Initial Blackbeard power survey results

The Blackbeard broadband VHF radio receiver is in low-earth orbit aboard the ALEXIS satellite. The receiver has been used to measure the transmitted power in four VHF bands (55.2-75.8, 28.0-94.8, 132.3-152.2, and 107.7-166.0 MHz) over quiet and noisy parts of the earth. The authors present the results of the survey and discuss their implications. They find that there are remote ocean areas over which the observed spectrum is largely free of man-made interference, but that the spectrum over most of the earth is dominated by broadcast VHF signals. The signal characteristics observed over a given area are quite constant when observed at different times of day and at intervals of several weeks to months. It appears that in many cases the bulk of the signal power is coming from a small number of sources