It’s well-trammelled ground, over whether Marconi really got a low-frequency signal across the Atlantic in 1901, like he’s famous for doing. More precisely, the issue is whether he could have. We don’t know what frequency he was using (Marconi didn’t either), and there are gaps in our knowledge about his equipment. So we don’t know for sure that it was possible. But David Sumner, G3PVH, in a superb piece of reconstructive detective work, has shown that the big jump may well have happened – but not at low frequency. If it happened, it very likely occurred by spurious emission in the 30 meter shortwave band.
It was John Belrose, VE2CV, who gave us the canonical 500 kHz, or 560 meters, at which we suppose the transmission occurred, and he it was who also pointed out the difficulty of a long-distance leap at that frequency, particularly during daylight. There sits the problem. But Sumner’s argument goes like this. A spark transmitter can generate secondary signals with high peak power. The ‘jigger’ coil Marconi was using may have a self-resonance at about 10 mHz. The transmitting antenna, from what we know of it, could have been resonant at that frequency, as could the receiving antenna (which, incidentally, was wind-borne on its kite in the right direction for great-circle propagation). The feed-point impedance at 10 mHz would suit Marconi’s particular coherer better than one at 500 kHz. This coherer and the earphones he used form a sensitive enough detector to receive HF broadcasting. Normal propagation on 30 meters at the time of Marconi’s documented reception is transatlantic. (I myself have crossed the Atlantic on 10 mHz lots of times, and at 100 watts peak, not his 10 megawatts.)
The technical details of Sumner’s sleuthing are a gripping read. He made his own jigger, after Ambrose Fleming’s Poldhu design, and tested it with an antenna. He sourced a Collier-Marr ‘phone at the Oxford Museum of the History of Science. He takes us through previous work on coherer curves, too, a fascinating trip all by itself. It’s a magnificent article, and its bibliography is full of treasures for the scholar, as you’d expect.
John S. Belrose, ‘A radioscientist’s reaction to Marconi’s first transatlantic wireless experiment,’ Conference Digest, 2001 IEEE Antennas & Propagation Society International Symposium, July 8-13, vol. 1, 22-5.
David Sumner, ‘UK to Newfoundland, 1901 Style – the possibility of HF communication,’ RadCom, July 2018, 44-54.
Picture: Wikimedia Commons (https://commons.wikimedia.org/wiki/File:Marconi_at_newfoundland.jpg)