Some of the instrumentation and science projects I've done, and students I was privileged to work with:
- Widely tunable Gunn oscillators (John Carlstrom).
In 1983 observations at BIMA were possible only from 86-89 GHz because of the limited tuning range of our local
oscillators. John Carlstrom was a new graduate student and we suggested that the investigate various designs
for tunable Gunn oscillators. Within about a year John developed an oscillator that tuned from 65-115 GHz -
for the first time we could observe the CO line at 115 GHz! John later formed a company to produce these oscillators,
which were then acquired by radio observatories around the world.
(Carlstrom, Plambeck, & Thornton 1985, IEEE MTT-33, 610C)
- The BIMA cryocooler (Niranjan Thatte). In 1995 BIMA was poised to switch from cooled
Schottky diode mixers to superconducting tunnel junction (SIS) mixers that had to be cooled to 4 Kelvin.
At the time, the only closed cycle cryocoolers were massive machines that used a hybrid Gifford-MacMahon
refrigerator to precool helium that then entered a Joule-Thompson expansion, prone to clogging by impurities.
I went to a Crycoolers Conference at UCLA to learn more, and was intrigued to hear that Japanese groups
at Toshiba and ... had succeeded in cooling to 4K with a Gifford-MacMahon refrigerator (they didn't emphasize
in their presentations that the machines failed after a day or so because the regenerator material turned
into a fine abrasive powder). It was a struggle, but with the help of Pat Sykes and Toru Kuriyama, we finally
produced cryocoolers - certainly the first in the US that used GM refrigerators at 4 K - . Nowadays these
machines are produced commercially by Sumitomo and other companies, and are used widely, e.g. on ALMA
(further information, including publications and Autocad drawings)
- 1mm orthomode transducer (Alessandro Navarrini) Building a waveguide orthomode transducer
separates X- and Y- polarized signals in a round waveguide into 2 rectangular waveguides. It isn't so
easy to build when the waveguides are less than 0.5 mm high. Alessandro designed this. We were fortunate
to have the parts machined by
Mike Maendl, Ferdinand Krall, and other very talented people at
- SIS mixers (Greg Engargiola)
- automated tuning (Niranjan Thatte)
- moving the BIMA antennas to CARMA Yeah, I know, this isn't really instrumentation, but it occupied
a couple of years of my life so I'm putting it here anyway. How do you move 9 telescopes, each weighing
xx tons and 20 ft in diameter, over 300 miles? The story is here in pictures.
- polarization measurements at 1mm (Ram Rao)
- waveguide circular polarizers.
- diagnosing the bad plastic!