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.

Fine structure of the auroral kilometric radiation: a Fermi acceleration process?

Abstract: The fine structure of the auroral kilometric radiation is explained as a nonlinear interaction between the locally generated cyclotron emission created in an electron plasma cavity and the cavity boundary. Specifically, it is demonstrated that broadband cyclotron emission can form discrete tones after numerous interactions with an oscillating boundary that has quasi-monochromatic wavelike motion. This boundary will Doppler shift most radio photons in a stochastic way, creating a diffuse background radio component. However, some radio photons will have regular, stable frequencies that form discrete tones that overlie on the diffuse background emission. The discrete tones are created in situations where the photon travel time in the cavity is an integer multiple of the boundary oscillation period, this effect establishing a resonance between the boundary oscillations and photon. A set of coupled nonlinear equations is used to describe the radio photon/cavity boundary interaction. Effects of wave growth in the local density cavity and boundary reflections are also included. As the character of the cavity slowly changes, the resonance condition also changes in an adiabatic way, shifting the resonance to different frequencies. The net result is the creation of drifting radio tones which are comparable to those actually observed on radio spectrograms of the auroral kilometric radiation.

A Three-Component Very-Low-Frequency Signal Receiver with Precision Data Synchronization with Universal Time

Abstract: A three-component receiver of very-low-frequency band signals has been developed. Using the receiver, it is possible to measure two horizontal magnetic components and a vertical electric component of the electromagnetic field in the frequency range from 300 Hz to 15 kHz. The use of galvanic isolation of the digital and analog sections of the recorder and the precise data synchronization with Universal Time with an error of 1 μs or less are features of the receiver.

A Derivation of the Spectra of N-Ary Orthogonal Comtinuous-Phase FSK Waveforms for ELF/VLF Communications

Abstract: The power spectral density of continuous-phase minimum-bandwidth waveforms composed from a set of N mutuallyorthogonal chips (pulsed sinusoids of equal amplitude and duration and constant frequency) is derived. The spectrum and its derivation for this class of signals are of particular interest in highpower extremely low frequency/very low frequency (ELF/VLF) communications where noise immunity is a prime consideration, but the signal bandwidth and transients at the transmitting antenna must be minimized. Exact formulas are also given without derivation for wider bandwidth signals in the same class but of less practical importance. Although the power spectra of more general binary signals are already known, the special case presented here permits a much simpler derivation than that given in an earlier paper [1]. In the N -ary case a previously derived formula for the spectra of continuous-phase multilevel FM signals [2] is augmented and evaluated to explicitly yield new spectral formulas useful in describing the frequency-hopping mode.

Subpacket structure in strong VLF chorus rising tones: characteristics and consequences for relativistic electron acceleration

Abstract: Van Allen Probes in situ observations are used to examine detailed subpacket structure observed in strong VLF (very low frequency) rising-tone chorus elements observed at the time of a rapid MeV electron energization in the inner magnetosphere. Analysis of the frequency gap between lower and upper chorus-band waves identifies fceEQ, the electron gyrofrequency in the equatorial wave generation region. Initial subpackets in these strong chorus rising-tone elements begin at a frequency near 1/4 fceEQ and exhibit smooth gradual frequency increase across their > 10 ms temporal duration. A second much stronger subpacket is seen at frequencies around the local value of 1/4 fce with small wave normal angle (< 10°) and steeply rising df/dt. Smooth frequency and phase variation across and between the initial subpackets support continuous phase trapping of resonant electrons and increased potential for MeV electron acceleration. The total energy gain for individual seed electrons with energies between 100 keV and 3 MeV ranges between 2 and 15%, in their nonlinear interaction with a single chorus element.