If memory serves the signal of the latter should have been ~3 orders of magnitude higher.
Using nukes to communicate is a bit intense, but a tuned receiver should be able to pick up lower energy levels.
Did you take into account that in a process like this, virtually none of the energy released can be put into gravitational waves? The efficiency of such transmission is extremely low for processes involving ordinary matter--many orders of magnitude less efficient than for electromagnetic waves. You need huge quantities of matter to overcome this problem--or, alternatively, you need very dense matter, like neutronium, or strong spacetime curvature like that of a black hole (but not too large a hole, since curvature at the horizon goes like the inverse square of the hole's mass).