Does SETI perform search of extremely low bandwidth signals?

Question

Sending a signal at interstellar distance requires enormous power - something of order not too far from energies of the stars. Even if we harness the power of stars, modulating that signal would take a lot of energy - though the actual power required could be reduced - at cost of bandwidth. Imagine a swarm of statites near Oort Cloud, designed for such task: crafts with solar sails large enough to eclipse the Sun as seen from other star to a visible degree, able to turn the sails to reveal it or obscure it - modulate Sun brightness as seen from the distant destination - but the process of turning the statite takes a week. So our bandwidth is of order of 1 bit per week.

Does SETI search signals modulated as slowly? Transmissions of order of bit per week, month, year?

Answer 1

SETI analyses signals in the 1000MHz to 9000MHz range. So you would expect communications modulated on these frequencies to utilise the high frequency to include more data rather than less.

That said, the data on, say, the hydrogen line at 1420 MHz and the methanol line at 6667 MHz are stored, and analyses are run on these over short, medium and long timeframes and yes, cycles or variations of this length are detected, and in fact have been used to identify interesting astronomical objects (variations in signal can imply occultation by something like a moon or other orbiting body)

This does present a problem - if low frequency variation could be occultation or other natural process, why would an alien civilisation use it to communicate? Rather than a large, slow solar sail, why not thousands of small sails acting in concert, able to change position rapidly and give you changes sub 1-second?

TL;dr - yes, SETI does consider low frequency variations, but it is not an ideal channel for communication.