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Showing papers on "Very low frequency published in 1976"


01 Oct 1976
TL;DR: MODESRCH is a FORTRAN computer program designed to obtain rapidly, economically, and accurately, the mode constants needed to describe propagation in the earth-ionosphere waveguide at ELF, VLF and LF.
Abstract: : MODESRCH is a FORTRAN computer program designed to obtain rapidly, economically, and accurately, the mode constants needed to describe propagation in the earth-ionosphere waveguide at ELF, VLF and LF (10 Hz to 60 kHz). It is suggested that MODESRCH, along with required mode summing procedures, be used to replace 'waveguide' and 'wave-hop' codes currently used in network analysis programs which cover the ELF to LF frequency bands. This report contains a discussion of the analytical approach taken in MODESRCH, a FORTRAN listing of the program, instructions for using the program and some sample calculations.

65 citations


Journal ArticleDOI
TL;DR: In this article, the effect of controlled phase changes of the transmitted wave on the magnetospherically propagated signal received in the conjugate region was investigated and it was found that the level at which the magnetic field of the wave saturated was 3.5 pT during the time period for which the data were analyzed.
Abstract: : During the 1973 operations of the transportable very-low-frequency (TVLF) transmitter near Anchorage, Alaska (L approx. 4), an experiment was performed to determine the effect of controlled phase changes of the transmitted wave on the magnetospherically propagated signal received in the conjugate region. At periodic intervals, the phase of the driving voltage was changed (essentially instantaneously) by 180 deg. The amplitude of the 6.6 kHz signal detected in the conjugate region went to zero and recovered with a characteristic time constant of 33 msec. This is ten times longer than the antenna current response time and is in fact comparable with characteristic electron interaction times with whistler-mode waves. Between the times at which the phase reversals occurred, the received signal was amplitude modulated. The period of the modulation was about 26 msec. An upper sideband was present in the spectrum while these pulsations were occurring. These characteristic times are in general agreement with theoretical predictions of bandwidths, growth rates, and particle trapping frequencies for whistler instabilities in the magnetosphere. Data obtained from the controlled transmissions and from lightning generated whistlers propagating in the same duct were combined to determine the plasma and wave parameters at the geomagnetic equator. Of particular interest is the level at which the magnetic field of the wave saturated. During the time period for which the data were analyzed, this was found to be 3.5 pT. (Author)

16 citations


Patent
Carl H. Savit1
08 Nov 1976
TL;DR: In this paper, a seismic exploration system includes a recording vehicle having a seismic cable connected thereto and one or more vibrator units, which are programmed by transmitting, at very low frequency (VLF), a frequency-modulated, coded control-signal from the recording vehicle into the unterminated conductor.
Abstract: A seismic exploration system includes a recording vehicle having a seismic cable connected thereto and one or more vibrator units. The seismic sensor cable includes at least one unterminated conductor. Operation of the vibrator units is programmed by transmitting, at very low frequency (VLF), a frequency-modulated, coded control-signal from the recording vehicle into the unterminated conductor. The conductor, acting as a VLF antenna, radiates a weak electrostatic E-field. A ferrite-core loop antenna on the vibrator unit detects the coded control signal, thereby to initiate the required vibrator operation. If desired, a reproduction of the seismic signal generated by the vibrator can be transmitted back to the recording truck over the same VLF radio link.

11 citations


Journal ArticleDOI
01 Apr 1976-Nature
TL;DR: In this article, the reception at low radio frequencies of radio pulses from three pulsars was reported and a similar method was used during 1973-74, and four more pulsars were detected.
Abstract: WE have reported earlier1 on the reception at low radio frequencies of radio pulses from three pulsars. A similar method2 was used during 1973–74, and four more pulsars were detected.

11 citations


Journal Article
TL;DR: In this paper, variations of the fluxes of electrons spilled out of the magnetosphere and short-period oscillations of the earth's magnetic field, stimulated by pulsed signals from a land-based VLF transmitter, were observed.
Abstract: We observed variations of the fluxes of electrons spilled out of the magnetosphere and short-period oscillations of the earth's magnetic field, stimulated by pulsed signals from a land- based VLF transmitter. (AIP)

6 citations


Patent
27 Jan 1976
TL;DR: In this paper, a wind measuring system utilizing a very low frequency (VLF) radio navigation system including an observation station, at least three transmitting stations for sending out the VLF signal, and a sounding device positioned in the atmosphere for receiving the signals from the transmitting stations and retransmitting them by way of a telemetric link to the observation station where processing equipment measures the phases of the signal transmission and determines therefrom the position or velocity directions of the sounding device.
Abstract: A wind measuring system utilizing a very low frequency (VLF) radio navigation system including an observation station, at least three transmitting stations for sending out the VLF signal, and a sounding device positioned in the atmosphere for receiving the VLF signals from the transmitting stations and retransmitting them by way of a telemetric link to the observation station where processing equipment measures the phases of the signal transmission and determines therefrom the position or velocity directions of the sounding device. The processing equipment includes a receiving circuit for receiving the VLF signal from the sounding device, and limiting circuitry for amplitude limiting the VLF signal. A local signal generator included in the observation station generates a reference signal which has the same frequency as the VLF signal. Polar cross correlation circuitry is also included for forming cross correlation functions of the amplitude limited VLF signals and the reference signal. The phase angles of the cross correlation functions are representative of the location of the sounding device.

5 citations


10 Oct 1976
TL;DR: In this article, an updated version of an earlier simplified mode conversion program for VLF/LF propagation in the earth-ionosphere waveguide is presented, which includes the provision for calculating at an arbitrary height within the guide all three electric field components generated by an electric dipole of arbitrary orientation and height.
Abstract: : This report presents an updated version of an earlier simplified mode conversion program for VLF/LF propagation in the earth-ionosphere waveguide. The new program includes the provision for calculating at an arbitrary height within the guide all three electric field components generated by an electric dipole of arbitrary orientation and height within the guide. The program is designed for treating air to air, ground to air or air to ground VLF/LF problems involving a waveguide channel which is horizontally inhomogeneous along the direction of propagation. (Author)

4 citations


17 Sep 1976
TL;DR: In this paper, the signal-to-noise (S/N) ratio power budgets for an ELF/VLF transmitting satellite using waveguide-mode field representations in the frequency range from 250 Hz to 9 kHz and for satellite heights from 120 km to 800 km.
Abstract: : Signal-to-noise (S/N) ratio power budgets are evaluated for an ELF/ VLF transmitting satellite using waveguide-mode field representations in the frequency range from 250 Hz to 9 kHz and for satellite heights from 120 km to 800 km. The low-order waveguide-mode parameters are presented. The propagation of the waveguide-mode fields into the lower ionosphere is evaluated using a full wave method. The propagation of the fields in the upper ionosphere is evaluated by a ray-tracing method. When these fields are known, the propagation from a ground-based transmitter to a satellite receiver may be evaluated, as well as the reciprocal transmission from a satellite transmitter to a ground-based receiver. The radiation resistance of a finite loop magnetic dipole antenna is evaluated for a variety of frequencies and locations in the ionosphere for both open and closed index of refraction surfaces. The satellite power required to provide a S/N ratio in excess of 0 dB in a 1-Hz bandwidth at a 1-Hertz bandwidth at a ground range of 1 Mm from the ionospheric exit point of the waves is evaluated for several cases. The power requirements (in the megawatt range) exceed the power supplied on current spacecraft missions, but they are within the realm considered possible for future space electric power systems.

3 citations


ReportDOI
01 Dec 1976
TL;DR: In this article, the effects of antenna elevation and inclination on the structure of air-to-air VLF/LF communication signals for frequencies between 15 and 40 kHz were analyzed.
Abstract: : The report analyzes the effects of antenna elevation and inclination on the structure of air-to-air VLF/LF communication signals for frequencies between 15 and 40 kHz. Considered are (1) propagation broadside to the horizontal component of trailing-wire transmitting antennas, and (2) ambient and moderately disturbed daytime ionospheric conditions and ground conductivities of 0.001 and 0.00001 mhos/m. The calculations use full-wave methods, and fully account for the vertical inhomogeneity of the ionosphere and the curvature of the earth. Numerical results are given for the excitation factors, height-gain factors, and attenuation rates of the first few TM and TE modes. Mode summations are carried out, and detailed plots are given for each field component versus distance for antenna altitudes between 0 and 40 kft.

1 citations



Journal ArticleDOI
TL;DR: This paper describes the system concept of controllable intermediate frequency (IF) bandwidth for FM radio receivers, which provide value improvement of the performance parameters for consumer expectation, i.
Abstract: This paper describes the system concept of controllable intermediate frequency (IF) bandwidth (BW) for FM radio receivers, which provide value improvement of the performance parameters for consumer expectation, i. e., signal to noise ratio (SNR), selectivity, and distortion.