Showing papers on "Very low frequency published in 1979"

Interplanetary phase scintillation and the search for very low frequency gravitational radiation

Abstract: Observations of radio-wave phase scintillation are reported which used the Viking spacecraft having an earth-spacecraft link very similar to that which will be used in very low-frequency (VLF) gravitational-wave searches. The phase power-spectrum level varies by seven orders of magnitude as the sun-earth-spacecraft (elongation) angle changes from 1 to 175 deg. It is noteworthy that a broad minimum in the S-band (2.3 GHz) phase fluctuation occurs in the antisolar direction; the corresponding fractional frequency stability (square root Allan variance) is about 3 x 10 to the -14th for 1000-s integration times. A simultaneous two-frequency two-station observation indicates that the contribution to the phase fluctuation from the ionosphere is significant but dominated by the contribution from the interplanetary medium. Nondispersive tropospheric scintillation was not detected (upper limit to fractional frequency stability about 5 x 10 to the -14th). Evidently, even observations in the antisolar direction will require higher radio frequencies, phase scintillation calibration, and correlation techniques in the data processing, for detection of gravitational bursts at the anticipated strain amplitude levels of no more than 10 to the -15th.

Radio emissions from the aurora

Abstract: Observations are reported of radio waves in the range 2.5-6 MHz, emitted by the aurora. Two distinct types of emissions are seen: bursts, which are broad band emissions with a time scale of the order of .1 sec, and roars, which are narrow band (300 kHz) emissions with a time scale of ten minutes.

Very low‐frequency (VLF) wind‐generated noise produced by turbulent pressure fluctuations in the atmosphere near the ocean surface

Abstract: Measurements of ambient noise for very low frequencies (VLF) from 5 to 50 Hz indicate that wind‐generated noise is a significant source of the total ambient noise field during high‐wind/sea‐state conditions. Determining dominant physical mechanism(s) for transfer of energy from the wind field into the underwater acoustic field is very important in modeling the wind‐generated noise field at very low frequencies. Frequency dependence, wind speed dependence, directivity characteristics, and dependence on oceanographic parameters of the wind‐generated noise source can be established only after the physical mechanism is understood. The objective of this paper is to extend the development of the theory of turbulent pressure fluctuations initiated by lsakovich and Kur'yanov. The wave height spectra of Mitsuyasu and Honda is incorporated into the theory, since this is the accepted wave height spectra in the VLF acoustic region. (These wave height data were not available to lsakovich and Kur'yanov at the time of p...

Some notes on ELF Earth-ionosphere waveguide daytime propagation parameters

Abstract: The transverse-electromagnetic (TEM) propagation constants for extremely low frequency (ELF) daytime propagation in the earth-ionosphere waveguide have been calculated for frequencies of 5-2000 Hz. The recently developed theory of Greifinger and Greifinger and the Wait very low frequency (VLF) exponential ionospheric-conductivity profile have been used in the analysis. It is shown that the resulting values of ELF attenuation rate, phase velocity, and ionospheric-reflection height are in excellent agreement with the measured data.

Impedance measurements of Deception Island as a natural very‐low‐frequency antenna

Abstract: In 1960 I suggested that Deception Island, near the northern end of the Antarctic Peninsula, might serve as a useful naturally resonant VLF slot antenna. Connection across the island was subsequently made and impedance measurements were obtained. Contrary to theoretical predictions by Galejs and by Staras, a strong resonance was obtained. However, it occurred at 9.5 kHz, rather than at 5 kHz as anticipated. This is ascribed to a short, low cut through one of the arms of the island which otherwise range from 500 to 1000 ft high. A composite transmission line model is constructed to represent the data. A first approximation to the efficiency suggests that it is in the range of 10–25%.

Omega: global navigating by vlf fix

Abstract: Omega navigation system is described as a simple, economical moderately accurate system for navigation by sea and air. Seven of the eight planned Omega transmitting stations are now operational and provide almost complete coverage. Signal synchronization, VLF propagation, accuracy, equipment costs are considered.

Method and apparatus for transmitting periodic electrical signals with a very low frequency-error tolerance

Abstract: 1. Method for transmitting periodic electrical signals with a very low frequency-error tolerance, in particular in single sideband mode, in which messages constituted from fixed frequencies taken from a spectrum of relevant frequencies are transmitted, in which one frequency from the relevant frequencies is chosen as a marker frequency, in which, after reception, the marker frequency is used for the demodulation of the received frequencies (fo) and in which the received frequencies, demodulated in terms of useful frequencies (fu), serve to actuate devices with a very low frequency-error tolerance, characterized in that, before their transmission, all the fixed frequencies, including the marker frequency, are shifted relative to a subcarrier and that the marker frequency, shifted by a constant value, is transmitted as a start of message signal ; in that on reception, the received, shifted marker frequency is measured and in that the frequency of a local oscillator (7) of the receiver is controlled in order to make this frequency coincide with a reference frequency (fr) equal to the measured, received, shifted marker frequency, but once more shifted by the same said constant value, this time in the opposite direction, this reference frequency (fr) serving for the demodulation of the received signals (fo) in a demodulator (5).

Computer Simulation of VLF Power Amplifiers under Reactive Loading

Abstract: Recent efforts have been made to achieve substantially increased baud rates with the U. S. Navy's very low frequency (VLF) communication system. Because of the constraints imposed by existing transmitter and antenna structures it was necessary to reexamine the operation of every major system component. Each particular VLF transmitter was subjected to an extensive theoretical analysis followed by a detailed on-site measurement program. Following a review of three major systems, Cutler, Lualualei, and North West Cape, a sufficient body of data was available to substantiate the validity of the computer-simulated transmitter analysis presented here. With this method it is possibe to predict frequency-shift keying (FSK) and minimum shift keying (MSK) performance limitations for particular VLF transmitting systems based primarily on the 0 of the antenna at the operating frequency.