Reducing Effects of Cross-Talk in a Radio Telescope Using Walsh Modulation

Abstract

Traditional Walsh technique is used to eliminate cross-talk in a array of radio telescope where achieving synchronization between modulator and demodulator without compromising sensitivity is a real challenge. The paper describes a novel approach named Walsh Delay Hunting (WDH) to synchronize independently running modulator and demodulator with no additional hardware. This approach is unique and can easily be implemented in any existing radio telescope with minimal changes, thus by putting Walsh modulator at telescope and demodulation can be done in digital back-end. The scheme greatly reduces antenna electronics and overhead of sending synchronizing Walsh start pulse back to center station and vice versa. The paper describes WDH method and its feasibility study for Giant Meterwave Radio Telescope (GMRT) along with test results. The modulator is a low cost CPLD-based module and demodulation is done in a Reconfigurable Open Architecture Computing Hardware (ROACH)-based digitizer and packetizer. The scheme requires noise injection facility before modulator, which GMRT has for antenna calibration.