The Big Knob: An Obituary
In the beginning, there was no Big Knob. You turned on your “apparatus” for receiving spark signals, and if there were any, you heard a “click-buzz-tap” as the Morse characters were received by the coherer. If by some chance there was more than one transmitter within range at the same time, you heard them both, the Morse characters garbled together. With the great invention and infant birth of radio, signals could be heard over incredible distances — more than 60 miles sometimes. The magic of radio was that it could transmit sounds over long distances without wires, distances that couldn’t be traversed by any other known means at the time. As Einstein said, “You see, the wire telegraph is a kind of very, very long cat. You pull his tail in New York and his head is meowing in Los Angeles. Do you understand this? And radio operates exactly the same way: you send signals here, they receive them there. The only difference is there is no cat.”
Making Radio Coherent
The coherer was the first detector. It was a glass tube filled with metal filings and other ingredients. When a strong enough RF signal came to it from the antenna, the filings, previously in a non-conducting state, would move slightly, creating a conducting path through the tube. This allowed a larger DC current to pass, which was large enough to activate a relay or a Morse sounder. Once the path was created by the RF, it would remain conducting until the filings were mechanically separated. So, there was a mechanism that would tap the glass tube and cause the filings to become nonconducting again for the next character. The coherer didn’t care what the frequency of the RF was. Any RF energy strong enough to activate the filings would result in a signal being registered on the sounder. Anyone with working hearing could hear the signals being transmitted from far away.
It is incredibly amazing that this was the apparatus used by the first amateur operators (Marconi’s workers) to work the first transcontinental DX from Poldhu, England (G) to St. John’s Newfoundland (VE1). Even more amazing was the fact that all the “experts” of the time swore it couldn’t be done, save one, Oliver Heaviside. They claimed that because of the curvature of the earth, the radio signals, which they correctly concluded traveled in a straight line, would travel off into space and not be received. But Marconi, having no solid knowledge of the ionosphere and only blind faith that his invention would work at such large distances, invested the time and money to build the first DX
