Showing papers on "Frequency band published in 1977"

Importance of physical dispersion in surface wave and free oscillation problems: Review

Abstract: Physical dispersion resulting from anelasticity is investigated from the point of view of linear viscoelastic models and causality relations. It is concluded that inasmuch as Q in the earth's mantle is nearly independent of frequency, at least in the seismic frequency band, a dispersion relation in the form of C(ω) = C(ω_r)[1 + (1/πQ_m) In (ω/ω_r)] must be used for correcting the effect of physical dispersion arising from anelasticity. (Here C(ω) is the phase velocity of either body waves, surface waves, or free oscillations, ω is the angular frequency, ωr is the reference angular frequency, and Q_m is the path average Q for body waves or Q of a surface wave or a mode of angular frequency ω; for surface waves and free oscillations, C(ω_r) should be understood as the phase velocity at ω computed by using the elastic moduli at ω = ω_r.) The values of Q outside the seismic frequency band affect mainly the absolute value of the phase velocity but do not affect significantly the relative dispersion within the seismic frequency band. Even if the microscopic mechanism of attenuation is nonlinear, this dispersion relation can be used if departure from elasticity is relatively small, so that the signal can be approximated by a superposition of propagating harmonic waves. Since surface wave and free oscillation Q is 100–500 for fundamental modes, a correction of 0.5–1.5% must be made for joint interpretation of body wave and surface wave data. This correction is nearly 1 order of magnitude larger than the uncertainties associated with these data and are therefore very significant. When this correction is made, the discrepancy between the observed surface wave phase velocities and free oscillation periods and those predicted by the Jeffreys or Gutenberg model becomes much smaller than has previously been considered.

Method of obtaining radiowave propagation parameters for the Earth-ionosphere duct at e.l.f.

Abstract: The wave impedance of the Earth-ionosphere duct is investigated numerically and analytically in the frequency band 1 to 60 Hz. Data are presented enabling the determination of the propagation parameters of the duct by experimental measurement of the argument of the wave impedance.

Multi-band tuner

Abstract: OF THE DISCLOSURE A tuner for receiving a broadcasting signal whose frequency band is divided into high and low channels is disclosed. In this case, the tuner has first and second filters whose pass bands are fixed, a switch changeably connected to one of output terminals of said first and second filters, said switch being so changed that upon receiving a low channel said switch is changed to one state to deliver only a signal belonging to the low channel in said broadcasting signal from said first filter while upon receiving a high channel said switch is changed to the other state to deliver only a sig-nal belonging to the high channel in said broadcasting signal from said second filter, a third filter, a local oscillator, a mixer which is supplied with a local oscillation signal from said local oscillator and a signal from one of said first and second filters through said third filter to be multiplied with each other, and means for deliving a signal from said mixer which belongs to a predeter-mined band as an intermediate frequency signal, and if it is assumed that the lowest frequency in the lowest band of said low channels of said broadcasting signal is taken as f1L; the highest frequency of the highest band of the low channels as f3H; the lowest frequency in the lowest band of said high chan-nels as f4L; the highest frequency in the channel occupying the highest band of said high channels as f12H; the band width of one channel of said broad-casting signal as fB; and the lowest frequency of the intermediate frequency signal as fL, respectively, the local oscillation frequency of said local oscillator is selected higher than the frequency of the broadcasting signal at a channel when the channel is received so as to satisfy the following condi-tions (1) to (3): (1) (2) or ....... (3)

Explicit formulas for the synthesis of optimum broad-band impedance-matching networks II

Abstract: The paper shows that the most practical RLC load can be optimally matched to a resistive generator over a finite frequency band to achieve the Butterworth or Chebyshev transducer power-gain characteristic of arbitrary order, justifying and extending the procedure given in the literature. Explicit formulas for the optimum design of these matching networks are presented, thus avoiding the necessity of using the design curves and solving the nonlinear equations for selecting the optimum design parameters. The significance of these formulas is that they reduce the design problem to simple arithmetic. Illustrative examples are provided to demonstrate the usage of the formulas.

Time division multiplied speech scrambler

Abstract: A privacy communication system in which increased security is provided in the scrambling of speech signals. Input speech is separated into a high frequency band and a low frequency band, and each band is time scrambled independently and recombined prior to transmission. Additional security is obtained with randomly selected segments of the scrambled speech being reversed in time. Further randomizing of the pseudorandom sequence which controls the scrambling operation is also provided, as well as simplified computing of delay times for the descrambling operation.

An antenna for limited scan in one plane: Design criteria and numerical simulation

Abstract: An analytical and numerical study has been performed on a novel design scheme for an antenna system for limited one-dimensional scan. The system has a number of control elements approximately equal to the minimum theoretically compatible with the aperture size and field of view (FOV). The radiating structure consists of a "bootlace" lens with linear outer and circular inner profiles. This geometry plays a basic role in determining excellent scan performance over a moderate frequency band. A linear array whose size depends critically upon the scan requirements and the lens focal length is located on the focal plane and is focussed onto the inner lens profile. The array is fed by a hybrid network (HN) performing a spatial Fourier transformation. The input ports of the HN are fed by the output ports of a beam forming network (BFN) through a set of variable phase shifters. The BFN has separate input ports for the sum and difference patterns, controlled independently, The system works as follows. The antenna illumination is synthesized as the weighted superposition of components illuminations or "overlapping subarrays" each of which is due to the excitation of one of the ports of the HN. The amplitudes of the subarray excitations are fixed and determined by the power divisions provided by the BFN. Their phases are controlled by the set of variable phase shifters. A desirable feature of the scheme is that for a fixed phase shifter setting neither the beam scan nor its width changes for a moderate frequency variation. Through a suitable design of the BFN, ultralow sidelobes outside the FOV can be achieved at the expense of a slight reduction of the illumination efficiency, which is, however, always high, since the aperture is fully used. Extensive numerical computations for an antenna having a half-power beamwidth of 1.2\deg show that the sum beam can be scanned in a sector greater than \pm3 beams, on a band of 20 percent with excellent performance form the viewpoint of gain and sidelobes-the scan sector being slightly less for the difference beam.

Satellite switching system

Abstract: A multi-beam satellite switching system employs onboard switching for the purpose of increasing the up path and down path antenna gains. A multiplicity of up path antenna beams and of down path antenna beams (not necessarily the same number of each direction) are provided by the system. A number of amplifier systems are distributed across the frequency band of interest. These amplifier systems comprise input amplifiers including filters, frequency converters and output amplifiers. A switching and control circuit accepts an up path signal from only the desired input amplifier and connects the desired output amplifier to the desired down path beam. Each earth station transmits to the satellite a suitable signal to perform the desired switching functions.

Wide band monopulse antennas with control circuitry

Abstract: A wide band monopulse antenna includes a plurality of contiguous square quad-ridged waveguides arranged in a geometric array. Proper orientation of the array permits connection to circuitry to permit use of the individual waveguides for development of azimuth, elevation and sum pattern signals. Further, orientation of concentric arrays permits extension of the frequency band.

Rotating field polarization antenna system

Abstract: An antenna system particularly suitable for permitting low cost reception of broadcasted circularly polarized television low and high VHF signals is provided by arranging all of the broadcast antennas so that the low and high VHF television frequency signal waves are radiated in opposite directional senses of circular or elliptical polarization. The low cost receiving antenna for receiving both of these bands comprises a pair of linear elements with the first of the pair of elements adapted to receive linearly polarized waves in a first linear polarization and a second of the elements adapted to receive linearly polarized waves in a second orthogonal polarization. A combining means includinga delay is provided for combining the signal waves received at one of the pair of elements with delayed signal waves received at the other of the receiving elements where the delay is on the order of one-quarter wavelength at a frequency within the low VHF frequency band.

Automatic cable balancing network

Abstract: A hybrid circuit for coupling a bidirectional telephone cable to two unidirectional cables is balanced automatically by employing an adjustable balance network and a control circuit. Optimum adjustment of the balance network is achieved over a frequency band of interest by employing a signal source having one or more frequency components within the frequency band of interest and by generating signals for controlling magnitude and phase components in the balance network. The magnitude control signal is representative of the difference between the absolute magnitudes of signals detected at the bidirectional cable connection to the hybrid and at the balance network connection to the hybrid in the frequency band of interest. Signals for controlling the phase components of the balance network are representative of the difference between the absolute magnitudes of the detected signals modified by a first prescribed weighting function less a component proportional to the phase difference between the detected signals modified by a second prescribed weighting function within the frequency band of interest. The weighting functions are obtained by employing a filter having a prescribed low-pass characteristic. The component values of the filter are determined by the locations of adjustable pole(s) and/or zero(s) within the frequency band. The filter characteristic may be adjusted during the balance process further to optimize the balance network adjustments.

Method for testing radomes

Abstract: The radio-frequency performance at localized areas of a radome is determined by a method which includes illuminating at normal incidence a local radome patch with a sweep-frequency band of microwaves having a frequency band of at least two-thirds octave surrounding the design frequency of the radome. Alternatively, a harmonic band of three times the design frequency band may be utilized in the method when compact equipment is important. A sweep-frequency generator is coupled to a reflectometer for response to the band of illuminated and reflected microwaves from a local radome patch to provide an X-Y plot of reflectivity as a function of the sweep-frequency. The sweep-frequency is related to scan angle using known radome equations.

Automatic communication signal monitoring system

Abstract: A system for automatic monitoring of a communication signal in the RF or IF spectrum utilizes a superheterodyne receiver technique with a VCO to select and sweep the frequency band of interest. A first memory is used to store one band sweep as a reference for continual comparison with subsequent band sweeps. Any deviation of a subsequent band sweep by more than a predetermined tolerance level produces an alarm signal which causes the band sweep data temporarily stored in one of two buffer memories to be transferred to long-term store while the other buffer memory is switched to its store mode to assume the task of temporarily storing subsequent band sweeps. Each alarm signal alternates the roles of the two buffer memories. In a second embodiment, the roles of the two buffer memories are switched at the end of each heterodyne receiver band sweep for display of successive band sweeps at a faster rate and for automatic long-term store of any band sweep producing an alarm.

Full-Band Low-Loss Continuous Tracking Circulation in K Band (Short Papers)

Abstract: The continuous tracking principle is applied to the design of a wide-band Y-junction stripline circulator for the 18-26.5-GHz frequency band. Near octave low-loss and high isolation performance is demonstrated without the need for repeated design cycles. Design data and construction details are presented.

Digital remote control system with improved noise immunity

Abstract: A remote control receiver for selectively actuating a plurality of functions, each function uniquely corresponding to control signals lying in a respective band of frequencies. The function determining control signal is supplied to a digital counter which, during each of a continuous series of fixed duration timing intervals, develops an output count representative of the frequency of the received control signal. A portion of each count comprising the most significant bits thereof is processed for identifying the condition wherein the frequency of the received control signal lies in the same frequency band for successive timing intervals. The remaining portion of each count comprising the least significant bits thereof is processed for identifying the condition wherein a subsequent count is within a restricted range of counts centered about a prior count for successive timing intervals. Coincidence of the two conditions for a predetermined number of consecutive timing intervals results in actuation of the function corresponding to the frequency band for which the conditions were satisfied.

Analog dereverberation system

Abstract: Room reverberation characteristic of monaural systems is removed, in accordance with the principles of this invention, by employing two microphones at the sound source and by manipulating the signals of the two microphones to develop a single nonreverberant signal. Both early echoes and late echoes in the signal received by each microphone are removed by manipulating the signals of the two microphones in separate frequency bands of the signal. Corresponding frequency bands of the two signals are co-phased and added and the magnitude of each resulting frequency band is modified in accordance with a computed phase difference average between the corresponding frequency bands. The modified frequency bands are combined, thereby forming the nonreverberant signal.

Material scanning apparatus

Abstract: Apparatus and method for producing maps of thickness or elastic constant iations of nominally plane sheet or plate materials. Amplitude variation at a set frequency on a normal resonance peak is recorded to determine resonance peak variation and thus specimen thickness or elastic constant variation. A mechanical scanner moves a transducer across the material submerged in a water tank for performing an ultrasonic C-scan. A transmitter or pulse generator repeatedly pulses the transducer to produce a focused narrow pulse of ultrasound which reverberates within the material. Echoes from the material in response to the pulse are received by the same or another synchronously moving transducer, whose resulting signal then passes through a gate, which removes extraneous signals and selects the number of multiple echoes and thus amplitude range desired, and a variable filter controlled by a function generator which selects the desired frequency, to a pen recorder. The desired frequency is selected at or near a resonance peak for the material. The variable filter produces a signal in the desired narrow frequency band whose amplitude variation is indicative of variation in the material's properties with position of the transducer. The amplitude of the gated filtered signal is used to control the intensity of the recorder, which moves synchronous with the motion of the transducer. The recorder produces a map of the material at the desired frequency.

30-GHz-Band Periodic Branching Filter Using a Traveling-Wave Resonator for Satellite Applications

Abstract: A periodic branching filter consisting of three directional couplers, a traveling-wave resonator, and connecting waveguides is used as a band diplexer with a broad 3-dB bandwidth and sharp selectivity for a satellite communication system application. This paper describes a theoretical analysis, a design method, and experimental results for this periodic branching filter. The fabricated periodic branching filter for separating the 30-GHz frequency band 27.0-29.2 GHz into two subbands of equal 3-dB bandwidth of about 900 MHz has sharp frequency selectivity. Measured branching losses and relative delay time are 0.35-0.5 dB and 0.4 ns, respectively, within each frequency subband (f /sub 1,2/ /spl plusmn/ 300 MHz). The 96-g diplexer is made of thin-walled aluminum. Its size is 15 x 9 x 4 cm.

Fm demodulation circuit by phase tracking loop system

Abstract: PURPOSE: To make unnecessary the Hilbert filter by using a variable LPF as a tracking filter, and to obtain excellent operation even at high frequency band for such as tuners. COPYRIGHT: (C)1979,JPO&Japio

Duplex data transmission modem utilizing an injected tone for shifting power within the transmit spectrum

Abstract: A full duplex communication system including a pair of full duplex modems. Each modem has both a call originate mode of operation and a call answer mode of operation. In the call originate mode outgoing data is transmitted by modulation of a carrier frequency F2 and incoming data is received by demodulation of a data modulating carrier of frequency F1. When in the answer mode of operation, the data is received on frequency F2 and transmitted on frequency F1. Means are provided for injecting a carrier frequency F6 in the outgoing data transmission path. The frequency F6 is near the midpoint between F1 and F2. The amplitude is such that the distribution of power within the transmission band is balanced so that the power in the frequency band set aside for single frequency signaling systems does not exceed the power in the remainder of the transmission band. This prevents the false operation of signal frequency systems triggered by the transmission of certain bit patterns, which could result in improper billing, intermittent transmission interruptions, insertion of a band elimination filter in the transmission path or the complete disconnection of a call.

Video recorder having means for maintaining constant the amplitude of the frequency-modulated signal

Abstract: In apparatus for recording, or otherwise transmitting, video or other information signals, and in which at least a portion of the signal to be recorded, for example, the luminance component of a color video signal, is frequency modulated and then passed through a filter for limiting the frequency band of the resulting frequency modulated component or signal which is recorded; a signal processor, such as, an automatic gain control or limiter, acts on the frequency modulated output of the filter to eliminate or compensate for amplitude variations that may occur therein by reason of the filter, for example, at portions of the signal where substantial pre-emphasis was applied.

Frequency band compression of FDM using time expansion

Abstract: A frequency band compression method, using Time Compression, for use with a frequency division multiplex (FDM) signal carrying voice signal. On the transmission end, the multiplexed signal is divided into a plurality of time segments, each segment having a certain duration, then deleting a part of the each segment and time-expanding the remaining part of the segment by a sawtooth variable delay, thus lowering the frequency of the signal to a predetermined ratio. On the receive end, the signal segments are compressed by a corresponding variable delay, thus making the received frequency higher and reproducing the original multiplexed voice signals.

Betweennframe coding equipment

Abstract: PURPOSE:When input signal is made into code, the variable property high-band breaking filter is inserted into the front stage of encoder in order to limit highfrequency element by memory quantity of buffer memory. This, transmission frequency band is compressed, lowering the transmission cost.

Miniature, flush mounted, microwave dual band cavity backed slot antenna

Abstract: A miniature, flush mounted, microwave dual band antenna which radiates omirectional microwave signals from a single flush mounted cylindrical array at frequency bands separated by 1.5 octaves. The antenna has a Y-shaped cavity with the leg of the Y being taken up by a probe and surrounding dielectric block. The cavity resonates the lower frequency band energy primarily in the open non-dielectric spaces and resonates the higher frequency band energy primarily in the dielectric space.

Passive intrusion detection system

Abstract: An intrusion detection system in which crystal oscillators are used to provide a frequency which varies as a function of fluctuations of a particular environmental property of the atmosphere, eg, humidity, in the protected volume The system is based on the discovery that the frequency of an oscillator whose crystal is humidity sensitive, varies at a frequency or rate which is within a known frequency band, due to the entry of an intruder into the protected volume The variable frequency is converted into a voltage which is then filtered by a filtering arrangement which permits only voltage variations at frequencies within the known frequency band to activate an alarm while inhibiting the alarm activation when the voltage frequency is below or above the known frequency band

Constant-phase delay network

Abstract: A method of obtaining a constant-phase across a frequency band between points containing delay elements is shown. The delayed output is subtracted from the undelayed input in demodulators operating in quadrature to obtain quadrature phase-error signals. The phase-error signals are filtered and then additively modulated onto the delayed output with single-sideband techniques to correct the phase, thereby producing a delayed output signal that is in-phase with the undelayed signal.

The Use of Time-Domain Techniques for Microwave Transistor s-Parameter Measurements

Abstract: The determination of microwave transistor s parameters over a frequency band up to 10 GHz by means of timedomain techniques, involving Fourier analysis and deconvolution of transient response data, is described. Details of the measurement system are presented and advantages of such techniques over conventional network analyzer techniques are discussed. Results obtained for developmental ion-implanted/diffused-silicon bipolar transistors with ft values above 5 GHz are presented.

Radio relay channel branch cascade exhibiting uniform transit-time-and-attenuation-characteristics of all channels

Abstract: A multi-channel radio relay system in which a plurality of high-frequency channels are provided in a link between a transmitting station and a receiving station, said channels being combined to form a high-frequency group, and separated at the receiving end, utilizing therefor, at each station, a cascade circuit of channel branch elements, which comprise circulators and band-pass filters, in which one of the two edge channels located at the respective upper and lower edges of the frequency band to be transmitted, at the transmitting end, is assigned to the channel branch element furthest from the antenna terminal thereat, and the other of such two edge channels, at the receiving end, is assigned to the channel branch element furthest from the antenna terminal thereat, with the band-pass filters of the respective channel elements for the two edge channels being detuned, with respect to their middle frequencies, relative to the middle frequency of their assigned edge channels, by an amount Δ f, in the direction of the middle frequency of the respective channel adjacent in frequency position.

Broad-Band Operation of Stripline Y Circulators

Abstract: The broad-band operation of stripline Y circulators is treated from the viewpoint of the double circulation frequency operation (DCFO) which is performed with conductor-dielectric-ferrite composites (CDF composites), without any broad-banding circuit externally connected. It is recognized that the conductive post inserted inside the dielectric-ferrite composite (DF composites--a CDF composite is made thereby) is effective to improve the isolation characteristics of a CDF composite circulator to achieve the broad-band operation. The experiments showed that the frequency band was continuously broad-banded by sequentially changing the biasing magnetic field intensity; whereupon the frequency band reached about 45 percent. The largest broad-band operation was obtained when four circulation frequencies were put into use. In this paper, all ferrites are biased magnetically above resonance.