[quahaug]

I have a different mental model of the nature of the signal. I don't imagine that it was transmitted as a focused beam attenuated by an aperture. My thinking is that it was a sphere shaped pulse generated by an apparatus like a broadcasting tower, or perhaps discharged from a device that targets a specific band of the EM spectrum.

When you think of it as an event similar to an electromagnetic pulse from a hydrogen bomb, and not as a beam from a laser pointer, it changes the rationale for why it might not be a repeatable event. If it was a pulse and not a beam, it might still be prone to occlusion, in terms of whether pulse were generated on the surface of a planet, and on the side that only happened to be facing toward us at the time (not away), while our antenna was pointed at the night sky, but that still increases the probability of reception.

The alternative concept for a pulse, is that it was generated from a small space craft or space probe, and not on a planet capable of eclipsing the signal.

Considering that it lasted 72 seconds, that might fit the profile of a weapon, if you consider the duration of typical video of a mushroom cloud. 72 seconds might also fit the profile of a jamming signal generated while a weapon was en route, to prevent detection while being delivered to a target.

[TrainedMonkey]

Amount of power that would be required for that is ginormous. Somewhere around the scale of supernova.

[bmelton]

72 seconds is the duration of time that any particular patch of sky is in range for Big Ear to listen to. To offer another imperfect analogy, imagine yourself on a train in a pitch black tunnel. There's a break in the tunnel that lasts for 72 seconds at your current speed. The light signals you noticed for those 72 seconds didn't necessarily last for only 72 seconds, they were simply not visible after you went back into the tunnel.