I think Q brought NEW CLAS TECH online. (17sec signature).  I think Q did it as a way to A) talk to other Q units and/or detect other DS units.  I will presume all or a majority of the target units are underwater since ELF is uniquely effective COMM methodology for that scenario.  I will assume many if not all targets are submarine or UFO craft since they are the only imaginable vehicles that can cary and sustain crew deep underwater.  I will assume the 17sec repeating waveform contained encoding, or that the 17sec wafeform itself was a “trigger symbol” with some predetermined meaning.  I will assume that such a communication would be one-way, and intended to deliver un-reversible commands/orders/intel.  Nothing will stop what is coming. Nothing.  Trust the plan.  GODSPEED, Q.  SO MOTE IT BE!