Digital Receiver for SALSA

Abstract

The SALSA receiver uses a 2.3m parabolic antenna steerable in azimuth and elevation by motor driven mount. A horn with a probe integrated with a Low Noise Amplifier (LNA) is mounted in the focus of the parabola. The horn and the antenna are optimized for 1420 MHz, which is the frequency at which atomic hydrogen in the Milky Way is emitting. This Master thesis, entitled "Digital Receiver for SALSA", describes the upgrade of the existing receiver and antenna control. We designed the new digital receiver system that use a reconfigurable I/O (RIO) FPGA in conjunction with antenna control software and a software receiver (Software-Defined-Radio or SDR). The purpose of upgrading the system was to include some enhancements in the antenna controller as well as in the receiver. In the previous system a C program just worked as a GUI for the user, taking data and sending it to a microcontroller based hardware system, which decodes this data signal and sends appropriate signal to the antenna mount and then reads feedback encoder. In this project, a flexible and scalable software is realized to replace this complicated hardware. In the upgraded receiver, a Antenna Motion Controller software completely controls antenna. The software is designed in such a way that it does not miss even a single feedback pulse (there are 4 feedback pulses in one degree). The accuracy factor of software is 0.25 degrees. The old receiver was hardware-based, thus every new configuration required new hardware. However, in our case, the software receiver is highly flexible in which a wide range of configuration is possible without changing or upgrading existing hardware. The new receiver also works in real-time mode (real-time signal processing) while the old one used to do store-and-process. This upgrade reduces the user interaction to continuously obtain signal spectra, and also minimizes the hardware needs.