Showing papers on "Pulse-frequency modulation published in 1979"

Temporal modulation transfer functions based upon modulation thresholds

Abstract: The detectability of amplitude modulation in the absence of spectral cues provides a quantitative description of temporal resolution for steady‐state signals with relatively small amplitude changes. Modulation thresholds for sinusoidally amplitude‐modulated wideband noise were measured as a function of modulation frequency. The resulting ’’Temporal Modulation Transfer Function’’ (TMTF) shows a lowpass characteristic for modulation frequencies below about 800 Hz. The lowpass characteristic is extended up to approximately 2 kHz when the increment in average power produced by modulation is eliminated. The important parametric effects are summarized as follows: (1) TMTFs are independent of overall level, except at very low intensities; (2) the time constant indicated by the TMTF decreases as the center frequency of the band‐limited, modulated noise is increased; (3) modulation thresholds generally decrease with increasing duration of modulation, particularly at low modulation frequencies; (4) when the carrier is gated for the duration of modulation, the TMTF shows a highpass segment at low modulation frequencies. Although the TMTFs are not directly consistent with the attenuation characteristic of a simple lowpass filter, a model which incorporates such a filter, with a time constant of 2.5 ms, describes the entire TMTF and also describes the modulation functions obtained with square‐wave and pulse modulation. The wide bandwidth of initial filtering indicated by the model raises the important question of the role of peripheral filtering in determining the detectability of high‐frequency modulation.

Amplitude and frequency modulators using a switchable component controlled by data signals

Abstract: A modulated signal source derives its modulation information from digital data held in a data store. The digital data is arranged to operate a switch which in the case of amplitude modulation produces pulses of carrier frequency and in the case of frequency modulation introduces phase transitions into a carrier frequency. The use of the digital data and the switch enables the modulation characteristics of the signal source to be exactly predictable and reproducible and it is not degraded by non-linearities of the kind introduced by conventional mixers.

Scattering by linearly vibrating objects

Abstract: The scattering problem for a plane wave incident upon a perfectly conducting linearly oscillating object is investigated both theoretically and experimentally. The theoretical analysis, accurate to order v/c where v and c axe the velocities of object and light, respectively, shows that the target oscillation changes the scattered far field of a motionless target only in phase. The oscillation is assumed to be periodic, and this period is shown to be impressed on the scattered field. Spectral analysis of the modulation shows that the power distribution varies with the shape of the motion, wavelength of the incident field, and the magnitude of the projections of the oscillation in the direction of incidence and receiver. Power spectra have been calculated for square, triangular, and sinusoidal target motion and, in general, the power content in the higher harmonics is found to increase with cartier frequency and magnitude of oscillation. For backscattering from an object moving sinusoidally along the direction of incidence, the power in the first harmonic is shown to exceed that at the carrier frequency when d > 0.23\lambda where d is the magnitude of the oscillation. These calculations are shown to agree with experimental measurements of the phase modulation of the field scattered from a vibrating disk at the X -band. Experimental results were obtained with continuous wave backscatter equipment at 10 GHz that utilized separate tunnel antennas for transmitting and receiving. The receiving section of this equipment was modified to separately display phase modulation and amplitude modulation characteristics of the backscattered signal in both time and frequency, as well as characteristics of the overall modulation envelope. Phase modulations introduced by target oscillations as small as \pm 0.001 in were readily detected, as were amplitude modulations of a few percent.

Method and apparatus for modulating a phase locked loop

Abstract: A phase locked loop provides frequency modulation over an extended frequency range by summing a modulation signal with the loop signal at two separate points within the loop. The modulation signal is directly applied to the control input terminal of the voltage controlled oscillator. In addition, the modulation signal is processed to compensate for the transfer functions of loop components, and the processed signal is summed with the loop signal at an additional point between the output terminals of the phase detector and the lowpass filter of the loop. The processing of the modulation signal consists of preshaping of the signal to compensate for the transfer functions of loop circuitry located between the voltage controlled oscillator and the summing junction.

A system for driving a motor by a pulse width modulation inverter

Abstract: A system for driving an alternate current motor including a pulse width modulation inverter having the two-range driving characteristics, wherein the motor is driven by the pulse width modulation output having a simulated sine wave form at the speed lower than the base speed of the motor and by the pulse width modulation output having a rectangular wave form at the speed higher than the base speed of the motor.

A New Optical Communication System Using the Pulse Interval and Width Modulated Code

Abstract: This paper proposes a new optical communication system using the Pulse Interval and Width Modulated Code. It is constructed as combinations of pulse width and interval. Then it is easy to understand that the transmission capacity of this Code is bigger than those of Pulse Width Modulation and/or Differencial Pulse Position Modulation.

Minimizing pattern effects in semiconductor lasers at high rate pulse modulation

Abstract: This paper deals with analytical and experimental work related to modulation of a semiconductor laser used in high bit rate communication. The approach is based upon minimizing the charge storage effect by a proper choice of the area of the modulating pulses and the bias current. The concept of using additional current pulses to probe for variations in electron density between pulses is investigated. The primary limitation on bit rate is found to be the ability to generate laser drive pulses free of ringing or similar transients. This and the 300 ps pulsewidth, an experimental constraint, limit the bit rate to about 1 Gbit/s. However, by using this approach it appears that bit rates considerably higher than 2 Gbits/s could be reached with sufficiently accurate control of drive pulse shape. It is found that the laser bias and the current pulse area had to be controlled within 1 percent and 10 percent, respectively.

Digital majority noise filter for bi-level data reception

Abstract: Apparatus for filtering high frequency noise pulses from alternating analog data of a frequency F, which includes means to convert the analog signal to a square wave bi-level signal, sampling the square wave signal at a clock frequency of at least 8F, loading the sampled signals into a digital shift register at the clock rate, reading out in parallel at least the last three samples, and passing said samples to a majority gate, which outputs a signal representing the majority polarity of the three signals read. The output of the majority gate is then applied to a latch in synchronism with the clock signal, which converts it back to a square wave signal representing the noise filtered version of the input signal.

Method and apparatus for quadriphase-shift-key and linear phase modulation

Abstract: A submultiple (30Fl) of an S-band transmitter output frequency (240Fl) is divided equally between a linear phase modulation branch and a QPSK modulation branch. The linear modulation branch includes a multiplier (X7) to increase the carrier frequency to a level (210Fl) which, when combined with the carrier in the QPSK branch in an up-converter (utilizing a mixer at the input thereof followed by a bandpass filter), produces the transmitter output frequency. This allows the QPSK modulator to operate at one-eighth of the output frequency where repeatable and precisely controlled modulation can be easily achieved. This also allows linear phase modulation at one-eighth the output frequency where low modulator deviation and good linearity can be easily maintained.

Modulation strategies of three phase PWM inverters: Analysis and comparative study

Abstract: Presents a systematic study and analysis of the various modulation strategies for three phase pulse width modulated (PWM) inverters. Analytical expressions are derived to obtain harmonic components of output voltages for duty ratio, sine, triangular and step modulation. A comparative study of the merits and demerits of the various modulation technique is presented. The effects of ratios of carrier and reference frequencies, and the instant of synchronisation are investigated. Use of a particular modulation strategy for a particular application is discussed.

Frequency modulators with compensation for variations in modulation sensitivity

Abstract: In a frequency modulation system, the frequency modulation sensitivity of an oscillator is itself a function of the carrier frequency of the oscillator. The frequency modulation sensitivity is measured and stored for particular carrier frequencies, and subsequently used to control the amplitude of the modulation signal, so that when a frequency modulation signal is fed to the oscillator, a frequency deviation is obtained which is accurately related to the amplitude of the modulation signal.

Fiber Optic Video Transmission System Employing Pulse Frequency Modulation

Abstract: A nonlinear analog modulation scheme, Pulse Frequency Modulation (PFM), is highly amenable to fiber optic transmission, attaining performance characteristics which are attractive in the context of fiber optic tether cables between undersea vehicles and their support platforms. PFM, contrasted with traditional fiber optic modulation techniques, is shown to exhibit superior characteristics for video bandwidth, long haul transmission. A specific hardware realization which employs PFM is presented, and its operating characteristics discussed.

Frequency modulator having linearized operation

Abstract: A frequency modulator comprising an oscillator the output frequency of which is dependent upon the amplitude of a modulating signal, modulating signal control means via which the modulating signal is fed to the oscillator to produce a corresponding frequency modulation on the output signal from the oscillator, a discriminator responsive to the frequency modulation for producing a corresponding amplitude signal, and a comparator responsive to the corresponding amplitude signal and to the modulating signal for providing a control signal which is fed back to control the gain provided by the signal control means so as to maintain constant the amplitude of the amplitude signal with respect to the modulating signal, whereby operation of the modulator is linearized.

Instrumentation devices using synchro-resolver drive circuitry

Abstract: Circuitry for producing the signals necessary for driving and controlling a synchro-resolver is disclosed. The circuitry includes a reference generator (84) which is driven by an AC reference signal and thus, the resulting output DC reference voltage on line (82) is locked to the AC reference signal. The DC reference voltage is then combined with a computer generated digital command signal by a MDAC (Multiplying Digital to Analog Converter) (74) to provide a control signal which varies around a selected reference level. A pulse-width modulator (112) provides a high frequency square wave output which square wave is pulse-width-modulated by the AC reference voltage. The pulse-width-modulated high frequency square wave is then provided to an amplitude modulator circuit (106) where the high frequency square wave is itself amplitude modulated by the control signal. The output of the amplitude modulator is then passed through a four-pole, low pass filter (114) to obtain an AC amplitude modulated signal which has had substantially all of the high frequency components eliminated. The AC amplitude modulated signal is then provided to a power amplifier (116) which in turn drives one of the resolver coils (117).

Detection of amplitude modulation

Abstract: The detection of frequency modulation at high modulation frequencies seems to be based upon detection of the first lower modulation sideband in the presence of the carrier as masker. This conclusion followed from a series of interleaved experiments on modulation detection and sine tone masking. [W. M. Hartmann, J. Acoust. Soc. Am. 63, S66(A) (1978)]. The present paper reports a similar combined study of amplitude modulation detection and masking. The AM detection experiment used an 80 dB. 1000 Hz carrier with high and low modulation frequencies. The masking experiment used an 80 dB, 1000 Hz masker and a target tone with frequency equal to a sideband frequency from the AM experiment. Each experimental run consisted of an AM detection half and a masking half. Both halves employed a 2IFC staircase method. The results for three subjects show that for modulation frequencies of 200, 150, and 100 Hz, AM detection threshold occurs when the lower modulation sideband is at masked threshold. For modulation frequenci...

Analysis and Design of Pulse Ratio Modulated Feedback Control Systems

Abstract: An exact method of analysis is presented for a class of pulse-modulated feedback control systems which can be modeled by a multiple-loop nonlinear feedback system The nonlinearity has a hysteresis characteristic By means of the Tsypkin-Hamel criterion, suitably modified, a set of equations is obtained, determining the switching frequency, duty cycle, and steady-state dc error Based on the graphical form of these equations, a design procedure is set forth Specific cases have been examined and peculiar phenomena are evidenced; experimental data verify both the chosen model and the suggested procedures A simplified pulse ratio modulator is also presented

DC power line with superimposed information transmission - has amplitude demodulator recovering square pulse DC modulation frequency

Abstract: D.C. power is transmitted from a station lift of the line L to a distant consumer right of the line L over two conductors, (1, 2) which are at the same time used to transmit information. The d.c. source (3) supplies the power and a switching transistor (6), controlled by a pilot transistor (7) superimposes square pulses on the d.c. across the resistor (4). The receiver station includes an a.c./d.c. converter (9) and a d.c./a.c. converter (8). The modulation frequency of the information signal is recovered by an amplitude demodulator (10) consisting of an optucoupler (11). This is controlled by a pulse amplifier (12, 14, 15, 16). A trigger (18) feeds the output to a discriminator (19).

Correlation Measurement by Delta-Sigma Modulation

Abstract: Details of the design and the underlying principle of a correlator using delta-signal modulation are presented in this paper. It is shown that the circuit components involved are readily available and inexpensive. This is achieved by using digital delay and analog switching. With the adjustment of the clock frequency, the correlator can be used for input signals of different frequencies.

Discriminator circuit for frequency modulation receivers

Abstract: A frequency modulation receiver uses a low intermediate frequency (IF) signal for good image frequency rejection. The intermediate frequency signal is discriminated (or demodulated) after amplitude limiting the intermediate frequency signal by doubling the limited signal and providing pulses whose average value represents the modulating information. The pulses are applied to a low pass filter which rejects the doubled frequency signal relatively easily.

Optical coherence modulation by two ultrasonic waves

Abstract: Some theoretical discussions are made of a coherence modulation function formulated in the presence of two plane ultrasonic waves The modulation function is dependent on whether or not a definite

Ranging radar including a modulating reflector

Abstract: A ranging radar of the radio frequency (RF) frequency modulated-continuous wave (FM-CW) type transmits an RF FM-CW signal to a reflecting surface at an unknown range R from the radar. The reflecting surface reflects the signal to a modulating device. The modulating device further modulates the signal at a frequency F which is high in comparison to the modulating frequency of the FM-CW signal. The further modulated signal is transmitted by the device to the reflecting surface and back to the ranging radar where it is subtractively mixed with a sample of a transmitted signal. The mixed signal is at frequency F amplitude modulated by a beat frequency, the period of which corresponds to range R. The frequency F is removed from the mixed signal leaving the beat frequency signal from which is determined range R.

Recovery and demodulation of a pulse width modulation encoded signal recorded on magnetic tape

Abstract: A method of demodulating a pulse width modulation encoded analog signal wherein the analog signal is retrieved from individual pulse width modulation cycles. A method of sampling and outputing the retrieved analog signal only if missing pulse detectors confirm that the pulse width modulation cycle was valid. And a method generating a second but inverted play-back signal permitting use of two identical pulse width modulation transition descriminators-detectors.

Wideband frequency modulation of frequency synthesisers

Abstract: Two-point frequency modulation gives a flat frequency response irrespective of the loop cutoff frequency of a p.l.l. digital frequency synthesiser. The spurious modulation components otherwise generated are also then suppressed. The modulation index is typically limited to Nπ where N is the divider ratio.

Apparatus and method for generating chorus and celeste tones

Abstract: The operation of the chorus generator of FIG. 3 may be summarized as follows. The generation of a realistic chorus tone depends upon the simultaneous amplitude and phase modulation of a tone signal which initially has little or no choral characteristics. When a tone signal generator is so modulated, the derived audio tone from a loudspeaker will exhibit choral characteristics. A random low frequency signal generator serves as an input to both the amplitude and phase modulation channels. The amplitude modulation signal is merely a suitably delayed replica of the low frequency signal. The phase modulation signal is derived from the low frequency signal by first modifying its amplitude excursions by means of a function generator and then filtering the derived signal by means of a suitable non-minimum phase shift filter.

Effect of Random Frequency Modulation on ECG Power Spectra

Abstract: Electrocardiographic signals are an example of biological signals whose fundamental characteristics may be altered by environmental factors Frequency modulation due to the influence of respiration and other factors may alter the signals and affect the characteristic power spectrum Here the effects of random frequency modulation on ECG power spectra are examined in two cases: when there is random phase modulation in the periodic Fourier series model and when the consecutive cycles for a given sequence of beats deviate from periodicity due to random variation in the fundamental frequency about its mean It is concluded that the differential effects of random frequency modulation on the power spectrum can be detected and its contribution defined Thus, the underlying power spectrum of identical signals with and without random phase and frequency modulations can be defined

Bandwidth limitations due to harmonic distortion in single-mode optical fibers

Abstract: The bandwidth of the single-mode fiber is discussed for the intensity modulation and detection system provided that the spectral width of the light source is much less than the modulation bandwidth. The harmonic distortions reduce the bandwidth by the factor 0.5 to 0.1 compared to the amplitude modulation (AM) system.

Milliwave Fabry-Perot tuning and modulation by electrically variable external reactance

Abstract: Fast frequency modulation of millimetric radiation in an open resonator is described. The frequency variation is obtained by means of a lumped electrically variable external reactance. The maximum modulation depth obtained is 30 kHz peak-peak. The possible applications to far-infrared lasers modulation are discussed.

Normalization method and apparatus used when quantitatively measuring the reception quality of a received frequency-modulated ultrashort-wave signal

Abstract: A frequency-modulated ultrashort-wave signal is received, but due to wave-reflection phenomena from physical bodies reflecting towards the receiving antenna is amplitude modulated, this amplitude modulation being dependent upon frequency. Derived from the frequency-modulated signal is a frequency-deviation signal indicating its instantaneous frequency deviation, and also an amplitude-indicating signal indicating its instantaneous amplitude. These can be fed to the x- and y-inputs of an oscilloscope for display of an amplitude versus frequency curve used to generate a quantitative characterization of reception quality, the oscilloscope screen being provided with a horizontal reference axis. In order that the horizontal reference axis implied by such curve stay in register with that on the screen, even during rotation of the receiving antenna, the amplitude-indicating signal is normalized with respect to the reflection-free amplitude value which the frequency-modulated signal would have in the absence of these wave-reflection phenomena. This is accomplished by applying the amplitude-indicating signal to a clocked amplitude regulator, which is clocked only when the frequency-deviation signal indicates substantially zero frequency deviation of the received frequency-modulated signal.

Wide-band spectrum analysis with area modulation.

Abstract: Nonlinearity of the film characteristics is a major problem in optical spectrum analysis with density modulation. The problem of nonlinearity can be avoided by using area modulation due to its binary recording format. The feasibility of using area modulation for wide-band signal analysis [ ThomasC. E., Appl. Opt.5, 1782 ( 1966)] is demonstrated. The results obtained with area modulation is shown to be similar to that of density modulation. However, area modulation requires a larger system space. Therefore, the available space–bandwidth product for a given system size is smaller with area modulation than with density modulation.

A new family of low-delay FM detectors

Abstract: Describes a new family of FM detectors having extremely low delay with excellent sensitivity. It is achieved by the use of zero group delay circuits, balance at RF, quasi synchronous detection, and carrier cancellation. The components are compatible with integrated-circuit technology. The performance of the detectors is analyzed for both narrow- and wide-band modulation conditions indicating low distortion under normal operating conditions. Advantages are indicated over the conventional limiter-discriminator for sine wave interference conditions. Realization of the detection is discussed, and performance results of a working model are shown.