Technical Notes on Project META

by Paul Horowitz, Professor of Physics, Harvard University


META looked for narrow-band radio signals near the 1420 MHz line of neutral hydrogen and its second harmonic using an 8.4 million channel Fourier spectrometer of 0.05 Hz resolution and 400 kHz instantaneous bandwidth. The observing frequency was corrected both for motions with respect to three astronomical inertial frames (heliocenter/LSR, galactic barycenter and cosmic microwave background), and for the effects of Earth's rotation, which provided a characteristic changing Doppler signature for narrowband signals of extraterrestrial origin. The search covered most of the northern sky (-30 to +60 degrees declination) in meridian transit mode, with each potential source passing through the antenna beam pattern in approximately 2 minutes, during which the three reference frames were covered once in each antenna polarization.

META control room The META control room.

Designed in 1983, META's hardware consisted of GaAsFET low-noise front ends in each polarization, image-reject downconverters with programmable phase-continuous 2nd LO, 7-bit quadrature digitizers, a 144-point channelizing DFT feeding an array of 144 68000-based 64K-point FFTs, and a central "workstation" of modest performance. In an analysis of 5 years of data, during which 60 trillion channels were searched, we found 37 candidate events exceeding the average detection threshold of 1.7e-23 W/m^2, none of which has been detected upon repeated reobservations. For a technical summary, see "Five Years of Project META: An All-Sky Narrowband Radio Search for Extraterrestrial Signals," by Carl Sagan and Paul Horowitz in the Astrophysical Journal, vol. 415, no. 218, Sept. 1993, pp. 218-235. A non-technical version of this article appears in The Planetary Report as "Project META: What Have We Found?," vol. 13, no. 5, Sept/Oct. 1993, pp. 4-9. This issue is available from The Planetary Society.