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.

Radio interferometric Quasi Doppler bearing estimation

Abstract: The paper introduces a novel technique for the bearing estimation of radio sources that can be used for the precise localization and/or tracking of RF tags such as wireless sensor nodes. It is well known that the bearing to a radio source can be estimated by an array of antennas typically arranged in a circular manner. The method is often referred to as Quasi-Doppler measurement. The disadvantage of the existing method is that the receiver is relatively large because of the multiple antennas (typically 8 or 16) and it is computationally intensive to process the high frequency radio signals. Thus, it cannot be done on small, inexpensive radio tags. Instead, we propose to use the array on the transmitter side utilizing as few as three antennas. We use a radio interferometric technique to transform the useful phase information from the high frequency radio signal to a low frequency signal (≪ 1 kHz) that can be processed on low-cost hardware. Utilizing three anchors nodes with small antenna arrays, any number of low cost wireless nodes with single antennas can be accurately localized.

Behaviour of electron content in the ionospheric D-region during solar X-ray flares

Abstract: One of the most important parameters in ionospheric plasma research also having a wide practical application in wireless satellite telecommunications is the total electron content (TEC) representing the columnal electron number density. The F region with high electron density provides the biggest contribution to TEC while the relatively weakly ionized plasma of the D region (60 km - 90 km above Earths surface) is often considered as a negligible cause of satellite signal disturbances. However, sudden intensive ionization processes like those induced by solar X ray flares can cause relative increases of electron density that are significantly larger in the D-region than in regions at higher altitudes. Therefore, one cannot exclude a priori the D region from investigations of ionospheric influences on propagation of electromagnetic signals emitted by satellites. We discuss here this problem which has not been sufficiently treated in literature so far. The obtained results are based on data collected from the D region monitoring by very low frequency radio waves and on vertical TEC calculations from the Global Navigation Satellite System (GNSS) signal analyses, and they show noticeable variations in the D region electron content (TECD) during activity of a solar X ray flare (it rises by a factor of 136 in the considered case) when TECD contribution to TEC can reach several percent and which cannot be neglected in practical applications like global positioning procedures by satellites.

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%.