ALMA-J Site Testing
ALMA-J Site Testing Archive
Last update 2005-01-24

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.


    Primary mirrorOpticsOffset parabola
    Diameter83 mm
    Surface accuracy< 5 um
    Beam width63'' (FWHM) at 220 GHz
    FrontendFeedCorrugated horn
    MixerUncooled GaAs Shottky diode harmonic mixer
    Noise figure7.5 dB
    Conversion loss9.2 dB (DSB)
    LOFrequency109.25 GHz
    OscillatorInP Gunn diode
    IFFrequency1.4 GHz
    Bandwidth400 MHz
    Noise temperature of preamp.51 K
    ScanScan angle0 - 70.5 deg
    Stepping anglesec(Z) = 0.5
    Scan time60 s
    Integration time0.5 - 1.0 s (variable)
    SystemTotal weight?? kg
    Power consumption200 W

Technical Description

    Figure 1: Schematic drawing

    Figure 2: Block diagram



  • Reduced data
  • Summary: Comparison of the 220 GHz opacity at Pampa la Bola and the 225 GHz opacity at Llano de Chajnantor