Development of a wide dynamic ranged radio wave receiving system with an optical modulator and DFB laser

Abstract

We have developed a radio wave receiving system using an LN (LiNbO3) optical modulator as a remedy to the coupling loop interference of a station's own signal, which is a major problem when constructing a Single Frequency Network (SFN) for terrestrial digital television broadcasts. A reduction in the system noise figure (NF) was designed in conventional systems to suppress signal degradation when receiving weak input by adopting light-powered head amplifiers. However, the price of this was degradation of the signal by third-order intermodulation distortion (IM3) when a strong input was received. Therefore, we examined expanding the dynamic range of the input. Initially, we adopted the Automatic Gain Control (AGC) method that can handle Orthogonal Frequency Division Multiplexing (OFDM) signals transmitted together over many channels and obtained excellent results. Simultaneously, we studied the possibility of replacing the expensive, high-power-consuming solid-state laser light source, which posed problems in the past, with a compact, inexpensive semiconductor laser (DFB-LD). A smaller size and lower price were achieved without lowering the carrier-to-noise ratio (C/N). © 2005 Wiley Periodicals, Inc. Electron Comm Jpn Pt 2, 88(9): 29–37, 2005; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecjb.20176