I'm not an electrical engineer, but even if the obelisk is transmitting the signal straight up I don't think that shielding only the ceiling immediately above it will block all of the radio signal.
I am not an electrical engineer either, but I believe this should work, since radio waves are just photons (the same waves/particles - light is made of) at a particular wavelength. You can block a flashlight with a piece of cloth, and x- and gamma rays with sufficiently thick lead, so it would stand to reason that radio waves are stoppable with shielding in one direction. Your dentist's office isn't completely lead shielded to protect the technician that gives you a bitewing x-ray - just "down range" of the emission source is blocked.
Of course, I'll defer to an expert here.
Nothing in the article suggests this to me. Now if the obelisk started sending a copy of an SCP-1050-3, that would suggest something like a series of bonfires.
Uh, it does. "SCP-1050-1 emits SCP-1050-3 from its apex."
Might want to have a note on how embedded Foundation agents are preventing SETI from finding out about this.
I rather thought that was implied, so I didn't say it explicitly. Also, even without this SCP, I'd imagine the Foundation would have SETI infiltrated, just in case.
the length of Earth years to generate the numbers.
Yeah, I know. It's a matter of balancing realism with something followable by somebody who is neither an astronomer nor a theoretical mathematician. (Which, for the record, I am neither.) So, I'm chalking this last one up to suspension of disbelief and acceptable breaks from reality. I figure that it also allows it to be more conceivable that the Foundation would be able to have spotted the pattern and covered it up than if they were trying to cover up unknown and conjectural repeating patterns of numbers coming from unknown directions in interstellar space, especially since patterns of numbers are exactly the sort of thing SETI and the like look for (and would shout from the mountaintops if they discovered).