The Single-Pixel 1mm Receiver installed in the LMT instruments room.

Single-Pixel 1mm Receiver

The single-pixel 1mm receiver (or MSIP1mm) is a dual-polarization sideband-separation receiver that operates in the frequency range of 210 – 280 GHz. The receiver is primarily used for observations with the Event Horizon Telescope (EHT) array, but is also available for general astronomical use. The receiver uses super-conducting junctions, and features ALMA Band-6 mixer-preamplifiers. The cryostat is cooled to 4 Kelvin, and has a square corrugated feedhorn followed by an orthomode tranducer (OMT) which splits the two polarizations into two separate mixer-preamplifiers. Each of these polarizations further separate the upper and lower sidebands of the intermediate frequency (IF) of 4 – 12 GHz. In all four separate IF bands are available simultaneously and is fed into a spectrometer system. The orthogonal polarizations can be averaged together for each sideband. The receiver was designed and built at UMass, and provides characteristic receiver noise temperature of 60-75 K across the 210 – 280 GHz band. A flexible computer controlled local oscillator (LO) system allows tuning across the RF frequency range.

The receiver was installed and commissioned in Spring 2018, and has been used for EHT runs and for spectral line observations. The receiver is connected to the same spectrometer system as SEQUOIA. The FPGA based spectrometer system has bandwidth options of 200, 400, and 800 MHz. The upper and lower sidebands of the receiver can be tracked to independent frequencies, so different spectral lines can be observed in each sideband.

Sensitivity and integration time calculators for the 1mm receiver system will soon be available in LMT-Hedwig, the LMT’s proposal submission system. Documentation and a simple example on how to use this calculators will also be available.