Showing papers on "Frequency band published in 1981"

Dual band communication receiver

Abstract: Diclosed is a dual band communication receiver for use in a burst communication sytem. The receiver is capable of esentially simultaneous reception at a first carrier frequency (L), such as L-band and a higher carrier frequency (H), such as S-band, using distinct codes and replying in the frequency band received. A typical system is composed of a transponder and an interrogator. The incoming coded signal is down converted to an i.f. frequency compatible with surface acoustic wave (SAW) convolvers. The i.f. signal is then divided between two SAW convolvers, each having a convolution interval of two times the message symbol length (2T). Reference signals A and B are composite signals comprised of alternate L-band and H-band signals, each having a time period equal to T and each L- or H-band signal operating at a 50% duty cycle. Reference signals A and B are time reversed to the input signals applied to the convolver and are orthogonal to one another. Each of the convolver outputs are processed through log video detection circuits to reduce the dynamic range followed by peak detecting and stretching to reduce the pulse bandwidth. The outputs from each peak detection and stretching circuitry are coupled to a smaple-and-hold circuit which are in turn divided such that one path is to synchronization and interrogation sidelobe suppression (also referred to as sidelobe inhibit, ISLI or control signal) matched filters designed to look for the particular symbol sequences between the two convolver channels characteristic of the preamble and ISLI signals. The synchronization signal and the sidelobe suppression signal are used in order to determine if a valid preamble has been detected by the receiver and if the receiver is in a desired portion of the interrogator radiation pattern; if so, then a timing or address signal and the remaining portion of the message which contains the data is clocked into a memory.

An introduction to the coherence function and its use in EEG signal analysis

Abstract: The coherence function quantifies the association between pairs of signals as a function of frequency and has been shown to be useful for measuring changes in EEG topography related to cognitive tasks, psychopathology, and other aspects of brain organisation. For a narrow frequency band, its magnitude is analogous to the correlation coefficient between the signals limited by that band, but its value may differ because of the way that smoothing over frequency is achieved. The coherence function is described in physical terms using simple waveforms.

Adaptive spread spectrum FH-MFSK transmitter and receiver

Abstract: The present invention relates to a transmitter, a receiver and techniques for use in a frequency-hopping, multilevel frequency shift keyed (FH-MFSK) radio system which permits the selective concurrent transmission of one or two encoded frequencies per time slot of the transmitted sequence for improving reception at a receiver experiencing interference from the system transmitters above a predetermined interference threshold level. An alternative arrangement permits all transmitters and receivers to communicate with one another by transmitting a separate one of multiple frequencies in a separate one of an equal number of multiple frequency subbands forming the system frequency band during each time slot for providing flexibility in system design. Combinations of the two arrangements can also be employed.

Electrical filter circuit operated with a definite sampling and clock frequency fT which consists of CTD elements

Abstract: The invention relates to an electrical filter circuit operated with a definite sampling and clock frequency fT, such filter being made up of CTD elements, and having at least one bipolar or quadripolar resonator in the form of a self-contained conductor loop (for example, C1, C2) with unidirectional transmission behavior. Differences in the transfer capacitances of such circuits are reduced, as far as possible, in order to thereby simplify integrated manufacture as far as possible, by positioning the frequency band to be filtered out at a frequency position which lies above half the clock frequency (fT /2), or in the range from fT /2 through 3fT /2.

Fundamental limitations caused by RF propagation

Abstract: Propagation phenomena affect the design of radio frequency (RF) transmission systems. Propagation phenomena limit the suitability of portions of the frequency band for some applications, limit the reliability of RF transmission systems, and provide a means of coupling unwanted signals from one system to another with the potential of producing interference. The possiblity of interference is the fundamental limitation to the unrestricted use of the frequency band. Phenomena affecting suitability, reliability, and the potential for interference are considered for frequencies in the 1- to 300-GHz range.

Modem to be coupled to a directional transmission line of an SS multiplex communication network

Abstract: In an SS (spread spectrum) modem, a high-pass filter (81) for rejecting a low frequency component including an information signal received by demodulation, produces an SS signal component modified by a PN (pseudo noise) code sequence used for the demodulation. A multiplier (82) substantially regenerates the SS signal component. Band division may be resorted to, in which case an input filter (161) selects a partial band SS signal for the demodulation. A transit filter (164) rejects the partial band SS signal. An SS signal is sent to a destination modem through one of output filters (162) selected for the destination modem. Each generator (67, 71) may generate a PN code sequence given by a product of PN codes, one having a frame period equal to an integral multiple (unity allowed) of the PN clock period of another. Each partial band may be about 1/5 of the entire frequency band of the PN code sequence. A center portion of the band may be used in transmitting a narrow-band synchronizing signal. In a band division network, the highest partial band may be used for an SS (multiplex) signal and other partial bands, collectively for a baseband TDM signal.

Spectral analysis vs. period-amplitude analysis of narrowband EEG activity: a comparison based on the sleep delta-frequency band.

Abstract: This paper presents a comparison of spectral analysis with period-amplitude analysis when applied to the quantification of narrowband electroencephalographic (EEG) activity. In particular, it examines their respective usefulness in quantifying on the average the electrographic content within the delta-frequency band of EEG epochs during human stage 4 sleep. It is shown that while the power spectrum efficiently quantifies the overall power trends in the EEG data, period-amplitude analysis seems to offer more resolution than the power spectrum in detecting electrographic details in amplitude and incidence within relatively narrow frequency bands. Examples are given of the sensitivity of spectral analysis ot both wave amplitude and incidence, and of the fact that--due to the inherent averaging process in the power spectrum generation--spectral analysis cannot differentiate between low-amplitude, high-incidence EEG activity and high-amplitude, low-incidence EEG activity, in contradistinction to period-amplitude analysis. It is also shown that although two EEG epochs may exhibit similar power spectrum plots, their corresponding period-amplitude plots may not be similar. It is emphasized that discrepancies may exist when comparing spectral to period-amplitude analysis due to differences in the definition of "frequency" in the two techniques.

Broad-Band Active Phase Shifter Using Dual-Gate MESFET

Abstract: This paper describes a broad-band, dual-gate MESFET phase shifter (vector generator), operating over the 4- 8-GHz frequency band and capable of a continuous phase shift and multiplicity of modulations including digital phase shift and amplitude modulation directly, and indirectly (with additional information processing circuits), single sideband modulation, frequency modulation, and phase modulation, etc. A dual-gate FET is used as a variable gain amplifier and phase shift is obtained by complex addition of two orthogonal variable vectors. The principle of the phase shifter and the experimental results are presented.

Method and apparatus for monitoring electrocardiogram (ECG) signals

Abstract: A method and apparatus for monitoring ECG signals are described characterized in that an ECG signal wave is detected, filtered to pass only a frequency band within a range of about 25-300 Hz, and stored in a first storage device; and each successive ECG signal wave is then detected, similarly filtered, and stored in a second storage device. Each of the successive signal waves, when stored in the second storage device, is cross-correlated with the signal wave stored in the first storage device, and a determination is made whether the maximum cross-correlation coefficient exceeds a predetermined value. Each of the successive signal waves having a maximum cross-correlation coefficient exceeding the predetermined value is averaged with the waves stored in the first storage device following which it is stored in the first storage device in place of the signal wave previously stored therein, and is also displayed.

Frequency modulated phase-locked loop signal source

Abstract: A programmable phase-locked loop frequency synthesizer having a feedback path that includes a tuned discriminator circuit is frequency modulated by coupling a portion of the modulating signal into the feedback path to effect modulation at rates which exceed the bandwidth of the phase-locked loop and by utilizing a portion of the modulating signal to frequency modulate the phase-locked loop reference signal to effect modulation at rates within the bandwidth of the phase-locked loop. A digitally controlled phase shifter that forms a portion of the discriminator tuning circuits in effect divides the phase-locked loop tuning range into a series of relatively narrow centiguous frequency bands. Data, representing deviations in the discriminator characteristics for each of these frequency bands, are stored in an erasable programmable read only memory. As the phase-locked loop is tuned to a particular frequency, a microprocessor determines the associated frequency band, accesses the stored data appropriate to that frequency band and establishes the proper setting of the digitally controlled phase shifter. The accessed data is coupled to a multiplying digital to analog convertor to automatically adjust the level of the modulating signal so that the system exhibits relatively constant modulation characteristics for each frequency band within the tuning range of the phase-locked loop. Low distortion is achieved within each of the relatively narrow frequency bands by circuitry which reduces or eliminates amplitude variations within the feedback path that includes the discriminator circuit, band pass filtering within this feedback path, and a feed-forward circuit arrangement that prevents modulation components from adversely affecting the discriminator tuning circuits. Additionally, a gain switching arrangement that automatically reduces the gain of the feedback loop and the phase-locked loop gain ensures system stability for all operating and tuning conditions.

Data over voice transmission arrangement

Abstract: A system for interpolating digital data signals to a frequency band above analog speech signals in a common transmission channel is disclosed. The system utilizes short time frequency analysis techniques to determine the cutoff frequency of the speech signal. Data signals temporarily held in storage within the system are thereafter modulated into an unused frequency band of the transmission channel above that needed for speech signals. The combined speech and data signals in the system are sent to a receiver which relays the respective speech and data signals to their appropriate locations. This system is compatible with digital signal processing techniques using Fast Fourier Transform Technology in conjunction with solid state logic elements.

Method for jam-resistant communication transmission

Abstract: A method for jam-resistant transmission speech signals by radio which have been processed via vocoders, utilizing spread spectrum multiple access modulation (SSMA) or rapid frequency hopping (FH) provides, with respect to the danger of an inherent jamming brought about when a great number of stations simultaneously use the same frequency band for the same radio channel frequency group, activation and deactivation of the transmitter and receiver at the rate of the internal system frame clock pulse during a frame clock pulse period only when useful information is present. In this manner, in the case of simplexcommunication connections, on the average approximately 40% and, in the case of duplex operation, more than 60%, of the transmitting time can be saved, and hence, the inherent jamming of the system can be reduced in a corresponding fashion.

Input device for computer speech recognition system

Abstract: Systems for the recognition of speech by computer have usually required t the speech be of a strictly standarized nature, free of such features as regional accent, and unaccompanied by background noise. The problem has been to produce a system providing information which will allow accurate recognition in the presence of noise, and with non-standard speech sounds. The invention provides to a computer in a speech recognition system information in parallel streams on a number of factors, viz, the existence, in any signal which may contain speech sounds, of a fundamental repetitive structure and its periodicity; the existence of a high frequency component having a wide frequency band; the existence of a component having energy relatively stable with respect to time and characteristic of background noise; the peak frequency, peak amplitude and band width of sounds lacking a low frequency component; and the frequency of resonant content of any component having a fundamental repetitive structure and the level of correlation.

Speaker and speaker system

Abstract: A speaker in which a voice coil bobbin (4) is connected through a mechanical filter to vibrating members (11, 14) for limiting the reproducing frequency band in predetermined range by the mechanical filter, and a speaker system employing the speaker. A pneumatic suspension V is used as the mechanical filter to eliminate the variations in the reproducing frequency band even for long term usage.

The Use of a Matched Symmetrical Five-Port Junction to Make Six-Port Measurements

Abstract: A new configuration for six-port measurements is proposed. It consists of a symmetrical five-port junction and a directional coupler. Assuming the components to be ideal, it is shown that the proposed six-port has optimal properties for accurate determination of complex reflection coefficients. An experimental coaxial five-port junction has been designed and used in a six-port measurement system. After calibration, using five impedance standards, measurements on precision loads indicate good measurement accuracy over the frequency band where the five-port is well matched.

Broaddband reverseddllshaped antenna

Abstract: PURPOSE:To widen the frequency band of synthetic input impedance with a passive element roughly coupled, by adding a compensating element to a reversed-L-shaped antenna and then by varying the input impedance of the reversed-L-shaped antenna. CONSTITUTION:Electric current, once fed from input terminal 1, is shunted to radiating element 2 and parallel element 4 to radiate an electromagnetic wave into the air, but part of the electromagnetic wave propagates to passive element 6 to generate electric current on element 6 in proportion to the extent of coupling, so that part of it will be radiated again. When the extent of coupling between the reversed-L-shaped antenna and passive element 6 increases up to >= one tenth, rough coupling should be applied since an influence on directivity increases and, in consequence, mutual interference lessens, so that the frequency band of input impedance can not be widened. For the purpose, compensating element 7 with distribution constants of fine inductance L and fine capacity C is added to vary the input impedance of the reversed-L-shaped antenna, thereby widening the frequency band of the synthetic input impedance.

Piezoelectric knock sensor

Abstract: A broadly tuned self resonant knock sensor includes a piezoelectric element mounted on a central mounting stud. The element includes a generally annular vibratable portion having a variable radial dimension so as to exhibit resonant vibrations at a plurality of relatively closely spaced resonant frequencies essentially spanning an engine determined knock frequency band. In its preferred embodiment the element comprises a circular plate having piezoelectric generating means and an axis offset from the axis of the mounting stud.

Tuning display for a television receiver

Abstract: In television (TV) receivers, the VHF-TV band including channel 2-13 is perceived by most viewers as being a single TV band even though it is in fact partitioned into lower and upper frequency portions, including channels 2-6 and 7-13, respectively, which are separated by a gap. Voltage controlled tuning systems for such TV receivers employ a tuning voltage which varies over substantially the same range of magnitudes from a lower voltage to a higher voltage for each of the frequency portions of the VHF band. Accordingly, conventional channel indicators responsive to the magnitude of the tuning voltage partition the bands to avoid ambiguity in the channel indication. In the present arrangement, a tuning indicator produces an on-screen bar display having a position which is indicative of the selected channel for all VHF channels as if the VHF frequency band was continuous and not partitioned thereby being consistent with the perception of most viewers. Specifically, the tuning indicator includes a divider device for attenuating the tuning voltage when a channel in the lower or upper VHF band is selected, a device for developing an offsetting voltage when the selected channel is in the upper VHF band, and a device for combining the attenuated tuning voltage and the offsetting voltage to develop a control signal which determines the position of the bar on the TV screen.

Wideband, synthesizer switched element voltage controlled oscillator

Abstract: An exceptionally wideband, synthesizer controlled voltage controlled oscillator is disclosed which is characterized by a plurality of pin diode frequency shift networks which, when actuated shifts the frequency of the oscillator in selectable binary steps within a wide frequency range in the order of 48 MHz. Special means are included to prevent undesireable parasitic oscillation modes when such frequency shift networks are in an inactuated, switched off mode. A multiple varactor tuning circuit is provided for selecting a precise frequency within a relatively narrow frequency band on the order of 6 MHz.

Apparatus for acquiring and collecting radio signals coming from a plurality of stations

Abstract: An apparatus for acquiring and collecting messages aboard a satellite which are transmitted via respective radio-signals over different frequencies from a plurality of beacons comprises a receiver having an adjustable gain control input. An automatic gain control loop is provided for maintaining the gain of the receiver at a constant value. While the input frequencies of each input signals and time of arrival thereof are not exactly known, it is known that all these input frequencies are contained within a predetermined input frequency band which is periodically scanned by a frequency analyzer. This analyzer operates by scanning the center frequency of a band pass filter over the input frequency band and detecting the level of signals at the output of this filter for a plurality of successive frequencies within this input frequency band. The detected levels are digitized. The resulting digitized level indications are statistically analyzed and the result of this statistical analysis is used for adjusting the level of the gain control input of the receiver. According to an embodiment, only those detected levels which correspond substantially to input signals carrying messages retained for demodulation are used for determining an average level indication over a time period such as that for a full revolution of the satellite. The thus determined average level is compared with a reference value to adjust the receiver gain, thus eliminating gain variations due, for example, to aging of the components.

Equipment for single band multiplexing through digital processing

Abstract: The equipment disclosed in the present invention provides means for SSB multiplexing and demultiplexing base-band signals, equal in number to a power of two, digital signal processing techniques. The frequency modulation process of the base-band signals is partly performed with a discrete Fourier Transform (D.F.T.), the dimension of which is appreciably reduced with respect to the number of signals to be multiplexed, and partly with modulators (multipliers), some of which are of simple construction and which are fewer in number than the number of signals to be multiplexed. Filtering is effected with a set of filters with different frequency repetition periods and which, when cascade connected, from a pass-band filter equal to the frequency band which characterizes every base-band signal. The frequency repetition period of the entire filter is equal to the sampling frequency of the multiplexed signal.

Noise reduction system having series connected variable frequency filters

Abstract: A noise reduction system having a compressor and an expander. The compressor comprises series connected high and low frequency band filters of the variable frequency type, the cut-off frequencies of which are respectively controlled in response to high and low frequency components of the output of the series connected filters so that they are shifted in opposite directions to each other independently as a function of the amplitude of the respective frequency components, whereby the amplitude range of the respective frequency band is emphasized to a constant value while the frequency range of the emphasized band is varied in response to the amplitude of the respective component. The expander comprises series connected high and low frequency band filters of the variable frequency type of which the cut-off frequencies are respectively controlled in response to high and low frequency components of the input to the expander so that they are shifted in opposite directions to each other in a manner similar to that of the compressor. Each of the filters of the expander has a complementary frequency response characteristic to that of the corresponding filter of the compressor to de-emphasize the emphasized frequency components to restore the normal amplitude and frequency ranges of the original signal.

Regulating device for control variables of an internal combustion engine

Abstract: A regulating device is proposed for control variables of an internal combustion engine, in particular for the fuel metering signal and the ignition signal, which has an intervention capability for signals of at least one knocking sensor on the engine via a knocking-signal evaluation circuit; this knocking-signal evaluation circuit includes a frequency recognition circuit and preferably an amplitude recognition circuit, and it detects and evaluates the knocking signal only during specific times or angles relating to the ignition signal. The frequency recognition circuit is realized by means of two counters. The counting range of the first counter marks the value of the upper threshold frequency which can be recognized, while the counting range of the second counter characterizes the frequency band. Finally, by means of a third counter, a specific disturbance interval can be established, in order to cause the frequency recognition circuit to respond only after the appearance of a predetermined number of pulses of the predetermined frequency, thus bringing about an adjustment of the control variables.

Speech recognition systems

Abstract: Systems for the recognition of speech by computer have usually required that the speech be of a strictly standardised nature, free of such features as regional accents, and unaccompanied by background noise. The problem has been to produce a system providing information which will allow accurate recognition in the presence of noise and with non-standard speech sounds. The invention provides to a computer in a speech recognition system information in parallel streams on a number of factors, viz the existence, in any signal which may contain speech sounds, of a fundamental repetitive structure and its periodicity; the existence of a high frequency component having a wide frequency band; the existence of a component having energy relatively stable with respect to time, and characteristic of background noise; the peak frequency, peak amplitude and band width of sounds lacking a low frequency component; and the frequency of resonant content of any component having a fundamental repetitive structure and the level of correlation.

Loudspeaker circuit with treble loudspeaker pointing at ceiling - has middle frequency and complete frequency loudspeakers radiating horizontally at different heights

Abstract: The loudspeaker circuit has a main loudspeaker system (18,20) to which the entire frequency range of the audio signal is passed. This system is located a small distance above the floor of the room and radiates sound horizontally. The middle-region of the audio signal's frequency band is passed to a first auxiliary loudspeaker (46,50) located at a greater distance from the floor than the main loudspeaker system and radiating sound in a horizontal direction. The h.f. band of the audio signal is passed to a second auxiliary loudspeaker (48,52) located at a greater distance from the floor than the first auxiliary loudspeaker and radiating sound vertically upwards towards the ceiling of the room.

Signal-seeking tuning system with automatic bandswitching for a television receiver

Abstract: A signal-seeking tuning system for a television receiver scans the VHF and UHF signal bands until a present TV channel signal is detected. Tuning voltage is developed by a digital-to-analog converter in response to a binary word stored in an up/down counter. The value of the binary word increases when a scan-up signal is applied and decreases when a scan-down signal is applied. Band signals are automatically sequenced to the next higher frequency band when the binary word "rolls-over" from a maximum to a minimum value, or to the next lower frequency band when the binary word rolls-over from its minimum to its maximum value. Scanning is stopped by inhibiting changing of the binary word when a valid sequence of AFT signals is detected. Thereafter, the tuning voltage is compensated for drifts by incrementing or decrementing the binary word whenever the AFT signal departs from a predetermined condition. This correction is inhibited, however, when the binary word is at its minimum or maximum value so that unwanted bandswitching is avoided.

Apparatus and method for acquiring and processing radio signals received at different frequencies

Abstract: Apparatus for acquiring and processing incoming radio signals received from a plurality of stations, the frequencies of which are contained in a predetermined frequency band. The received signals are mixed with a local oscillator frequency which is repeatedly scanning the input frequency band at a fast rate produced from a frequency synthesizer whose control input is modified step by step to cycle through a corresponding predetermined set of programming values. The sweep rate of the programming value of the frequency synthesizer is so high that the stabilization time for the frequency at its output is significant with respect to the dwell time of the control signal of each programming value. The varying frequency signals at the output of the mixer are applied to the inputs of band pass filtering channels, to derive the frequency range of the incoming signals for frequency selective circuitry arranged to demodulate the received signals. The invention is useful to the processing messsages transmitted by beacons by a satellite receiver.

High frequency hybrid integrated circuit

Abstract: PURPOSE:To amplify the desired frequency band only, by providing HPF through the signal in desired frequency band with an input circuit. CONSTITUTION:An HPF10 is connected, consisting of coils 7, 8 and a capacitor 9, between an input terminal 2 and a matching circuit 6. With the circuit constitution like this, in the frequency band less than objective frequency band, the gain can remarkably be reduced. By constituting the device through the use of high frequency hybrid integrated circuit, the instability of operation can be rejected and if the frequency components less than the objective frequencies are included in the input signal, the components can remarkably be attenuated and the unnecessary radiation from the device can be made less.

Low frequency, log-periodic acoustic array

Abstract: A method for determining optimum element spacing for a low frequency, log-periodic acoustic line array comprising a plurality of omnidirectional hydrophones arranged in a line wherein the spacing between hydrophones is based on a logarithmic relationship using multiple dipole pairs, each pair centered about the acoustic axis of the array, such that the distance between each dipole pair bears a constant ratio to the wavelength of the acoustic frequency band to be investigated by that hydrophone pair. Each dipole pair relates to a particular frequency band and the assembled array covers at least a decade range of frequencies through juxtaposition of contiguous frequency bands. The overall arrangement assures retention of selected beam pattern directionality over the entire decade range of frequencies.

Wind wave directions determined from synthetic aperture radar imagery and from a tower in Lake Michigan

Abstract: Directional wave spectra calculated from digitized synthetic aperture radar (SAR) images of waves on Lake Michigan are compared to a wave directional spectrum determined from measurements taken at a tower and to a one-dimensional spectrum determined from a Waverider buoy. The comparison is within one frequency band for peak energy frequency and within 20° for direction, but the SAR image intensity spectrum does not have the same shape as a wave height spectrum. Wave refraction directions observed in the SAR spectra are within 10° of classical wave refraction calculations.