This Nb junction mixer, installed in August 1992, will be replaced this summer. We expect improvement in the SSB receiver temperature (presently 130K at 115 GHz, and 70--140 K below 100 GHz), a better rejection of the upper side band, and improved stability around and below 100 GHz. Note that the IF frequency of this receiver is 1.5 GHz, and not 3.9 GHz as for the 1.3 mm and 2 mm receivers. When tuned to the CO 115.27 GHz line in the LSB, the oxygen 118.75 GHz line falls in the USB; this has two consequences for the observations: i) the sky seen in the USB is warm, leading to an increase of the system temperature, and ii) the atmospheric opacity in the LSB, calculated by OBS/ATM, can be quite wrong if the assumed gain in the USB (GAINi) is poorly known. It is therefore advantageous to use a large (>10 dB) USB rejection. The observation of continuum sources of known flux (e.g. planets, HII regions,...) is also recommended for calibrating your 115 GHz line observations. We intend to replace this summer the present mixer with a new one of comparable or better temperature and allowing higher USB rejections.
It is important to check your calibration on strong reference sources (see IRAM line catalog and updates [1, 10, 15]). Beware also of possible interference between the `second' 1.3 mm receiver, 230G2, and this receiver when operating at harmonic frequencies (the two receivers receive the same polarization; the interference will be a strong and narrow line).