Development of a Leo Beacon Receiver System for Tec Measurement and Simulation of an Orthogonal Carrier Spread Spectrum System

The ground-based reception of radio beacon signals transmitted from LEOS is a historical method to measure the total electron content (TEC) of the ionosphere. Observations of this kind were initiated right from the beginning of the space era as reported by Aitchison and Weekes [1959] and Garriott and Little [1960]. The principle of the experiment is based on the frequency dependence of the refractive index of radio waves in the ionospheric plasma. The most commonly used frequencies are 150 and 400 MHz, in a ratio of 3:8, generated from a common oscillator signal at 50 MHz. The most common beacon satellite constellation is the polar-orbiting Navy Navigation Satellite System (NNSS), detailed by Newton [1967], and renamed later as Navy Ionospheric Monitoring System (NIMS) as mentioned in Leitinger et al [1984]. Beacon receivers developed in the past have been mostly analog receivers for 150 and 400 MHz signals where the phase relationship between the two signals is detected by an analog circuit and the resultant phase values digitized at tens of Hz.