1. The second 3 mm receiver (3mm2) is now available. Its performance is superior to that of 3mm1 (see below). It is usable simultaneously with the present 3 mm receiver (3mm1) and, with some extra losses, with 230G1 and 230G2. In the 4-receiver operation mode, the noise of 230G2 is significantly increased due to losses in the frequency splitter. For the sake of simplicity, we ask you to consider only three receivers (e.g. 3mm1 + 3mm2 + 230G1, or 3mm1 + 230G1 + 230G2) in the telescope time calculations.
2. An On-the-Fly observing mode (OTF) has been implemented for heterodyne observations. In this mode, the telescope beam drifts continuously across the source, while data is dumped every 1 or 2 s (depending on the number of frequency channels). Any scanning direction can be chosen and successive scans can be concatenated to make a map (like in the bolometer `mapping' mode). Individual drift scans can have any length; they are interleaved with OFF source reference subscans of any duration. This mode ensures a better homogeneity of the data and can make a much more efficient use of observing time.
Up to 4 receivers can be used simultaneously. The backends can be the filter banks and/or the autocorrelators. OTF observations were carried out successfully in December 1995 on two test programs (M 31 and Cep B). The large acquisition rate has however caused data storage and handling problems: although a new version of CLASS has been developed, the software is not yet user-friendly and remains experimental. Because of these shortcomings, we intend to open the OTF observing mode on a restricted basis only, for the coming May-November session. Only a limited number of new OTF programs will be accepted and all of them should be co-signed by an astronomer of the IRAM-Granada team, who should be responsible for the technical aspects and for the data reduction. You may contact Drs. H. Ungerechts and W. Wild at IRAM-Granada for more information.
3. A handbook collecting most of the information necessary to plan and reduce 30m telescope observations is now available .