Atacama Pathfinder EXperiment APEX
Heterodyne Instruments
MPIfR Bonn   ESO   Onsala Space Observatory

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The APEX-2A receiver specifications 
RF tuning range 282-378 GHz (possibilities to extend this range by careful manual tuning down to 279 GHz and up to 381 GHz).
IF frequency Centered at 6 GHz. IF bandwidth is 4-8 GHz
Noise temperature 40 ± 15 K (DSB) across RF band. Corresponds to 2-3 quantum noise.
Optics Flat and active cold mirrors + 9 warm mirrors to obtain a beamwaist of 6 mm to match the APEX Cassegrain waist
Cryogenics Old SEST SESIS cryostat. Closed cycle cooling system. 1 compressor CTI 8500 with cold head CTI1020 to produce 80K and 12K. 1 compressor Quantum J20 for 4K stage. Cooling time of 14hours.
Calibration External closed-cycle calibration unit in Cabin A providing 73 K for cold load and about 288 K for the hot load.
Computer control Control system using National Instrument Fieldpoint modules. Ethernet connection to the telescope network. Virtually possible to tune from anywhere.
Tuning Tuneless mixer. A full automatic tuning procedure takes less than 3 minutes to tune the receiver. Manual tuning is possible to optimize further for stability or reach the edges of the receiver band.