HamSCI: Measurement and Analysis of Low and High Frequency Radio Propagation for Study of Ionospheric Physics

Abstract:

The dynamic ionosphere modifies both the frequency and amplitude of low (LF, 30-300 kHz) and high (HF, 3 – 30 MHz) frequency radio signals that propagate through the ionospheric medium. These ionospheric dynamics are often the result of varying solar inputs. Analyses of amplitude variations that impact the quality of communications links and frequency variations that significantly degrade on-the-air frequency measurements can be used to deduce underlying physical processes. Members of the Ham Radio Science Citizen Investigation (HamSCI) present precision amplitude and frequency measurements made in Mico, TX of transmissions from the LF WWVB and HF WWV standard time and frequency stations located in Fort Collins, CO. During the 2017 North American Eclipse the signal amplitude of both 5 MHz WWV and 60 kHz WWVB increased 10 dB over a Colorado-Texas path, even though the entire path was completely below the path of totality. This data could be used to quantify the decrease in D layer absorption from diminished solar illumination. Over this same path and nearly every morning in response to sunrise the carrier of 5 MHz WWV has components observed to swing high in frequency by several hundred milliHertz and additionally split into multiple frequency tracks in a geometrically increasing progression that can peak as high as 3 Hz. Measurements of the upwards swing in frequency vs. time can be used to infer the descent rates of ionization in response to the increasing and descending sunlight that occurs at dawn. Similarly, the mode splitting can be used in analysis of multiple-hop modes as the rapidly increasing ionization enables propagation at higher angles. Additionally, we discuss science tradeoffs between single frequency and spectral analysis methods for frequency determination, the use of precise timing measurements on the WWV timing ticks to identify and quantify single and multi-hop propagation modes, the spectral mixing that occurs during simultaneous reception of stateside WWV and Hawaiian WWVB, and techniques for their separation into individual data records. Instrumentation block diagrams, data records, and propagation insights are given.