PARI Summer 2007 Student Research Proceedings
101
Prototype Development of the S/X RF-to-IF System for the Dedicated
Interferometer for Rapid Variability
PARSEC Summer Intern
David W. Edwins, Furman University
Working under the supervision of Dr. David Moffett
Abstract
We discuss the development of low-noise, radio-frequency receivers at S-band
(2.2 GHz) and X-band (8.4 GHz) to be used for the Dedicated Interferometer for Rapid
Variability, or DIRV. Components selected for the receivers were individually and
collectively tested for their noise characteristics and their susceptibility to outside radio-
frequency interference. The completed system had noise figures of 62K at S-band and
108K at X-band.
Introduction
When completed, DIRV will be a two-element radio interferometer located at the
Pisgah Astronomical Research Institute (PARI). Two hybrid S/X (2.2 and 8.4 GHz)
feeds, originally built and used in NRAO’s Greenbank Interferometer, will be installed at
the prime focus of PARI’s two 26-m radio antennas. The scientific goal of the
instrument is to observe the rapid variability of extragalactic radio sources due to
scintillation originating in our own galaxy. The radio flux of these sources is too weak to
be measured by a single 26-m antenna, so, we are constructing an interferometer to
reduce confusion and improve signal-to-noise. In addition, we must optimize the
receivers to have low noise and high gain so that the system temperature is minimized.
PARI Summer 2007 Student Research Proceedings
102
S/X Receiver
The prototype receiver system, designed by C. Osborne (PARI, 2007), begins at
each frequency band with a high gain, low noise, pre-amplifier that is followed by
isolators, filters and post-amplifiers prior to transmission of the signal via fiber optics
from the antenna to the control room at PARI. A fiber optic receiver converts the signal
back to a radio-frequency band (RF), where it is then downconverted to a low
intermediate frequency (IF) band for