Three Time-of-Flight Measurement Projects on a Common Hardware Platform

Three undergraduate electrical engineering project groups at Case Western Reserve University are investigating distributed ionospheric sounding through time-of-flight measurements.  All use GPS pulse-per-second signals for precise timing of received signals.  Two use as their "radar signals of opportunity" LF, MF, and HF beacons from the US Department of Commerce National Institute of Science and Technology installations north of Fort Collins, Colorado and near Kekaha, Hawaii (radio stations WWVB, WWV, and WWVH).  The third project modernizes the on-off telegraphy variant known as "coherent CW" (CCW). CCW uses amateur radio QSO or beacon transmissions as the measured signals.  It facilitates Technician-licensee participation in active HF research and in keyboard-to-keyboard digital contacts, within FCC regulations.  Using computed matched-filter techniques along the lines of FT8, CCW has a nearly optimal information-theoretic data recovery.  With transmission or lookup of station locations, it can provide automated time of flight measurements while making a contact.  The three projects use a common hardware platform for receiver or transceiver interfacing, involving synchronized analog data collection and front-end data processing with the Teensy variant of the Arduino platform.  Teensy was chosen primarily for its sampling and computing speed. WWVB’s signal can be sampled directly with the Teensy front-end and some data processing can done between sample acquisitions through timer interrupt programming.  WWV/H second ticks delay measurements use inexpensive shortwave radio audio outputs, sampled and processed by the Teensy.  The CCW sampling and matched filtering, plus synchronized Morse keying, are similarly done by the Teensy. Data presentation, user interface, and data uploading to repositories are done by minimal general purpose computers such as Raspberry Pi boards.  We will present the common hardware and interrupt strategies along with a brief overview of the three projects.  Comments and suggestions will be solicited, and of course participation in the projects is invited.  The three projects are supported by a generous grant to the Case Amateur Radio Club W8EDU from ARDC.  CARC is providing oversight of the projects and the projects use the club station as a laboratory facility.