GOPAL NARAYANAN's Past Instrumentation Projects

• Installation of new AST/RO Receivers: I have been involved in the design, construction and testing of a 492/810 GHz dual channel receiver system for the South Pole submillimeter telescope, AST/RO. With Chris Walker, I traveled to Antarctica in December, 1996 to install this receiver system at AST/RO.

• 810 GHz Array Receiver: I modeled the performance of a new SIS mixer using HP's High Frequency Structure Simulator (HFSS) software and my own code. We came up with an innovative mixer design for the construction of a 4-element 810 GHz array receiver to be used at the the South Pole AST/RO facility.

• Multi-Channel AOS: At the Steward Observatory Radio Astronomy Laboratory (SORAL), I led an effort in field testing a new multi-channel AOS acquired from NASA as a long-term loan. I designed and built a RF frequency calibration and linearity testing box for the AOS system. I wrote extensive data acquisition and analysis software to transfer the data over network sockets to a PC running the Linux Operating System. At the Linux end, through a user-friendly, Tcl/Tk interface, the observer can control, observe and test the multi-channel spectrometer. With the help of an undergraduate student, I performed integration, linearity, and Allan Variance tests on the AOS.

• Submillimeter Receivers: I helped start and establish a laboratory for the development of state-of-the-art submillimeter receiver systems at Steward Observatory. I worked with Chris Walker in the design and construction of receivers at 230 GHz, 345 Ghz, 492 GHz and 810 GHz. The 230 GHz and 492 GHz receivers are now facility receivers at the SMT. Several of these receivers are being constructed in a collaborative effort with the MPIfR. I have written extensive shot noise analysis software to characterize receiver performance. As part of the SORAL team, I helped install the facility 230 and 492 GHz receivers on the SMT, and performed beam efficiency tests, obtained first light and spectra. I used HP's EESOF microwave analysis software to design a 4-6 GHz matching network and bias circuit for the proposed upgrade of SORAL's LNAs to the 4-6 GHz band. I worked with Chris Walker and an engineer at SORAL in the design, building and testing of a two channel downconverter/total power box that could flexibly downconvert one receiver's 4-6 GHz output to two AOSs or handle two separate receivers. The downconvertor box was used in the 1995-96 season at AST/RO and is currently being used at the SMT. I also headed the SORAL effort in setting design specifications, constructing test equipment for careful characterization of cryogenic amplifiers at 1-2 GHz and 4-6 GHz for use with submillimeter receivers.

• Holography Receiver for the SMT: I worked with Robert Martin and members of the SMT staff in the setting of the SMT 10m dish to a surface accuracy of $\sim 25\mu$m. I modified the 38 GHz NRAO holography frontend for use at the SMT. I designed, built and tested a new primary feedhorn and mounting system for the frontend. I designed and built (with the help of a technician) a new backend for the holography receiver. The backend consists of image-rejection mixers which downconvert the primary and reference signals from the frontend to 10 KHz baseband, A/D converters and a Digital Signal Processing (DSP) card that performs the cross and autocorrelations between the signal and the reference channels. I wrote the DSP and data acquisition software in assembly language, and the holography analysis and calibration software in Fortran. We performed repeated holography runs on LES-8, a geosynchronous satellite, iteratively improving the surface accuracy of the dish.

• Holography of the NRAO 12m: I worked with Darrel Emerson and the NRAO 12m staff in a few holography runs (1992-93) to improve the surface accuracy of the 12m dish. At that time, I wrote the first On-the-Fly (OTF) mapping analysis software for holography, performed data analysis and obtained phase maps of the dish.

• OVRO Instrumentation: I worked with John Carlstrom on the design and implementation of a sideband separation mixer at 115 GHz for the millimeter array at Owens Valley. I also worked on the design of a comb generator to optimize sideband tuning. As a summer research engineer at Owens Valley, I worked with Steve Padin in the design and construction of a wideband continuum correlator for the millimeter interferometer. I also worked on microstrip circuit design and in-house photolithography to manufacture the analog correlator boards.