When you think of an old radio it’s possible you imagine a wooden-cased tube radio receiver as clustered around by a 1940s family anxious for news from the front, or maybe even a hefty 19-inch rack casing for a “boat anchor” ham radio transmitter. But neither of those are really old radios, for that we must go back another few decades to the first radios. Radio as demonstrated by Giulielmo Marconi didn’t use tubes and it certainly didn’t use transistors, instead it used an induction coil and a spark gap. It’s a subject examined in depth by [The Plasma Channel] and [Blueprint], as they come together to build and test a pair of spark gap transmitters.
This is a collaboration between two YouTube channels, so we’ve put videos from both below the break.They both build simple spark gap transmitters and explain the history behind them, as well as running some tests in RF-shielded locations. The transmitters are fairly crude affairs in that while they both use electronic drives for their induction coils they don’t have the resonant tank circuitry that a typical early-20th-century transmitter would have had to improve its efficiency.
They are at pains to remind the viewer that spark gap transmitters have been illegal for nearly a century due to their wideband interference so this is definitely one of those “Don’t do this at home” projects even if it hasn’t stopped others from trying. But it’s still a fascinating introduction to this forgotten technology, and both videos are definitely worth a watch.
The place is the historic lecture theater of the Royal Institution in London. The date is the 4th of June 1903, and the inventor, Guglielmo Marconi, is about to demonstrate his new wireless system, which he claims can securely send messages over a long distance, without interference by tuning the signal.
The inventor himself was over 300 miles away in Cornwall, preparing to send the messages to his colleague Professor Fleming in the theater. Towards the end of Professor Flemings lecture, the receiver sparks into life, and the morse code printer started printing out one word repeatedly: “Rats”. It then spelled out an insulting limerick: “There was a young man from Italy, who diddled the public quite prettily”. Marconi’s supposedly secure system had been hacked.
The pioneering years in the history of capacitors was a time when capacitors were used primarily for gaining an early understanding of electricity, predating the discovery even of the electron. It was also a time for doing parlor demonstrations, such as having a line of people holding hands and discharging a capacitor through them. The modern era of capacitors begins in the late 1800s with the dawning of the age of the practical application of electricity, requiring reliable capacitors with specific properties.
One such practical use was in Marconi’s wireless spark-gap transmitters starting just before 1900 and into the first and second decade. The transmitters built up a high voltage for discharging across a spark gap and so used porcelain capacitors to withstand that voltage. High frequency was also required. These were basically Leyden jars and to get the required capacitances took a lot of space.
In 1909, William Dubilier invented smaller mica capacitors which were then used on the receiving side for the resonant circuits in wireless hardware.
Early mica capacitors were basically layers of mica and copper foils clamped together as what were called “clamped mica capacitors”. These capacitors weren’t very reliable though. Being just mica sheets pressed against metal foils, there were air gaps between the mica and foils. Those gap allowed for oxidation and corrosion, and meant that the distance between plates was subject to change, altering the capacitance.
In the 1920s silver mica capacitors were developed, ones where the mica is coated on both sides with the metal, eliminating the air gaps. With a thin metal coating instead of thicker foils, the capacitors could also be made smaller. These were very reliable. Of course we didn’t stop there. The modern era of capacitors has been marked by one breakthrough after another for a fascinating story. Let’s take a look.
The early days of electricity appear to have been a cutthroat time. While academics were busy uncovering the mysteries of electromagnetism, bands of entrepreneurs were waiting to pounce on the pure science and engineer solutions to problems that didn’t even exist yet, but could no doubt turn into profitable ventures. We’ve all heard of the epic battles between Edison and Tesla and Westinghouse, and even with the benefit of more than a century of hindsight it’s hard to tell who did what to whom. But another conflict was brewing at the turn of 19th century, this time between an Indian polymath and an Italian nobleman, and it would determine who got credit for laying the foundations for the key technology of the 20th century – radio.