The topic of arc converters for radio wave generation carries an addictive fascination with it for certain, Ed. And Dr. Goldsmith, despite a certain pedantic floridness of writing style at times, was a thorough chronicler of the essential technologies of his day.I read the entire book at one sitting this evening. Last time I did that was when I could not put down our library's copy of Dracula (an old first edition, adding to the verisimilitude that Bram Stoker's journal writing style already exuded) while I was in junior high school. I finished by bed time, just as I had promised my parents...but it didn't really matter, because I couldn't bring myself to close my eyes from then until daybreak!
No problem like that tonight, fortunately. However, my poor ancient brain is now numb with excess information, most of which I will have to reference several times to retain any significant percentage thereof. I knew, for instance, that there were more types of CW converters other than just the Poulsen arc, some of which employed negative resistance principles, and others which were based on high-speed quenched sparks; but all previous encounters with such devices were curt, cryptic mentions without any useful detail. This book contains enough such details for an experienced practitioner of the art to comprehend the basic principles involved, if not necessarily to reconstruct individual devices.
I'm especially curious about the gap invented by Dr. E. L. Chaffee in conjunction with Prof. G. W. Pierce (of crystal oscillator fame), which could apparently operate as high as 1 MHz; and the oscillator invented by W. W. Hanscom which had its electrodes immersed in liquid alcohol rather than enclosed in the usual potentially-explosive atmosphere of hydrocarbon gases. (Although I notice there was also one that used pressurized carbon dioxide.) Even W. T. Ditcham, later the Marconi engineer whom we featured in my LOWDOWN column a few years ago as the newsreader beside the 2LO longwave transmitter at Chelmsford, but then still known as Lt. Ditcham during the war, had developed a workable radiophone as far back as 1912.
Amplitude modulation was still a rather primitive process, though the book does take away some of the mystery about how carbon microphones could be configured to survive multiple amps of RF in antenna circuits. I was delighted to see (at long last!) an actual description of the Majorana microphone, about which I had previously read only tantalizing hints. It even appears that Fessenden was the inventor of the capacitance microphone--and thereby, also frequency modulation, although not for its own unique benefits, but mainly to produced amplitude shift through detuning the tank circuit in step with the audio waveform (sort of a supply side version of slope detection, one might say).
Tubes were just coming into their own at that time, I suppose, but it was still rather surprising that nobody seems to have thought of plate modulation yet in 1918. The vast majority of audion based radiophone circuits employed control grid modulation of the oscillators. In that sense, all those early control grid designs also reinvented FM, although it was entirely an incidental effect for them. Even "Heising" in that day meant only screen grid modulation. The oscillator tank circuits as drawn by Dr Goldsmith also reveal that the early radiophone designers like De Forest and Alexanderson were, in practice, pretty much the real inventors of the Hartley and Colpitts oscillators too.
I was aware of the three different basic approaches to alternator designs that he discusses, but Goldsmith's descriptions of the differences are easier to follow than those of M. Berthiot, the Frenchman whom I was planning to quote regarding competitors to GE's design in our next installment on RCA's Radio Central centennial.
Good luck with the pencil lead experiments if you try them, Ed. I would not be surprised if you can achieve positive results, given that many CW receiving stations in that era employed hand-holdable miniature laboatory arcs as local RF sources to produce beat notes with incoming signals.
John