In 1995, two American scholars used a radio telescope with a diameter of 26 meters to look for unknown signals emitted from the depths of the vast universe. However, so far, no radio source with the characteristics of received signals has been found, and there are no special stars in the direction of these radio waves.
The statement 'The signal has been received, but its electric wave source cannot be determined' means that no radio source with the characteristics of received signals.