Four Channel Predetection Combiner for use with Troposcatter Communication Systems

Abstract

This paper describes a four-channel Predetection Combiner developed in Defence Electronics Applications Laboratory, Dehra Dun for use with Troposcatter Communication Systems working with a maximum voice channel capacity of 120. It gives an improvement by 5.5 dB in carrier-to-noise ratio at IF (70 MHz) when the levels of the four received signals are equal and thus lowers FM threshold of the system by the same value. It has a noise power ratio (NPR) of 55 dB at the highest baseband frequency. An extra 4 dB improvement in FM threshold is achieved when a PLL type of threshold extension demodulator is used.