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.

Temperature Effect on the Tropospheric Radio Signal Strength for UHF Band at Terengganu, Malaysia

Abstract: In tropospheric layer, radio waves can propagate in a number of different physical mechanisms such as free-space propagation or line-of-sight propagation, reflection, transmission, diffraction, scattering and wave guiding The constituents in weather such as the wind, air temperature and atmospheric water content may combine in many ways Certain combinations can cause radio signals to be heard hundreds of miles beyond the ordinary range of radio communications This study investigates the effect of weather (temperature) on radio wave propagation up to 9GHz Continuous-wave (CW) envelope fading waveforms were recorded over a period of the one-hour using patch antenna The observations were conducted at KUSZA Observatory, East Coast Environmental Research Institute (ESERI), UniSZA which is situated in Merang, Terengganu Spectrum Analyser was used for RFI measurement and weather station for weather effect The graphs of radio signal attenuation for weather parameter (temperature) against time were plotted The findings indicate that there is a relationship between radio signals with the change of temperature The correlation between RFI frequencies and temperature give negative effect for frequency 945 MHz, was r = -0085, while for 383 MHz (r = 0249), 1800 MHz (r = 0268) and 2160 MHz (r = 0134) These findings will benefit radio wave propagation research field which includes radio astronomy observations, space science, wireless communication, satellite, antenna and mobile communication and also electromagnetic radiation (EMR) research for health

Very-low-frequency propagation below the bottom of the sea

Abstract: Radio-wave propagation at very low frequencies (VLF) in the stratified rock below the bottom of the sea is studied. A reasonable assumption of extremely low electrical conductivity in the stratified rock is based upon available geological data. The surface wave traveling along the interface between this region of low conductivity and the highly conducting sea is compared with the vertically polarized ground wave found in VLF radio-wave propagation at the surface of the earth. When extremely low frequencies (ELF) are transmitted, the highly conducting layer found at greater depths below the bottom of the sea forms the lower surface of a spherical waveguide. This waveguide at ELF supports a propagation mode similar to the mode existing at VLF between the surface of the earth and the lower boundary of the ionosphere. The similarity in propagation mechanisms leads to the name "inverted ionosphere" (described by Wheeler [1]) for the underground region. The sea or relatively highly conducting soil at the surface of the earth is an almost impregnable shield against atmospheric noise and effects from sudden ionospheric disturbances or solar flares. In addition to providing a noise-free medium, the sea has the advantage that construction costs are much less than those of a VLF transmitter at the earth's surface. Presumably communication between shore installations and submarines on the floor of the ocean could be achieved with the inverse ionosphere. The power requirement for such communication with existing VLF transmitters at the earth's surface renders such transmission unattainable.

Modulated beam injection from the space shuttle during magnetic conjunctions of STS 3 with the DE 1 satellite

Abstract: An electron beam emitted from the Office of Space Sciences 1 pallet on STS 3 was pulsed with specially designed very low frequency (VLF) formats in an attempt to generate whistler mode waves. Modulated operations of the beam emitted by a fast pulse electron generator (FPEG) were initiated during times of magnetic conjunctions between STS 3 and the high-altitude DE 1 satellite equipped with broadband VLF receivers. Coordinated FPEG/VLF modulation and DE 1 wideband data acquisition were achieved in 12 different cases. No evidence of any waves generated by FPEG were detected on the DE 1 analog wideband data. However, it is shown that in all of the cases, either the STS 3 attitude was such that the emitted electrons struck the main body of the vehicle, or it was not possible for whistler mode waves to propagate from the STS 3 location up to the vicinity of the DE 1 satellite.

Observations of VLF hiss at very low L values

Abstract: VLF radio noise at low altitudes near magnetic equator from Injun III satellite observations