The Submillimeter Array

Receiver Lab Talks: 2021

Questions: Edward Tong
Time: Wednesday 1:00 PM EDT (5:00 PM UTC)
Where: Zoom

Date Speaker Title Summary
April 21Alex Raymond
Resampling of SWARM Phased Array Output for VLBI CorrelationThe SWARM Phased Array produces four-bit real, four-bit imaginary channelized samples across a 2288 MHz Nyquist band. For correlation with other EHT stations, those data must be down-converted to 2048 MHz, two-bit time-domain samples. This talk will explain how this conversion is done using tools developed by Katherine Rosenfeld, André Young, Mark Peryer, and Jonathan Weintroub, and how we hope to do conversion in the future
TBDRam Rao
Polarimetry at the SMA: Current Status and EvolutionI will be presenting a primer on polarization observations with an interferometer array especially focussing on the SMA. Polarimetric observations were first started in 2003 and were aimed at measuring the polarization of the galactic center. They have been extensively used to study polarization phenomena from different types of astrophysical objects including solar system objects, star forming regions, and also AGNs. This talk will cover the basics of the technical aspects of conducting polarization observations and also discuss the future system when the wSMA is online.
April 7TK Sridharan
Coherence, Interferometry & Phase Noise - SMAStarting with a quick conceptual introduction to coherence and interferometry we will discuss the impact of phase fluctuations on interferometric observations. The electronic component of the phase fluctuations arising from the local oscillator (LO) and its quantification will be outlined. Measurements of the phase noise performance of the voltage controlled oscillator (VCO) based wSMA LO will be presented and its adequacy discussed.
March 31 Edward Tong &
John Test
Sideband Separation using Analog Circuits from I and Q Outputs of 2SB Receivers at Low IFLast week, Karto has proposed a digital approach to separate the 2 sidebands detected by 2SB SIS receivers of an interferometer -- an approach particularly appealing to IF near DC. As a follow-up of his talk, we are examining the various schemes by which the sideband separation at low IF can be implemented using analog circuits, which would be useful for single dish radio-telescopes as well as for lab and initial interferometric tests. Assuming a pair of 0.2-4 GHz in-phase(I) and out-of-phase(Q) outputs from the cryostat, the proposed schemes will generate the 2 sidebands from these baseband signals
March 24 Garrett Keating
A Potential Astronomical Calibration Technique for a 2SB InterferometerAs discussion surrounding a potential 2SB system on SMA has increased, a question has arisen about the optimal technique for separating the two sidebands, particularly at the near-DC IF frequencies that the SMA is slated to expand down to. In this talk, I will discuss a potential technique utilizing astronomical sources to digitally reconstruct the separated sidebands in offline processing, in similar fashion to how astronomical calibrators are used for bandpass calibration. If validated, it could provide a natural, efficient path for upgrading the SMA from a DSB to 2SB receiver set at some future date.
March 10Todd Hunter
ALMA Front-End and Digitizer Technical Requirements to Enable the ALMA 2030 Development RoadmapThe ALMA Development Roadmap defines a new long-term development strategy for the upgrade of hardware, software, and analysis tools to enhance the science capabilities of ALMA for the next decade. I will present highlights of the draft report from the working group on the ALMA Front End and Digitizer Requirements Upgrade, beginning with a summary of the original specification and current performance of these components of the ALMA system. I will then show the proposed new specifications, which are still under review.
March 3Edward Tong &
John Garrett
Implementation of 2SB ReceiversIn this talk, we will examine how digital signal processing techniques have helped to advance the state-of-the-art of side-band-separating receivers (2SB receivers). These techniques open the possibility for 2SB receivers for wSMA, which will feature a dual IF system, extending from close to DC to 16+ GHz. The goal of the talk is to initiate further discussions to develop a road map for the development and deployment of 2SB receivers for wSMA.
February 24Lingzhen Zeng
Development of orthomode transducers for the wSMAOrthomode transducers (OMTs) are important passive components widely used in millimeter wave and Terahertz band for remote sensing and astronomical observations. By separating the received signal into two orthogonal linearly polarized components, the OMT proves to be an essential for receiver systems designed to observe the two orthogonal polarization simultaneously. In this presentation, I will first summarize the popular OMT designs in millimeter/submillimeter wavebands. Then I will focus on the wSMA OMT design, fabrication, measurement and integration.
February 10Edward Tong
Tuning circuits for SIS mixersThis is a follow-up of the introductory talk I gave in May 2020: "The Superconductor-Insulator-Superconductor mixer -- some basic concepts and history". I will review the different tuning circuits used in SIS mixer design. These circuits tune out the geometrical capacitance of the SIS junction and allow the SIS mixer to deliver quantum-limited sensitivities.
February 3John Garrett
Waveguide Attenuation: Conductor and Dielectric LossIn this talk, we present a new technique to measure waveguide attenuation. We have used this technique to measure the conductor loss of different WR-2.8 waveguides (copper, gold and aluminum) at both room and cryogenic temperatures. We have also measured the loss tangent of different dielectric materials loaded inside a WR-28 waveguide (HDPE, PTFE and nylon).
January 27Kuan-Yu Liu
Replacement SIS mixers for HARP at JCMTReplacement superconductor-insulator-superconductor (SIS) mixer chips have been developed and fabricated for the 16-element Heterodyne Array Receiver Program (HARP) instrument, which operates between 330 and 375 GHz on the James Clerk Maxwell Telescope (JCMT). The availability of these new mixer chips is very important for the repair and upgrade of HARP. Three of the sixteen mixers have been replaced and the results indicate that the performance of these new mixers is as good as the best original mixers.

Previous presentations available here: CfA managed Google Drive