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

492 GHz Radiometer

    A portable 492 GHz radiometer fabricated at the Depertment of Physics (Yamamoto group) of the University of Tokyo was used to measure the correlation between the atmospheric transparency at 492 GHz with that at 220 GHz. The 492 GHz radiometer was temporally operated with the NRO 220 GHz radiometer at Pampa la Bola (4800 m a.s.l.) from 1997 June 28 to July 1 and at Rio Frio (4100 m a.s.l.) from 1997 July 2 to 4. Shown on the left-hand side of the photograph is a 492 GHz telescope, which succeeded to the 492 GHz radiometer, developped by the same group. One of the NRO 220 GHz radiometer is seen on the right-hand side.


    Primary mirrorOpticsOffset parabola
    Diameter50 mm
    Beam width1 deg (FWHM) at 492 GHz
    FrontendFeedConical horn
    MixerUncooled GaAs Shottky diode harmonic mixer
    System temperature12000 K (DSB)
    LOFrequency82.25 x 3 GHz
    OscillatorGunn diode
    IFFrequency1.5 GHz
    Bandwidth500 MHz
    ScanScan angle-90 - +82.8 deg
    Stepping angle0.72 deg
    Scan time120 s
    Integration time0.2 s
    SystemTotal weight25 kg
    Power consumption30 W

Technical Description

    Figure 1: Block diagram