Showing papers on "Pulse-frequency modulation published in 1969"

Pulse compression by means of linear-period modulation

Abstract: In applications where large time-bandwidth products and high target speeds combine, linear FM pulse-compression systems used in radar or sonar suffer considerable losses in performance. This paper deals with the problem of wide-band signal optimizintion for the purpose of minimizing signal degradation resulting from Doppler distortion effects. The equation for the instantaneous frequency of a Doppler-transformed signal is derived. The optimum frequency-modulation law is then shown to be the linear period modulation (it can be with equal rights called hyperbolic frequency modulation or logarithmic phase modulation). It is interesting to note that some kinds of bats use this type of signal in their "sonar." Exact and approximate expressions for the spectrum of a linear-period-modulated rectangular pulse are given, and the shape of the compressed output pulse is considered. Signal degradation due to Doppler distortion is shown to be negligible in the case of linear-period-modulation pulses. The influence of pulse envelope on the compressed signal waveform is discussed, and envelope-optimization examples are presented. A possibility for active generation of the optimum signal is mentioned. Significant properties of linear FM and linear-period-modulation pulse compression systems are compared.

Switching of phase-locked states in the intracavity phase-modulated He-Ne laser

Abstract: It is known that there exist two solutions for the He-Ne laser phase locked by synchronous internal phase modulation. One corresponds to a phase difference between adjacent modes of even integers of π (even state) and the other to odd integers of π (odd state). Although their frequency power spectra in general look similar, they appear in the time response as two different sets of pulse trains 180° out of phase with respect to each other. Of the two, for a given set of conditions, it has not yet been possible to predict which state will oscillate. In our observations we find that, if the modulation frequency is fixed slightly higher than the average axial-mode spacing near the line center, the two states can be controlled by varying the amplitude of the modulation signal, resulting in a switching action between the two states. Furthermore, we find that in a narrow region of "detuning" and in a small range of modulation amplitudes, both states oscillate simultaneously. The above results were analyzed by considering the asymmetry in the frequency characteristics of the gain medium due to the presence of the isotope Ne22in the He-Ne mixture. Based on this fact and the concept of "supermode" competition, we give a physical explanation for the observed behaviors. This is supported by the absence of amplitude-dependent switching in a He-Ne tube containing only pure isotope Ne20. We observe also in a He-Ne tube containing 75% Ne20and 25% Ne22the dominance of one state over the other; this result is consistent with the qualitative theory given.

Delta modulation granular quantizing noise

Abstract: We present a statistical analysis of a single integration delta modulation system in which slope overload effects are negligible. In defining the delta modulation signal ensemble, we identify a binary phase parameter and show that when this parameter is random, the signal statistics are stationary, provided the input is stationary. Thus the delta modulation correlation functions depend on a single time variable and have Fourier transforms that are the power spectra of the delta modulation signals. After deriving the delta modulation correlation statistics and power density spectra, we use these functions to investigate the properties of the delta modulation granular quantizing noise. We demonstrate the ratio of input signal power to the quantizing noise power of three signals that approximate the system input. These signals are the integrated delta modulation signal, the signal at the output of the ideal low-pass interpolation filter usually considered in delta modulation studies, and the signal at the output of the optimum interpolation filter. We determine the properties of this filter by referring to the derived spectral density functions.

Digital-to-analog converter utilizing pulse duration modulation

Abstract: Described is a novel digital-to-analog converter employing pulse duration modulation techniques, and wherein the desired analog signal is derived by integrating pulses of short duration and relatively high repetition rate rather than longer pulses of lower repetition rate. This materially reduces the ripple content of the filtered pulses and reduces the requirements of the lowpass filter connected to the output of the converter.

Device for the transmission of rectangular synchronous information pulses

Abstract: A system for the transmission of rectangular synchronous information pulses from an information source to an information consumer within a prescribed frequency band in which the information pulse is in coincidence with different pulses from a series equidistant clock pulse generator, in which system use is made of a switching modulated device for the direct modulation of rectangular information pulses on to a rectangular carrier oscillator. A band-pass filter and a correction circuit follow the switching modulation device for the suppression of unwanted modulation products generated in the switching modulation device.

Analog signal modifying apparatus

Abstract: In an electrolytic paper recorder of electric signals, an analog signal is converted by a voltage controlled oscillator to a series of pulses with rises spaced in inverse proportion to the analog signal amplitude. The spaced rises trigger a pulse generator whose output is a corresponding series of constant amplitude marking pulses with a spatial density proportional to the original signal amplitude. The marking pulses are applied to the blade and helical electrodes of the recorder through a current starved amplifier which adjusts the pulse amplitude to compensate for random variations in the resistance of the electrolytic recording paper between the marking electrodes. The width of the marking pulses may be varied by a variable current source for the pulse generator so as to compensate for the nonlinear gamma characteristic of the paper.

Variable frequency oscillator and modulator circuits including colpitts transistor and feedback transistor

Abstract: The basic variable frequency oscillator circuit includes a transistor connected in a Colpitts configuration. An effective tank circuit capacitance is varied in accordance with a control signal to vary the circuit oscillation frequency. When the effective capacitance is provided by the transistor base-emitter capacitance, the frequency variation may be achieved by varying the transistor emitter current or the collector-base voltage. Alternatively, the effective capacitance may be varied by varying the transconductance of a second transistor coupled in a feedback arrangement with the Colpitts transistor. Frequency modulation may be achieved when a modulating voltage is used as the control signal. Circuit variations involving phase locking of the feedback employing embodiment onto an input signal include a frequency demodulator, a phase modulator and an amplitude modulation limiter. Further variations include a harmonic signal generator and frequency multiplier/divider circuits.

Signal recovery system utilizing amplitude comparison at the beginning and end of a bit period

Abstract: Readback signals from a magnetic media are characterized by having signal components respectively with a frequency F and a double frequency 2F with shifts between such signal components indicating recorded data. Usually, the lower or F frequency signal component has a greater amplitude than the 2F frequency signal. In the recording of binary digital data, a bit period of recording is defined as equal to the wavelength of the 2F signal component. Higher frequency harmonics may be used as the high frequency component wherein the bit period is an integral number of wavelengths of such higher frequency signal component. For data signal recovery, the signal amplitude at the beginning of a given bit period is compared with the signal amplitude at the end of such bit period. If the amplitude comparison shows a substantial difference in amplitude, then the first signal component is indicated; whereas, if the amplitudes are substantially similar, the second or higher frequency signal component is indicated.

Second and third order modulation terms in the distortion produced when noise modulated FM waves are filtered

Abstract: This paper is concerned with the distortion produced in a frequency modulation wave when it passes through a filter. The phase or frequency modulation representing the signal is assumed to be a band of gaussian noise. The main result is an expression for the power spectrum W Θ (f) of the output phase angle Θ(t). This expression holds for any filter, contains all of the distortion terms due to second and third order modulation, and is suited to computer evaluation. It is useful in many cases, but it has the shortcoming of not containing any modulation terms higher than the third order. A second result is an approximation to W Θ (f), based on log (1 + x) ≈ x (that is, a “first-order” approximation), which is encountered in the derivation of the main result. Although it does not contain all of the second and third order modulation terms, it does contain higher order modulation terms which may give most of the distortion in some cases. The results given here are compared with those obtained earlier.

Pulse-frequency modulation and dynamic programming

Abstract: The application of dynamic programming to pulse-frequency modulated (PFM) control systems is discussed. In the PFM systems considered the control function consists of a series of standard pulses. Because, in general, the peformance index is not Markovian, which is a requirement for the application of dynamic programming, a restriction is imposed upon the control function. This restriction, which specifies the allowable instants of time where pulses may occur, may cause the resulting control function to yield a less desirable performance index than the one obtained with a control function derived by means which do not impose this restriction, i.e., modified maximum principle [8], [9]. An example belonging to a class of systems in which the equations are separable and linear with respect to the state variables, with no final value constraints is presented. It is shown that for this class of systems the optimum control function is independent of the initial values of the state variables. Consequently, the search for the optimum control function is simplified.

Afc system for microwave energy sources

Abstract: The output of a microwave oscillator is mixed with an FM modulated crystal controlled reference frequency to develop a difference frequency. The resulting difference frequency is filtered in a low pass filter having a predetermined slope and detected. The detected modulation signal has a phase angle according to whether the output signal is greater or less than the reference signal. The detected modulation signal is compared in a phase sensitive discriminator with the reference modulation signal to develop a DC signal which is applied to the microwave oscillator to change the frequency thereof.

Periodic cycles in integral pulse frequency modulation (IPFM)systems

Abstract: Periodic cycles of bounded amplitude may exist in a closed-loop system consisting of an integral pulse frequency modulator and a linear element. This paper develops theoretically the conditions for the existence of these cycles, explicit formulae for their periods, and a criterion for their stability. Cases are examined where the linear element is both singular and non-singular, and also where the ‘equivalent linear system’, i.e. one wherein the modulator is replaced by a unity transmission link, is both singular and non-singular. Discussion is made on the possibility of predicting the form of the cycles, once determined that they may exist. The theoretical conclusions are supported by experimentally observed cycles in such systems simulated on an analogue computer.

Bulk negative resistance device operated in a relaxation mode

Abstract: A bulk GaAs semiconductor negative resistance device has been operated in a relaxation mode analogous to tunnel diode operation. The output consists of a closely-packed train of narrow, high-voltage pulses. The circuit consists of an inductor in series with the parallel combination of the active device and the load resistor, driven by a low impedance generator. By shunting the device with a suitable load resistor, avalanche breakdown, which would normally occur, is prevented and the generated voltage pulses are impressed directly across the load. The circuit is constructed in a coaxial line and operates without a cavity or other tuning elements. By driving this circuit with a pulse of about 100 ns duration, an output pulse train having an amplitude of over 200 V (10 times Gunn threshold) was obtained across a 3000 Ω load. The output pulses were of about 1 ns duration and spaced about 10 ns apart. Since the pulse spacing varies with the amplitude of the drive voltage, pulse frequency modulation is possible. The ramifications of a time-variant characteristic caused by the formation of a traveling Gunn domain during part of the cycle are discussed.

Combined pulse-modulation scheme for feedback systems

Abstract: A new form of combined pulse modulator using integral pulse-frequency modulation and pulse-width modulation is proposed in the letter. Using this modulator in a feedback system, a nonlinear discrete equivalent system is established, and a method for computation of state trajectories is indicated. It is also shown that systems having pulse-frequency modulation only or pulse-width modulation only reduce to special cases.

FM modulation of mm-wave IMPATT oscillators with PCM baseband pulses

Abstract: The modulation sensitivity, linearity, and FM noise performance of a mm IMPATT oscillator is described. It is shown that when the oscillator is FM modulated with short rise time pulses, the detected FM pulses show almost no distortion compared to the original modulating baseband pulses.

Frequency dividing and multiplying circuits using a sampling technique

Abstract: In a frequency division circuit a sampling pulse occurring at a period of IS FORMED FROM AN INPUT SIGNAL OF FREQUENCY F, THE SAMPLING PULSE IS USED TO EFFECT SAMPLING OF THE INPUT SIGNAL TO PROVIDE AN OUTPUT SIGNAL HAVING A REDUCED FREQUENCY AND A WAVEFORM SIMILAR TO THAT OF THE INPUT SIGNAL. To effect frequency step-up a signal of the reduced frequency produced by the frequency division circuit is compared with a stable reference frequency in a comparator to provide a control signal which is used to control a controlled oscillator such that the reduced frequency and the reference frequency coincide each other.

Intelligence transducing beam modulation method and apparatus

Abstract: Image intelligence signals to be transduced for display are converted to a pulse width modulated signal including pulses whose widths are varied in accordance with the image intelligence signal strength The pulse width modulated image intelligence signal is coupled to switch a transducing beam between selected high and low intensity levels at the rate of the pulse width modulated image intelligence signal The transducing beam is maintained at one of the selected intensity levels for the duration of the width of the pulses and at the other level for the interval between consecutive pulses

Parametric amplification and oscillation using an inverted maser material

Abstract: Experimental results are reported demonstrating the possibility of achieving parametric gain in an inverted paramagnetic medium. In this case the parametric pump frequency may be lower than the signal frequency. The authors used chromium-doped rutile as the active material, a pump frequency of 150 MHz, and a signal frequency of 4.25 GHz. The parametric effect is strongly supported by adjusting the idling circuit for high master gain.

Induction coupled amplitude modulation system

Abstract: A system for coupling the output of a modulating amplifier to a radio frequency amplifier, requiring no blocking capacitor and utilizing separate modulation transformer and modulation reactor units to isolate the modulation transformer from heavy direct currents In one embodiment, the system includes an auxiliary modulation transformer for simultaneous modulation of multiple electrodes in two or more RF amplifier stages

A Class of Signals for Analog Telemetry over a Coherent Channel

Abstract: This paper proposes and studies a class of signals which generalize frequency position modulation (FPM) and pulse position modulation (PPM). The generalization adds a degree of freedom analogous to a duty factor. Varying this quantity has an effect similar to that of varying the time-bandwidth occupancy in an FPM or PPM system, but it does not significantly increase the channel occupancy. The mean-square error is studied under large signal-to-noise ratio conditions and in the threshold region. We find that the additional degree of freedom allows us to trade between performance in these two ranges of signal-to-noise ratio. The nature of the signals, and their error behavior make them well suited to adaptive telemetry over a coherent channel. Small degrees of channel incoherence are considered and shown to produce only a small degradation in performance.

Investigation of the stability of control systems with double (frequency and width) pulse modulation by the direct lyapunov method

Abstract: : Discussion is based on a typical control system comprised of a continuous linear section (CLS) and combined pulse modulator (CPM). The modulator converts continuous output signal into a sequence of pulses of constant amplitude and modulated in sign, frequency, and duration. The modulation law is expressed. The development consists of the following: application of the direct Lyapunov method to the study of stability of a system with double pulse modulation; the Lyapunov function and its first difference; conditions of complete stability of a static system; and conditions of complete stability of a set of equilibrium positions of astatic systems. The method presented is applicable not only to systems with double pulse modulation but to all pulse systems which may be regarded as a special case of such a system.

Amplitude and Frequency Modulation of CW Gunn Oscillators

Abstract: The use of Gunn oscillators in CW Doppler RADAR, as local oscillators, and in other system applications often requires automatic frequency and/or phase control, frequency modulation or amplitude modulation. The frequency modulation of CW Gunn oscillators by simultaneously applying ac and dc bias voltages has been described by King and Wasse, who discussed possible modulation mechanisms. Hobson has reported an experimental study of voltage tuning using a biconical cavity. In this paper we present the results of a theoretical and experimental study of AM, FM and AFC of wide-band tunable Gunn oscillators operating in the X-band. The oscillators consist of a Gunn diode mounted on a post in rectangular waveguide. The circuit is loaded with an iris and is tuned over the band with a sliding short located behind the post. The output power as a function of frequency is shown in Fig. 1 for a typical oscillator.

Sawtooth frequency modulation system including a waveshaping frequency multiplier chain

Abstract: A modulation system includes a serrasoid modulator to provide a relatively high phase-shift capability and a broadband, uptuned frequency multiplier chain to achieve the required amount of frequency deviation when operating at the commercial broadcasting frequencies.

Nonlinear frequency modulation by noise

Abstract: Prior analyses of frequency modulation by noise have assumed a perfectly linear modulator. The effect of nonlinearity on spectral shape and bandwidth is exhibited in one specific case of interest. In the linear case, a discrete spectral line may exist at carrier frequency; it is shown that such a line can never exist under nonlinear modulation.