- A HamSCI science objective for the 2023 and 2024 eclipses is to measure how HF propagation changes with eclipse passage. Two parameters of interest are the change in effective F2 ionization layer height caused by the momentary blockage of solar radiation and the symmetry in recovery as solar radiation returns after eclipse. The focus of this effort was to devise a simple way to measure layer height that could be accomplished using amateur radio stations.
- Layer height could be deduced from absolute Time of Flight measurements, but this would require precision absolute time references for both the transmitting and receiving stations such as the 1-pps output available from a GPS Disciplined Oscillator. It would also require extensive characterization of the relatively lengthy propagation delays through the DSP transmit and receive audio processors used in modern amateur radios.
- Over propagation paths that support transmission of multiple hops, short pulse and audio chirp waveforms can be used to measure the Time Difference of Arrival (TDOA) between multipath modes, particularly the 1- and 2- hop modes. TDOA can be processed to infer layer height and it eliminates the need both for absolute time references and for TX/RX time delay characterization. With the TDOA approach, audio signals can simply be fed to the microphone input and recovered from the speaker output of amateur radio equipment using .wav programs on a computer or the built-in audio memories available on many modern transceivers.
- This paper gives details and results of initial on-air experiments to evaluate the TDOA approach to layer height measurement.
- The experiments were conducted between two amateur radio stations in Texas near both the expected Path of Totality and the Austin Ionosonde used for ground truth data. The inferred layer heights gave good agreement to hmF2 ionosonde data.