Time delay variations in HF propagation

Abstract

An experiment has been established to determine the range of environmentally induced fluctuations in the propagation of HF radio signals. Data are collected with a fully digitized system that is stablized with a cesium beam standard. Initial efforts have been directed toward monitoring at San Diego, California, the time of arrival of WWV transmissions from Fort Collins, Colorado, for the frequencies 5, 10, 15, and 20 MHz. Variations in these arrival times from 25 to 175 μs have been observed depending upon frequency, mode of propagation, time of day, and solar activity.

Cross-channel sounding for HF geolocation: concepts and experimental results

“…where ⎺ denotes the complex conjugate, and ⋆ denotes the cross-correlation operator. The autocorrelation of the transmitted signal ( ) is expressed in a similar manner as in (2). As per the convolution and correlation properties, these correlation functions are linked by a convolution equation where (1) and (2) combine to give the following:…”

“…The ionosphere varies highly with respect to the solar activity and geographic location. This leads to an extremely space-time variable nature of the HF propagation paths which in turn results in the variation of the signal arrival times [2].…”

High‐resolution HF time of arrival measurements (1981–1985)

“…The objective of this work was to determine the range of environmentally induced errors in a sky wave time difference of arrival (TDOA) measurement, thereby bounding the geolocation accuracy one could expect from this technique in the absence of models to compensate for the ionospherically induced errors. The first experimental measurement system, as described by LaBahn [LaBahn and Rose, 1982], started operation in early 1981. This effort involved establishing a continuous absolute time of arrival (TOA) experiment over the one-hop mid-latitude path between San Diego, California and Fort Col-This paper is not subject to U.S. copyright.…”

“…To resolve these issues, care was exercised to identify, resolve, and mitigate error sources. A complete description of the TOA calibration was given by LaBahn [LaBahn and Rose, 1982]. It should suffice for this paper to assure the reader that the ionospheric variations shown in the illustrations are real.…”