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Recent improvements in hardware, software and mixers have made possible frequency-switching. In several test periods during 1994 the behaviour of the receivers (stability of phase lock, baseline quality, blanking time, efficiency etc.), the data acquisition, control software and system interfacing were investigated and improved. Several limitations exist e.g. in terms of frequency throw (max. 18 MHz), backends, phase times etc. For details see the report by Wild & Thum in this Newsletter. Frequency switching is now open for public use (at present, however, only with the 3 mm SIS and the 1.3 mm 230G1 receivers operating simultaneously).
The new 3mm SIS receiver can be tuned to a high rejection of the upper sideband (25-30 dB) and is much more stable for continuum observations. It is now used as the standard pointing receiver. Pointing sources with fluxes Jy can generally be used. The 3 mm Continuum Schottky receiver remains in stand-by in case of a failure of the 3 mm SIS receiver.
A second 3 mm receiver is being built presently. When operational, it will be usable with the present 3 mm receiver and, with some extra losses, with receivers 230G1 and 230G2. Although simultaneous 4-receiver operation is expected to become possible before the end of the coming session, it should not be considered in the telescope time calculations.
Most proposals submitted for the 30 m telescope underestimate the observing time needed to carry out the programme, even during excellent weather. We ask you to pay special attention on this matter as time underestimation becomes a major criterium for proposal rejection. A technical report has been issued to help you (see below); you may also ask for IRAM's assistance (but only well ahead of the deadline!).
Finally, to help us keeping up a computerised source list, we ask you to fill in your `list of objects' as explained below.