Analysis of FM Modulated Wave Propagation at 4.5 GHz Using SDR in a Controlled Scenario

This paper focuses on the propagation of frequency modulated (FM) waves at 4.5 GHz using USRP and Software Defined Radio (SDR) technology in a highly controlled environment. The analysis was carried out in a classroom at the Escuela Superior Politécnica de Chimborazo, with dimensions of 7.20 m in width, 12.50 m in length, and 2.90 m in height, under conditions designed to minimize reflections. Two logarithmic antennas were used with a 2-meter separation between transmitter and receiver to avoid secondary reflections. The orientation and gain of the antennas, ranging from 1 to 100, were precisely controlled using GNU Radio software. During reception, power data were recorded over a range from –98 dB to –26 dB. The analysis considered two rays reaching the receiver: a direct wave and a reflected wave, as other possible reflections were negligible in the given scenario. The reflected wave was assumed to originate from the ceramic floor, which has a permittivity of 5.5 and negligible conductivity; using these values, a reflection coefficient of 0.20 was considered. This reflection introduced a variation of approximately 2 dB in the received signal strength.