An implementation of portable ILS Localizer signal receiver using SDR

This paper presents an ILS Localizer signal receiver implementation based on Software Defined Radio (SDR) platform using GNU Radio software and USRP hardware. Two algorithms of signal analysis in discrete-time domain and discrete-frequency domain technique are proposed in this paper to measure the Difference in Depth of Modulation (DDM) and Sum of Depth of Modulation (SDM) of radio reception. The envelope detector in discrete-time method had successfully detected the peak envelope value of the AM signals which were needed to calculate for the modulation index. Also, a comparative method in discrete-frequency domain based on the Goertzel algorithm had efficiently provided the magnitude of the selected frequency components, which subsequently were used to calculate for the modulation index. These two presented methods are individually evaluated by comparing their measured DDM and SDM against two avionics ILS signal generators. Test results show the effectiveness of the receiver system and the possibility of future SDR development in avionics area.