The On-the-Fly observing mode (OTF) is implemented for heterodyne observations (with some limitations concerning data acquisition rate and reduction). In this mode, the telescope beam drifts continuously across the source, while data are dumped every 1s (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 much more efficient use of observing time, particularly for several arcmin-wide maps of lines stronger than 0.5 K. More (and up-to-date) information can be found on the OTF page of the IRAM Granada Web pages (http://www.iram.es, and following the links). In particular, a first version of an ``OTF User's Guide''(postscript, 1.2 Mb) can be downloaded from this page. It describes the current status in detail and gives cookbook recipes for OTF observations and data reduction.
Up to 4 receivers can be used simultaneously for OTF observations, although the optimum scanning velocity usually depends on the observing frequency. The backends can be the filter banks and/or the autocorrelators. The large data acquisition rate causes data storage and handling problems and although a new version of CLASS has been developed, the software is not yet user-friendly. We recommend that you contact an astronomer with a demonstrated experience in OTF observations on the 30m Telescope prior to selecting this observing technique. Astronomers from the IRAM-Granada staff are willing to help you in the planning of your observations. Please contact Drs. H. Ungerechts (ungerech@iram.es) or W. Wild (wild@iram.es) at IRAM-Granada well before the deadline for more information.
Frequency switching is possible. It yields satisfactory baselines within certain limitations (maximum frequency throw of 45 km/s, backends, phase times etc.; for details see [8]). Up to 3 receivers (e.g. 3mm1, 230G1 and 2mm) can be frequency switched simultaneously. Baselines are ordinarily flatter when using one single receiver.
An instantaneous IF bandwidth of 1 GHz is available for the 230G2 receiver. The two 1 MHz filter banks (512 MHz each) can be combined to provide 1 GHz bandwidth. The use of the 1 GHz wide filter bank excludes the simultaneous use of any other backend with the 230G2 receiver (the other receivers are not affected).
Many proposals underestimate the observing time needed to carry out the programme, even under excellent weather conditions. We ask you to pay special attention to this matter as time underestimation is now a major criterion for proposal rejection.
A handbook (``The 30m Manual'') which contains most of the information necessary to plan 30-m telescope observations is available [10]. The report Calibration of spectral line data at the IRAM 30m telescope explains in detail the applied calibration procedure. Both documents can be retrieved through the IRAM Granada web pages (http://www.iram.es).
Finally, to help us keeping up a computerized source list, we ask you to fill in your `list of objects' as explained below.