Hearing Spark
Yes, I am interested in "spark," and I even heard one on the job once in 1962. I had only been working for AT&T for about 6 months, in their HF station at Ft. Lauderdale, FL, where we had the HF ship station WOM (the shore end of "The Love Boats." A number of our technical operators had been ship radio officers and were real whizzes on the Morse key - and I mean the American Morse used on our order wire to the transmitter plant, or the International Morse used on the radio (which we were licensed for to use in calling and setting up links). One day, one of them called me over and said, "Listen, that's a sparker!" It must have been a Poulsen arc, as it sounded rather musical and was transmitting up around 8 mHz with a fairly narrow bandwidth.
I later learned that some US Navy ships of WWI and a bit later still carried a Poulsen arc (made by Federal at San Francisco, FYI) as a backup. Apparently someone was just testing it.
For example, there is, near you, history of the Federal Radiotelegraph Company of San Francisco, at which a young Stanford student went to Denmark and got himself the US license for Valdimer Poulsen's megnetically-quenched arc, which he ultimately sold to the US (and other friendly) navies. That culminated in building four monstrous one megawatt arc converters for a gigantic 12 kHz link between the US Navy at Arlington, VA and the shore of Bordeaux in France. It had been ordered by "Blackjack" Pershing as a fallback to the transatlantic cables in WWI, fearing the Germans would cut the cables across the Atlantic.
It turned out the war ended before the French station was completed, and the French then, out of a sort of honor we no longer seem to have, purchased it as a means of appreciation for saving them from the Germans. That was all well and good, but when the French tried to use it, they found the beast generated harmonics of 12.7 kHz that interfered with all the other nascent forms of radio that were emergining in France by 1920 -- so it had to be abandoned. Today, the tower bases are still there, and there's a small local group who try to keep the memory alive. You can see their website at:
http://www.u-e-f.net/uef-histoire/croixhins.htm