The Seoul Radio Astronomy Observatory (SRAO) operates a 6.1-meter radio telescope on the Gwanak campus of Seoul National University. We present the efforts to reform SRAO to a Very Long Baseline Interferometry (VLBI) station, motivated by recent achievements by millimeter interferometer networks such as Event Horizon Telescope, East Asia VLBI Network, and Korean VLBI Network (KVN). For this goal, we installed a receiver that had been used in the Combined Array for Research in Millimeterwave Astronomy and a digital backend, including an H-maser clock. The existing hardware and software were also revised, which had been dedicated only to single-dish operations. After several years of preparations and test observations in 1 and 3-millimeter bands, a fringe was successfully detected toward 3C 84 in 86 GHz in June 2022 for a baseline between SRAO and KVN Ulsan station separated by 300 km. Thanks to the dual frequency operation of the receiver, the VLBI observations will soon be extended to the 1 mm band and verify the frequency phase referencing technique between 1 and 3-millimeter bands.

Abstract
1. INTRODUCTION
2. RETROFIT OF THE RECEIVER SYSTEM
    2.1. Import of a CARMA Receiver
    2.2. Cryogenic System
    2.3. Signal Chain
    2.4. Alignment of the Receiver
3. INSTALLATION OF VLBI EQUIPMENT
4. TEST OBSERVATIONS
    4.1. Single-Dish Observations
    4.2. VLBI Test Observations
5. DISCUSSION AND CONCLUSIONS
ACKNOWLEDGMENTS
REFERENCES

• Naeun Shin(Department of Physics and Astronomy, Seoul National University, Korea Astronomy and Space science Institute)
• Yong-Sun Park(Department of Physics and Astronomy, Seoul National University, SNU Astronomy Research Center, Seoul National University) Corresponding Author
• Do-Young Byun(Korea Astronomy and Space science Institute, University of Science and Technology)
• Jinguk Seo(Department of Physics and Astronomy, Seoul National University)
• Dongkok Kim(Department of Physics and Astronomy, Seoul National University)
• Cheulhong Min(Department of Physics and Astronomy, Seoul National University)
• Hyunwoo Kang(Korea Astronomy and Space science Institute)
• Keiichi Asada(Academia Sinica Institute of Astronomy and Astrophysics)
• Wen-Ping Lo(Academia Sinica Institute of Astronomy and Astrophysics)
• Sascha Trippe(Department of Physics and Astronomy, Seoul National University, SNU Astronomy Research Center, Seoul National University)