Technical Notes on Project BETA

by Paul Horowitz, Professor of Physcis, Harvard University


BETA control room Paul Horowitz in the BETA control room.

Project BETA started observing on October 30, 1995, and features

BETA uses the 26-meter dish with dual (east-west) feedhorns (and a third low-gain terrestrial discone) to feed a 240 million channel Fourier spectrometer (80 million channels of 0.5 Hz resolution and 40 MHz instantaneous bandwidth for each feed) whose outputs feed an array of programmable "feature recognizers." These recognizers sift through 250 MByte/sec of spectral data, seeking distinctive spectral features that transit from the east to the west horn without appearing in the low-gain terrestrial antenna.

BETA's contemporary hardware consists of HEMT low-noise frontends, an array of 63 quadrature mixer/digitizers with GPS phase-locked local oscillators, and an array of 63 4-million-channel complex FFT boards feeding a flexible state-machine based feature recognizer/correlator array resident in a set of Pentium motherboards; the latter communicate with a UNIX workstation via thin-wire Ethernet.

BETA searches the full "waterhole" of 1.4-1.7 GHz as 8 hops of 40 MHz, each hop taking 2 seconds (16 seconds for a full cycle through the waterhole; thus each potential source is visited 8 times at each frequency hop, in each sky beam). A good candidate (seen first in east, then west, never terrestrial) triggers the antenna to leapfrog a few beamwidths to the west, inviting the source to perform an encore. If that ever happens, the antenna will break off its survey and go into sidereal tracking mode, repeatedly moving on and off the candidate source, archiving all integrated spectra.

BETA's designers and builders include Derrick Bass, Greg Galperin, Neil Hendin, Paul Horowitz, Darren Leigh, Suhail Shah, Nick Shectman, Jonathan Weintroub, Eric Wey and Bill Yerazunis. The FFT processor evolved from a design of the Berkeley SETI group.