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Showing papers on "Pulse-frequency modulation published in 1978"


Journal ArticleDOI
F. Jager1, C. Dekker1
TL;DR: This paper describes a new type of frequency modulation, called Tamed Frequency Modulation (TFM), for digital transmission, where the desired constraint of a constant envelope signal is combined with a maximum of spectrum economy which is of great importance, particularly in radio channels.
Abstract: This paper describes a new type of frequency modulation, called Tamed Frequency Modulation (TFM), for digital transmission. The desired constraint of a constant envelope signal is combined with a maximum of spectrum economy which is of great importance, particularly in radio channels. The out-of-band radiation is substantially less as compared with other known constant envelope modulation techniques. With synchronous detection, a penalty of only 1 dB in error performance is encountered as compared with four-phase modulation. The idea behind TFM is the proper control of the frequency of the transmitter oscillator, such that the phase of the modulated signal becomes a smooth function of time with correlative properties. Simple and flexible implementation schemes are described.

247 citations


Journal ArticleDOI
TL;DR: Pulse interval and width modulation (PIM) as discussed by the authors is a pulse analog modulation system suitable for light emitting diodes that is characterized by the following compared with Pulse Interval Modulation: Pulse repetition frequency is reduced by one half.
Abstract: This paper proposes new pulse analog modulation system; Pulse Interval and Width Modulation suitable for light emitting diodes. In this system pulses have information on both their width and interval between them. Pulse Interval and Width Modulation is characterized by the following compared with Pulse Interval Modulation. First: Pulse repetition frequency is reduced by one half. Second: Duty ratio is 50 % on the average. Third: More power is needed while carrier to noise ratio could be improved instead. The paper shows how it works and comparison with another pulse analog modulation such as Pulse Frequency Modulation or Pulse Interval Modulation. The paper also shows an experiment of twin channel transmission employing two light emitting diodes, two optical fiber transmission lines and two PIN photodiodes as an example of application of Pulse Interval and Width Modulation.

57 citations


Journal ArticleDOI
TL;DR: In this paper, a CW dye laser was converted into a train of 0.5 ns pulses by frequency modulation and passage through a near-resonant atomic vapor delay line of Na.
Abstract: The 5890 A output from a CW dye laser was converted into a train of 0.5 ns pulses by frequency modulation and passage through a near-resonant atomic vapor delay line of Na. The theory of the process is discussed in both the time and frequency domains. Using a modulation index of 120 at a frequency of 17.8 MHz, we obtained values for the temporal compression ratio and intensity enhancement of 112 and 14, easily the largest that have been reported.

49 citations


Journal ArticleDOI
TL;DR: Modulation threshold, that is, the modulation depth required to discriminate a sample of amplitude-modulated (AM) noise from a samples of unmodulated noise, was measured as a function of modulation rate, modulator waveform (sine or square), and the bandwidth of the AM noise.
Abstract: Modulation threshold, that is, the modulation depth required to discriminate a sample of amplitude‐modulated (AM) noise from a sample of unmodulated noise, was measured as a function of modulation rate (16–320 Hz), modulator waveform (sine or square), and the bandwidth of the AM noise (0.5–8.0 kHz). Modulation threshold increases monotonically with modulation rate, sine‐wave thresholds are greater than square‐wave thresholds, and threshold rises as the bandwith of the AM stimulus decreases. These effects all support the use of some form of energy detection model to explain modulation threshold. The modulation thresholds were compared with pitch thresholds gathered under precisely the same conditions. Pitch threshold or, alternatively, rate threshold was taken to be the modulation depth required to decide which of two samples had the higher modulation rate; the rate difference was 20%—just over three semitones. In the region above about 70 Hz, rate threshold is essentially a constant multiple of modulation threshold, indicating that the primary constraint on rate threshold is the audibility of the modulation. Below 70 Hz, rate and modulation threshold diverge; it is argued that the limit on rate threshold in this region is probably the length of the correlation required to extract the periodicity.

28 citations


Patent
09 Nov 1978
TL;DR: In this paper, a method and apparatus of compatibly and simultaneously transmitting and receiving an encoded signal with the normal visual and aural carrier of a television signal is disclosed. But, the method is not suitable for the use of a large number of sideband components in the form of constant amplitude components.
Abstract: A method and apparatus of compatibly and simultaneously transmitting and receiving an encoded signal with the normal visual and aural carrier of a television signal is disclosed. The encoded signal is used as a modulating signal to frequency modulate the visual carrier frequency signal prior to amplitude modulating the visual carrier frequency signal with a source of composite video signals. Normally, the introduction of additional sideband power even in the form of constant amplitude components will cause visual distortion to a received picture due to the normal Nyquist shaped bandpass characteristics of the intermediate frequency amplifier in the television receiver. This distortion is reduced or eliminated in several ways. The maximum allowable frequency modulation deviation can be limited so that the visual distortion is substantially reduced. Where greater frequency modulation deviation is required, the interfering beats which appear as horizontal lines are made less visable by adjusting the frequency modulation deviation so that these lines roll vertically at a maximum rate. A more desirable approach is to amplitude predistort the frequency modulated visual carrier frequency signal in a complimentary mode to the slope of the video intermediate frequency amplifier circuits of the television receiver. In this manner, an incidental amplitude modulation would be added to the television visual carrier at the transmitter, and this incidental amplitude modulation is in the opposite polarity of the slope of the modulation taking place in the receiver. In other words, by predistorting the frequency modulated visual carrier frequency signal, the signal is in effect pre-equalized to the Nyquist bandpass characteristics of the television receiver intermediate frequency amplifier. The predistortion of the frequency modulated visual carrier signal may be accomplished passively with a bandpass filter having its lower frequency slope at the television picture carrier frequency and having bandpass response characteristics which are complimentary to the Nyquist bandpass characteristics of the television receiver intermediate frequency amplifier. Instead of a passive bandpass filter, similar results are obtained by active, pre-equalizing circuits in the transmitter. Specifically, a phase opposite correction signal derived from the encoded signal is added to the composite video signal prior to amplitude modulating the frequency modulated visual carrier frequency signal. In any case, normal aural carrier generation methods avoid any interference by the addition of a frequency deviation of the visual carrier. The received signal is detected to separately reproduce the encoded signal.

23 citations


Patent
17 Jan 1978
TL;DR: In this article, an off-frequency monitor is attached to a radio receiver to monitor and test a detected intermediate frequency signal and audio signal from a demodulator portion of the receiver to determine whether a transmitted radio frequency signal is within frequency tolerances and modulation limits and to provide an alarm, either visual or audio, when the limits or tolerances are exceeded.
Abstract: Circuitry for attachment to a radio receiver to monitor and test a detected intermediate frequency signal and an audio signal from a demodulator portion of the receiver to determine whether a transmitted radio frequency signal is within frequency tolerances and modulation limits and to provide an alarm, either visual or audio, when the limits or tolerances are exceeded. An off frequency monitor tests the DC component of the radio demodulator detected IF signal and includes input signal conditioning circuitry for filtering the audio signal, high impedance for minimal loading of the radio, and level shifting. Upper and lower level voltage references indicate maximum permissible frequency deviation from the nominal transmitting frequency. Upper and lower level comparators compare the conditioned direct current (DC) signal to the respective voltage references and provide a changed output state upon an out of tolerance transmission. An over modulation detector, generally in parallel with the off frequency monitor, provides a changed output state of a minimum time duration whenever the modulation limits are exceeded, and includes AC coupling to block the DC component of the radio detector signal, a voltage reference indicative of the maximum modulation level, a comparator for comparing the audio signal to the voltage reference, pulse stretching circuitry to provide a minimum time duration output for intermittent over modulation conditions. The frequency monitor and modulation detector independently control switching of alarm circuitry to enable either a light emitting diode, or a volume controlled audio oscillator.

21 citations


Journal ArticleDOI
TL;DR: In this paper, an equation identical with the Adler equation of oscillator phase locking is obtained for the phase of the pulse with respect to the active modulation, and the effect of noise on the pulse timing is investigated.
Abstract: The equations of combined active and passive mode-locking are solved approximately in the limit when the saturable absorber determines the width of the pulse, and the active modulator the timing. An equation identical with the Adler equation of oscillator phase locking is obtained for the phase of the pulse with respect to the active modulation. In the case of synchronization between the mode-locked pulse-train and the active modulation (time independent solution), the phase of the pulse with respect to the modulation maximum is determined as a function of detuning and modulation (depth. Beyond a critical detuning of the round-trip time Tn from the modulation period TM, synchronisation ceases and the pulses' slip through ' the active modulation with a phase that has a periodic variation superimposed on the uniform slippage rate. Finally, we investigate the effect of noise on the pulse timing. The spectrum of the pulse phase is the same as the spectrum of the phase of an injection-locked single-mode oscill...

17 citations


Patent
William G. Crouse1
13 Jun 1978
TL;DR: In this paper, a hybrid technique of combined pulse width and pulse rate modulation was proposed to achieve improved performance with reduced logic and circuitry requirements, where the high-order bits of an N-bit digital data input for conversion to a corresponding analog output voltage level were treated in a manner similar to pulse-width modulation approaches utilized previously.
Abstract: A digital-to-analog converter method and apparatus is disclosed which utilizes a hybrid technique of combined pulse width and pulse rate modulation to achieve improved performance with reduced logic and circuitry requirements. Lower order bits of an N-bit digital data input for conversion to a corresponding analog output voltage level are treated in a manner similar to pulse rate modulation approaches utilized previously. High order bits are handled together in a variant form of pulse width (duration) modulation in which the pulse width required to generate the given analog voltage level corresponding to the high order digital bit inputs is divided into a fixed number of slices in a given sample time, each slice having a width or duration of pulse output which is variable in itself in correspondence to a function of both the high and low order bit value inputs. A low pass filter or integrator combines all of the pulses in a given sample to produce the analog voltage level output.

14 citations


Patent
27 Jul 1978
TL;DR: In this article, a differential pulse code modulation (DPC) system is proposed, in which an input signal is at first approximated to a stepwise waveform having level changes at a constant number n of sampling points selected in the order of level magnitude from a predetermined number N of samples in the input signal.
Abstract: A differential pulse code modulation system, in which an input signal is at first approximated to a stepwise waveform having level changes at a constant number n of sampling points selected in the order of level magnitude from a predetermined number N of samples in the input signal. The remainder of the above approximating operation is secondary followed-up by delta modulation, which uses a variable step level controlled in accordance with the variation feature of the remainder. The differential pulse code modulation output is provided by the above two approximating operations.

12 citations


Patent
31 Jan 1978
TL;DR: In this article, a continuous wave frequency modulated signal is radiated from a range rate measuring system and returned by a target, the range rate of which, relative to the measuring system, is to be determined.
Abstract: A continuous wave frequency modulated signal is radiated from a range rate measuring system and returned by a target, the range rate of which, relative to the measuring system, is to be determined. The radiated signal and return signal are mixed to produce a beat frequency signal which is converted to a square wave signal marking passage of the beat frequency signal above and below its average value. A detector produces signals indicative of the presence and absence of transitions of the square wave signal at the turnaround points of the modulation waveform. The range rate of the target is directly related to the rate of the presence and absence of such signals.

12 citations


Journal ArticleDOI
TL;DR: A digital modulator and synchronous demodulator system has been developed which more effectively recovers signals buried in noise than does its analog counterpart and is especially useful when interfaced with a laboratory computer.
Abstract: A digital modulator and synchronous demodulator system has been developed which more effectively recovers signals buried in noise than does its analog counterpart. Circuitry of integrated design is described for controlling the modulation in physical measurements and the simultaneous, synchronous demodulation and conversion of the signal into a binary number. This system is especially useful when interfaced with a laboratory computer. The square wave which produces the modulation has purposely lengthened transition times to minimize modulation transients. Demodulation is accomplished by feeding the amplified AM signal into a voltage‐controlled oscillator and counting the resulting pulses with counters gated, by the modulation reference circuitry, to count up and down on alternate half‐cycles. The number accumulated by the counters is proportional to the true integral of the demodulated signal over a preset number of modulation cycles. The period of the modulation cycle is, in turn, determined by a quartz crystal oscillator. The demodulator can be gated to ignore excessively noisy portions of the modulated signal. Four demodulators with relative gains in ratios of eight operate simultaneously to provide a large dynamic range of more than 106. Application of this system to a computer‐controlled microwave spectrometer is described. A sample spectrum is given to illustrate the wide dynamic range.

Patent
14 Mar 1978
TL;DR: In this article, an amplitude modulation circuit for a transmitter has an automatic level controlled circuit (ALC circuit), including in its negative feedback loop a series circuit of a high-pass filter, a rectifier circuit and an eliminator circuit, for modulation degree suppression, thereby avoiding overmodulation.
Abstract: An amplitude modulation circuit for a transmitter has an automatic level controlled circuit (ALC circuit), including in its negative feedback loop a series circuit of a high-pass filter, a rectifier circuit and an eliminator circuit, for modulation degree suppression, thereby avoiding overmodulation. The high-pass filter is so designed that the negative feedback signal level for modulation degree suppression of the ALC circuit is raised as the audio-signal frequency supplied to the transmitter increases. In the modulation circuit having such ALC circuit, a sufficiently high mean modulation degree may be obtained without encountering overmodulation if the main spectrum components of the input audio-frequency signal are distributed in the intermediate range of the audio-signal frequency band. On the other hand, if the main spectrum components of the audio-frequency signal are distributed in the higher (high-pass) range, the upper limit of the modulation degree is restricted to a moderately lower value so as to reduce production of spurious signals. Here the ALC circuit operates so as not to change the frequency characteristic of the audio-frequency input signal but to suppress the modulation degree uniformly throughout the frequency band of the audio-frequency input signal. Therefore, the modulation circuit does not cause variation in a tone quality of the input signal.

Patent
03 May 1978
TL;DR: In this article, the volume control magnitude supplied from the control element can be additionally superposed by a fixed direct voltage to establish the average pulse length of the output pulses of the pulse duration modulator.
Abstract: The transmitter has a carrier control and includes an exciter for supplying the carrier voltage to a modulation stage, usually the final RF-power amplifier of a broadcast transmitter, with the modulation voltage having a controlled dc content. The modulation voltage is amplified in a modulation amplifier and the amplified modulation voltage is supplied to the modulation stage. The modulation amplifier includes a switching amplifier producing pulse duration modulated pulses, a modulation voltage controlled pulse duration modulator preceding the switching amplifier and a filter section following the switching amplifier. An adder element is connected in advance of the modulation amplifier, specifically in advance of the modulation voltage-controlled pulse duration modulator. The applied modulation voltage is supplied to a rectifier followed by a filter section and the filter section is connected to a control element and supplies thereto a variable direct voltage as a volume-dependent control magnitude which contains also very low frequency components in accordance with the volume of the modulation voltage. The output of the control element is supplied to the adder element for combining with the modulation voltages supplied to the modulation amplifier to change the pulse duty factor of the output pulses of the switching amplifier as required for carrier control of the transmitter. The volume control magnitude supplied from the control element can be additionally superposed by a fixed direct voltage to establish the average pulse length of the output pulses of the pulse duration modulator and thus to establish the average direct voltage value of the filter section of the modulation amplifier and the average operating point of the modulation stage.

Journal ArticleDOI
TL;DR: This procedure presents a better picture of the effectiveness of the pulsewidth modulation schemes and presents a method of translating the frequency-spectrum characteristics of a pulsewidth-modulated inverter into its output filter kVA characteristics.
Abstract: The paper discusses two-and three-level types of pulse-width modulation and presents a method of translating the frequency-spectrum characteristics of a pulsewidth-modulated inverter into its output filter kVA characteristics. The effect of the modulation scheme on the kVA ratings of the inverter and its transformer are also discussed. This procedure presents a better picture of the effectiveness of the pulsewidth modulation schemes.

Patent
25 Aug 1978
TL;DR: In this article, a low-pass filter is used to convert a square wave to sine wave converter using a low pass filter, whose cut-off frequency is variable in accordance with the frequency of the square wave applied to it.
Abstract: A square wave to sine wave converter using a low-pass filter. The cut-off frequency of the filter is variable in accordance with the frequency of the square wave applied to it. This is achieved by the effective value of a frequency-determining impedance in the filter varying with the square wave frequency. A resistor is switched in and out of circuit at a rate which is at least a multiple of 100 of the square wave frequency.

Journal ArticleDOI
TL;DR: Methods are presented for determining the modulation limits of phase lock loop (PLL) FM demodulators, which establish the maximum deviation that the PLL can support (i.e., remain "inlock") based on the loop design parameters.
Abstract: Methods are presented for determining the modulation limits of phase lock loop (PLL) FM demodulators These limits establish the maximum deviation that the PLL can support (ie, remain "inlock") based on the loop design parameters The modulation limits are derived from experimental data on first and second order loops using sinusoidal and Gaussian noise modulation The analysis of each PLL is broken into two regions, low frequency and high frequency modulation It is shown that the deviation limit remains constant with modulation frequency for a first order loop in the low frequency region In the high frequency region the deviation limit increases with increasing modulation frequency for both first and second order loops The deviation limit in a second order loop increases with decreasing modulation frequency in the low frequency region and is a function of the loop damping

Patent
17 May 1978
TL;DR: In this article, a pulse width modulation system for encoding and decoding digital information in which the encoded signal comprises a series of transitions among different signal levels wherein the length of time between transitions determines the value of a digit, so that each digit is represented by one and only one transition.
Abstract: A pulse width modulation system for encoding and decoding digital information in which the encoded signal comprises a series of transitions among different signal levels wherein the length of time between transitions determines the value of a digit, so that each digit is represented by one and only one transition.

Journal ArticleDOI
TL;DR: A lower bound is found on the mean square error achievable by any nonlinear pulse modulation system without memory, which differs by 6 dB from the limit given by Shannon theorems, at high signal-to-noise ratios.
Abstract: A lower bound is found on the mean square error achievable by any nonlinear pulse modulation system without memory. This bound differs by 6 dB from the limit given by Shannon theorems, at high signal-to-noise ratios. The bound is obtained by finding the signal locus which minimizes a simple lower bound on mean square error, for a given average signal energy and without bandwidth constraints. For the locus that we have found, an upper bound on error shows that the degradation with respect to Shannon's limit is within 8 to 9 dB. The locus, however, does not seem of practical interest.

Patent
22 Sep 1978
TL;DR: In this paper, a D-A converter for converting a digital signal to a duty factor of a pulse train signal and for averaging the pulse signal by a low-pass filter to convert it to an analog signal is disclosed.
Abstract: A D-A converter for converting a digital signal to a duty factor of a pulse train signal and for averaging the pulse signal by a low-pass filter to convert it to an analog signal is disclosed. A plurality of pulses which are to be selected in accordance with the input digital signal comprise a plurality of basic pulses of different phases and pulse widths derived by frequency division and auxiliary basic pulses which occur at a cycle period which is at least twice as long as a repetition cycle period of the basic pulses. The basic pulses are selected by high order bits of the digital signal while the auxiliary basic pulses are selected by low order bits of the digital signal to produce an output pulse train signal a duty factor of which changes in accordance with the digital signal. The pulse train signal is then averaged to convert it to an analog signal.

Proceedings ArticleDOI
27 Jun 1978
TL;DR: In this paper, a linear FM modulation circuit with a microstrip oscillator and a modulation circuit and an oscillator in microstrip has been described with exceptional slope linearity and group delay with no external frequency compensation.
Abstract: This paper describes a linear FM modulation circuit. The modulation circuit and oscillator, which are in microstrip, exhibit exceptional slope linearity and group delay with no external frequency compensation over a deviation bandwidth of 2% of the RF frequency. The baseband frequency response of the modulator/oscillator is greater than dc to 150 MHz. This modulation circuit has been used with microstrip oscillators at 1.8 and 5 GHz.

Journal ArticleDOI
TL;DR: In this paper, the inter/cross modulation levels occurring in signals from stripe-geometry (GaAl) were investigated by computer simulation for the case of time-division multiplexed (TDM) pulse-analog modulation (PAM).
Abstract: Inter/cross modulation levels occurring in signals from stripe-geometry (GaAl)As double-heterostructure diode lasers are investigated by computer simulation for the case of time-division multiplexed (TDM) pulse-analog modulation (PAM). It is shown that pulse-position modulation (PPM) is the preferred modulation scheme for high pulse rates, and inter/cross modulation levels are evaluated for the format TDM-PPM. It is shown that the inter/cross modulation level is greatly improved when diode lasers are biased above threshold. Based on this evaluation, it is concluded that effectively inter/cross modulation-free optical transmission at a pulse rate up to 108 \times 10^{6} pulses per second by TDM-PPM is feasible. This limiting rate permits the transmission of 12 color TV channels or 10800 telephony channels.

Patent
Hisao Okada1, Yukihiro Kawamoto1
12 Dec 1978
TL;DR: In this article, an automatic modulation control in a transmitter consisting of an alternating modulation signal source, a modulation signal amplifier, a carrier generator, a modulator for modulating the carrier signal as a function of the output of the modulation signal, and a smoothing circuit for smoothing the threshold detected output is presented.
Abstract: An automatic modulation control in a transmitter, comprising an alternating modulation signal source, a modulation signal amplifier, a carrier generator, a modulator for modulating the carrier signal as a function of the output of the modulation signal amplifier, a threshold detector coupled in a direct current manner to the output of the modulation signal amplifier for threshold detecting the modulation signal output, a smoothing circuit for smoothing the threshold detected output, an amplifier for the threshold detected and smoothed output, and a control circuit for controlling the input of the modulation signal to the modulation signal amplifier as a function of the output of the threshold detected output amplifier.

Patent
08 May 1978
TL;DR: In this paper, a digital signal recording system capable of a self-clocking and a peak detection is presented, where binary data is represented by bi-level signal pulses which are spaced apart by a time interval which is a positive integral multiple of time interval of clock pulses (referred to as T 0 ).
Abstract: A digital signal recording system capable of a self-clocking and a peak detection. Binary data is represented by bi-level signal pulses which are spaced apart by a time interval which is a positive integral multiple of time interval of clock pulses (referred to as T 0 ). The width of the signal pulses at their one level is a constant value less than T 0 and where the time spacing between such signal pulses is greater than 2 T 0 , a selected number of pseudo pulses having the same pulse width as such signal pulses are inserted between the adjacent signal pulses with a time interval therefrom which is an odd multiple of T 0 /2.

Journal ArticleDOI
TL;DR: In this article, a digital system for a programmable frequency synthesiser is described, which performs a staircase frequency sweep with a step of 1 Hz and digitally programmed bidirectional square-wave frequency modulation in an NQR spectrometer with a frequency-locked super-regenerative oscillator.
Abstract: A digital system for a programmable frequency synthesiser is described. It performs a staircase frequency sweep with a step of 1 Hz and digitally programmed bidirectional square-wave frequency modulation in an NQR spectrometer with a frequency-locked super-regenerative oscillator. The system is particularly convenient when using digital averaging techniques. NQR spectra parameters are not influenced by frequency modulation even when extremely large frequency modulation deviations are used. Parameters such as the sweep rate and the amplitude of frequency modulation deviation are stable, accurately fixed and independent of the running frequency. NQR spectra of 35Cl in p-dichlorobenzene and 65Cu in Cu2O were plotted against frequency by an X-Y recorder.

Journal ArticleDOI
01 May 1978
TL;DR: In this paper, a novel approach to the analysis of modulation processes in power convertors is developed, where the single harmonic components of the modulator output spectrum are given in terms of series with fast convergence rate.
Abstract: A novel approach to the analysis of modulation processes in power convertors is developed. The single harmonic components of the modulator output spectrum are given in terms of series with fast convergence rate. The method set forth is based on the theory of the Kapteyn series. Both the cases of rational and irrational frequency ratio are treated and some typical peculiarities of the modulation processes are stressed.

01 Jan 1978
TL;DR: In this article, four examples of specific fiber optic sensor system designs, each of which demonstrates a different optical modulation format, are described; the birefrigent temperature transducer illustrates direct digital signal modulation, while the temperature/pressure dependent semiconductor filter illustrates high-pass optical wavelength signal encoding.
Abstract: Four examples of specific fiber optic sensor system designs, each of which demonstrates a different optical modulation format, are described. The birefrigent temperature transducer illustrates direct digital signal modulation. The temperature/pressure dependent semiconductor filter illustrates high-pass optical wavelength signal encoding. The coupled polarized-mode transducer shows how a solid-state sensor can produce narrow-bandpass optical wavelength signal encoding. The luminescent temperature sensor illustrates a way to construct a solid state sensor in order to produce pulse width modulation of an optical signal.

Journal ArticleDOI
TL;DR: A technique is used to reduce the base line by a factor of about 10(-5) and which can be used to study the spectra of species contained in a glow discharge and may be considered to behave like a high-pass filter which discriminates against features that vary slowly with frequency.
Abstract: In a microwave spectrometer, systematic variations of the rf source amplitude with frequency can cause a spurious signal (base line) which severely limits the attainable sensitivity. Normally, the base line is eliminated by using Stark or Zeeman modulation. However, these modulation methods cannot be used in an experiment on nonparamagnetic molecular ions contained in a glow discharge. This paper discusses a technique which we have used to reduce the base line by a factor of about 10−5 and which can be used to study the spectra of species contained in a glow discharge. The scheme uses wideband sinusoidal frequency modulation of the microwave source combined with synchronous detection at the nth harmonic of the modulation frequency. The system produces a signal proportional to the nth derivative with respect to frequency of the base line. However, the signal due to an absorption line is only slightly smaller than that produced by other modulation methods. The system may be considered to behave like a high‐pass filter which discriminates against features that vary slowly with frequency.

Journal ArticleDOI
TL;DR: In this paper, the design of an equal-ripple modulator for regulator systems with type o plants is presented, which produces an equalripple steady-state response regardless of system parameter values.
Abstract: The design of an equal-ripple modulator for regulator systems with type o plants is presented in this paper. The goal of this design is to produce an equal-ripple steady-state response. To conserve the control effort, rids modulator drives the system output towards the desired level and lets it relax naturally to the zero-state. A number of systems using this modulator were simulated on a digital computer and the results are presented. It can be seen from these results, that the modulator achieves an equal.ripple steady-state response regardless of system parameter values. To employ the modulator in a control system requires only a noncritical choice of the pulse height and width. Large pulse sizes will decrease the transient rise time but will increase the magnitude of the steady-state error. As the modulator threshold level is obtained recursively from information gained from the system error, it possesses "adaptive" qualities. Therefore, it particularly recommends itself to situations in which system parameter variations are expectecd.

Patent
04 Apr 1978
TL;DR: In this paper, the difference in the width of the pulses from the two generators is fed back as an error signal to adjust the frequency of the clocking signal until the two waveforms are aligned.
Abstract: A frequency lock loop circuit has a pair of square-wave pulse generators which are clocked from a common input. The width of the pulses from the first generator is dependent on the frequency of the clocking signal; the width of the pulses from the second generator is dependent on a reference frequency. The difference in the width of the pulses from the two generators is fed back as an error signal to adjust the frequency of the clocking signal until the two waveforms are aligned. In a heterodyne receiver, the clocking signal may be the intermediate frequency signal from the mixer and it may then be adjusted by adjusting the frequency of the local oscillator in accordance with the pulse-width difference signal.

Journal ArticleDOI
TL;DR: In this paper, the authors investigate the stability of systems containing a Pulse Ratio Modulator (PRM), which was introduced almost accidentally by surrounding simple relay-type switching logic with a feedback loop containing a first-order lag to provide derived rate damping.
Abstract: Most spacecraft attitude control systems employing mass-expulsion techniques use some form of pulse modulation at the output from the control system to the gas control valves. In a number of early designs such modulation was introduced almost accidentally by surrounding simple relay-type switching logic with a feedback loop containing a first-order lag to provide ‘derived rate’ damping. This arrangement gives pulse width and pulse frequency modulation (Combined pulse modulation). Such a modulation scheme was devised by Schaefer in 1962 which he called a Pulse Ratio Modulator (PRM). His main concern was the mechanisation of the quasistatic equations of the modulator and he did not investigate the stability of systems containing a PRM.