Aims. In March 2008, the APEX facility instrument was installed on the telescope at the site of Lliano Chajnantor in northern Chile. The main objective of the paper is to introduce the new instrument to the radio astronomical community. It describes the hardware configuration and presents some initial results from the on-sky commissioning. Methods. The heterodyne instrument covers frequencies between 211 GHz and 1390 GHz divided into four bands. The first three bands are sideband-separating mixers operating in a single sideband mode and based on superconductor-insulator-superconductor (SIS) tunnel junctions. The fourth band is a hot-electron bolometer, waveguide balanced mixer. All bands are integrated in a closedcycle temperature-stabilized cryostat and are cooled to 4 K. Results. We present results from noise temperature, sideband separation ratios, beam, and stability measurements performed on the telescope as a part of the receiver technical commissioning. Examples of broad extragalactic lines are also included.

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Aims. The new APEX telescope, located on Llano Chajnantor in Northern Chile, will have high resolution spectroscopic instruments covering the wavelength region from 0.20 to 1.30 mm (210−1500 GHz). Methods. In May 2005, the first facility receiver for the band 0.79−1.07 mm (279−381 GHz) was installed together with backends providing down to 60 kHz spectral resolution. This instrument that operates in double sideband mode uses superconducting tunnel junctions (SIS) as mixing elements operating at 4 K to achieve close to quantum-limited noise performances. The receiver is cooled by a closed-cycle cooling machine that allows continuous operation. The receiver design minimizes moving parts and is fully operated by remote to improve its reliability and the ease of use. Results. The double sideband (DSB) receiver temperatures are in the range 50−70 K, which typically results in a DSB system noise temperature of about 100 K in excellent weather conditions and between 100−200 K in good weather conditions.

A new receiver for the Onsala 20 m antenna with the possibility of being equipped with 3 mm and 4 mm bands has been built and the 3 mm channel has been commissioned during the Spring 2014. For single-dish operation, the receiver uses an innovative onsource/off-source optical switch. In combination with additional optical components and within the same optical layout, the switch provides two calibration loads (for the 3 mm and 4 mm channels), sideband rejection measurement, and tuning possibilities. The optical layout of the receiver employs all cold (4 K) offset elliptical mirrors for both channels, whereas the on-off switch employs flat mirrors only. The 3 mm channel employs a sideband separation (2SB) dual polarization receiver with orthomode transducer (OMT), 4-8 GHz intermediate frequency (IF), x 2pol x upper and lower sidebands (USB + LSB). The cryostat has four optical windows made of high density polyethylene (HDPE) with anti-reflection corrugations, two for the signal and two for each frequency band cold load. The cryostat uses a two-stage cryocooler produced by Sumitomo HI RDK 408D2 with anti-vibration suspension of the cold-head to minimize impact of the vibrations on the receiver stability. The local oscillator (LO) system is based on a Gunn oscillator with a phase lock loop (PLL) and four mechanical tuners for broadband operation, providing independently tunable LO power for each polarization. This paper provides a technical description of the receiver and its technology and could be useful for instrumentation engineers and observers using the Onsala 20 m telescope.