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Very low frequency

About: Very low frequency is a research topic. Over the lifetime, 1540 publications have been published within this topic receiving 24233 citations. The topic is also known as: VLF.


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Proceedings ArticleDOI
06 Oct 2002
TL;DR: In this paper, the authors investigated a new life estimation method for service-aged, water tree deteriorated 22-77 kV XLPE cables by voltage withstand test, and they selected more suitable waveform for testing voltage from damped oscillating wave (OSW) and very low frequency wave (VLF) voltage as the instead of AC and DC.
Abstract: The authors investigated a new life estimation method for service-aged, water tree deteriorated 22-77 kV XLPE cables by voltage withstand test. At first, they selected more suitable waveform for testing voltage from damped oscillating wave (OSW) and very low frequency wave (VLF) voltage as the instead of AC and DC. It was found that VLF voltage has high ability to detect of water tree, while was less harmful for water tree deteriorated cables. Breakdown tests under AC and VLF were carried out, using model cables and service aged XLPE cables. Based on the breakdown tests, they calculated optimal test voltage for remaining life estimation. Recently, they had onsite testing and confirmed the effectiveness of VLF testing.

3 citations

27 Oct 1965
TL;DR: In this article, a very low-frequency (vlf) radio-wave propagation experiment has been designed to study modal interference effects and the extent of agreement with theoretical results obtained previously.
Abstract: : A very-low-frequency (vlf) radio-wave propagation experiment has been designed to study modal interference effects and the extent of agreement with theoretical results obtained previously. The experimental data are the field strengths of the vlf transmissions from the U. S. Navy transmitting stations NPM and Haiku in Hawaii and NPG near Seattle, Washington. These data were recorded aboard an aircraft while in flight between California, Guam, and Japan, and also at a field site near Washington, D. C. During the experiment, NPM transmitted for various periods on 16.6, 19.8, 22.3, 24.0, and 26.1 kc/s. The Haiku transmissions were on 16.6 and 19.8 kc/s, while NPG was on 18.6 kc/s continuously. The experimental field-strength-versus-distance graphs show considerable modal interference and very good agreement with the theoretical results for the isotropic case. For frequencies above 20 kc/s the experimental data indicate the existence of at least the first three modes for propagation to the west and to the east, out to distances greater than 3 megameters. The data at 19.8 kc/s, however, indicate first-three-mode effects for propagation to the east but only two modes to the west. The fading of the field strengths at Washington, D. C., during sunrise was frequently greater than 20 db. The depth of the fades, in general, increased with frequency, whereas their time of occurrence was relatively independent of frequency over the range of 19.8 to 26.1 kc/s. (Author)

3 citations

Patent
John O Schroeder1
01 Mar 1962

3 citations

Journal Article
TL;DR: In this article, a method of monitoring the VLF, LF, and HF power spectral components of heart rate variability, has been developed, where the power of the LF and HF spectral components were proved to be continuously changing.
Abstract: A method of separate monitoring "instant" changes of the VLF, LF and HF power spectral components of heart rate variability, has been developed. The power of the LF and HF spectral components were proved to be continuously changing. The period of these power fluctuations could stay within 15 to 150 sec. Comparison of the heart rate variability spectrum with LF and HF spectral components power fluctuations' spectrums has shown that the frequencies of the LF and HF spectral components power fluctuations stay within the VLF range. The co-operative spectrum form of these fluctuations repeats the form of the VLF peak. In cases when the LF and HF spectral components power fluctuations' periods do not coincide, VLF has two peaks. The frequency of one VLF peak coincides with frequency of the HF power fluctuations, and the frequency of another--with the frequency of LF power fluctuations.

3 citations

Journal ArticleDOI
TL;DR: In this paper, the results of two methods of calculation of the charge moment change (CMC, also called the dipole moment change) of cloud-to-ground lightning discharges were compared.
Abstract: We compare the results of two methods of calculation of the charge moment change (CMC, also called the dipole moment change) of the cloud-to-ground lightning discharges. The first method uses multistation ground-based measurements of the E field change for the purpose of the lightning flash location and charge analysis. Our six stations, called the Local Lightning Detection Network (LLDN), were set up in the Warsaw region. The second method is based on measurements of the horizontal magnetic field component of electromagnetic waves generated by atmospheric discharges in the ELF (extremely low frequency) range. Our ELF station is equipped with two magnetic antennas, east-west and north-south and is located in a sparsely populated area of the Bieszczady Mountains in Poland (49.19°N, 22.55°E). We present and discuss the results obtained by both methods, focusing on the negative return stroke (RS) and the return stroke with continuing current (RS and CC) lightning discharges. Results show a good correlation between the CMC obtained by the two methods. For the negative RS and CC and RS the correlation coefficient is equal to +0.50 and +0.80, respectively.

3 citations


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Performance
Metrics
No. of papers in the topic in previous years
YearPapers
202320
202232
202156
202048
201942
201852