Abstract Details

Name: Ashish Mhaske
Affiliation: IUCAA
Conference ID: ASI2017_1369
Title : Horn antenna and Software Defined Radio for detecting 21 cm hydrogen line
Authors and Co-Authors : Ashish Mhaske, IUCAA Prof. Joydeep Bagchi, IUCAA
Abstract Type : Poster
Abstract Category : Instrumentation and Techniques
Abstract : The 21 cm hydrogen line is important in astronomy. Since radio astronomy is highly dominated by instrumrntation and signal processing a simple hydrogen line detection system is designed and built for educational purpose. A radio telescope consists of three major sections the antenna, front end and back end. A parabolic reflector antenna has been a tradition in radio astronomy. But because of the bulkyness and cost of the antenna other options were considered. A horn antanna was chosen due to its superior noise performance and low cost. It is also easier to construct and easy to replicate. The horn is a dual mode conical horn antenna. Dual mode nature of the horn reduces the sidelobes and hence improves noise performance of the antenna. Hence although it has a small aparture it is possible to detect hydrogen line with this antenna. Since hydrogen line is narrowband a 2 MHz receiver will be sufficient for studying the spectrum of the line. Keeping in mind the cost of the project software defined radio(SDR) was used. SDR is a flexible hardware which can be programmed to perform a perticular task which is controlled via software. A very good receiver that fits the description is the DVB-T dongle which has a R820T front end IC and RTL2832U signal processing IC. The dongle has variable gain up to 50 dB and a tuning range from VHF to microwave L band which covers the desired 1420 MHz frequency. The instantaneous bandwidth is 2 MHz which is sufficient to see the hydrogen line profile within the antenna beam width. The samples provided by the dongle can be converted to FFT plot on a computer. Using the described radio telescope we were able to detect the galactic hydrogen at various galactic longitudes. Multiple peaks were observed at some longitude and measurable red shifts were seen. Rotation curve of Milky Way was estimated. We plan to build multiple horn antennas for projects involving interferometry. Concepts of radio interferometry, closure phase and aparture synthesis can be explored with this setup. The estimated cost of the telescope is around 20 thousand rupees which is the cheapest telescope at L band. We plan on providing the design or low cost kits to institutes and interested individuals so that they can build and observe H1 line and get a hands-on experience in the methods and instruments involved in radio astronomy. ASI is the best platform for promoting this project as astronomers from around the country will be present.