Build a century-old radio transmitter
Our Hackaday team is spread all over the world, but stays in easy contact thanks to the magic of the internet. A number of us have amateur radio call signs, so could, with a little effort and expense, do the same on the air. A hundred years ago, this would have seemed barely conceivable as amateurs were limited to the HF frequencies then considered unusable.
So in December 1921, a group of American radio amateurs gathered in a field in Greenwich Connecticut to attempt to cross the Atlantic. Their 1.3 MHz transmitter using the 1BCG callsign appears oddly low-frequency a hundred years later, but their success in securing reception in Ardrossan, Scotland has proven intercontinental communication on higher frequencies to be a practical proposition. A century later, a group of the Antique Wireless Association give life to a replica transmitter to recreate the event.
A free-running oscillator is rarely seen in a radio transmitter today, but back then their Colpitts single-tube oscillator using a UV-204 transmission tube would have been considered a stable source. This fed a 1kW power amplifier using three more UV-204s in parallel, which in turn fed a Marconi-style T-antenna design with a terrestrial counterweight of several radial wires. The replica was originally built for an event in 1996 and replaces the 204A tube similar to the now untraceable UV-204. Even then, century-old hits are hard to find in 2021, so they might only muster one working example for the AP.
All in all, this is a very interesting project, and we hope to hear more from it as the anniversary approaches. If we can get the details of the transmission, we’ll share them with you, and see if the same distances can be covered in the noisiest conditions here in 2021.
To show just how advanced this transmitter was for 1921, take a look at the Alexanderson Alternator, its mechanical contemporary.