Showing papers on "Modulation published in 1968"

Detection, Estimation, and Modulation Theory. Part 1 - Detection, Estimation, and Linear Modulation Theory.

Abstract: Detection, estimation and linear modulation theory, Part 1, covering random processes, signal detection in noise and continuous waveforms

Spectral Analysis of Pulse Frequency Modulation in the Nervous Systems

Abstract: Spectral analysis is one of the more important design and evaluation tools available to the communications engineer and it could also be a key to increased understanding of the nervous system. Some results of an analysis of the spectrum of the frequency modulated pulses of the nervous system show that 1) change in average pulse frequency is the likely information-carrying parameter of a neural pulse train, since distortion-free recovery of this variable is possible by simple low-pass filtering, and 2) phase relationships existing between signal components and distortion components of a neural pulse train imply unusual distortion attenuating properties of multiple or duplicate information channels. These results are discussed in light of some known nervous system structures.

Electronically controlled antenna system

Abstract: IN A TACAN BEACON ANTENNA, A MONOPOLE RADIATOR SURROUNDED BY TWO OR MORE CONCENTIC CIRCULAR ARRAYS OF PARASITIC ELEMENTS, WHICH ELEMENTS ARE DIGITALLY INHIBITED IN SEQUENCE IN A PREDETERMINED MANNER, IS USED TO PRODUCE A ROTATING RADIATION PATTERN CAPABLE OF PRODUCING 15 AND 135 CYCLE-PER-SECOND SIGNALS AT A RECEIVER. PARASITIC ELEMENTS ARE INHIBITED BY BEING OPEN CIRCUITED BY DIGITALLY CONTROLLED SWITCHING DIODES. RECIRCULATING SHIFT REGISTERS ARE USED TO INHIBIT PARASITIC ELEMENTS IN THE CIRCULAR ARRAYS TO PRODUCE THE REQUIRED MODULATION RADIATION PATTERN. A COMMON CLOCK IS USED TO STEP SAID REGISTER ALONG TO PRODUCE THE DESIRED ROTATING PATTERN.

Method and apparatus for measuring delay distortion including simultaneously applied modulated signals

Abstract: A common modulating signal is applied to a plurality of carrier signals of differing frequency to provide signals with phase coincident modulation envelopes. These are simultaneously transmitted across transmission circuit being investigated, received at distant terminal, and individually demodulated. Phase separation between demodulated envelopes is ascertained as indication of delay distortion in transmission circuit.

Carrier lifetime measurement of a junction laser using direct modulation

Abstract: A carrier lifetime measurement under lasing conditions using microwave techniques is reported. The direct modulation characteristic of a junction laser is analyzed, based on the rate equations, and a resonance-like phenomenon of the modulated output is calculated at a fixed frequency determined by the parameters of the junction diode. This frequency occurs just before the modulation cutoff frequency of the diode. The minority carrier lifetime in the active region of the junction laser is expressed in terms of this frequency and other parameters. A modulation experiment was performed using a microwave frequency modulated bias pulse current. The resonance-like phenomenon was confirmed experimentally and the carrier lifetime was determined from the analysis presented here.

Performance Monitor Techniques for Digital Receivers Based on Extrapolation of Error Rate

Abstract: There is a need in many digital communication systems to estimate the current digital error rate of the receiver without the use of special transmissions and without interrupting traffic flow. Devices for performing this function have been termed performance monitor units (PMU). As an element of an adaptive communication system, the PMU could be used to determine when adaptive change is needed and, by comparing the error rates which would result from the various available choices of adaptation, to select the best change to be made at any time. This paper describes a PMU technique which is applicable to a wide class of digital modulation methods. Details are given for the cases of noncoherent frequency shift keying (FSK), differentially coherent phase shift keying (PSK), and coherent PSK receivers operating over a fading channel.

Interference suppression in a receiver by envelope variation modulation

Abstract: A nonlinear signal-processing circuit, especially useful in the receiver of a quaternary-phased spread spectrum communication system, for suppressing interfering signals that are stronger than the desired signal and have relatively constant waveform envelopes. The circuit includes an envelope detector combined with an averager and difference amplifier for deriving from the composite received signal a control voltage which is a function of the instantaneous phase difference between the interfering and desired signals. This control voltage and the composite received signal are then multiplied to produce as an output the desired signal with the interfering signal substantially suppressed.

Laser-beam modulation using grating diffraction effects

Abstract: An optical-diffraction modulator, using an electro-optic crystal excited by a periodic array of metallic conductors, is described. The operation of the device is in some ways similar to that of an acoustoelectric modulator; it differs from it in that it has a bandwidth, potentially very wide, which extends from d.c. It may therefore find application as a baseband modulator.

Companded Delta Modulation for Telephony

Abstract: An experimental delta modulation system that appears to satisfy Bell System telephone requirements in the telephone plant environment is described. A significant improvement in signal-to-noise ratio over a large dynamic range has been achieved with a modification that is akin to syllabic companding. It consists in adapting the modulator quantizing step size to the signal level over part of the dynamic range. The development was stimulated by the suitability of delta modulators for low-cost integrated circuits. The implementation is based on repeated use of two standard monolithic integrated circuits: an RTL logic gate and an operational amplifier. Several laboratory models have consistently satisfied Bell System transmission requirements with a bit rate of 96.5 kHz and a companding range of 26 dB. A series of subjective evaluation tests are being carried out at this time to assess listener reactions and to optimize system parameters accordingly. Indications are that a reduction of the bit rate will result from these tests. The delta modulation scheme is economically more attractive than pulse-code modulation (PCM) in telephone applications that require digital coding of the analog signal close to its source and with a minimum of common equipment.

Broadband optical coupling modulation

Abstract: A KD*P internal coupling modulator has been operated in a high-power single-frequency 0.63-micron He-Ne laser similar to that described earlier by Smith. It is shown that distortion in the output due to resonant buildup of energy in the passive cavity modes when the modulation frequency is equal to c/2L can be reduced to an acceptable level. The modulator bandwidth was greater than 700 MHz, and the maximum optical output power was 3.6 mW. For an optical output power of 0.5 mW, the performance index was estimated to be 0.4 mW of RF driving power for each MHz of bandwidth.

Computation of FM distortion in linear networks for bandlimited periodic signals

Abstract: Computations of the distortion generated in passing large-index, frequency-modulated signals through symmetrical single-pole and three-pole bandpass filters are presented. The computation is for a bandlimited periodic modulation signal; noise modulation is simulated by the use of periodic noise samples in a Monte Carlo procedure. The convergence of the Monte Carlo procedure is illustrated for the case of the single-pole filter and the results are in good agreement with measurements. Computations of envelope distortion are also presented. These data give the amplitude-to-phase conversion in the receiver containing the filter to within a constant factor, the constant being the AM/PM conversion coefficient of the limiter.

Correlative Data Transmission with Coherent Recovery Using Absolute Reference

Abstract: A new data-transmission method that has twice the speed capability of the duobinary technique over an identical bandpass transmission medium is presented. Advantages of this method include promising performance and completely digital manner of signal generation, thus considerably reducing the circuit complexity. The system is based on correlative techniques in which the digital encoding forms an integral part of the carrier modulation. The process is sufficiently general to be applicable to both voice anti broadband communication channels.

Ellipsometric method and device

Abstract: An ellipsometric device and method for applying a phase modulation and a polarization direction modulation to a beam of light at two different frequencies and using a polarized parallel monochromatic light beam, a polarization modulator, a phase modulator, and means to angularly displace with respect to each other, an assembly having on one hand a beam polarizer phase and azimuth modulator and on the other hand the sample, an equalizer, analyzer and photoreceiver.

Differential phase modulator and demodulator utilizing relative phase differences at the center of the modulation periods

Abstract: Digital data transmission at a very high bit rate through randomly selected voice-grade telephone lines by the use of a transmitter which includes digital differential angle modulation; and a receiver which includes digital differential angle demodulation is disclosed. Binary data wherein the individual bits are represented by a discrete level format during bit cell times is stored in multibit groups of randomly varying data patterns. Each multibit group is converted from its digital level format to a predetermined phase level format which includes a plurality of different phase, or angle, increments. At the transmitter a divider circuit receives a high-frequency signal which is many times higher than the bit rate of the data to be transmitted, and divides it into an intermediate frequency square wave signal which is still many times higher than the bit rate. The predetermined phase levels representative of each multibit group are compared with divider output taps by a comparison circuit which selectively alters the dividing operation so that an information-representing phase-shifted intermediate frequency signal is emitted. This information-representing phase-shifted signal is filtered and translated down to a low-frequency analog signal which is passed through a narrow band pass communication link exhibiting a linear phase over the band pass width.

Derived clock from carrier envelope

Abstract: DIGITAL DATA TRANSMISSION AT VERY HIGH BIT RATES THROUGH RANDOMLY SELECTED ORDINARY VOICE-GRADE TELEPHONE LINES BY THE USE OF A TRANSMITTER WHICH INCLUDES DIGITAL DIFFERENTIAL MODULATION AND A RECEIVER WHICH INCLUDES A DIGITAL DIFFERENTIAL ANGLE DEMODULATION, TOGETHER WITH A DERIVED CLOCK CIRCUIT AT THE RECEIVER, IS DISCLOSED. THE COMMUNICATION LINK INCLUDES BANDPASS FILTERS WHICH BLOCK SIDEBAND FREQUENCIES LOCATED AT 1/T FROM THE CENTERPOINT, FO, OF THE FILTER, WHEREIN T IS THE MODULATION PERIOD, AND FO IS THE CARRIER FREQUENCY. FOR RANDOM DATA PATTERNS, THE ENVELOPE AT THE RECEIVER, DUE TO BAND-LIMITING, IS PEAKED AT THE MIDDLE OF A CENTER MODULATION PERIOD AND DROPS SUFFICIENTLY TOWARD ZERO AMPLITUDE BETWEEN MODULATION PERIODS SO AS TO CONTAIN STRONG 1/T HARMONICS WHICH PROVIDE FOR CLOCK DERIVATION BY SLAVING A LOCAL OSCILLATOR WITH A 1/T OUTPUT SIGNAL. FOR SOME NON-VARYING DATA PATTERNS, THE ENVELOPE DOES NOT INCLUDE SUFFICIENT RIPPLE FOR CLOCK DERIVATION. AMPLITUDE MODULATION OF THE DIGITAL ANGLE MODULATION SIGNAL AT A PREDETERMINED FREQUENCY IS PROVIDED AT THE TRANSMITTER SO AS TO PRODUCE A SIGNAL HAVING 1/2T SIDEBANDS WHICH ARE PASSED BY THE FILTER AND THUS ARE AVAILABLE AT THE RECEIVER FOR CLOCK DERIVATION.

Modulation control circuits for delta-modulation telecommunication systems

Abstract: A DELTA-MODULATION TELECOMMUNICATIONS SYSTEM CAN BE MADE TO CARRY SIGNALS OF WIDER DYNAMIC RANGE BY PULSEDURATION MODULATING FEEDBACK SIGNALS IN THE TRANSMITTER CIRCUIT AND RECEIVED SIGNALS IN THE RECEIVER CIRCUIT. THE MODULATION SHOULD VARY WITH THE AMOUNT OF INFORMATION CARRIED OR INVERSELY WITH THE FREQUENCY OF REVERSALS IN THE DELTA-MODULATED SIGNAL. A MODULATION CONTROL SIGNAL MAY BE DERIVED BY A CIRCUIT COMPRISING A TWO-STAGE SHIFT REGISTER, THREE GATES, AND AN R-C INTEGRATING NETWORK. SEVERAL PULSE-DURATION MODULATING ARRANGEMENTS ARE DESCRIBED. THESE IMPROVEMENTS CAN BE INCORPORATED IN A COMPACT FORM, USING INTEGRATED CIRCUITS.

Contiguous subcarrier barrage jamming method and apparatus

Abstract: A method and apparatus for providing a radar jamming signal by simultaneously frequency-modulating a voltage-tunable oscillator with a large-amplitude, periodic, sawtooth waveform and a small-amplitude random waveform. The periodic, sawtooth modulation produces a series of radio frequency spectral lines (subcarriers) of nearly uniform amplitude over a frequency range proportional to the peak-to-peak sawtooth amplitude. The spacing between adjacent subcarriers is equal to the fundamental sawtooth frequency. The secondary random modulation added to the primary sawtooth modulation produce simultaneous, random, frequency modulation of each of the subcarriers created by the primary modulation.

Method and apparatus for the recognition of errors at the receiver in a data transmission system

Abstract: An error recognition process for a system in which data is transmitted in a one out of m different modulation characteristics (e.g. frequencies) code and wherein errors at the transmitter, or in the transmission system can cause a plurality of modulation characteristics to exist simultaneously at the receiver. The method of the invention takes advantage of the fact that modulation products outside of the assigned frequency band result when two different modulation characteristics are combined in a nonlinear device. Frequencies outside of the assigned band are detected to furnish an error voltage which blocks the decoded output at the receiver to prevent errors.

Use of field modulation with boxcar integrator to measure relaxation time in electron spin resonance experiments.

Abstract: Field modulation is used with pulsed electron spin resonance apparatus to measure the relaxation time T1 of weak but easily saturable paramagnetic resonances. Both a boxcar integrator and lock-in detector are used to recover the field modulation signal from the noise. The method works best for T1 between about 1 μs and 1/10 of the field modulation period (e.g. approximately 1 ms for 100 cycles) but it may be used to measure longer relaxation times also.

Synthesizing optimal controls for modulated discrete-time systems†

Abstract: The methods of steepest descent and gradient projection are used to solve the two-point boundary value problem associated with the optimal control of open-loop aperiodically modulated discrete-time systems. A comparison of optimal systems employing various combinations of pulse-width and pulse-amplitude modulation is presented. Numerous examples illustrate the diverse nature of the open-loop solutions for different types of modulation.

Improvements in or relating to static inverters

Abstract: 1,166,841. Inverting circuits. PLESSEY CO. Ltd. 11 Jan., 1967 [21 Jan., 1966], No. 2814/66. Heading H2F. [Also in Division G3] A static inverter, of the type in which the third harmonic is eliminated from the output by combining two square waveforms which have the same frequency but are 60 degrees out of phase, is regulated by pulse width modulating each waveform or the combined output by a modulation signal of predetermined frequency and varying the degree of modulation to maintain a predetermined output, third harmonic cancellation being preserved by maintaining a fixed phase relationship between the modulating signal and the combined output. The Figure shows a three-phase arrangement in which the six square waveform outputs of a ring counter 16 are pulse width modulated at 18 by a trigger pulse generator 17 whose square-wave gating signal has its mark/ space ratio varied by a control 21 in accordance with variations of the output voltage of the inverter which is thereby maintained constant. The control 21 advances or delays the leading edge of the square waveform of generator 17 to vary its mark/space ratio. The fixed phase relationship is maintained by using a master oscillator 15 to supply the ring counter 16 and the pulse generator 17. After pulse width modulation the six ring counter outputs are amplified at 19 and then corresponding pairs are combined at 14 to produce a three-phase third harmonic free output which is filtered at 20 to produce a sinusoidal waveform. Transistors may be used as switching elements in the gating circuit 18 whose output may be switched off under overload conditions by protection circuits 22. Typical waveforms before and after pulse width modulation are illustrated and discussed, Fig. 1, 2 and 3 (not shown).

Computor Simulation of Narrowband Systems

Abstract: —Any narrowband signal can be represented by two low-frequency functions, containing only frequencies lower than the bandwidth, which represent the envelopes of the in-phase (cosine) and quadrature ( sine) components of the carrier frequency. To obtain the transient response of a narrowband system efficiently by computer simulation, the system can be represented by a low-frequency equivalent system, avoiding time-consuming direct simulation of carrier frequencies. This paper presents techniques by which a wide variety of narrowband systems, expressible mathematically as block diagrams, can be converted into block diagrams consisting only of low-frequency functions. The resulting low-frequency equivalent systems can be simulated on either an analog or digital computer by well-known techniques. Although the low-frequency equivalent representation presented here includes an extension of the bandpass low-pass analogy, it is not subject to many of the restrictions normally applied to this analogy. It is not necessary that the modulation be simple AM, that the filtering be symmetrical, or that only the envelope velope of the output be of interest.

Synchronous pulse transmission system with selectable modulation mode

Abstract: A modulator for modulating a digital carrier with digital information pulses features logic gates, inverters and a switch. The switch has three positions for connecting the circuit into three different configurations for achieving AM, FM and PM. A digital filter is used in conjunction with the modulator for attenuating any possible undesired sidebands resulting from the modulation.

Dual pilot control for re-phasing a signal carrier

Abstract: In a communication system transmitting both the lower sideband of a modulated signal and the carrier, the phase shift of the recovered carrier relative to the signal spectrum can be adjusted to improve signal demodulation. Two pilot frequencies, one higher than and one lower than the signal frequencies to be transmitted and having a known phase relationship are mixed with the signal for modulation by the carrier and transmission. In the receiver, the signal is demodulated with a recovered carrier signal and the pilot frequencies are phase compared to determine the magnitude and direction of their relative phase shift. The recovered carrier signal is then phase shifted to reduce the relative phase shift of the pilot frequencies to within a limited range.

Wideband frequency translating circuit using balanced modulator

Abstract: A WIDEBAND FREQUENCY TRANSLATING CIRCUIT ESPECIALLY SUITED FOR CONVERTING, EN MASSE, TELEVISION AND FM SIGNALS IN A GIVEN FREQUENCY RANGE TO A HIGHER FREQUENCY RANGE FOR TRANSMISSION OVER A MICROWAVE LINK. BRIEFLY, THE FREQUENCY TRANSLATING CIRCUIT UTILIZES A MODULATOR COMPRISING ONE OR TWO VARACTOR DIODES COUPLED TO A FIRST PAIR OF CONJUGATE ARMS OF A BICONJUGATE HYBRID NETWORK. MICROWAVE ENERGY IS APPLIED TO A THIRD ARM AND THE MODULATED MICROWAVE ENERGY IS COUPLED OUT OF THE FOURTH ARM. THE WAVE ENERGY CORRESPONDING TO THE TELEVISION AND FM SIGNALS TO BE TRALSLATED IS DIVIDED IN A POWERDIVIDING NETWORK AND APPLIED TO THE DIODES IN OPPOSITE ARMS IN ANTI-PHASE RELATIONSHIP. THIS MODULATING SIGNAL CAUSES THE EFFECTIVE IMPEDANCE OF THE DIODES TO VARY THEREBY MODULATING THE MICROWAVE ENERGY PROPAGATING IN THE DIODE-CONTAINING CONJUGATE ARMS. APPROPRIATE FILTERING MEANS CAN BE PROVIDED AT THE MODULATOR OUTPUT FOR ELIMINATING THE CARRIER AND LOWER SIDEBAND MODULATION COMPONENTS.