Showing papers on "Very low frequency published in 1978"

Satellite observation of discrete VLF line radiation within transmitter‐induced amplification bands

Abstract: Narrow-band VLF signals with a frequency separation of 100–130 Hz have been detected by a receiver aboard the S3-3 satellite. The observations were made at L = 2.9 at an altitude of 5700 km. Satellite nadir was 45°N and 151°E. The radiation has the same characteristics as those reported for ground-based observations of magnetospheric lines resulting from the nonlinear amplification of power line radiation. As is seen in ground-based observations, the lines are not exact harmonics of the power system frequency, nor are they spaced at exactly 2 or 3 times that frequency. The frequencies of the three dominant lines were typically 7364, 7494, and 7598 Hz. During the time period of these observations the transportable very low frequency (TVLF) transmitter was performing magnetospheric wave injection experiments from a site in Central Otago, New Zealand. The modulation was 0.5 Hz frequency shift keying between 7350 and 8780 Hz. The narrow-band signals detected by the S3-3 satellite were observed in the 250-Hz band above the lower frequency. The narrow-band magnetospheric lines were apparently observed because power line harmonic radiation was amplified to detectable levels by a nonlinear interaction involving the TVLF signal. The most likely sources of the power line radiation are the 50-Hz power grids in Tasmania, southeastern Australia, or New Zealand.

On the impedance of a long buried horizontal wire antenna

Abstract: Simple engineering expressions for the external impedance per unit length of a long buried horizontal electric antenna are derived by employing finitely conducting earth image-theory techniques. The results should be applicable to horizontal wire antennas employed in the extremely low frequency (ELF) and very low frequency (VLF) bands.

VLF loop array antenna

Abstract: A directional loop array antenna for very low frequency (VLF) reception. array comprises four closely spaced loop antennas forming a unidirectional reception pattern with a main beam of less than 43° between half power points. The array combines two double loop coaxial antennas dispersed with their axis parallel along 45° lines. The signal from one double loop array is delayed sufficiently such that a unidirectional reception pattern is formed.