We are developing a 1.4 THz receiver to explore the far infrared
universe, such as probing high mass star forming regions using,
e.g., the high J transitions of CO, investigating the warm
interstellar medium in N+ or probing cold and dense stellar cores in H2D+. Due to the poor atmospheric transmission at these frequencies we are planning to use this modular receiver on high altitude ground based observatories, for example the Atacama Pathfinder EXperiment (APEX), and as an additional channel for the German Receiver for Astronomy at Terahertz Frequencies (GREAT) on the Stratospheric Observatory For Infrared Astronomy (SOFIA) located on an airplane. To allow successful astronomical observations under poor atmosphere transmission a low receiver noise temperature and a high receiver stability are mandatory. To achieve a low receiver temperature the main effort is directed to develop phonon-cooled NbTiN HEB mixers. For optimum coupling with the telescope beam and easier alignment we are focussing on waveguide mixers. A phase locked Gunn (114-135 GHz) and three multipliers will be used as the Local Oscillator (LO) of 1370-1500 GHz. A liquid He Dewar will be used for operation on SOFIA and a closed-cycle system with a pulse-tube cooler on APEX. Initially, we are aiming for 1 GHz IF bandwidth (214 kms-1 at 1.4 THz) sufficient for galactic
observations. First tests and astronomical observations with a similar but lower frequency HEB at 800 GHz have yielded encouraging results.