Ask Dr. SETI ®

The Doctor Responds:
4 GHz (the band at which your satellite TV equipment operates) is just as viable a frequency for SETI as any other, so by all means, this is worth a try. The LNA, polarization rotor and feedhorn could certainly be used as-is. The receiver itself is not likely to be particularly useful (unless, as happened in the film Contact, the aliens choose to send us TV signals!) The downconverter would probably require extensive modification. The reason is, a satellite TV channel is typically 40 MHz wide, so the converter need not exhibit particularly good frequency stability (and in fact, does not). Our FFT bins for SETI are typicaly 10 Hz wide, so we expend a lot of effort on making our converters very frequency stable. You could probably phase-lock the LO in the downconverter to a very stable reference oscillator, and use a communications receiver at the IF output, but this becomes a major engineering effort (and may or may not be worth the bother).

One very successful 4 GHz SETI system based upon TVRO hardware is Project BAMBI. You may wish to visit their web site for technical details.

By the way, 4 GHz is a great frequency range for continuum radio astronomy (for which you can use a TVRO receiver). In fact, the discovery of the cosmic background radiation was made in this band (by Penzias and Wilson at Bell Labs; work which won them their Nobel Prize. Only don't expect to be able to measure the cosmic background radiation with a satellite TV dish!)