Showing papers on "Frequency band published in 1976"

Methods and apparatus for the generation and transmission of seismic signals

Abstract: Methods and apparatus for generating and transmitting seismic signals for the purpose of seismic exploration are disclosed. The signals are force pulses shaped to have a spectrum constrained to the range of frequencies which are necessary for penetration to desired depths within the earth and for resolution of the geological reflection surfaces therein. These pulses are provided in a non-repetitive or aperiodic train, constructed to produce a transmitted energy spectrum whose mean energy extends smoothly at a substantially constant level over the spectrum frequency range, notwithstanding that the repetition frequency of the pulses may be swept over a frequency band much narrower than the spectrum range. The transmitted spectrum can exhibit an auto-correlation function having a major lobe which is predominant over any side lobes, corresponding to a desired level of resolution of the geological reflection surfaces.

CW ultrasonic bolt tensioning monitor

Abstract: This invention is a CW ultrasonic device for measuring frequency shifts of the peak of a mechanical resonance in a body. One application of the device is measuring the strain in a bolt. It also has other applications such, for example, as measuring the thickness of a body, measuring the depth of a flaw in a body, measuring the elongation of body and measuring changes in velocity of sound in a body. The body is connected, by means of a CW transducer, to electrical circuit means including a narrow band RF amplifier to form a closed loop feedback marginal oscillator that frequency locks the device to the peak of a mechanical resonance in the body. Thereafter, when the frequency of this peak changes, because of a physical change in the body, the frequency of the oscillator changes. The device includes an automatic frequency resonant peak tracker that produces a voltage that is related to a change in frequency of the oscillator. This voltage is applied to the RF amplifier to change the center of its frequency band to include the frequency of the peak and is a measure of the frequency shift. The device also includes a special transducer which requires contact to only one side of the body and provides high electrical isolation between its parts.

Digital frequency synthesizer receiver

Abstract: A scanning type frequency synthesized receiver utilizing a voltage controlled oscillator (VCO) for producing a local oscillator signal. The control voltage for the VCO is provided in response to the division rate of a programmable divider. A control circuit programs the divider which control circuit operates to vary the divisor of the divider within a predetermined range as determined by information stored in a memory corresponding to a range of frequencies in a frequency band to be scanned and received by the receiver. Upon a command signal the control circuit operates to vary the divisor of the divider either up or down to cause the frequency of VCO, and thereby the receiver, to scan in a given direction and upon a signal being received the variation of the divider divisor and the receiver scanning is terminated. The VCO can be scanned either up or down in frequency, and the scanning can be either from the upper (or lower) end of a frequency range back to the lower (or upper) end and then reversed or a repetitive scanning from one end of the range to the other in the same direction. In the preferred embodiment disclosed is a multiband scanning receiver in which the stored information for the control circuit corresponds to the extremities of each of a plurality of frequency bands, the information corresponding to a particular band being utilized in response to selection of the band for reception by a band switching means.

Reactively decoupled dual channel keying circuit for wide-band frequency modulated keyable control circuit

Abstract: A keyable control circuit, has sensing coils located in the vicinity of a plurality of locations where lock control is desired. At least one swept high-frequency oscillator, which is connected to each sensing coil, generates an rf signal, rapidly swept over a wide frequency band. When an external keying circuit, containing more than one resonant circuit, each correctly tuned to a predetermined keying frequency, is inductively coupled to a sensing coil, each resonant circuit absorbs rf energy as the oscillator frequency is swept past its resonant frequency. Electrical interaction between the resonant circuits is accomplished by reactive cancellation. Energy absorption in the external keying circuit induces corresponding reductions in rf energy in the sensing coil as the oscillator frequency is swept past the keying frequencies. Tuned detectors within the keyable control circuit produce a control signal when energy reduction is sensed at each of the predetermined keying frequencies. If correct absorption fails to occur at any one or more of the predetermined frequencies, the control signal is withheld. A time-gating system enables selective direction of the control signal to one or more using locations while excluding others. This function finds convenient application in automotive use where it is frequently desired to enable simultaneous unlocking of one or more doors while excluding unlocking of the deck lid. A dead-oscillator detector averts attempted actuation of the unlocking function by the coupling of untuned energy-absorbing material, such as iron, to a sensing coil.

Heater glass sheet with broad band receiver antennae

Abstract: A glass sheet with broad band receiver antennae and an area to be heated, comprising a glass sheet, a first means provided in the heating area of the glass sheet and capable of functioning both as a heating conductor wire and as a first receiver antennae for receiving waves in predetermined frequency band, an electric source connected to the first means for supplying a heating current to the first means, and a second means provided in an area of the glass sheet other than the heating area and capable of functioning as second receiver antennae for receiving waves in a frequency band different from the frequency band for the first receiver antennae. This glass sheet further includes a stub one end of which is connected to the first means and the other of which to the second means, and a feeder connected to the second means.

Microwave level gaging system

Abstract: A method and apparatus for measuring liquid level. A generated broad-band swept-frequency C.W. microwave signal (2-4 GHz) is upverted to a high frequency band signal (34-36 GHz), which is transmitted towards, and reflected from, a liquid surface. The reflected signal is downverted to the frequency band of the original generated signal, and then the phase difference between the original and downverted signals is measured by a microwave phase discriminator and a quantizer, which generates video pulses proportional to the total phase shift across the swept C.W. band. During an adjacent sweep in the same direction, the original signal is compared with a signal transmitted through a calibration cable equivalent to a known free-space path length. The unknown signal path to and from the liquid surface, can then be calculated by comparison of the video pulse train outputs during the CALIBRATE and OPERATE modes of operation, either by the ratio of the number of pulses, or the average time between pulses during each sweep. Alternately, the mode of operation can be switched several hundred times during a single sweep across the bandwidth, and the unknown signal path corresponding to a particular liquid level can be calculated by comparison of the spacing during adjacent CALIBRATE and OPERATE modes to give several hundred measurements at different frequencies. Deviate measurements can then be eliminated, and the remaining measurements can be averaged to give a highly accurate true average measurement by known methods.

Systems and methods for determining radio frequency interference

Abstract: The presence, frequency and amplitude of radio frequency interference superimposed on communication links originating from a terrestrial region and including a relay in a geostationary spacecraft are determined by pointing a narrow beam antenna on the satellite at the terrestrial region. The level of noise radiated from the region, in a predetermined frequency band of interest, to the antenna is measured at a terrestrial station that is usually remote from the region. Many of the measurements are performed in each of a plurality of frequency bands across the spectrum. Calibrating radio signals having a plurality of predetermined EIRP's (Effective Isotropic Radiated Power) and frequencies in the spectrum are transmitted from the region through the spacecraft narrow beam antenna back to the station. At the station, the levels of the received calibrating signals are separately measured for each of the frequency bands and EIRP's. In response to comparisons of the measured amplitudes of like frequencies of the calibrating signals and noise, the presence, frequency and amplitude of sources of radio frequency interference originating from the region are determined.

System filter for double frequency utilization

Abstract: A system filter for double frequency utilization, including a broadband polarization filter in conjunction with frequency filters for separating two different frequency bands with each frequency band being doubly orthogonally polarized. The broadband polarization filter of singly symmetrical construction includes a doubly polarizable waveguide section which is axially divided by means of a partition into two symmetrical partial waveguides and the two frequency bands of the wave which is polarized parallel to the partition are each coupled out through a respective coupling window in two oppositely disposed walls of the waveguide section into a respective waveguide tee. The higher frequency band of the decoupled wave is available at the sum arm of a magic tee which has two symmetrical arms each connected via a respective highpass filter to a respective arm of one of the waveguide tees, while the lower frequency band is available at the sum arm of a further magic tee which has two symmetrical arms each connected via a respective bandpass filter to a respective arm of one of the waveguide tees. The orthogonally polarized wave is divided into the two further frequency bands in a further frequency filter which is connected in series with the doubly polarizable waveguide section via a transition piece.

Radio-frequency coupler

Abstract: A radio-frequency coupler comprising a first terminal for interconnection with a conventional automobile receiving antenna used for receiving rf transmissions within a first radio-frequency band, a second terminal for interconnection with a receiver operating within the first radio-frequency band and a third terminal for interconnection with a transceiver operating within a second frequency band different from the first band. A first rf transmission path extends between the first terminal and the second terminal and a second rf transmission path extends between the first terminal and the third terminal. A first resonant circuit is connected in the first rf transmission path and tuned to pass rf transmissions in the first band but substantially block those in the second band. A second resonant circuit is connected in the second rf transmission path and tuned to resonate at a frequency within the second band so that rf transmissions within the second band are passed but those within the first band are substantially blocked. A third resonant circuit is connected between the third terminal and electrical ground and tuned to resonate at a frequency outside the second band. The second and third resonant circuits form a series-connected path between the first terminal and electrical ground and the impedance of the third resonant circuit at the second frequency band allows maximum rf energy within the second band to be transferred between the antenna and the transceiver thereby permitting the conventional automobile receiving antenna normally used only for receiving rf transmissions within the first frequency band to also be used for sending and receiving rf transmissions within the second frequency band.

Quasioptical band-rejection filter at 100 GHz

Abstract: We describe a tunable Fabry–Perot type filter which has application to radio astronomy in the frequency band 80–110 GHz. The filter causes image sideband suppression when used with a heterodyne spectral line receiver having an intermediate frequency of 4.75 GHz. The transmission loss in the signal sideband is about 0.4 dB, while the image sideband rejection is more than 15 dB; there appears to be little if any problem with scattering or distortion of the antenna radiation pattern.

Antenna system with automatic depolarization correction

Abstract: A spectrum reuse antenna system is described for transmitting orthogonally polarized RF waves at one frequency band to a satellite and for receiving orthogonally polarized RF waves from a satellite at a second frequency band through a common antenna. A local generator provides a first control signal which varies as a function of the typical rotation of the polarization of a transmitted wave at the one frequency band travelling through the ionosphere. The local generator also provides a second control signal which varies as a function of the typical rotation of the polarization of a received wave at the second frequency band travelling through the ionosphere. A driven means responsive to the first control signal causes a rotation of the polarization of the transmitted waves to correct for Faraday rotation in the ionosphere and a driven means responsive to the second control signal causes rotation of the polarization angle of the antenna system for the received waves to correct for the Faraday rotation.

Circuit arrangement for selective frequency analysis of the amplitudes of one or more signals

Abstract: A circuit arrangement for the frequency selective analysis of the amplitudes of one or more signals in which a selective receiver is automatically scanned through a given frequency band and the scanning speed of its frequency settings is controlled as a function depending upon the difference in amplitude of signal voltages consecutively received in time and including a second selective receiver is provided which has its frequency setting changed synchronously with that of the first receiver with a constant frequency spacing between the two receivers and with the frequency of the second receiver being ahead of the first receiver and including an analysis device connected to the second receiver to derive control signals.

Launching and/or receiving network for an antenna feedhorn

Abstract: A launching and/or receiving network is disclosed capable of coupling radio signals in a first frequency band, e.g., 2 GHz into and/or out of an existing antenna system without perturbing the signals being transmitted in other frequency bands, e.g., 4, 6 and/or 11 GHz. The first frequency band signal is launched through an evanescent mode waveguide filter which is both coupled to the flared sidewall of a feedhorn through an H-plane, T-junction, and provides a very broad stopband for the signals in the other frequency bands being launched in the feedhorn. To minimize mode conversion for the signals in the other frequency bands, a dummy evanescent mode waveguide filter is connected at one end thereof to the feedhorn facing the first frequency band launching network and at the other end thereof to a matched load through a waveguide section. A second launching and/or receiving network can be similarly coupled to the feedhorn in a plane normal to the first network to permit a different orthogonally polarized beam, at the first frequency band, to be simultaneously transmitted and/or received by each of the two networks.

Absorption and the low velocity zone

Abstract: It is well known that elastic wave velocities are independent of frequency only for a non-dissipative medium. In a real solid dispersion must accompany absorption. This effect has been emphasised by Randall and Liu et al. The effect is small when the seismic quality factor Q is large or unimportant if only a small range of frequencies is being considered—that is, the spectra of P waves. Even in these cases, however, the measured velocities, or inferred elastic constants, are not the true elastic properties but lie between the high frequency and low frequency limits or the so-called ‘unrelaxed’ and ‘relaxed’ moduli. The magnitude of the effect depends on the nature of the absorption band and the value of Q. When comparing data taken over a wide frequency band the effect of absorption can be considerable especially considering the accuracy of present body-wave and free-oscillation data. Thus, Jeffreys questions conclusions based on free oscillation data, particularly where they differ from body-wave results which are based on much shorter periods. Carpenter and Davies and Davies attempted to reconcile body-wave and surface-wave Earth models by allowing for physical dispersion using Futterman's and Kolsky's dispersion–absorption relationships. Jeffreys used Lomnitz' relationships. Liu et al. have shown that dispersion depends to first-order on absorption in the seismic frequency band and derived a linear superposition model that gives a Q that is independent of frequency. It can be shown that all of the above theories give equivalent absorption–dispersion relations for moderate absorption. Liu et al. and Anderson et al. have shown how to correct surface-wave and free-oscillation data for physical dispersion. Much of the support for the existence of an upper mantle low velocity zone has come from the inversion of normal mode data that have been uncorrected for physical dispersion due to absorption. In the light of these developments, we decided to re-examine the question of a shearwave low velocity zone.

Method and apparatus for the scrambled transmission of spoken information via a telephony channel

Abstract: A method of scrambling and unscrambling speech transmissions by first dividing the speech frequencies into two frequency bands and reversing their order by modulating the speech information, the width of the bands being varied by varying the carrier frequency used in the modulation process, adding to the reversed frequency bands at least one supplementary signal derived from the modulation process and transmitting the resultant signal. The transmitted signal is unscrambled by first subtracting from it a supplementary signal which is generated at the receiving station from the received scrambled signal, the last mentioned supplementary signal being identical to that added to the reversed frequency band signal prior to transmission and then subjecting the resultant signal to the same modulation processes as referred to above to reassemble the frequency bands into a frequency band containing substantially the same speech frequencies as those that are scrambled. Apparatus for carrying out the above method can comprise a separate transmitter and receiver or a single transmitter/receiver whose mode of operation is controlled by a speech key, the transmitter and receiver each including a frequency scrambling device employing modulators and a time scrambling device for generating the supplementary signal.

Repeater monitoring and fault location

Abstract: A repeater monitoring and fault location system is disclosed for a submarine cable system which includes repeaters of the type having separate high band and low band amplifiers for two-way transmission over one cable. Each repeater includes an oscillator for generating a signal at a frequency in the cutapart region between the high frequency and low frequency transmission bands and which is uniquely identifiable to that repeater. A test tone at a frequency in the low frequency transmission band is transmitted from the low frequency transmitting end along the cable. The low band amplifiers intermodulate the local oscillator signals with the transmitted test tone to generate a series of seond order modulation products at frequencies in the high frequency band. A low pass filter, designed to have a controlled moderate level of loss in the portion of its high frequency stop band over which the frequencies of the second order modulation components lie, is connected to the output of each low band amplifier. A series of second order modulation components at frequencies uniquely identifiable to each repeater is coupled to the high frequency transmitting path for transmission to the low frequency transmitting end. By comparing the magnitudes of the returned modulation components with reference levels, the modulation performance of each low band amplifier is determined and a faulty amplifier can be located.

Photoelectric gas analyser with tunable laser radiation source - has radiation passing through test gas sample to detector feeding logarithmic signal processing circuit

Abstract: The signal output of the detector is connected to a logarithmic network. At any time interval in which the laser frequency changes in a frequency band outside and in the region of the absorption line the time control unit switches the output of the logarithmic network to a channel with integrating and holding circuits. The output signal of the analyser is formed by forming the difference of the stored values. A beam splitter produces a reference beam path and a motorised diaphragm alternately frees the two beam paths which are united again into one beam path by a beam fusion device in front of the receiver.

Acquisition technique for time division multiple access communication system

Abstract: An initial acquisition technique for a time division multiple access (TDMA) communication system, employing an access signal of a frequency varying periodically in a predetermined relation to the TDMA time frame. Means are provided for detecting when the frequency of the signal as relayed back to the accessing station is at a predetermined value or within a predetermined frequency band to obtain the desired transmission timing information without necessitating use of any automatic frequency control means despite any deviation in the central frequency of the signal occurring during its travel.

Programming unit for a television tuning phase locked loop

Abstract: A phase locked loop type of television tuning apparatus includes an apparatus for dividing the frequency of a local oscillator signal by a number equal to the frequency of the local oscillator signal, in MHz, corresponding to the presently selected channel. The divider forms an output signal including first and second portions having durations respectively equal to first and second predetermined numbers of periods of the local oscillator signal. The first number is related to the number of the selected channel. The second number is related to the frequency band in which the selected channel resides. To determine the frequency band of the selected channels, band traversed signals are generated whenever the number of periods of the local oscillator signal generated since beginning of the first portion corresponds to the first channel in a band. When a new band traversed signal is generated, the previous band traversed signal is terminated. The band traversed signal remaining at the end of the first portion determines the band in which the selected channel resides.

Reflector with frequency selective ring of absorptive material for aperture control

Abstract: An antenna is made operative for two frequency bands, ΔFB and ΔFH, the latter higher than the former, by means of a frequency selective absorber, covering, in its edge region, a reflector of the antenna in order to reduce the diameter of the reflecting surface of the reflector and therefore the gain of the antenna for frequency band ΔFH.

Frequency spectra of extensional vibration in Pb(Zr⋅Ti)O3 disks with Poisson’s ratio larger than 1/3

Abstract: The frequency spectra of axially symmetric extensional vibration in piezoelectric Pb(Zr⋅Ti)O3 ceramic disk plates having Poisson’s ratio (σ) of 0.37 have been investigated theoretically and experimentally. The theoretical frequency spectra were calculated with approximation of elastically isotropic disk plates for r (diameter/thickness) of 1 to 30. It was found that the terrace‐type spectra which appear in a frequency band between the cutoff frequency of the symmetric thickness‐shear mode and the frequency minimum Ω* do not construct a constant frequency bandwidth, in contrast to the case of σ<1/3. Experimental spectra were observed with the Pb(Zr⋅Ti)O3 disk plates for r of 4.8 to 7.2. The experimental spectral agreed well with the theoretical ones, by fitting the cutoff frequency of the fundamental thickness‐extensional mode of the elastically isotropic plate to that of the piezoelectric Pb(Zr⋅Ti)O3 ceramic plate. From the results of these analyses, it has been found that the Pb(Zr⋅Ti)O3 ceramic disk pla...

Variable gain amplifier with adjustable upper frequency limit

Abstract: An amplifier circuit including a differential amplifier and having an effective transmission frequency band delimited by a lower limit frequency which can be varied by application of a control voltage is also given a defined upper limit frequency by connecting a resistance in series with a frequency dependent impedance between an inverting input of the amplifier and a point at the circuit reference potential. The value of the resistance can be adjusted to provide the desired upper limit frequency value and can be varied to change that frequency value.

Band pass amplifier

Abstract: A frequency band pass circuit having an amplifier that has an amplifying state and may be selectively deenergized to a non-amplifying state. A reverse bias is placed on the amplifier when in the deenergized state to provide substantially the same band pass characteristics of the circuit in the non-amplifying state as in the amplifying state and to reduce the insertion loss impedance through the amplifier in the non-amplifying state.

Frequency bands changeover transceiver - uses several varactor-tuned oscillators with capacitors

Abstract: The transceiver has its oscillators switched with no delay from transmit to receive frequency bands. Each frequency band has its own oscillator and each oscillator has a varactor diode and fixed capacitor. The varactor diodes have values such that the same change in the magnitude of the control voltage for all oscillators causes roughly the same absolute change in the frequencies of the oscillators. The series-coupled varactor and fixed capacitor are shunted by the inductor belonging to the that oscillator's resonant circuit.

Dual channel wide-band frequency modulated keyable control circuit and keying circuit therefor

Abstract: A dead-oscillator detector in a wide band frequency modulated keyable control circuit averts attempted actuation of the unlocking function by the coupling of untuned energy-absorbing material, such as iron, to a sensing coil. The energy absorbing material, being unresponsive to frequency, reduces the rf energy in the sensing coil approximately uniformly at all swept frequencies. The dead oscillator detector, lacking an ac component in the rf envelope over the entire frequency band, generates an inhibit signal which prevents the unlocking function. When a tuned circuit is properly coupled to the sensing coil, the resulting ac component in the rf envelope provides one required enable signal to unlock circuits.

Constant delay resonant tank circuit combination for frequency discrimination

Abstract: The method of designing a circuit having a substantially constant delay over a given frequency band and having a substantially linear attenuation characteristic or amplitude change characteristic over the same frequency band and the product resulting from such a design approach. One such approach uses a primary tank circuit having a given Q and amplitude response feeding two secondary tank circuits each of which have a higher Q and amplitude response and wherein the resonant points are on either side of the resonant point of the primary tank. By adjusting the Q, amplitude response and resonant frequency of the three tanks, the "delayless" and linear amplitude change characteristics over a given frequency band can be achieved.

Automatic fine tuning circuit

Abstract: A relatively broad band automatic fine tuning circuit covering a frequency band at least approximately as broad as a television channel and including means to shift the frequency of the television tuner up or down, as necessary, to the proper frequency within the automatic tuning range. A first control signal is obtained by comparing the average value of the envelope detected signal from the video detector with a voltage equal to the pedestal level if the signal were a properly tuned video signal. If the actual average value of the envelope is between zero volts and the pedestal voltage, the tuner is either correctly tuned or tuned at a somewhat lower frequency than is correct. If the voltage average value has a greater magnitude than the pedestal voltage the tuning of the tuner is too high. A frequency discriminator receiving the video IF signal controls the automatic tuning operation close to the desired frequency. A noise detector in the audio circuit controls a muting circuit to disable AFT operation if the receiver is so far out of tune as to receive noise instead of an audio signal.

Frequency marker generator

Abstract: A frequency marker generator for providing marker pulses corresponding to known frequencies over a wide band of frequencies is disclosed. A signal having a predetermined frequency or known frequency as well as the output unknown frequency or frequencies of the signals from a system under test are both applied to a phase and frequency detector. A sweep generator provides a signal which is variable in frequency over the frequency band of interest, and is applied to the system under test. The phase and frequency detector having two discrete output states provides a transition of its output state when the variable frequency output signal from the system under test passes the predetermined frequency and a differentiator differentiates the output signal from the phase and frequency detector and transmits it through a pair of steering diodes to provide a frequency marker signal which may be recorded separately or mixed in a mixer with the output of the system under test to provide a display of the amplitude versus frequency of the system under test at the predetermined frequency or frequencies.

Method and apparatus for cancelling chrominance artifacts

Abstract: A color video recorder/reproducer records wide bandwidth luminance information alternately with narrow bandwidth luminance information plus chrominance information for the transmitted lines of a television picture frame. Before recording, the chrominance information is frequency converted to occupy a frequency band substantially adjacent to the frequency band occupied by the narrow bandwidth luminance information. Upon playback, the frequency converted chrominance information is separated from the narrow bandwidth luminance information and converted to its originally occupied frequency band. A video signal is then reconstructed by combining the signal recorded for a given line with a complementary portion of the signal recorded for the preceding line. Upon display of a picture thus produced, an artifact pattern is observed. The present invention recognizes the source of this artifact pattern to be the imperfect separation of the narrow bandwidth luminance information from the chrominance information. Rather than employ expensive and complicated filtering devices to better separate the two signals, the present invention permits the small portion of chrominance information to stay in the luminance channel but compensates therefor by so frequency converting the chrominance information before recording that the artifacts thus produced in one line of the picture frame are 180° out of phase with the artifacts in an adjacent line and thus are effectively cancelled out by the integrating characteristics of the eye.