Some results of studies on crowding of the radio spectrum in the SW range

The statistical distribution of the crowding of the spectrum in the 4-5 MHz range in the Warsaw region was studied. Measurements were made over summer and fall, 1977, and winter 1978/1979. A high level of interference in the fall was noted, due to ionospheric propagation conditions. On the assumption that atmospheric interference has a pure Rayleigh distribution, it is found that in summer at 7:30 AM about 40% and at 10:30 AM about 78% of the band is filled with atmospheric noise. For winter the values are 50% and 61%, respectively. Some results on the measurement of the effects of different types of noise on digital transmission are presented.