J. Mc Laughlin wrote:
Dear Group: Frank Drake hired me for my first job in radio astronomy.
Years latter, I learned that he was most impressed that I had a first class
FCC commercial license (that type of license is long gone). Did some neat
propagation research in the hills of West Va. (where we did use antennas!)
Prof. Drake had an involved mathematical model that he used to suggest
existence of other people.

The December 1959 paper by Costas made clear the inherent advantages and
disadvantages of wide-bandwidth modulation systems. As others have
observed, narrow bandwidth emissions are most unlikely.

73, Mac N8TT

And there's another factor, brilliantly illuminated in a short story in
Analog magazine years ago. A series of scenes took place, each involving
a different alien species in some distant solar system. In each scene a
discussion was taking place, involving budgetary restraints and the
prohibitive expense of transmitting powerful signals for other
civilizations to pick up. Each one, in turn, decided to reduce expenses
by listening only. . .

Roy Lewallen, W7EL