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2 Observations

The observations presented here were done with the Metsähovi Radio Telescope during 1990.5-1995.5 at 22, 37 and 87 GHz. The Metsähovi 13.7 m diameter ESSCO design antenna is placed inside a radome. In August 1991 the original radome was replaced with a new one. Also the reflector panels and the back structure of the antenna were replaced with more accurate ones during the summer of 1994. The receiving system parameters are listed in Table 1. The flux density scale is calibrated against DR 21, our primary calibration source. Its fluxes at 22, 37 and 87 GHz are 19.0, 17.9 and 17.0 Jy, respectively, according to Baars et al. (1977) and Ulich (1981). As secondary calibration sources we have used 3C 274 and planets like Jupiter. The receivers at 22 and 37 GHz are of a dual beam type with a ferrite swich operating at 25 Hz. At 87 GHz the beam switching at a rate of 20 Hz is performed with a rotating chopper-wheel. The old 22 GHz mixer front end receiver was replaced with a more sensitive one with a low noise HEMT amplifier as a first stage in June 1993. The 37 GHz receiver is a mixer front end receiver operating at room temperature. The 87 GHz receiver is a Schottky mixer front end receiver cooled to 20 K.

Table 1: Receiver parameters

${\rm Frequency}$\space & $HP...
 ... & $3.2'$\space & $500$\space & $200$\\ \noalign{\smallskip}
  • [a] Before June 1993.
  • [b] After June 1993.

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