On which two radio frequencies did Sputnik 1 transmit its famous beeping signals?

Sputnik 1 transmitted its famous beeping signals on 20.007 and 40.002 megahertz.

The Soviet Union launched Sputnik 1 on 4 October 1957, making it the first artificial satellite to orbit Earth. Its radio transmitters sent regular pulses that could be received by radio amateurs and tracking stations around the world. The signals made the satellite’s presence audible and helped confirm that it was circling the planet.

The two frequencies were chosen so that the satellite could transmit while its power system supported the instruments. Sputnik 1’s batteries lasted about three weeks, after which the satellite continued orbiting silently until atmospheric drag caused re-entry in January 1958.

The beeps were not spoken messages or scientific data in the modern sense. They were simple radio pulses, but their worldwide reception had enormous political and psychological impact, intensifying the United States–Soviet space competition.