An Amateur Radio HF Channel Sounder

This presentation will provide a description of a channel sounding architecture that is accessible to the amateur radio community. It is used to study selected radio channels between an HF transceiver and a remote software-defined radio receiver. A system has been implemented that employs a combination of a Flex 6700 SDR transceiver and a remote Kiwi SDR. An audio file containing a series of a repeated maximum-length sequence is transmitted over the air by a Flex 6700 transceiver to a selected Kiwi SDR that generates an audio recording of the received signal. The recording is sent back to the transmitting station over the Internet for post processing. A software analysis tool is used to cross correlate the original transmitted audio file with the received signal recording. This process generates a multiple-period channel impulse response, which is used to construct a channel impulse response matrix. The channel impulse response matrix provides the basis for quantifying channel characteristics such as delay, Doppler, and time variability. This system has been used to perform a series of over-the-air tests in the 60 m amateur band and selected Kiwi SDRs. This presentation will describe the system architecture, signal generation and processing, validation using audio baseband channel simulators, and over-the-air measurements. Measurement results from a sporadic-E event that occurred on June 21, 2025 will be highlighted. This system should be useful for citizen science efforts to study solar events and for intercomparisons with other measurement techniques. The waveforms developed in this effort might be highly useful for incorporation into the WWV special tests waveform, and it might facilitate some very interesting propagation measurements and studies.