Showing papers on "Modulation published in 1969"

Coherent Emission from Rare Earth Ions in Electro‐optic Crystals

Abstract: We report the observation of coherent emission from three rare‐earth ions in electro‐optic crystals. Oscillation is observed from Nd3+ ions in Bi4Ge3O12, LiNbO3, and Ba0.75Ca0.25Nb26O at room temperature, and from Tm3+ and Ho3+ ions in LiNbO3 at 77°K. Second‐harmonic radiation is obtained from LiNbO3:Tm3+ and electric‐field modulation of threshold is observed for certain crystals of LiNbO3:Nd3+. The latter effect is believed to arise from crystal strain. The propagation angle for phase‐matched second‐harmonic generation is calculated to lie at 43° to the c axis for both LiNbO3:Tm3+ and LiNbO3:Ho3+ at 77°K. Phasematched second‐harmonic generation from LiNbO3:Nd3+ is not possible, since the maser line is an extraordinary wave. However, the polarization of the maser line in LiNbO3:Nd3+ is appropriate for phasematched parametric frequency conversion in the near infrared. Attempts to observe such radiation were not successful due to the limited power available in the fundamental.

Automotive multiplex system

Abstract: A multiplex system for controlling and sensing various component parts such as head lights, engine temperature, fuel level, and turn signal lights is disclosed. The system employs a single twowire cable to communicate both power and signals between such components and a central control and metering console which may be the instrument dash console. Time multiplex is employed using a reverse polarity for clock pulses from that of the information pulses. Both analog and digital data may be accommodated by using pulse-width modulation as well as bi-level modulation. Receiving units employ a N delay one-shot triggered by the clock pulse and an AND circuit driven by the output of the N delay one-shot and the signal present on the single signal wire, to drive a one-shot which controls a switching device. Similar circuitry is employed for the digital transmitting and the analog transmitter and receiver. A socket input unit for tapping into the single cable in parallel to other input units by employing a piercing plug is disclosed.

Simple analytic expressions for am and fm mode‐locked pulses in homogeneous lasers

Abstract: Simple expressions for the mode‐locked pulses induced by either intracavity phase or amplitude (FM or AM) modulation in a homogeneous laser are developed by following a Gaussian pulse through one pass around the laser cavity. The predicted pulsewidth in either case is τp ∼ (g0/δ)1/4 × (ΔfaxialΔfatomic)−1/2, where g0 = saturated single‐pass excess laser gain, δ = single‐pass modulation index, Δfaxial = axial mode spacing, and Δfatomic = atomic linewidth. The FM case also shows a frequency `chirp' equal to the pulsewidth. Experiments with the FM case in a Nd:YAG laser show excellent agreement with the analysis.

Digital fsk/psk detector

Abstract: The digital FSK/PSK detector demodulates digital data from a frequency shift keyed modulation signal (FSK) or a phase shift keyed modulation signal (PSK) for moderate data rates including at least 1200 bits per second and is capable of operating over switching networks. The digital FSK/PSK detector comprises a binary amplitude quantizer, a clock, a digital time quantizer, a digital delay coacting with an Exclusive-OR circuit for detecting the digital data signal from the FSK/PSK modulated signal and a digital filter and smoothing circuit for eliminating undesirable noise from the digital data signal.

Binary code suitable for line transmission

Abstract: A practical method is described for encoding an unrestricted binary signal into a form suitable for transmission through a binary regenerated signal path while incurring only a small increase in modulation rate

Two-way communication system employing two-clock frequency pseudo-noise signal modulation

Abstract: A digital two-way communication system utilizing RF transmissions that are phase-shift-keyed (PSK) by binary pseudo-noise (PN) code generators operating at different clock rates. Transmissions in the first and second directions are modulated by composite PN code generators operating at different first and second clock frequencies f1 and f2, respectively, where f1 = NF2, with N being a positive integer having no factors in common with the lengths of the component PN coder from which the composite is formed. The binary digital data signals that are to be transmitted in either direction modulate a binary PN code which is a composite code generated from a plurality of component PN codes. Each of these data-modulated composite PN codes, which are generated at clock frequencies f1 and f2, respectively, modulates, in turn, an RF carrier signal.

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.

Phase and amplitude modulated modem

Abstract: A method and apparatus for generating phase and amplitude modulated signals to be transmitted and for demodulating the transmitted signals with improved reliability and accuracy is disclosed. A modulator at the transmitter is adapted to continuously group digital data into multibit words of equal length. The modulator is responsive to predetermined multibit subgroups within each multibit word to differentially phase modulate a carrier signal during successive modulation periods. The modulator is further responsive to the remaining bits within each multibit word to amplitude modulate the carrier signal during successive modulation periods. A demodulator is provided at the receiver. A differential phase detection portion of the demodulator reconstitutes the multibit subgroup digital data phase encoded at the modulator. A variable gain amplifier at the receiver varies the amplitude of the received signal in accordance with derived gain selection commands. The gain selection commands are derived from an amplitude detection portion of the receiver. The amplitude detection portion also provides a digital output indicative of the remaining portion of the multibit words originally encoded. The derived gain selection commands vary the gain of the receiver amplifier to cause the output amplitude levels of the amplifier to accurately correspond to the originally encoded amplitude levels. The accurately corresponded amplitude levels insure correct amplitude detection at the receiver.

Modulator stabilization circuits

Abstract: The operating point of a modulator is stabilized by superimposing a pilot signal upon the information bearing modulating signal. The resulting modulation produced by the pilot signal is compared with a reference signal in a phase detector and a control signal generated which is used to counteract any drift of the operating point. Alternatively, the average intensity of the modulator output signal is detected and used to alter the net bias applied to the modulator as a means of stabilization.

Single-sideband modulation system

Abstract: A multichannel, frequency-division multiplex, single-sideband modulation system is realized by using digital filters and product modulators in lieu of conventional analog filters and product modulators. Extremely high multiplication rates resulting from a direct substitution of digital for analog operations are substantially reduced by using multirate digital filters and a combined multichannel implementation of said product modulators and a portion of said multirate digital filters.

Method and apparatus for mapping planets

Abstract: A radar system is disclosed for obtaining data to map planets employing and S-band ranging transponder (RT) that is widely separated from and in motion relative to a stationary transmitter-receiver station (STRS) on earth. The STRS transmits a ranging signal which is biphase modulated by a pseudonoise (PN) code, and the RT retransmits the PN-modulated signal on a different carrier frequency. The STRS receives the retransmitted signal as a reflected signal from an area of the planet (AP) being mapped. Three time-varying delay times (STRS to RT, RT to AP and AP to STRS) are involved in the round trip communication delay. That round trip delay and a doppler shift of the reflected signal are tracked by the STRS for mapping. That is done by recording the received signal in phase quadrature at baseband. The technique for obtaining mapping data then consists of multiplying the recorded signal by a locally generated PN code after synchronizing the PN code modulation of the signal to the local PN code, and separating the synchronized PN-code-modulated signal from the rest of the received signal by a low-pass filter. The separated PN-code-modulated signal corresponds to a narrow strip or contour line at constant range from the RT which is substantially orthogonal to virtually parallel contours of doppler shift caused by motion of the RT relative to the AP. A filter which matches the doppler shift can thus be employed to resolve individual mapping points for display.

Communications system with frequency and time division techniques

Abstract: A communication system for a substantial number of subscribers is shown having random access capabilities without the requirement for the usual central exchange. The system uses a frequency division scheme for separating the several communication information channels. The individual subscriber units are interconnected as by means of one or more wires which are also connected to a master clock which continually generates time division digital information consisting of a plurality of pulses and unused time spaces (ones and zeros) including binary circuit code information and synchronizing pulses. A relatively limited band width is required for carrying this control information which is substantially displaced in frequency from the band containing the several communication information channels. These channels are generated by means of a frequency synthesizer in each of the subscriber units, each of which continually monitors the digital control information to determine whether its address is being called and the circuit code representing the channel of the incoming call. Similarly, outgoing calls are initiated by picking up a headset at the subscriber unit which causes an unused channel to be selected, inserting its circuit code into the digital stream and causing the frequency synthesizer in responding to this code to generate the corresponding carrier frequency. The audio information is then converted to single side band (or other) modulation of the particular carrier frequency signal.

FREQUENCY PULLING AND PULSE POSITION MODULATION OF PULSING cw GaAs INJECTION LASERS

Abstract: The frequency pulling and locking of intensity pulsations from continuously operating GaAs injection lasers have been studied by varying the frequency of the externally applied locking signal in the vicinity of the self‐induced pulse rate or one of its harmonics. The ability of the laser pulse rate to follow a rapidly varying locking signal has led to the first realization of optical pulse position modulation with microwave repetition rates. Modulation rates attainable with this effect are expected to be as high as one‐half the self‐induced pulse rate.

Acoustic quantum oscillations and the fermi surfaces of cadmium and zinc

Abstract: Quantum oscillations have been observed in the absorption of longitudinal ultrasonic waves of frequencies 70 and 170 MHZ by single crystals of Cd and Zn at about 1·1°K in magnetic fields from 15 to 65 koe. Pulsed ultrasonics have been combined with low-field modulation and phase sensitive detection. The results are discussed in terms of the Fermi surfaces of the metals, and difficulties arise in the interpretation of certain frequencies in terms of current models.

Interchannel interference considerations in angle-modulated systems

Abstract: This paper considers the deterioration in performance of angle-modulated systems resulting from interchannel interference. We show that with band-limited white gaussian noise modulation (simulating modulation by a frequency division multiplex signal), we can derive an explicit expression for the spectral density of the baseband interchannel interference when two or more PM waves interfere with each other. We show that, if the interference is co-channel, maximum interference occurs at the lowest baseband frequency present in the system and we can derive upper and lower bounds to this minimum baseband signal-to-interference ratio. For high enough modulation index, we show that this minimum signal-to-interference ratio is proportional to the cube of the modulation index and that phase modulation can be used with advantage in interference limited systems. We do not consider the effects of linear filters on angle-modulated systems, but give some results about the effect of adjacent channel interference when the interference is in the passband of the receiver.

Modulation servo control for frequency modulated ring laser gyro

Abstract: A ring laser gyro has a pair of counter-rotating beams, the difference frequency between the beams being indicative of the rotational rate to which the instrument is subjected. The beams are frequency modulated to minimize frequency-locking therebetween. A servo control is provided to maintain the modulation index of the frequency modulation to an optimum value for minimal frequency-locking between the beams.

Phase shift data transmission systems having auxiliary channels

Abstract: In a data transmission system utilizing phase shift modulation of a carrier signal to transmit pulse coded data from one station to another an auxiliary low frequency signal is transmitted between said stations by frequency modulation of the carrier signal, the maximum phase shift of the carrier signal due to said frequency modulation during any one pulse interval of the data signals being much less than the minimum step phase shift utilized in transmitting said data.

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.

Electronic audiofrequency modulation system and method

Abstract: The invention is directed to modulation of the amplitude and frequency of an audiofrequency signal by passing the signal through at least two parallel channels, with phase-shifting circuitry in the channels providing signals of opposed phases. A low-frequency band is filtered from the signal in one of the channels and a high-frequency band is filtered from the signal in another of the channels and the signals shifted back into phase. The filtered signals are then combined into an output signal. The high- and low-frequency bands filtered from the signals are selectively varied to induce vibrato, tremolo, and other tonal effects into the output signal. In a preferred form of the invention, the high- and low-pass filters are matched so as to form substantially a 180* phase shift stage with a flat frequency response. Four stages are coupled to provide 720* of phase shift. The original audiofrequency signal is then summed with the phaseshifted signal in approximately equal proportions to produce a coordinated effect substantially duplicating that produced by a rotating speaker. The phase shift is started and stopped in a manner to duplicate the dynamic effects of starting and stopping a rotating speaker. A dual channel system is described for duplicating a multiple speaker system.

Phase shift keyed transmission of dibits encoded to eliminate receiver phase uncertainty

Abstract: A method and apparatus for transmission of a binary information signal comprising sequential digital signal steps consisting of binary states (''''o,'''' ''''1'''',) one of which represents a steady modulation condition of the binary information signal, by multistage phase modulation utilizing a plurality of determinate phase shifts of a carrier frequency in which a joint transmission is effected of respective binary sequences of ''''n'''' number (n being an integer greater than 1) of signal steps each different sequence group being transmitted as a group by a respective one of said determinate phase shifts, utilizing for the transmission of the binary information signal only the absolutely necessary number of 2n-1 phase shifts, utilizing an additional phase shift to transmit as a group, the fixed number of n signal steps of the binary state representing such steady modulation condition of the binary information signal, and transmitting any signal steps which number less than n, separating two successive groups, without a change in phase (0* phase shift) as a continuation of the immediately preceding phase position.

Minimizing frequency locking in ring laser gyroscopes

Abstract: A ring laser gyroscope utilizes a pair of oppositely rotating beams which are given a difference frequency in accordance with the rotation rate of their optical paths. A plurality of frequency modulated bias signals are imposed upon the beams, the modulation indices of these frequency modulation signals being chosen to minimize the effects of frequency locking at low rotation rates.

Transmission measurement with a two-component signal

Abstract: A system for measuring the transmission loss in a telephone customer''s loop. A diode network is connected at the customer''s premises across the loop. At the central office two alternating current signals are impressed on the loop. One signal is a low frequency, high amplitude signal used to switch the diode network alternately into its conducting and nonconducting states, thus causing the modulation of the second high frequency, low amplitude signal. The sum or the difference frequency is filtered out and measured at the central office.

Voice transmission and receiving system employing pulse duration modulations with a suppressed clock

Abstract: A voice transmission system including coded voice information using pulse duration modulation (PDM) with a suppressed clock and wherein this suppressed clock pulse duration modulated voice signal is used to modulate a phase shift keying modulator (PSK). The receiver includes a phase shift keying demodulator which feeds a limiter having a wide bandwidth so as to achieve the highest possible processing gain. The receiver also includes a voltage controlled oscillator which is fed an error signal derived from an integrator so as to produce an output signal from the voltage controlled oscillator to replace the suppressed clock.

Mode-locked frequency doubled laser

Abstract: This laser comprises an intracavity nonlinear crystal that converts fundamental frequency laser light to second harmonic light and is also modulated to mode lock the laser The modulation voltage, and thus the modulation depth, is varied to optimize the magnitude of the second harmonic power produced by the crystal

Amplitude compensated pulse duration modulator

Abstract: AN AMPLITUDE COMPENSATED PULSE DURATION MODULATOR INCLUDING A PULSE DURATION MODULATION SYSTEM HAVING MEANS FOR COMPENSATING FOR THE EFFECT OF STRAY CAPACITANCE AT THE AMPLIFICATION STAGES BY MEANS OF AMPLITUDE MODULATING THE PULSE DURATION MODULATED SIGNAL. THE AMPLITUDE MODULATED PULSE MODULATED SIGNAL IS APPLIED TO THE GRID OF AN AMPLIFIER MEANS AND THE OPERATION OF THE AMPLIFIER MEANS IS ESTABLISHED SUCH THAT THE AMPLIFIER IS DRIVEN INTO SATURATION FOR ALL PULSES EXCEPT COMPARATIVELY SMALLER AREA PULSES OF THE PULSE TRAIN. ACCORDINGLY, THE PULSE TRAIN RETAINS A MODULATION EFFECT ONLY FOR THE SMALLER AREA PULSES THEREBY ALLOWING THE AMPLITUDE MODULATION TO COMPENSATE FOR THE REACTANCE EFFECT OF THE AMPLIFIER ON THE SMALLER PULSES ONLY.

Threshold characteristics of FM signals demodulated by an FM discriminator

Abstract: An analysis of the threshold characteristic of FM signals when modulated by a Gaussian baseband signal and demodulated by an ideal FM discriminator has been derived. It is shown that there are two components in the demodulated output due entirely to modulation. This analysis serves also to unify the work of Rice [8], Wang [9], and Blachman [16].

Theory of Modulation Effects in Resonant Nuclear Disorientation Experiments

Abstract: An analysis is made of modulation effects in "resonant nuclear disorientation" experiments on radioactive nuclei which have been polarized by hyperfine interaction at low temperatures in ferromagnetic host metals. The inhomogeneously broadened nuclear magnetic resonance is detected through the destruction of the $\ensuremath{\gamma}$ radiation anisotropy by a resonant-frequency-modulated rf field. It is shown that to a good approximation the observed line shape is determined solely by the modulation amplitude and the distribution of hyperfine magnetic fields; for large rf fields, the signal amplitude depends separately upon the modulation amplitude and frequency. For finite rf field intensities, the signal amplitude also depends upon a parameter $k$ which is closely related to the saturation behavior which would be observed in the absence of inhomogeneous broadening. At high modulation frequencies, the dependence of the signal amplitude upon $k$ is easily calculated, and this should permit experimental determinations of $k$ values. Independent determinations should also be possible from studies of the time rate of destruction of the $\ensuremath{\gamma}$ radiation anisotropy immediately after applying a resonant rf field.