Fig.1 Feed Positions Secondary Focus (View from Prime Focus)
Receivers can be operated on the 100m telescope from either the prime focus or the secondary (Gregory) focus. Prime focus systems are in receiver boxes and can be interchanged as required. There is room for up to three systems in the cabin. Changes between primefocus receivers have to be done manually by the systems group.
Receivers in the secondary focus cabin are mounted at fixed positions and are normally in standby mode. (See Fig. 1) A change from one receiver to another is possible under computer control within seconds.
The use of the central position of the secondary cabin is currently under discussion. The MPIfR receivers have configurations which differ according to the application, see chapter Receiver Specifications for block diagrams and specs. The interfaces to the supply and control electronics, to backends and monitoring devices are however standardized. Changing a receiver from standby to operation requires therefore only changing of some cables (sometimes not even that) and, at the prime focus, installing the frontend-box at the focus-position.
Almost all first stage amplifiers, and in some cases parts of the input waveguide assembly including the prime focus feed horn are cooled to about 15K, for the maser 4.5K, by closed cycle Helium refrigerators. At present the prime focus cabin can accommodate 2 and the secondary focus cabin up to twelve 15K refrigerators. Cooled receivers on the telescope are generally not switched off when not being used for observation.
The 100 m telescope is a multipurpose instrument and is used for continuum, spectroscopy, pulsar and VLBI observations. All measurements are made under computer control. (See Fig. 2)
