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    Anomalia equatorial de ionização e a propagação de sinais de rádio
    Silva, Gilmar Alves (2018-01-31)

    Escola de Engenharia Mackenzie (EE)

    The ionosphere plays an important role in the propagation of electromagnetic waves, providing valvable opportunity to study its variability and effects on radio signals. The continuous changing in the ionospheric conditions caused by space weather strongly affects the propagation of electromagnetic waves, particularly in high frequency (HF).This work aims to investigate the propagation of radio signals in the equatorial region, between November 2013 to October 2014 in the following frequencies: 1,8 MHz, 14 MHz, 28 MHz and 50 MHz. The study was performed using DPS4 digisonde data, propagation model (VOACAP) and amateur radio receivers. The work consists of radio signals analysis emitted by two amateur radio stations located in Punta Arenas (latitude: 53.15°S; longitude: 70.92°W; dip. latitude: 39.37ºS) and in Nairóbi (latitude: 1.28ºS; longitude: 36.88ºE; dip. latitude: 10.74ºS). These radio signals were recorded at the amateur radio receiving stations located in Boa Vista (latitude: 2.82°N; longitude: 60.76°W; dip. latitude: 15,14ºN), Campo Grande (latitude: 20.5oS; longitude: 54.7oW; dip. latitude: 16.99ºS) and São Luís (latitude: 2.53oS; longitude: 44.30oW; dip. latitude: 3.28ºS) located in the region of the equatorial ionization anomaly (EIA) and at the magnetic equator in the Brazilian sector. It was emphasized the analysis of the maximum usable frequency (MUF) obtained from the foF2 ionospheric parameter and the signal-to-noise ratio (SNR) in each path between radio amateur transmitters (Tx) and the receivers (Rx). Results indicate that the ionosphere response was different in relation to the radio signals that propagate in and out of the equatorial region. According to SNR values measured at the receiving stations, The communications in 1.8 MHz were only possible at evenings of winter months between Punta Arenas and Boa Vista and between Punta Arenas an Sao Luis. The communications in 14 MHz were possible on all routes during the summer months and during equinoxes period at any hour of the day, but during the winter period the transmissions from Punta Arenas were only received in São Luís and Campo Grande during daylight hours. The 28 MHz transmissions from Nairobi were received during the summer months in all stations 24 hours by day, but transmissions at the same frequency from Punta Arenas only were received in São Luís and Campo Grande. At other times of the year the communications over the same frequency were only possible during daylight hours. The communications in 50 MHz were only possible in the summer months coming from Nairobi station.