December 12, 1901

Transatlantic wireless telegraphy

Marconi claims reception of Poldhu's transatlantic Morse signal

The first reported transatlantic radio reception left no tape — only three faint clicks heard in headphones by two men on a Newfoundland hilltop.

12 December 1901, Signal Hill

At Signal Hill in St John's, Newfoundland, on 12 December 1901, the 27-year-old Guglielmo Marconi and his assistant George Kemp reported hearing the prearranged three-dot Morse letter S transmitted by the Poldhu station in Cornwall.

A kite held up the roughly 500-foot receiving wire after balloon and kite difficulties; Kemp's diary records receiving repeated three-dot signals that day.

Storms had wrecked the original large aerials at Poldhu and Cape Cod, which is why the experiment ran on a substitute transmitter and an improvised receiver.

Heard, not recorded

Marconi later reported reception at 12:30, 1:10 and 2:20 local time — but only through a telephone receiver, never on the ordinary recording receiver.

The signal was too weak to print on telegraph tape, leaving no contemporaneous instrumental record.

The three dots were a test signal, not a telegram.

Doubts, then better evidence

The date on which Marconi and Kemp said they heard the signal is well documented. Whether the sounds were actually Poldhu's transmission remains disputed: they were heard aurally, and modern analysis finds the claimed daytime propagation at the presumed medium frequency extremely difficult.

Within twelve days a cable-telegraph monopoly threatened legal action, and Marconi left Newfoundland on 24 December to pursue a permanent station in Cape Breton.

Later shipboard tests aboard Philadelphia produced recorded nighttime signals over comparable distances, supplying much stronger evidence that transatlantic radio propagation was possible.

Sources

Researched 23 Aug 2026 6 sources 2 audit passes Date disputed

How this was checked

Researched from the web into a fact sheet, rewritten from that sheet, then audited against it by a different model. How the pipeline works →

Date disputed. Sources disagree about when this happened.

What the sources leave uncertain

December 12 is well documented as the date on which Marconi and Kemp said they heard the signal.
Whether the sounds were actually Poldhu's transmission remains disputed. They were heard aurally, not recorded, and modern analysis finds the claimed daytime propagation at the presumed medium frequency extremely difficult.
Later shipboard tests aboard Philadelphia produced recorded nighttime signals over comparable distances and supplied much stronger evidence that transatlantic radio propagation was possible.