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| ALMA-J Site Testing |
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| ＞ALMA-J Site Testing Archive |
Last update
2005-01-24
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220 GHz Radiometer
Two tipping radiometers fabricated at Nobeyama Radio Observatory have been operating to monitor the atmospheric transparency at 220 GHz. The first one has been operating since 1994 July, when it was installed at Paranal (2400 m a.s.l.), Chile. Owing to the portability of this instrument, it was also used at several other sites (2500 - 4700 m a.s.l.) in the Antofagasta Region in 1994 August. After basic measurements at Paranal, it was used at Rio Frio (4100 m a.s.l.) from 1995 June to 1997 May. The second radiometer has been operating at Pampa la Bola (4800 m a.s.l.) since 1996 July. The twin radiometers were simultaneousely operated in differencial radiometer mode at Pampa la Bola in 1998 June. Only one of them is operating now.
Specifications
| Primary mirror | Optics | Offset parabola |
| Diameter | 83 mm | |
| Surface accuracy | < 5 um | |
| Beam width | 63'' (FWHM) at 220 GHz | |
| Frontend | Feed | Corrugated horn |
| Mixer | Uncooled GaAs Shottky diode harmonic mixer | |
| Harmonics | Second | |
| Noise figure | 7.5 dB | |
| Conversion loss | 9.2 dB (DSB) | |
| LO | Frequency | 109.25 GHz |
| Oscillator | InP Gunn diode | |
| IF | Frequency | 1.4 GHz |
| Bandwidth | 400 MHz | |
| Noise temperature of preamp. | 51 K | |
| Scan | Scan angle | 0 - 70.5 deg |
| Stepping angle | sec(Z) = 0.5 | |
| Scan time | 60 s | |
| Integration time | 0.5 - 1.0 s (variable) | |
| System | Total weight | ?? kg |
| Power consumption | 200 W |
Technical Description
Figure 1: Schematic drawing
Figure 2: Block diagram
References
- Radford, S. J. E., Butler, B. J., Sakamoto, S., & Kohno, K. 2001, "Atmospheric transparency at Chajnantor and Pampa la Bola," ALMA memo 384
- Holdaway, M. A., Ishiguro, M., Nakai, N., & Matsushita, S. 1996, "Correlation between opacity and surface water vapor pressure measurements at Rio Frio," NROTR 52 (also LMSA Memo 1996-004)
- Holdaway, M. A., Ishiguro, M., Foster, S. M., Kawabe, R., Kohno, K., Owen, F., Radford, S. J. E., & Saito, M. 1996, "Comparison of Rio Frio and Chajnantor site testing data," NROTR 51 (also LMSA Memo 1996-003)
- Kohno, K., Kawabe, R., Ishiguro, M., Kato, T., Otarola, A., Booth, R., & Bronfman, L. 1995, ``Preliminary result of site testing in northern Chile with a portable 220 GHz radiometer,'' NROTR 42 (also 1995-001)
- Kohno, K., Kawabe, R., Ishiguro, M., Chung, H. -S., Xiao, K. -C., Yang, J., & Wang, Z. 1993, ``Site testing in Delingha using 220 GHz radiometer developped for Large Millimeter Array (LMSA) site evaluation,'' in Site Experiments for Astronomical Observations in North-West Region of China, 11
Data
- Reduced data
- Summary: Comparison of the 220 GHz opacity at Pampa la Bola and the 225 GHz opacity at Llano de Chajnantor
