Medium-frequency skywave propagation at high latitudes: results of a five-year study

Skywave transmission from selected standard AM broadcasting stations in the northern tier of the contiguous United States, Alaska and Canada were monitored near Fairbanks, Alaska from late 1981 to 1987. The objective of this work was to better understand, among other things, the effect of latitude on MF skywave propagation. A modern stable and selective receiver was electronically scanned continuously through 12 preselected frequencies in a five-minute cycle including a calibration. Frequent aural monitoring insured that the correct frequencies were being monitored. The main antenna used during this program was a 106-ft (35-m) vertical with modified top-hat and a 30-radial ground system. The daily, seasonal, and magnetic storm-time behavior of signal strength from selected stations was monitored over one-half of sunspot cycle 21. The latitudinal location of the auroral oval in the E-region in respect to the ionospheric reflection points on the propagation paths created profound variations of signal strength. There was also a very wide variation in signal strengths on long north-south paths as a function of sunspot cycle. The results are briefly discussed