signal is applied to intermediate-frequency amplifier 5| with this high sensitivity renders the receiving arrangement subject to interfering signals, such as reflected echoes or unusually large noise signals, the fast-acting pulse gain-contro1 system minimizes the effect of such,.undesired signals on thereceiver. The limiter stages suppress any residuum of such interfering signal components from the coded signal applied to the decoder.

Another especially desirable feature of the arv rangement is its ability to protect the units thereof as well as the decoder from the effects oi!V a nearby transmitting unit operating at approximately the same frequency. In such installations, the pulse gain-control system is ablev toderive a control potential in response to the leading portion of a transmitted signal intercepted by its antenna system and to reduce the gain of the arrangement to such an extent that the transmitted signal is not able to cause overloading and other undesired results.

The invention may be utilized for translating modulating signals of a variety of waveforms. 'I'he term modulated signal as used herein and in the appended claims is intended to mean a signal having a large amplitude level for a selected time interval followed by a low-amplitude portion o f substantial duration.

The control potential derived in the pulse gain-control systems of'Figs. l and 3 is applied to tubes of the gradual cutoff type, which preserves the wave shape of the signals translated in the associated signal-translating channels. However, if desired, the controlled tubes may have sharp cutoff characteristics. In such a case, the control potential from the pulse gain-contro1 system may cause all signals below a certain level of the incoming signal, say 50 percent, to be eliminated directly. Where the controlled tubes are of this type, limiter I3 need only clip the upper portion of its input signal to remove the noise components superimposed on the pulse components of the received signal.

For convenience of illustration, idealized wave forms are shown in Figs. 2 and 4. In practical operation the pulse components of the received coded signal are trapezoidal instead of rectangular in form. Limiting `or clipping of such pulse components may tend to cause the limited signal to have pulse widths that vary with the strength of the received signal. An arrangement for obviating this pulse width variation is fully disclosed in copending application Serial No. 597,037, filed June 1, 1945, and assigned to the same assignee as the presentinvention. v

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 modications may bevmade therein without departing from the invention, and it is, therefore, aimed in the appended claims to cover all such changes and modications as fall within the true spirit and scope of the invention.

What is-claimed is: 1. A wave-signal. translating arrangement for translating a modulated signal which may have a, predetermined maximum duration comprising, a sign -translating channel having a predetermined perating characteristic which has a normal value in the absence of said modulatedsignal, means responsive to said modulated signal for deriving a control potential starting early in the duration of said signal and tending to hold over for an interval substantially `greater than said maximum duration, means for utilizing said control potential to adjust said operating rcharacteristic to a value different from said normal value, and means for effectively interrupting said control potential and for restoring said operating characteristic to its normal value after a predetermined time interval at least approximately,

for deriving a control potential starting early inA the duration of said signal and tending to hold over for an interval substantially greater than said maximum duration, means for utilizing said contro1 potential to adjust. said operating characteristic to a value different from said normal value, and means for effectively interrupting said control potential and for restoring said operating characteristic to its normal value after a predetermined time interval greater than said maximum duration.- Y

3. A wave-signal translating arrangement for translating a modulated signal which may have a predetermined maximum duration comprising, a signal-translating channel having a predetermined operating characteristic which has a normal value in the absence of said modulated signal, means responsive to said modulated signal for deriving a control potential starting early in the duration of said signal and tending to hold over for an interval substantially greater than said maximum duration, means for utilizing said control potential to adjust said operating characteristic to a value different from said normal I value, and means for effectively interrupting said maximum duration and having a magnitude determined by the intensity of said modulated signal, means for utilizing said control potential to adjust said'operatingcharacteristic from its normal value to a different value determined by ther magnitude of said control potential, and means for effectively interrupting said control potential and for restoring said operating characteristic to its normal value after a predetermined time in- 11 terval at least approximately equal to said maximum duration.

5. A wave-signal translating arrangement for translating a modulated signal which may have a predetermined maximum duration comprising, a signal-translating channel having a predetermined operating characteristic which has a normal value in the absence of said modulated signal, rectifier meansresponsive to said modulated signal for deriving a control potential starting early in the duration of said signal, tending to hold over for an interval substantially greater than said maximum duration and having a magnitude determined by the value ofsaid modulated signal, means for utilizing said control potential to adjustv said operating characteristic from its normal value to a different value determined by the magnitude of said control potential, and means for effectively interrupting said control potential and for restoring said operating characteristic to its normal value after a predetermined time interval at least approximately equal to said maximum duration.

6. A wave-signal translating arrangement for translating a modulated signal which may have a.y predetermined maximum duration comprising,

\a signal-translating channel having a predetermined operating characteristic which has a normal value in the absence of said modulated signal, means exclusive of said channel and responsive to said modulated signal for deriving a control potential starting early in the duration of said signal and tending to hold over for an interval substantially greater than said maximum duration, means for utilizing said control potential to adjust said operating'characteristic to a value diil'erent from said normal value, and means for effectively interrupting said control potential and for restoring said operating characteristic to its normal value after a predetermined time interval at least approximately equal to said maximum duration.

7. A wave-signal translating arrangement for' translating a modulated signal which may have a predetermined maximum duration comprising, a signal-translating channel having a predetermined operating characteristic which has a, normal value in the absence of said modulated signal, means responsive to the leading portion of said modulated signal for deriving a control potential starting early in the duration of said signal and tending to hold over for an interval substantially greater thansaid maximum duration, means for utilizing said control potential to adjust said op- A erating characteristic to a value diierent from saidnormal value, and means for effectively interrupting said control potential and for restoring said operating characteristic to its normal value after a predetermined time interval at least approximately equal to said maximum duration.

8. A wave-signal translating arrangement for translating a modulated signal which may have a predetermined maximum duration comprising, a 'signal-translating channel having a predetermined operating characteristic which has a normal value in the absence of said modulated signal, means including an energy-storage device to be charged in response to said modulated signal for deriving a control potential starting early in the duration of said signal and tending to hold over for. an interval substantially greater than said maximum duration, means for utilizing said control potential to adjust said operating characteristic to a value diierent from said normal value, and means for discharging said energy.

storage device to interrupt said control potential and restore said operating characteristic to its normal value after a predetermined time interval at least approximately equal to said maximum duration.

9. A wave-signal translating arrangement for translating a modulated signal which may have a predetermined maximum duration comprising, a signal-translating channel having a predetermined operating characteristic which has a normal value in the absence of said modulated signal, means responsive to the leading portion of said modulated signal for deriving a signal pulse, means including an energy-storage device to be charged Vby said signal pulse for developing a control potential starting early in the duration ci said signal and tending to hold over for an interval substantially greater than said maximum duration, means for utilizing said control potential to adjust said operating characteristic to a value different from said normal value, and means for discharging said energy-storage device to interrupt said control potential and restore said operating characteristic to its normal -value after a predetermined time interval at least approximately equal to said maximum duration.

10. A wave-signal translating arrangement for translating a modulated signal which may have a predetermined maximum duration comprising, a signal-translating channel having a predetermined operating characteristic Which has a normal value in the absence of said modulated signal, means responsive to the leading'portion of said modulated signal for deriving a signal pulse of a given polarity, means including an energystorage device to be charged by said signal pulse for developing a control potential starting early in the duration of said/signal and tending to hold over for an interval substantially greater than said maximum duration, means for utilizing said control potential to adjust said operating characteristic to a value different from said normal value, and time-delay means for applying said signal pulse to said energy-storage device with reversed polarity to discharge said energy-storage device to interrupt said control potential and restore said operating characteristic to its normal value after a predetermined time interval at least approximately equal to said maximum duration.

11. 'A wave-signal translating arrangement for translating a modulated signal which may have a predetermined maximum duration comprising, a signal-translating channel having a predetermined operating characteristic which has a normal value in the absence of said modulated signal, means responsive to the leading portion of said modulated signal for deriving a signal pulse of a given polarity, means including an energystorage device to be charged by said signal pulse for developing a control potential starting early in the duration of said signal and tending to hold over for an interval substantially greater than said maximum duration, means for utilizing said control potential to adjust said operating characteristic to a value different from said normal value, and means` including a short-circuited time-delay network for applying said signal pulse to said energy-storage device with reversed polarity to'disclxarge said energy-storage device to interruptv said control potential and restore said `operating characteristic to its normal value after va predetermined time interval at least approxi- 13-w a predetermined maximum duration comprising, a signal-translating channel having a predetermined gain characteristic which has a. normal value in the absence of said modulated signal, means responsive to said modulated signal for deriving a control potential starting early in the duration of said signal and tending to hold over for an interval substantially greater than said maximum duration, means for utilizing said control potential toadjust said gain characteristic' to a value diiierent from said normal valuef'and channel and unresponsive to signals having an intensity less than said predetermined peak-value for deriving a signal pulse of a given polarity from the leading portion of said modulated signal, means including an energy-storage device t-o be charged by said signal' pulse for developing a control potential starting early in the duration of said signal and tending to hold over for an interval substantially greater than said maximum duration, means for utilizing said control potential to reduce the value of said gain characteristic so that the peak value of said modulated signal as applied to said amplitude-selective means is decreased early in the duration thereof to a value less than said predetermined peak value, and a time-delay means for applying said signal pulse to said energy-storage device with reversed polarity to discharge said energy-storage device to interrupt said control potential and restore said gain characteristic to its normal value after a predetermined time interval at least approximately equal to said maximum duration.

14. A'Wave-signal translating arrangement for translating a modulated signal rwhich may have a predetermined maximum duration comprising, a signal-translating channel having a predetermined operating characteristic and effective in the absence of said modulated signal to trans- 14 a normal value in the absence of said modulated signal, means responsive to said pilot-pulse component of said modulated signal for deriving acontrol potential starting early in the duration of said signal and tending to hold over for an interval substantially greater than said maximum duration, means for utilizing said control potential to adjustsaid operating characteristic to a value different from said normal value, and means for effectively interrupting said control potential and for restoring said operating characteristic toits normal value after a predetermined time inlate a quiescent signal representing inherent disv turbances within said translating arrangement, means responsive to said quiescent signal for stabilizing said operating characteristic at a desired normal value, means responsive to said modulated signal for deriving a control potential starting early in the duration of said signal and tending to hold over for an interval'substantially greater than said maximum duration, means for utilizing said control potential to adjust said operating characteristic to a value diierent from said normal value, and means for effectively interrupting said control potential and for restoring said operating characteristic to its normal value after a predetermined time interval at least approximately equal to said maximum duration.

15. A wave-signal translating arrangement for translating a modulated signal which may have a predetermined maximum duration and which includes a leading pilot-pulse component comprising, a signal-translating channel having a predetermined operating characteristic which has terval at least approximately equal to said maximum duration.

16. A wave-signal translating arrangement for translating a modulated signal which may have a predetermined maximum duration and ywhich includes a leading pilot-pulse component comprising, a signal-translating channel having a predetermined operating characteristic which has a normal value in the absence of said modulated signal, means responsive substantially only to said pilot-pulse component of said modulated signal for deriving a control potential starting early in the duration of said signal and tending to hold over for an interval substantially greater than said maximum duration, means for utilizing said control potential to adjust said operating characteristic to a value different from said normal value, and means for effectively interrupting said control potential and vfor restoring said operating characteristic to its normal value after a predetermined time interval at least approximately equal to said maximum duration.

17. A wave-signal translating arrangement for translating a modulated signal which may have a predetermined maximum duration comprising, a iirst signal-translating channel including means responsive to said modulated signal for deriving a control potentialstarting early in the duration of said signal and tending to hold over for an interval substantially greater than said maximum duration, a second signal-translating channel having a predetermined operating characteristic which has a normal value in the absence of said modulated signal, means for utilizing said control potential to adjust said operating characteristic of said second channel to a value different from said normal value, means for applying said modulated signal directly to said first channel and for applying said modulated signal-*to said second channel with a time delay at 'least equal to the delay of said first channel in deriving said control potential, and means for effectively interrupting said control potential and for restoring said operating characteristic of said second channel to its normal value after a. predetermined time interval at least approximately equal to said maximum duration'.

18. A wave-signal translating arrangement for translating a modulated signal which may have a predetermined maximum duration comprising,

' starting early in the duration of said signal and .tending to hold over for an interval substantially greater than said maximum duration, means for y utilizing said control potential to adjust the operating characteristic of each channel to a value different from said normal value, means for` applying said modulated signal directly to said tlrst REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Name Date Wilson Feb. 6, 1940 Number