Observations of substorm associated absorption events on a 3200 km high latitude HF propagation path

A computer controlled transmitter, capable of operation on a predetermined frequency and modulation schedule, was installed at Clyde River, Canada (70° N, 69° W). A receiver was located near Boston, USA (42° N, 71° W) to provide a 3200 km trans-auroral, near-meridional propagation path. The transmission schedule consisted of two minute sequences transmitted once per hour on each of 14 frequencies in the range 3-23 MHz. Each sequence included a 30 second period of continuous carrier during which the amplitude and Doppler spectrum of the received signal were measured. The sequence also included periods during which the callsign `CZB´ was transmitted in Morse code for recognition purposes. Tests performed on the received signals were capable of identifying the Clyde River transmission, noise, or an interfering signal dominating the channel. A month long experimental campaign was undertaken between 16 January and 10 February 1989. The 6.800 MHz transmission was identified as being relatively free of interference and suitable for the investigation of absorption