Electric field strength analysis of 216 and 270 kHz broadcast signals recorded during 9 years

[ 1] The electric field strength analysis of Czech Republic (CZE) ( 270 kHz) and Monte Carlo (MCO) ( 216 kHz) broadcast signals, collected with a 10 min sampling frequency by a receiver located in central Italy from 1996 to 2004, is presented. The distance from transmitter to receiver ranges from 515 km ( MCO) to 818 km ( CZE). The daytime data and the nighttime data were extracted and then in the daytime data the data collected in winter ( 21 December to 21 March) were separated from the data collected in summer ( 21 June to 21 September). Under the hypothesis that the simple addition of the ground wave and sky wave contributions holds, at first, the analysis was focused on the comparison between the experimental and theoretical values of these waves. The theoretical values were calculated by the ground wave (GRWAVE) algorithm and the wave hop theory, respectively. Ratios between the experimental and theoretical values ranging from a few tenths of decibels to some decibels were obtained. Then the analysis of the sunspots' influence on the sky wave propagation mode was performed, and the electric field strength of the two radio signals reveals a reduction of some decibels in sunspot maximum years with respect to the values during the sunspot minimum years. In addition, an influence of the sunspots also was recognized for the ground wave propagation mode