A detailed account of the performance of the VATLY radio telescope, operated in Ha Noi on and near the 21 cm HI line, is given. Drift scans across the Sun are used to measure the dependence of the gain on frequency and power, revealing small nonlinearities at or below the percent level. Interferences associated with the electromagnetic pollution in the Ha Noi environment are described. The sensitivity of the instrument is discussed and demonstrated with the detection of the Crab. The reliability of the measurement of the spectral flux density is illustrated by comparing solar flux data measured in Ha Noi and at the Australian observatory of Learmonth. | Communications in Physics, Vol. 24, No. 3 (2014), pp. 257-266 DOI: THE VATLY RADIO TELESCOPE: PERFORMANCE STUDY NGUYEN THI PHUONG, PHAM NGOC DIEP, PIERRE DARRIULAT, PHAM TUYET NHUNG, PHAM TUAN ANH, PHAM NGOC DONG, DO THI HOAI, NGUYEN THI THAO VATLY, INST, 179, Hoang Quoc Viet, Cau Giay, Ha Noi, Vietnam. E-mail: phuonghus91@ Received 07 May 2014 Accepted for publication 30 June 2014 Abstract. A detailed account of the performance of the VATLY radio telescope, operated in Ha Noi on and near the 21 cm HI line, is given. Drift scans across the Sun are used to measure the dependence of the gain on frequency and power, revealing small nonlinearities at or below the percent level. Interferences associated with the electromagnetic pollution in the Ha Noi environment are described. The sensitivity of the instrument is discussed and demonstrated with the detection of the Crab. The reliability of the measurement of the spectral flux density is illustrated by comparing solar flux data measured in Ha Noi and at the Australian observatory of Learmonth. Keywords: Radio Telescope, 21 cm HI line, sensitivity. I. INTRODUCTION The VATLY radio telescope is operated in Ha Noi (Vietnam) at or near the frequency of the HI 21 cm line, GHz. Its main features have been described in earlier publications [1] and observations of the disk of the Milky Way [2] and of the Sun [3] have been previously reported. Fig. 1. Close-up view of the antenna and feed horn (left panel) and block diagram of the electronics [4] (right panel). c 2014 Vietnam Academy of Science and Technology 258 NGUYEN THI PHUONG et al. The telescope is equipped with a fully steerable parabolic dish, m in diameter, remotely adjustable in elevation and azimuth (Fig. 1). The reflected power is collected at the focus, where it is locally pre-amplified, shifted to lower frequency using standard super-heterodyne, amplified and digitized. Standard data collection consists in a .
