The Hitachi and Takahagi 32 m radio telescopes: Upgrade of the antennas from satellite communication to radio astronomy

Abstract The Hitachi and Takahagi 32 m radio telescopes (former satellite communication antennas) were so upgraded as to work at 6, 8, and 22 GHz. We developed the receiver systems, IF systems, back-end systems (including samplers and recorders), and reference systems. We measured the performance of the antennas. The system temperature including the atmosphere toward the zenith, $T_{\rm sys}^{\ast }$, is measured to be ∼30–40 K for 6 GHz and ∼25–35 K for 8 GHz. $T_{\rm sys}^{\ast }$ for 22 GHz is measured to be ∼40–100 K in winter and ∼150–500 K in summer seasons, respectively. The aperture efficiency is 55%–75% for Hitachi at 6 GHz and 8 GHz, and 55%–65% for Takahagi at 8 GHz. The beam sizes at 6 GHz and 8 GHz are ∼4${^{\circ}_{.}}$6 and ∼3${^{\circ}_{.}}$8, respectively. The side-lobe level is less than 3%–4% at 6 and 8 GHz. Pointing accuracy was measured to be better than ∼0${^{\circ}_{.}}$3 for Hitachi and ∼0${^{\circ}_{.}}$6 for Takahagi. We succeeded in VLBI observations in 2010 August, indicating good performance of the antenna. We started single-dish monitoring observations of 6.7 GHz methanol maser sources in 2012 December, and found several new sources showing short-term periodic variation of the flux density.